constructed_response.csv

exam,subject,domain,context,question,answer
naep,economics,The National Economy,Identify two economic costs of unemployment,A high rate of unemployment that lasts for several years has economic costs for a nation. What are two of these economic costs?,The response provides two economic costs of unemployment.
naep,economics,The International Economy,Describe how a change in the dollar-euro exchange rate will impact purchases of goods outside of the U.S.,"Annette is going on a trip to France. The currency used in France is the euro. When Annette planned for the trip, the exchange rate was 1 United States dollar = 1.40 euros. On the day Annette exchanges her money, she discovers that the exchange rate is now 1 United States dollar = 0.80 euros.

Describe what effect this change will have on Annette's ability to make purchases in France and explain why.","The response provides both the correct effect (A) and the correct explanation (B).

A. Response must state that the effect is that Annette will make fewer purchases (not buy as much, have fewer euros to spend) or she will need more dollars to purchase the same amount of goods.

B. The correct explanation: The dollar is weaker (depreciated, worth less in exchange for the euro, lost value in exchange for the euro) or the euro is stronger (appreciated, worth more in exchange for the dollar, gained value in exchange for the dollar)."
naep,economics,The Market Economy,Explain the rationale for a purchasing decision when considering interest rates and inflation,"Nancy has just inherited \$2,000. Within the next year, she needs to purchase furniture that costs \$2,000. If Nancy puts the \$2,000 in her savings account, she will earn 2 percent interest for the year. Nancy expects that the current inflation rate of 3 percent will continue for at least one year. From an economic perspective, explain why Nancy should buy the furniture now instead of putting the \$2,000 into her savings account.","The response explains that the real interest rate is negative or otherwise demonstrates an understanding that the purchasing power of Nancy's savings is decreasing (e.g., by saying that given the rate of inflation is greater than the interest she is earning, so at the end of the year Nancy would not be able to take her savings and purchase the same furniture). The response demonstrates an understanding that the negative real interest rate reduces the economic incentive for Nancy to deposit her money in the bank and not purchase the furniture."
naep,economics,The Market Economy,Describe two economic factors that could influence a household's decision making process,"Robert and Sally are a two-income married couple. They are starting a family and deciding whether one parent should stay at home with the children and not work for money. Briefly describe two economic factors that are most likely to influence their decision.

1)

---

---

---

2)

---

---

---

---

---",The response includes two economic factors.
naep,economics,The Market Economy,Determine how changes in production costs will affect the level of production and product price,"To meet new regulations, a company has decided to upgrade the pollution control equipment used in its production process. The equipment will increase the cost of production.

How will the installation of this equipment affect (1) the company's level of production and (2) the price of the company's product?","Response recognizes that the legislation will have the following effects:

(A) The firm's level of production will decrease. (Output will decrease.)

(B) The price of the product will increase."
naep,economics,The Market Economy,Identify and explain how a change in the price of a product affects quantity demanded,Suppose that the price of grapes increases by a large amount. What will happen in the short term to the quantity of grapes demanded? Explain why.,"The response states that quantity (demanded) decreases and offers one of the following explanations. [Note - if the explanation implies that quantity (demanded) decreases, the response need not say so explicitly]:

- Because of the law of demand (or the response can describe the law of demand by saying there is an inverse relation between price and quantity or that when price increases, quantity decreases and vice versa)
- Because of costs vs. benefits
- Because consumers might buy substitutes"
naep,science,life_science,Explain the evolution of an organism,The overuse of antibiotics has led to an increase in the prevalence of antibiotic-resistant strains of bacteria. Explain how this occurred.,"Student response explains that a mutation occurred in the DNA of some bacteria, so they were resistant to the antibiotic. The antibiotic-resistant bacteria then passed the resistance on (DNA mutation) when they reproduced."
naep,science,life_science,Explain fossil evidence based on evolutionary change,"Fossils of *Basilosaurus*, a primitive whale that lived in water and existed about 50 million years ago, have well-defined ankle bones and toes.

What does this suggest about how the ancestors of this primitive whale moved and where they lived?","Student response explains that the ancestors of this whale probably walked (on limbs, feet) and lived on land (ground)."
ib,biology,life_biology,There are a number of advantages to specificity.,Explain how vaccination can result in specific immunity to a viral disease.,"a. vaccinations are specific to a specific disease;
 b. vaccines contain non-self antigens/antigens from pathogens;
 c. can be live relative/attenuated version of the virus;
 d. trigger a primary immune response (without causing the disease);
 e. lymphocytes with specific receptors (are activated and) produce memory cells;
 f. (memory cells) cause a faster production of antibodies on a second exposure/exposure to the disease;
 g. (memory cells) provide long term immunity;"
ib,biology,life_biology,There are a number of advantages to specificity.,Outline the role of membrane proteins in the movement of specific ions at specific times in the transmission of nerve impulses.,"a. (during depolarization) Na+ channels open;
 b. allowing Na+ to flow into the axon;
 c. (during repolarization) K+ channels open;
 d. allowing K+ to flow out of the axon;
 e. the Na+/K+ pump returns the (axon) membrane to the resting potential;
 f. by moving 3Na+ out and 2K+ in;"
ib,biology,life_biology,There are a number of advantages to specificity.,Describe the barriers that exist to hybridization between species.,"a. courtship behaviour is often complex and unique to a species;
 b. (at several stages in courtship ritual) rejection occurs if characteristic behaviour not exhibited;
 c. species-specific egg fertilization;
 d. compatibility of acrosome with vitelline layer;
 e. inability of successfully attached wrong species sperm to develop continuity with egg membrane;
 f. sterility of interspecific hybrids;
 g. due to differences in chromosome number;"
ib,biology,life_biology,Various mechanisms can lead to inhibition in biological systems. A toxin is a substance capable of disrupting metabolic processes in organisms.,Describe how toxins such as DDT might concentrate in the bodies of birds.,"a. some toxins/DDT are persistent/degrade slowly (once released into the environment);
 b. (some toxins/DDT) enter the food chain through producers/lower trophic levels;
 c. (some toxins/DDT) are passed on to higher trophic levels in the food chain;
 d. (they are) difficult to excrete / are not excreted;
 e. (they) accumulate in fatty tissues of animals;
 f. higher trophic levels/top consumers have higher/the highest concentration of pesticides in their bodies;
 g. they bioaccumulate/biomagnify;"
ib,biology,life_biology,Various mechanisms can lead to inhibition in biological systems. A toxin is a substance capable of disrupting metabolic processes in organisms.,Toxins often act as inhibitors. Compare and contrast competitive and non-competitive enzyme inhibition.,"a. slow down enzyme activity;
 b. interact with R chains of amino acids at the surface of enzyme molecule;
 c. inhibitor binds to active site
 d. inhibitor does not bind to active site
 e. inhibitor does not bind to active site;
 f. inhibitor binds to allosteric site;
 g. substrate cannot bind due to blockage of active site
 h. substrate cannot bind due to disruption/change in shape of active site;
 i. inhibition is reversible
 j. inhibition is (usually) permanent;
 k. inhibitor has similar shape to substrate
 l. inhibitor does not have similar shape to substrate;
 m. can be reversed by increasing substrate concentration
 n. adding substrate does not reduce inhibition;
 o. a valid example of each;"
ib,biology,life_biology,Various mechanisms can lead to inhibition in biological systems. A toxin is a substance capable of disrupting metabolic processes in organisms.,Rotetext is a naturally occurring toxin that blocks the electron transport chain in insects and fish. Outline the consequences of exposure to a toxin like rotetext for cell respiration.,"a. lower rate of aerobic respiration / inhibits aerobic respiration;
 b. reduced NAD (not oxidised) accumulates;
 c. fewer/no electrons (from reduced NAD and FADH) to be transported by carriers;
 d. less/no energy to transfer protons (from matrix to intermembrane space);
 e. proton gradient cannot be maintained;
 f. less/no diffusion of protons through ATP synthase;
 g. ADP is not phosphorylated / less ATP produced / no energy to produce ATP;
 h. oxygen not binding to protons / accepting electrons / no water formed;"
ib,biology,life_biology,Changes in the form of biological molecules lead to changes in their function.,Outline the role of UV radiation as a mutagen.,"a. affects/damages/causes change in oncogenes/errors in DNA repair;
 b. UV radiation might alter complementary base pairing/break hydrogen bonds/fuse bases;
 c. double helix may uncoil;
 d. strands may separate/break;
 e. DNA sequence may be altered/DNA bases may re-connect to different bases after separating;
 f. DNA strand may break into pieces / fragments of DNA may be lost;"
ib,biology,life_biology,Changes in the form of biological molecules lead to changes in their function.,Explain how the function of DNA is linked to its molecular structure.,"a. DNA base sequence provides information;
 b. gene expression / genes provides a template for the construction of a protein;
 c. transcription occurs / mRNA is built using DNA as a template;
 d. DNA nucleotide structure described/sugar and phosphate and base;
 e. polymer of nucleotides makes a DNA strand;
 f. DNA has two anti-parallel strands;
 g. complementary base pairs/A pairs with T and C with G;
 h. strands linked by hydrogen bonding between bases;
 i. double helix shape / helix held by hydrogen bonds;"
ib,biology,life_biology,Changes in the form of biological molecules lead to changes in their function.,Describe the use of gene knockout technology in research.,"a. gene knockout technology is a genetic engineering technique/intentional alteration in the sequence of a gene;
 b. making a gene inactive;
 c. using site specific nucleases / CRISPR;
 d. researcher observes changes in phenotype of organism;
 e. allows researcher to determine function of the gene;
 f. entire library of knockout organisms exists;
 g. made available to researchers;"
ib,biology,life_biology,There are a number of advantages to specificity.,Explain how vaccination can result in specific immunity to a viral disease.,"a. vaccinations are specific to a specific disease;
 b. vaccines contain non-self antigens/antigens from pathogens;
 c. can be live relative/attenuated version of the virus;
 d. trigger a primary immune response (without causing the disease);
 e. lymphocytes with specific receptors (are activated and) produce memory cells;
 f. (memory cells) cause a faster production of antibodies on a second exposure/exposure to the disease;
 g. (memory cells) provide long term immunity;"
ib,biology,life_biology,There are a number of advantages to specificity.,Outline the role of membrane proteins in the movement of specific ions at specific times in the transmission of nerve impulses.,"a. (during depolarization) Na+ channels open;
 b. allowing Na+ to flow into the axon;
 c. (during repolarization) K+ channels open;
 d. allowing K+ to flow out of the axon;
 e. the Na+/K+ pump returns the (axon) membrane to the resting potential;
 f. by moving 3Na+ out and 2K+ in;"
ib,biology,life_biology,There are a number of advantages to specificity.,Describe the barriers that exist to hybridization between species.,"a. courtship behaviour is often complex and unique to a species;
 b. (at several stages in courtship ritual) rejection occurs if characteristic behaviour not exhibited;
 c. species-specific egg fertilization;
 d. compatibility of acrosome with vitelline layer;
 e. inability of successfully attached wrong species sperm to develop continuity with egg membrane;
 f. sterility of interspecific hybrids;
 g. due to differences in chromosome number;"
ib,biology,life_biology,Various mechanisms can lead to inhibition in biological systems. A toxin is a substance capable of disrupting metabolic processes in organisms.,Describe how toxins such as DDT might concentrate in the bodies of birds.,"a. some toxins/DDT are persistent/degrade slowly (once released into the environment);
 b. (some toxins/DDT) enter the food chain through producers/lower trophic levels;
 c. (some toxins/DDT) are passed on to higher trophic levels in the food chain;
 d. (they are) difficult to excrete / are not excreted;
 e. (they) accumulate in fatty tissues of animals;
 f. higher trophic levels/top consumers have higher/the highest concentration of pesticides in their bodies;
 g. they bioaccumulate/biomagnify;"
ib,biology,life_biology,Various mechanisms can lead to inhibition in biological systems. A toxin is a substance capable of disrupting metabolic processes in organisms.,Toxins often act as inhibitors. Compare and contrast competitive and non-competitive enzyme inhibition.,"a. slow down enzyme activity;
 b. interact with R chains of amino acids at the surface of enzyme molecule;
 c. inhibitor binds to active site
 d. inhibitor does not bind to active site
 e. inhibitor does not bind to active site;
 f. inhibitor binds to allosteric site;
 g. substrate cannot bind due to blockage of active site
 h. substrate cannot bind due to disruption/change in shape of active site;
 i. inhibition is reversible
 j. inhibition is (usually) permanent;
 k. inhibitor has similar shape to substrate
 l. inhibitor does not have similar shape to substrate;
 m. can be reversed by increasing substrate concentration
 n. adding substrate does not reduce inhibition;
 o. a valid example of each;"
ib,biology,life_biology,Various mechanisms can lead to inhibition in biological systems. A toxin is a substance capable of disrupting metabolic processes in organisms.,Rotetext is a naturally occurring toxin that blocks the electron transport chain in insects and fish. Outline the consequences of exposure to a toxin like rotetext for cell respiration.,"a. lower rate of aerobic respiration / inhibits aerobic respiration;
 b. reduced NAD (not oxidised) accumulates;
 c. fewer/no electrons (from reduced NAD and FADH) to be transported by carriers;
 d. less/no energy to transfer protons (from matrix to intermembrane space);
 e. proton gradient cannot be maintained;
 f. less/no diffusion of protons through ATP synthase;
 g. ADP is not phosphorylated / less ATP produced / no energy to produce ATP;
 h. oxygen not binding to protons / accepting electrons / no water formed;"
ib,biology,life_biology,Changes in the form of biological molecules lead to changes in their function.,Outline the role of UV radiation as a mutagen.,"a. affects/damages/causes change in oncogenes/errors in DNA repair;
 b. UV radiation might alter complementary base pairing/break hydrogen bonds/fuse bases;
 c. double helix may uncoil;
 d. strands may separate/break;
 e. DNA sequence may be altered/DNA bases may re-connect to different bases after separating;
 f. DNA strand may break into pieces / fragments of DNA may be lost;"
ib,biology,life_biology,Changes in the form of biological molecules lead to changes in their function.,Explain how the function of DNA is linked to its molecular structure.,"a. DNA base sequence provides information;
 b. gene expression / genes provides a template for the construction of a protein;
 c. transcription occurs / mRNA is built using DNA as a template;
 d. DNA nucleotide structure described/sugar and phosphate and base;
 e. polymer of nucleotides makes a DNA strand;
 f. DNA has two anti-parallel strands;
 g. complementary base pairs/A pairs with T and C with G;
 h. strands linked by hydrogen bonding between bases;
 i. double helix shape / helix held by hydrogen bonds;"
ib,biology,life_biology,Changes in the form of biological molecules lead to changes in their function.,Describe the use of gene knockout technology in research.,"a. gene knockout technology is a genetic engineering technique/intentional alteration in the sequence of a gene;
 b. making a gene inactive;
 c. using site specific nucleases / CRISPR;
 d. researcher observes changes in phenotype of organism;
 e. allows researcher to determine function of the gene;
 f. entire library of knockout organisms exists;
 g. made available to researchers;"
ib,biology,genetics,"In humans, sex is determined genetically and human populations have approximately equal numbers of males and females in each generation.",Outline how sex is determined in humans.,"a. genetically determined/determined by (pair of) sex chromosomes/X and Y chromosomes;
b. sperm carry either an X or a Y chromosome;
c. egg is X and if fertilized by X sperm leads to a female child / XX female OR egg is X and if fertilized by Y sperm leads to a male child / XY male;"
ib,biology,genetics,"In humans, sex is determined genetically and human populations have approximately equal numbers of males and females in each generation.",Explain how sexual reproduction gives rise to genetic variation.,"a. recombination of parental alleles during fertilization;
b. fertilized egg contains a mixture of paternal and maternal chromosomes;
c. crossing over/meiosis gives rise to new combinations of alleles;"
ib,biology,molecular_biology,Mutations have a range of consequences for organisms.,Outline how mutation can lead to cancer.,"a. mutations are random changes in the sequences of genes/DNA;
b. (mutation) may involve addition/deletion/substitution/inversion of DNA bases;
c. (mutations) in tumour suppressor genes/oncogenes;
d. uncontrolled cell division/mitosis occurs;
e. abnormal cells cannot perform their function;
f. they divide repeatedly to form tumours;"
ib,biology,genetics,Mutations have a range of consequences for organisms.,Outline one example of a human disease caused by an autosomal recessive allele.,"a. name of condition e.g. PKU / other example;
b. mutation in the gene for (the enzyme) phenylalanine hydroxylase (PAH) / if other example used name of gene that is mutated;
c. outline of inheritance pattern, e.g. both parents need to carry the recessive allele;
d. (without dietary modification, result is) toxic build-up of phenylalanine in the blood / low levels of tyrosine / symptoms if other example used;
e. phenylalanine is not converted to tyrosine (by the enzyme) / effect of the mutation on the protein/enzyme/metabolism if other example used;
f. requires dietary modification (as treatment) / treatment for other example used;"
ib,biology,evolution_biodiversity,Mutations have a range of consequences for organisms.,Explain the role of mutations in evolution.,"a. new phenotypes/traits may result from mutations;
b. mutations increase variation/differences between individuals in a population/species;
c. individuals with new phenotype/trait may have more chances of survival;
d. (more chances of survival) in a changing environment / presence of selection pressures;
e. (selection pressure can be) intraspecific competition/abiotic factor;
f. natural selection occurs;
g. individuals with (advantageous) mutation have longer life spans/live longer;
h. (so) more chances of reproduction;
i. mutated gene passed on to new generations;
j. allele frequencies change in the population over time;
k. evolution is a consequence of natural selection;"
ib,biology,human_physiology,"Biological systems are sensitive to temperature changes, so they have mechanisms to resist temperature changes.",Explain the mechanisms involved in thermoregulation in humans.,"a. normal body temperature is 37°C;
b. peripheral thermoreceptors detect environmental temperature;
c. supporting conscious behaviour to avoid temperature extremes, e.g. wearing more clothing;
d. sends messages to hypothalamus/temperature control centre of the brain;
e. the hypothalamus sends messages to pituitary gland;
f. (pituitary) releases TSH;
g. stimulating thyroxin release from thyroid;
h. thyroxin controls metabolic rate / production of heat;
i. muscle random contraction/shivering to generate heat;
j. (brown) adipose tissue burns fat to generate waste heat;
k. vasoconstriction to conserve heat / vasodilation to exchange heat with the environment;"
ib,biology,human_physiology,"Biological systems are sensitive to temperature changes, so they have mechanisms to resist temperature changes.",Explain the relationship between temperature and the activity of enzymes.,"a. as temperature increases, the rate of molecular motion increases;
b. increasing the frequency of collision between enzyme and substrate;
c. increasing the rate of reaction;
d. until an optimum temperature is reached;
e. with further increase in temperature, enzymes denature;"
ib,biology,human_physiology,"Biological systems are sensitive to temperature changes, so they have mechanisms to resist temperature changes.",Distinguish between the thermal properties of air and water as they relate to the habitat of animals.,"a. water has a (much) higher specific heat capacity (than air);
b. water requires more energy gain/loss to change temperature;
c. (water) provides more stable thermal habitats than air / temperature of water bodies remains more constant than air temperature;
d. water has a higher thermal conductivity than air;
e. more heat is transferred from organisms to water than to air;
f. water is a good evaporative coolant and air is not;
g. aquatic mammals have (proportionally) more body fat as insulation;"
ib,chemistry,redox,"Hypochlorous acid, HOCl, is a sterilizing agent used in swimming pools and is produced when chlorine reacts with water.

$$\mathrm{Cl}_2(\mathrm{aq}) + \mathrm{H}_2\mathrm{O}(\mathrm{l})\rightleftharpoons \mathrm{HOCl}(\mathrm{aq}) + \mathrm{HCl}(\mathrm{aq})$$","(a) Deduce the oxidation states of chlorine in the reactants and products.

Reactant: $\mathrm{Cl}_2$

Products: HOCl:

HCl:","Reactant: Cl2 0
Products: HOCl +1
HCl -1"
ib,chemistry,equilibrium,"Hypochlorous acid, HOCl, is a sterilizing agent used in swimming pools and is produced when chlorine reacts with water.

$$\mathrm{Cl}_2(\mathrm{aq}) + \mathrm{H}_2\mathrm{O}(\mathrm{l})\rightleftharpoons \mathrm{HOCl}(\mathrm{aq}) + \mathrm{HCl}(\mathrm{aq})$$",(b) Explain why more chlorine reacts with water when $\mathrm{NaOH(aq)}$ is added.,equilibrium shifts to the right/product AND HCl/HOCl/H+ removed/neutralized <by NaOh>
ib,chemistry,acids_bases,"Hypochlorous acid, HOCl, is a sterilizing agent used in swimming pools and is produced when chlorine reacts with water.

$$\mathrm{Cl}_2(\mathrm{aq}) + \mathrm{H}_2\mathrm{O}(\mathrm{l})\rightleftharpoons \mathrm{HOCl}(\mathrm{aq}) + \mathrm{HCl}(\mathrm{aq})$$",(d) Suggest why chlorine is not often added to swimming pools directly.,"Any one of:
toxic
gas
difficult to handle/store"
ib,chemistry,redox,"Hypochlorous acid, HOCl, is a sterilizing agent used in swimming pools and is produced when chlorine reacts with water.

$$\mathrm{Cl}_2(\mathrm{aq}) + \mathrm{H}_2\mathrm{O}(\mathrm{l})\rightleftharpoons \mathrm{HOCl}(\mathrm{aq}) + \mathrm{HCl}(\mathrm{aq})$$

Ammonia released from sweat and urine reacts with HOCl to form a range of compounds including chloramines.","(i) Deduce an equation for the formation of dichloramine, $\mathrm{NHCl}_2$ (aq), from ammonia and HOCl (aq).",NH3(aq) + 2HOCl(aq) → NHCl2(aq) + 2H2O(l)
ib,chemistry,energetics_thermochemistry,"Hypochlorous acid, HOCl, is a sterilizing agent used in swimming pools and is produced when chlorine reacts with water.

$$\mathrm{Cl}_2(\mathrm{aq}) + \mathrm{H}_2\mathrm{O}(\mathrm{l})\rightleftharpoons \mathrm{HOCl}(\mathrm{aq}) + \mathrm{HCl}(\mathrm{aq})$$",(g) Suggest two reasons why operating a swimming pool at a lower temperature is favourable for the environment.,"Any two of
lower water evaporation
reduce energy consumption/less energy needed to heat the water
higher solubility of chlorine <so less chlorine lost>"
ib,chemistry,measurement_data_processing,A student investigates the effect of exposure to the air on the ascorbic acid (vitamin C) concentration in a specific orange juice. Equal volumes of orange juice are sealed into identical flasks and placed in a refrigerator for two weeks. The samples in the refrigerator are exposed to the air by removing the stopper for a different number of hours each day as shown.,(a) Identify two variables that are controlled.,Any two for [1 max] type of orange juice temperature light intensity «initial» surface area OR «initial» volume AND flask
ib,chemistry,measurement_data_processing,"A student investigates the effect of exposure to the air on the ascorbic acid (vitamin C) concentration in a specific orange juice. Equal volumes of orange juice are sealed into identical flasks and placed in a refrigerator for two weeks. The samples in the refrigerator are exposed to the air by removing the stopper for a different number of hours each day as shown.

The concentration of ascorbic acid is determined by titration with a standard iodine solution. Every few days, $10.00cm^3$ of orange juice is removed from each sample, diluted to $100.0cm^3$ , and titrated.",(i) Suggest why the juice is diluted before titration.,"Any one of: 
to perform multiple titrations
too concentrated «so using too much iodine solution»
end-point colour easier to see"
ib,chemistry,measurement_data_processing,"A student investigates the effect of exposure to the air on the ascorbic acid (vitamin C) concentration in a specific orange juice. Equal volumes of orange juice are sealed into identical flasks and placed in a refrigerator for two weeks. The samples in the refrigerator are exposed to the air by removing the stopper for a different number of hours each day as shown.

The concentration of ascorbic acid is determined by titration with a standard iodine solution. Every few days, $10.00cm^3$ of orange juice is removed from each sample, diluted to $100.0cm^3$ , and titrated.",(ii) Identify a possible systematic error with this method regarding the sample that is exposed for zero hours.,"flask has to be opened to withdraw samples «so not 0 h»
OR
air was present in the flask at the start «so the ascorbic acid was exposed to air»"
ib,chemistry,measurement_data_processing,"A student investigates the effect of exposure to the air on the ascorbic acid (vitamin C) concentration in a specific orange juice. Equal volumes of orange juice are sealed into identical flasks and placed in a refrigerator for two weeks. The samples in the refrigerator are exposed to the air by removing the stopper for a different number of hours each day as shown.

The concentration of ascorbic acid is determined by titration with a standard iodine solution. Every few days, $10.00cm^3$ of orange juice is removed from each sample, diluted to $100.0cm^3$ , and titrated.",(iii) Suggest how an additional flask could be set up to verify whether the systematic error in (ii) has occurred.,"titrate only once after two weeks
OR
fill flask with nitrogen/argon/inert gas
OR
withdraw samples with syringe «without opening flask»"
ib,chemistry,measurement_data_processing,"A student investigates the effect of exposure to the air on the ascorbic acid (vitamin C) concentration in a specific orange juice. Equal volumes of orange juice are sealed into identical flasks and placed in a refrigerator for two weeks. The samples in the refrigerator are exposed to the air by removing the stopper for a different number of hours each day as shown.

The concentration of ascorbic acid is determined by titration with a standard iodine solution. Every few days, $10.00cm^3$ of orange juice is removed from each sample, diluted to $100.0cm^3$ , and titrated.",(c) The following data are collected during a titration. Final burette reading $= 16.10 \pm 0.05 \mathrm{cm}^3$ Initial burette reading $= 1.10 \pm 0.05 \mathrm{cm}^3$ Calculate the percentage uncertainty of the titre.,"0.1 cm³
«15.0 cm³ × 100 = » 0.7 «%»"
ib,chemistry,measurement_data_processing,A student investigates the effect of exposure to the air on the ascorbic acid (vitamin C) concentration in a specific orange juice. Equal volumes of orange juice are sealed into identical flasks and placed in a refrigerator for two weeks. The samples in the refrigerator are exposed to the air by removing the stopper for a different number of hours each day as shown.,(e) Suggest an extension to the investigation that would generate further recommendations for the storage of orange juice.,"Any one of: effect of temperature/light AND would show the value of refrigeration/darkness effect of preservative
compare types of orange juice «e.g. fresh, from concentrate, etc.»"
ib,chemistry,energetics_thermochemistry,"A student investigates the effect of pressure on the volume of carbon dioxide gas released from a carbonated drink poured into a flask. To alter the pressure on the carbonated drink, masses are placed on top of the piston of the gas syringe as shown. The graph shows some of the data collected.",(c) Suggest two reasons why the volume of $\mathrm{CO}_2$ collected in the gas syringe is smaller when more masses are placed on top of the piston.,"Any two:
drink releases gas more slowly at higher pressure
gas occupies lower volume at higher pressure
gas is more soluble «in carbonated drink» at higher pressure"
ib,chemistry,measurement_data_processing,"A student investigates the effect of pressure on the volume of carbon dioxide gas released from a carbonated drink poured into a flask. To alter the pressure on the carbonated drink, masses are placed on top of the piston of the gas syringe as shown. The graph shows some of the data collected.","(d) Calculate the percentage decrease in the final volume of $\mathrm{CO}_2$ per $100\mathrm{g}$ mass placed on the piston, using the results of Experiment 1 and Experiment 3 at $100\mathrm{s}$ .","33.0 cm³ – 11.5 cm³ 100
« 33.0 cm³ × 4 16.3 «% per 100 g»"
ib,chemistry,stoichiometry,"A monoprotic acid, HX, is found to have the following composition by mass: C = 39.99% H = 6.73% O = 53.28%",(a) Determine the empirical formula of the compound HX.,"nC = ⟨39.99g / 12.01g mol⁻¹ = 3.33 (mol)⟩
nH = ⟨6.73g / 1.01g mol⁻¹ = 6.66 (mol)⟩
nO = ⟨53.28g / 16.00g mol⁻¹ = 3.33 (mol)⟩
CH₂O"
ib,chemistry,stoichiometry,"A monoprotic acid, HX, is found to have the following composition by mass: C = 39.99% H = 6.73% O = 53.28%","(b) 25.00 cm³ of a solution, containing 1.51 g of HX is titrated with a 0.750 mol dm⁻³ solution of NaOH (aq). The HX (aq) solution is exactly neutralized by 22.30 cm³ of the NaOH (aq) solution. Determine the molar mass (M) of HX.","nHX = ⟨nNaOH⟩ = 0.750 (mol dm⁻³) × 0.02230 (dm³) / 0.0167 (mol)
M_HX = ⟨1.51g / 0.0167mol⟩ = 90.4g mol⁻¹"
ib,chemistry,stoichiometry,"A monoprotic acid, HX, is found to have the following composition by mass: C = 39.99% H = 6.73% O = 53.28%",(c) State the molecular formula of HX.,C₃H₆O₃
ib,chemistry,organic_chemistry,"A monoprotic acid, HX, is found to have the following composition by mass: C = 39.99% H = 6.73% O = 53.28%",(d) HX reacts with aqueous sodium hydroxide according to the equation: HX(aq) + NaOH(aq) → NaX(aq) + H₂O(l). Identify a functional group present in HX.,carboxyl/COOH
ib,chemistry,atomic_structure,"Scientific models are used to explain the structure of matter.
An α-particle is a helium-4 nucleus. In an experiment, α-particles are accelerated towards a thin sheet of gold and their resulting paths are detected, giving evidence of the positive charge of the nucleus.",(b) (i) Outline the appearance of the emission spectrum of helium.,discrete/series of lines of different frequency/wavelength
ib,chemistry,atomic_structure,"Scientific models are used to explain the structure of matter.
An α-particle is a helium-4 nucleus. In an experiment, α-particles are accelerated towards a thin sheet of gold and their resulting paths are detected, giving evidence of the positive charge of the nucleus.",(c) Outline why models of the atom have evolved over time.,"Any one of:
new evidence
new technology
developments in related models
models incomplete/failed to account for all observations"
ib,chemistry,energetics_thermochemistry,"The development of the lithium-ion battery won the 2019 chemistry Nobel Prize.
The diagram represents a cell in such a battery delivering a current.The discharge of the lithium-ion battery is a spontaneous chemical reaction producing a potential difference and an increase in temperature.",(b) (i) Deduce the signs of the following: ΔH_discharge Ecell: ΔG_discharge,"ΔH_discharge: negative
AND
Ecell: positive
AND
ΔG_discharge: negative"
ib,chemistry,energetics_thermochemistry,"The development of the lithium-ion battery won the 2019 chemistry Nobel Prize.
The diagram represents a cell in such a battery delivering a current. The discharge of the lithium-ion battery is a spontaneous chemical reaction producing a potential difference and an increase in temperature.",(b) (ii) The lithium-ion battery can be recharged by reversing the reactions at each electrode. Compare the absolute value of ΔG_recharge and ΔG_discharge.,ΔG_recharge > ΔG_discharge
ib,chemistry,kinetics,"The development of the lithium-ion battery won the 2019 chemistry Nobel Prize.
In a simulation, equal masses of potassium and lithium are added to water and the time aken for the metals to fully react is recorded. Five different increasing masses of each metal are used, and the reaction is timed.",(c) (ii) Suggest a reason why comparing the time for complete reaction of equal masses is not a valid measure of reactivity.,equal masses «of different substances» do not contain equal amounts/moles
ib,chemistry,bonding_structure,"The development of the lithium-ion battery won the 2019 chemistry Nobel Prize.
In a simulation, equal masses of potassium and lithium are added to water and the time aken for the metals to fully react is recorded. Five different increasing masses of each metal are used, and the reaction is timed.","(c) (iii) Lithium carbide, Li2C2, is one of many compounds of lithium and carbon. Determine the percentage covalent character and bonding type in this compound by using sections 9 and 17 of the data booklet.","«Avg electronegativity = 1.8
Δ electronegativity = 1.6»
% covalent character = 45-55
ionic"
ib,chemistry,energetics_thermochemistry,The development of the lithium-ion battery won the 2019 chemistry Nobel Prize.,"(c) (iv) Calculate the Gibbs energy of formation, ΔG°, in kJ mol⁻¹, for Li₂C₂ at 298.15 K. Use the data provided.","«ΔG° = ΔH° - TΔS° = -62 - 298 x -0.011 =»
-59 «kJ mol⁻¹»"
ib,chemistry,bonding_structure,The development of the lithium-ion battery won the 2019 chemistry Nobel Prize.,(c) (v) Draw the Lewis formula of the anion in the salt Li₂C₂.,"[:C≡C:]²⁻
2- charge
:C≡C:"
ib,chemistry,bonding_structure,The development of the lithium-ion battery won the 2019 chemistry Nobel Prize.,(c) (vi) State the type of hybridization shown by the carbon atoms in the anion.,sp
ib,chemistry,acids_bases,"Hydrochloric acid is an important chemical reactant and industrial chemical.
A pH probe is placed in a small volume of 0.10 mol dm⁻³ solution of hydrochloric acid. The pH is recorded while a steady stream of distilled water is added to the acid at constant temperature.",(a) (ii) The experiment is repeated using 0.10 mol dm⁻³ ethanoic acid at the same temperature. Calculate the initial pH of the ethanoic acid.,"K_a = [H⁺][CH₃COO⁻]/[CH₃COOH]
OR
K_a = [H⁺]²/[CH₃COOH]
OR
pK_a = 2pH - 1
OR
pH = (pK_a + 1)/2 =
2.88"
ib,chemistry,energetics_thermochemistry,"Heptadecane, C₁₇H₃₆, can be extracted from crude oil or cactus plants.",(a) Write an equation for the complete combustion of C₁₇H₃₆.,C₁₇H₃₆(l) + 26O₂(g) → 17CO₂(g) + 18H₂O(l)
ib,chemistry,energetics_thermochemistry,"Heptadecane, C₁₇H₃₆, can be extracted from crude oil or cactus plants. Lithium carbide, Li2C2, is one of many compounds of lithium and carbon.",(b) (i) Calculate the maximum energy produced when 2.00 g of C₁₇H₃₆ is combusted.,"nC₁₇H₃₆ = (2.00 g / [(17 × 12.01 g mol⁻¹) + (36 × 1.01 g mol⁻¹)] = 2.00 g / 0.008315/0.00831 = mol)
« energy = 11350 kJ mol⁻¹ × 0.008315 mol = » 94.4 = kJ"
ib,chemistry,energetics_thermochemistry,"Heptadecane, C₁₇H₃₆, can be extracted from crude oil or cactus plants. Lithium carbide, Li2C2, is one of many compounds of lithium and carbon.",(b) (ii) Determine the maximum temperature change when 500.0 cm³ of water is heated by a 2.00 g sample of C₁₇H₃₆.,"94 400 = 500.0 g × 4.18 J g⁻¹ K⁻¹ × ΔT
ΔT = 45.2 = K"
ib,chemistry,measurement_data_processing,"Heptadecane, C₁₇H₃₆, can be extracted from crude oil or cactus plants. Lithium carbide, Li2C2, is one of many compounds of lithium and carbon",(b) (iii) Outline two assumptions made in the calculation in (b)(ii).,"Any two:
water does not evaporate
heat is not lost to the surroundings
OR
all heat is transferred to the water
density of water is 1 g cm⁻³
water is pure
complete combustion"
ib,chemistry,energetics_thermochemistry,"Heptadecane, C₁₇H₃₆, can be extracted from crude oil or cactus plants.",(c) Explain why biofuels contribute less to climate change than fossil fuels.,"CO₂ consumed while plant is growing «and later released when biofuel is combusted»
OR
photosynthesis uses up CO₂ «later released when biofuel is combusted»"
ib,chemistry,energetics_thermochemistry,"Heptadecane, C₁₇H₃₆, can be extracted from crude oil or cactus plants.","(d) (i) Determine the standard enthalpy change, ΔH°, for the reaction stated, using section 12 of the data booklet.","bonds broken: 4(C-C)/4×346
bonds formed: 2(C=C)/2×614
△H°= «4×346kJ-2×614kJ/1384kJ-1228kJ»= 
△H°= «+»156«kJ»"
ib,chemistry,energetics_thermochemistry,"Heptadecane, C₁₇H₃₆, can be extracted from crude oil or cactus plants.",(d) (ii) Determine the enthalpy change of reaction. Use the data provided and section 13 of the data booklet.,"«△H=Σ△Hf (products)-Σ△Hf (reactants)»
△H=(-311.5+2(52.0))-(-393.9)
△H= «+»186.4«kJ mol⁻¹»"
ib,chemistry,energetics_thermochemistry,"Heptadecane, C₁₇H₃₆, can be extracted from crude oil or cactus plants.",(d) (iii) Comment on the difference between the two values calculated in (d)(i) and (d)(ii).,"more accurate than (d)(i) as bond energies are average values
OR
(d)(ii) more accurate than (d)(i) as not specific to bonds in the reaction"
ib,chemistry,energetics_thermochemistry,"Heptadecane, C₁₇H₃₆, can be extracted from crude oil or cactus plants.","(d) (iv) Predict the sign of the entropy change of the reaction, giving a reason.",positive AND increase in number of moles/molecules «of gas»
ib,chemistry,energetics_thermochemistry,"Heptadecane, C₁₇H₃₆, can be extracted from crude oil or cactus plants.","(d) (v) Discuss, with reference to (d)(ii) and (d)(iv), how temperature affects the spontaneity of the reaction.","△H>0 «and △S>0» AND reaction spontaneous if △G «= △H-△S» < 0
at high«er» T reaction «more» spontaneous/△G «more» negative"
ib,chemistry,organic_chemistry,"Heptadecane, C₁₇H₃₆, can be extracted from crude oil or cactus plants.",(e) Ethene can be converted to ethanol in one reaction. State the equation for this reaction.,C₂H₄(g) + H₂O(g) → C₂H₅OH(g)
ib,chemistry,organic_chemistry,"Heptadecane, C₁₇H₃₆, can be extracted from crude oil or cactus plants.",(f) (i) Identify the type of reaction and the side product X(l).,condensation/esterification AND H₂O / water
ib,chemistry,organic_chemistry,"Heptadecane, C₁₇H₃₆, can be extracted from crude oil or cactus plants.",(f) (ii) Calculate the atom economy of the reaction.,"(20(12.01) + 38(1.01) + 2(16.00) = 310.58
100 × 310.58
(310.58 + 18.02) =
94.5 %"
ib,chemistry,organic_chemistry,"Heptadecane, C₁₇H₃₆, can be extracted from crude oil or cactus plants.",(f) (iii) Discuss why the atom economy of a reaction is an important consideration when evaluating the impact of a reaction in an industrial process.,"Any two of:
sustainable development
more economical/efficient
better use of natural resources
reduces waste"
ib,chemistry,equilibrium,"Heptadecane, C₁₇H₃₆, can be extracted from crude oil or cactus plants.","(f) (iv) Deduce the equilibrium constant expression, Kc, for the reaction. Assume that the reaction is homogeneous.","K= [C₁₇H₃₃COOCH₂CH₃][H₂O]
[C₁₇H₃₃COOH][CH₃CH₂OH]"
ib,chemistry,equilibrium,"Heptadecane, C₁₇H₃₆, can be extracted from crude oil or cactus plants.",(g) (i) Determine the amount of ethyl oleate present in the reaction mixture at equilibrium when 0.10 mol dm⁻³ of oleic acid reacts with 0.10 mol dm⁻³ of ethanol at 75°C and state any assumptions you have made in your calculation.,"K small AND [reactants]eqm = [reactants]0 /0.10
noleate = « (0.10 × 0.10 × 9.3×10⁻⁵)²/² » 9.6×10⁻⁴ «mol»"
ib,chemistry,equilibrium,"Heptadecane, C₁₇H₃₆, can be extracted from crude oil or cactus plants.",(g) (ii) State one method of increasing the yield.,"remove water
OR
add more oleic acid
OR
add more ethanol"
ib,chemistry,organic_chemistry,Halogens are important reactants in the laboratory and in the environment.,"(a) (i) Write an equation for the homolytic fission of chlorine under UV light, showing the movement of electrons.","Cl-Cl → 2 Cl·
2 Cl·
single-barbed/fish-hooks"
ib,chemistry,organic_chemistry,Halogens are important reactants in the laboratory and in the environment.,"(a) (ii) Under different conditions, chlorine molecules can break down by heterolytic fission. Write an equation showing the movement of electrons.","Cl-Cl → Cl⁺ + Cl⁻
full/double-barbed arrow AND charges on both ions are required for mark."
ib,chemistry,organic_chemistry,Halogens are important reactants in the laboratory and in the environment.,"(a) (iii) Identify, giving a reason, which one of the three species produced in (a)(i) and (a)(ii) is an electrophile.",Cl⁺ AND can accept a pair of electrons to form a new bond
ib,chemistry,organic_chemistry,Halogens are important reactants in the laboratory and in the environment.,(a) (iv) Draw the full structural formula of the most stable carbocation formed in the reaction between hydrogen chloride and propene.,"H H H
H - C - C - C - H
+
H H"
ib,chemistry,organic_chemistry,Halogens are important reactants in the laboratory and in the environment.,(a) (v) Outline why this intermediate is the most stable.,positive inductive effects from two -CH₃/methyl groups
ib,chemistry,bonding_structure,Halogens are important reactants in the laboratory and in the environment.,"(b) (iii) Predict, giving a reason, how the boiling points of branched fluoroalkanes compare to their straight-chain isomers.","lower
branched isomers have smaller surface area
weaker van der Waals' forces"
ib,chemistry,bonding_structure,Halogens are important reactants in the laboratory and in the environment.,(b) (iv) Explain why primary bromoalkanes have higher boiling points compared to the corresponding fluoroalkanes.,"bromine has higher electronegativity
higher dipole-dipole interactions
higher molecular mass
higher van der Waals' forces"
ib,chemistry,organic_chemistry,Halogens are important reactants in the laboratory and in the environment.,(c) (i) Draw the structures of 2-bromobutane and its tertiary isomer.,"H₃C
CH
CH₂
CH₃
Br
CH₃
C
CH₃
Br"
ib,chemistry,organic_chemistry,Halogens are important reactants in the laboratory and in the environment.,(c) (ii) One of the isomers in (c)(i) exists as enantiomers. Draw their stereochemical formulas.,"CH₂CH₃
CH₃
Br
CH₃
H
mirror
CH₃CH₂
C
CH₃
Br"