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The diagram below shows a common charcoal burner .Assume the burning take place in a room with sufficient supply of air. (a)Explain what happens around:
28 (i)Layer A Sufficient/excess air /oxygen enter through the air holes into the burner .It reacts with/oxidizes Carbon to carbon(IV)oxide Chemical equation C(s) + O2(... | {
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29 Dry carbon(IV)oxideHEATCopper(II)oxideBlue flame A (a)State and explain the observations made in the combustion tube. Observation Colour change from black to brown Explanation Carbon (II)oxide reduces black copper(II)oxide to brown copper metal itself oxidized to Carbon(IV)oxide. Chemical equation CO(g) + CuO (s) ->... | {
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Explain. -It is a green house gas thus causes global warming. -It dissolves in water to form acidic carbonic acid which causes “acid rain” (f)Explain using chemical equation why lime water is used to test for the presence of Carbon (IV) oxide instead of sodium hydroxide. 31 Using lime water/calcium hydroxide: - a visib... | {
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Ethan-1,2-dioic acid Chemical equation HOOCCOOH(aq) -> CO2(g)+CO(g)+H2O(l) (h)Both carbon(II)oxide and carbon(IV)oxide affect the environment.
Explain why carbon(II)oxide is more toxic/poisonous.
-Both gases are colourless,denser than water and odourless.
-Carbon(II)oxide is preferentially absorbed by human/mammalia... | {
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PRACTICAL CHEMISTRY
Introduction
Scientific subjects are, by their nature, experimental. It is accordingly important that an assessment of a student’s knowledge and understanding of Chemistry should contain a component relating to practical work and experimental skills. This booklet has been produced to help students p... | {
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The tip should be clean and dry before you take an initial volume reading.When your burette is conditioned and filled, with no air bubbles or leaks, take an initial volume reading. A burette-reading card with a black rectangle can help you to take a more accurate reading. Read the bottom of the meniscus. Be sure your e... | {
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Quickly, remove the pipette bulb and put your index finger on the end of the pipette. Gently release the seal made by your finger until the level of the solution meniscus exactly lines up with the mark on the pipette. Practice this with water until you are able to use the pipette and bulb consistently and accurately. (... | {
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Record mass of solid. Don't pick up tare containers with bare hands since your fingerprints add mass. Use tongs to prevent this.Don't lean on the bench while weighing.Do record the mass of your container, if you will need it later.Do check the level indicator bubble before weighing. The two rear balance feet serve as l... | {
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(i) Top-loading Balance
Use a top loading balance to weigh solid material when a precision of 0.1 g is adequate. For more accurate mass measurements or small amounts, use an analytical balance. Using a Top-loading Balance
Check if the balance is turned on. If not, press the on/off button and wait until the display read... | {
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(ii) Close the air hole. Hold a test-tube with its bottom end just above the flame. Carbon deposits on the glass. To test whether unburned carbon gives the yellow colour to the flame, sprinkle powdered charcoal into the flame to see if this gives the same effect. (iii) Open the air hole again. Note whether carbon depos... | {
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Put water in a test-tube and hold a thermometer with the bulb just under the water. Add boiling chips to prevent bumping. Bring the water to the boil with a very small flame and read the thermometer. Note any change in the reading if the thermometer touches the bottom of the test-tube. 5. Boiling point of inflammable l... | {
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Stop heating. Connect a water pump to the sidearm or to the second hole of the 2-hole stopper. When the water stops boiling, turn on the water pump to reduce the pressure. Read the temperature, heat to boiling and read the temperature again. 7(a). Solubility in water Test different salts taken to show that each has a d... | {
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The mass of the sodium bicarbonate dissolved = w3 - w1. The mass of water = w2 - w1 - w3. Calculate the solubility of the sodium bicarbonate as g per 100 g water at room temperature. 8(a) Solubility and particle size To show that small particles dissolve faster than the large particles, add 4 g of coarse able salt to o... | {
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Heat the mixture in an evaporating dish with a funnel placed over it. The iodine sublimes on to the cool sides of the funnel. SEPARATION OF MIXTURES
(b) Separate by distillation Put 10 mL ink in a flat bottom conical flask. Add boiling chips to prevent bumping. Fit a stopper with a delivery tube reaching half way down ... | {
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HEATING AND BURNING DIFFERENT SUBSTANCES Substances that gain mass when heated. Clean 25 cm of magnesium ribbon and cut into 1 cm pieces. Weigh a crucible plus lid, put the pieces of magnesium ribbon in the crucible and weigh again. Put the crucible on a pipe clay triangle supported on a tripod. Heat very gently then s... | {
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Note any loss in mass. (c) Effect of heat on copper sulphate crystals Crush blue copper sulphate crystals and put them into a dry test-tube to a depth of 4 cm. Heat the tube gently. Note whether vapour collects on the cooler parts, change of colour from blue to white, and any liquid collecting in the receiving tube. Id... | {
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(iv) Investigate whether hydrogen is lighter than air by "pouring" the gas into a test-tube held either above the first tube or below it. Use a lighted taper to investigate where the hydrogen has gone. (v) Blow soap bubbles by holding the delivery tube of the apparatus in detergent or soap solution. The hydrogen bubble... | {
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Note the solubility of hydrogen chloride. (ii) Hold a piece of cotton wool soaked in ammonium hydroxide at the mouth of a test-tube of hydrogen chloride. (iii) Shake a test-tube of the gas with water to obtain a solution of hydrogen chloride. Test the solution with an acid/base indicator. Put a piece of magnesium ribbo... | {
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Note: The presence of carbon dioxide can be confirmed by the fact that limewater becomes "milky" when the gas is Passed through it. (f) Cooking and carbon dioxide The purpose of baking powder or soda in cooking is to produce tiny bubbles of carbon dioxide. This expands the pastry, cake or dough, making it light and ple... | {
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Tube 4: Half cover 2 nails with water containing a little common salt dissolved in it. These nails are in contact with air, water and salt. Tube 5: Wrap a piece of zinc foil round part of a nail. Put the nail in the test-tube and almost cover with tap water. Tube 6: Wrap a piece of tin foil round part of the nail. Put ... | {
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Again add water to the beaker until the levels inside and outside the tube are the same and mark the new level. It will be seen that one fifth of the air volume has been used up, suggesting that oxygen has been used up in the rusting of iron. The residual gas does not support combustion of a lighted splint. 13 COLOURED... | {
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(v) Litmus, an extract of lichens, is another plant indicator. An acidic solution turns blue litmus red. An alkaline solution turns red litmus blue. (v) Universal Indicator can be in the form of a solution or dried on filter paper. Universal indicator not only indicates whether a substance is acidic or basic but also h... | {
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Leave to cool. Crystals may not form unless you drop a tiny seed crystal of sodium thiosulphate into the solution. Then crystal growth commences and spreads rapidly through the whole solution. Watch the growth from one centre. Hold the tube in the hand while crystallization occurs. (b) Crystals of naphthalene grow from... | {
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The seed crystal should then grow. Turn the crystal regularly so that growth on all faces is equal. 15. DIFFUSION
(a) Diffusion of heavy carbon dioxide gas upwards (i) Fill a jar with carbon dioxide and invert it over a similar jar full of air. After a few moments separate the jars, pour a little lime water in the lowe... | {
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The colour of the dissolving crystal will spread throughout the water in quite a short time. (ii) Fill a very small open bottle with a strong solution of potassium permanganate, potassium manganate (VII). Place this in a larger jar. Fill the larger jar very carefully by pouring water down the side until the water level... | {
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ELECTRICITY
(a) Solids that conduct electricity The source of the DC supply can be dry cells in series giving 6 volts. The bulb, which should be low power, indicates when the current is flowing. The electrodes may be carbon or steel, perhaps mounted in a wooden support, cork or rubber stopper so as to keep the electrod... | {
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The bulb does not light up so pure water does not conduct electricity. Very gradually stir small crystals of common salt into the water. Note any changes to the bulb as the salt dissolves. Classify substances into the following groups: (a) those which conduct electricity in the solid state and those which do not; (b) t... | {
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The products will be gaseous, or metals which are deposited on the negative electrode. It is composed of an open cylinder of glass approximately 8 cm high and 2.5 cm in diameter. A small bottle of similar size with the bottom cut off would do just as well. The cylinder has a 2-hole rubber stopper carrying two carbon el... | {
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Using carbon electrodes, the following results will be found. (d) ELECTROLYSIS OF WATER Pure water does not conduct electricity. For this reason 2 or 3 mL of dilute sulphuric acid or dilute sodium sulphate solution is added to the water in the electrolysis cell. Connect the cell to the DC supply and watch for bubbles o... | {
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Collect the copper and dry it. Mg(s) + Cu2+(aq) -> Mg2+(aq) + Cu(s) (ii) Repeat the experiment by attempting to displace copper metal using powdered zinc and iron metal. Note the comparative activity of the metals. (b) REACTION OF SODIUM WITH WATER (i) A very safe way of demonstrating the reaction of sodium and water i... | {
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(c) DISPLACEMENT OF HYDROGEN FROM ACIDS BY METALS (i) Pour 5 cm of the acids in the table below into test-tubes. Place a piece of metal foil in each test-tube. Note the formation of hydrogen and compare the different rates at which the bubbles are formed. Rate of formation of hydrogen gas - very rapid, rapid, slight, v... | {
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The sulphur dioxide produced can be collected in gas jars covered with cardboard discs, which have central holes for the delivery tube. (e) REDUCTION OF POTASSIUM PERMANGANATE WITH SULFUR DIOXIDE (i) Add 10 mL of 0.1M solution of potassium permanganate and 10 mL 3M solution of dilute sulphuric acid to 200 mL of water c... | {
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To this mixture of acid and indicator, add a dilute base drop by drop, and count the drops. Within experimental error, it will always take the same number of drops to neutralize the 20 drops of acid provided that the same dropper is used. A teat pipette makes a satisfactory dropper. If the concentration of the acid is ... | {
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On the other hand, when the water containing the ions becomes colder, it is the ions which have gained the energy and the water has lost an equivalent amount. (a) REACTIONS THAT GIVE OUT HEAT ENERGY Be careful! The reaction is vigorous so do not do the experiment in a stoppered bottle! (i) Put white anhydrous copper su... | {
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The increase of temperature should be about 13oC. (iii) Since the volume of water has been doubled by adding one solution to the other, the final solution contains 1 mole of OH- (aq) ions which reacted with 1 mole of H+(aq) ions to form 1 mole of water molecules. We must assume that the specific heat of this moderately... | {
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The potential or voltage will reflect the greater activity of zinc over copper. The current flowing will depend on the extent and rate of the reaction. 2.84 Electrical energy from the displacement of copper by zinc Put concentrated copper sulphate solution in a beaker. Connect copper foil to the positive terminal of a ... | {
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Instead of collecting the gas in a balloon or plastic bag, a more accurate method would be to collect the gas in a burette inverted over water and compare the volume of gas given off in unit time for each grade of marble chips. Another accurate method is to stand a conical flask containing the marble chips and acid on ... | {
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The time for the cross to become invisible should be greater than for the last experiment. Repeat the experiment using 30 mL, 20 mL and 10 mL of this sulphate mixed with 20 mL, 30 mL and 40 mL of distilled water. Plot concentration of the thiosulphate solution against time taken for the reaction. Concentration values m... | {
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Plot a graph for each experiment. Manganese (IV) oxide is usually used as a catalyst in this reaction. The catalyst is not used up during the reaction. A catalyst may slow down a reaction as well as speed it up. 19. BREAKDOWN OF STARCH TO SUGAR FEHLING'S TEST FOR REDUCING SUGARS Starch can be recognized by the deep blu... | {
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BREAKDOWN OF ETHANOL TO ETHENE (ETHYLENE) Absorb ethanol on to cotton wool or asbestos wool and push this to the bottom of a hard glass test-tube. In the middle of the test-tube pack small pieces of unglazed porcelain. Fit a delivery tube to collect ethene gas over water. Have 3 test-tubes ready to collect ethene. Firs... | {
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The liquid does not return to the solid state unless a catalyst is used. The specific catalysts are not usually available in school laboratories. GENERAL EXAMINATION REQUIREMENTS
Apparatus List
This list given below has been drawn up in order to give guidance to schools concerning the apparatus that is expected to be g... | {
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It is important that when candidates record reading they include the appropriate number of decimal places. For example a burette reading of exactly 24.7 cm3 should be recorded in a results table as 24.70cm3. A temperature of reading of exactly 350C should be recorded as 35.50C. When titres have to be averaged, it is im... | {
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The scales should be chosen so that the results are spread out as far apart as the size of the grid allows but not at the expense of using a sensible scale. For example using 1cm to represent 3 units might spread the readings better than using 1 cm to represent 4 units but the scale may be difficult to read. It is alwa... | {
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You can do this with a rapid spin of a Teflon stopcock or by partially opening the stopcock and rinsing the partial drop into the flask with a wash bottle. Ask your TA to demonstrate these techniques for you, in the lab.Make sure you know what the endpoint should look like. For phenolphthalein, the endpoint is the firs... | {
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Measurement of temperature based on a thermometer with 10C graduations. Problems of an investigatory nature, possibly including suitable organic compounds. Filtration. Identification of ions and gasses as specified in the curriculum. HEALTH AND SAFETY
Candidates must follow the health and Safety policy normally operate... | {
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The concentration of a solution is determined from the number of moles of solute dissolved in one litre (1dm3) of solution. If one mole of a solute is dissolved in water and the volume of the solution made up to 1litre (1dm3), this solution in known as a molar solution or 1M solution. If two moles are dissolved in 1lit... | {
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[Ar values: K = 39, Br = 80]
Moles = mass / formula mass, (KBr = 39 + 80 = 119)
mol KBr = 5.95/119 = 0.05 mol
400 cm3 = 400/1000 = 0.4 dm3
molarity = moles of solute / volume of solution
molarity of KBr solution = 0.05/0.4 = 0.125M
2.3 Volumetric calculations (acid-alkali titrations)
Chemical Equations
These balancing ... | {
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the point at which the acid has been neutralised. This process is done in three stages. The acid is poured into the burette. A known volume of the alkali is transferred using a pipette into four separate conical flasks. Two or three drops of suitable indicator are added to each of the conical flasks. The acid is run in... | {
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when the colour just changes. Show the values that can be averaged to obtain an acceptable value for use in calculations (only those values within 0.2 cm 3 should be averaged). Attempt to work out the questions from the first principles and not use the formula method, which has its own limitations. GENERAL NOTES FOR QU... | {
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FLAME TESTS
A tungsten wire loop is first dipped into some concentrated hydrochloric acid to dissolve any oxides and hence clean the wire. It is then dipped into salt powder and introduced into a colourless Bunsen burner flame. The colour is then observed and inferences made. TABLE 7: HEAT ANALYSIS
TABLE 8: SOLUBLE AND... | {
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This prevents combustion since carbon dioxide does not support it and the presence of carbon dioxide stops oxygen reaching the combustible material.
3.CHLORINE GAS
Physical Properties
Chemical Properties
Footnotes:
One of the "family" of halogen gases (iodine and bromine are in the same family)
Used in water purificat... | {
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18.0.0 ACIDS, BASES AND SALTS (25 LESSONS) A.ACIDS AND BASES At a school laboratory: (i)An acid may be defined as a substance that turn litmus red. (ii)A base may be defined as a substance that turn litmus blue. Litmus is a lichen found mainly in West Africa. It changes its colour depending on whether the solution it i... | {
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From this definition, an acid donates H+ . H+ has no electrons and neutrons .It contains only a proton. Examples I. From the equation: HCl(aq) + H2O(l) === H3O+(aq) + Cl- (aq) (a)(i)For the forward reaction from left to right, H2O gains a proton to form H3O+ and thus H2O is a proton acceptor .It is a Bronsted-Lowry bas... | {
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It is a Bronsted-Lowry conjugate base. 4. Acids and bases show acidic and alkaline properties/characteristics only in water but not in other solvents e.g. (a)Hydrogen chloride gas dissolves in water to form hydrochloric acid Hydrochloric acid dissociates/ionizes in water to free H+(aq)/H3O+(aq) ions. The free H3O+(aq) ... | {
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i.e. Ionically: -For a monovalent metal: M2O(s) + 2H+(aq) -> 2M+(aq) + H2O (l) MOH(aq) + H+(aq) -> M+(aq) + H2O (l)
-For a divalent metal: MO(s) + 2H+(aq) -> M2+(aq) + H2O (l) M(OH) 2(s) + 2H+(aq) -> M2+(aq) + 2H2O(l) -For a trivalent metal: M2O3(s) + 6H+(aq) -> 2M3+(aq) + 3H2O (l) M(OH) 3(s) + 3H+(aq) -> M3+(aq) + 3H2... | {
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This dissociation/ionization makes aqueous ammonia to: (i)turn litmus paper/solution blue. (ii)have pH 8/9/10/11 (iii)be a good electrical conductor (iv)react with acids to form ammonium salt and water only. NH4OH(aq) + HCl(aq) -> NH4Cl(aq) + H2O(l) (d)Ammonia gas dissolves in methylbenzene/benzene /kerosene but does n... | {
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I. Strong acids exists more as free H+ ions than molecules. e.g. HCl(aq) H+(aq) + Cl- (aq) (molecules) (cation) (anion) HNO3(aq) H+(aq) + NO3-(aq) (molecules) (cation) (anion) H2SO4(aq) 2H+(aq) + SO42-(aq) (molecules) (cation) (anion) II. Strong bases/alkalis exists more as free OH- ions than molecules. e.g. KOH(aq) K+... | {
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The concentration of an acid/base/alkali is based on the number of moles of acid/bases dissolved in a decimeter(litre)of the solution. An acid/base/alkali with more acid/base/alkali in a decimeter(litre) of solution is said to be concentrated while that with less is said to be dilute. 9. (a) (i)strong acids have pH 1/2... | {
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Some compounds exhibit/show both properties of acids and bases/alkalis. A substance that reacts with both acids and bases is said to be amphotellic. The examples below show the amphotellic properties of: (a) Zinc (II)oxide(ZnO) and Zinc hydroxide(Zn(OH)2) (i)When ½ spatula full of Zinc(II)oxide is placed in a boiling t... | {
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Basic oxide + Acid -> salt + water Examples: Chemical equation ZnO(s) + 2HNO3(aq) -> Zn(NO3) 2 (aq) + H2O(l) ZnO(s) + 2HCl(aq) -> ZnCl2 (aq) + H2O(l) ZnO(s) + H2SO4(aq) -> ZnSO4 (aq) + H2O(l) Ionic equation ZnO(s) + 2H+ (aq) -> Zn 2+ (aq) + H2O(l) (ii) when reacting with sodium hydroxide, the oxide shows acidic propert... | {
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i.e. (i) when reacting with nitric(V)acid, the hydroxide shows basic properties. It reacts with an acid to form a simple salt and water only. Basic hydroxide + Acid -> salt + water Examples: Chemical equation Zn(OH) 2 (s) + 2HNO3(aq) -> Zn(NO3) 2 (aq) + 2H2O(l)
Zn(OH) 2 (s) + 2HCl(aq) -> ZnCl2 (aq) + 2H2O(l) Zn(OH) 2 (... | {
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Zn(OH) 2 (s) + 2NaOH(aq) -> Na2Zn(OH) 4(aq) 2.When Zinc hydroxide is reacted with potassium hydroxide the complex salt is potassium tetrahydroxozincate(II) complex salt. Zn(OH) 2 (s) + 2KOH(aq) -> K2Zn(OH) 4(aq) Ionic equation Zn(OH) 2 (s) + 2OH-(aq) -> 2[Zn(OH) 4]2- (aq) (b) Lead (II)oxide(PbO) and Lead(II) hydroxide ... | {
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Chemical equation PbO(s) + 2HNO3(aq) -> Pb(NO3) 2 (aq) + H2O(l) Ionic equation PbO(s) + 2H+ (aq) -> Pb 2+ (aq) + H2O(l) (ii) when reacting with sodium hydroxide, the oxide shows acidic properties by reacting with a base to form a complex salt. Chemical equation 1.When Lead(II) oxide is reacted with sodium hydroxide the... | {
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Chemical equation Pb(OH) 2 (s) + 2HNO3(aq) -> Pb(NO3) 2 (aq) + 2H2O(l) Ionic equation Pb(OH) 2 (s) + 2H+ (aq) -> Pb 2+ (aq) + 2H2O(l) (ii) when reacting with sodium hydroxide, the hydroxide shows acidic properties. It reacts with a base to form a complex salt. Chemical equation 1.When Lead(II) hydroxide is reacted with... | {
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Pb(OH) 2 (s) + 2KOH(aq) -> K2Pb(OH) 4(aq) Ionic equation Pb(OH) 2 (s) + 2OH-(aq) -> 2[Pb(OH) 4]2- (aq)
(c)Aluminium(III)oxide(Al2O3) and Aluminium(III)hydroxide(Al(OH)3) (i)When ½ spatula full of Aluminium(III)oxide is placed in a boiling tube containing 10cm3 of either 2M nitric(V)acid or 2M sodium hydroxide hydroxide... | {
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Chemical equation Al2O3 (s) + 6HNO3(aq) -> Al(NO3)3 (aq) + 3H2O(l) Al2O3 (s) + 6HCl(aq) -> AlCl3 (aq) + 3H2O(l) Al2O3 (s) + 3H2SO4(aq) -> Al2(SO4)3 (aq) + 3H2O(l) Ionic equation Al2O3 (s) + 3H+ (aq) -> Al 3+ (aq) + 3H2O(l) (ii) when reacting with sodium hydroxide, the oxide shows acidic properties by reacting with a ba... | {
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i.e. (i) when reacting with nitric(V)acid, the hydroxide shows basic properties. It reacts with the acid to form a simple salt and water only. Chemical equation Al(OH) 3 (s) + 3HNO3(aq) -> Al(NO3)3 (aq) + 3H2O(l)
Al(OH)3 (s) + 3HCl(aq) -> AlCl3 (aq) + 3H2O(l) 2Al(OH)3 (s) + 3H2SO4(aq) -> Al2(SO4)3 (aq) + 3H2O(l) Ionic ... | {
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It reacts with a base to form a complex salt. Chemical equation 1.When aluminium(III) hydroxide is reacted with sodium hydroxide the complex salt is sodium tetrahydroxoaluminate(III) complex salt. Al(OH) 3 (s) + NaOH(aq) -> NaAl(OH) 4(aq) 2.When aluminium(III) hydroxide is reacted with potassium hydroxide the complex s... | {
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H2SO4, H2SO3, H2CO3,HOOCOOH. (iii)tribasic acids ; generally denoted H3X e.g. H3PO4. (c) Some salts are normal salts while other are acid salts. (i)A normal salt is formed when all the ionizable /replaceable hydrogen in an acid is replaced by a metal or metallic /ammonium radical. (ii)An acid salt is formed when part/p... | {
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(i)A normal salt is formed when all the ionizable /replaceable hydrogen in an acid is replaced by a metal or metallic /ammonium radical. (ii)An acid salt is formed when part/portion the ionizable /replaceable hydrogen in an acid is replaced by a metal or metallic /ammonium radical. Table showing normal and acid salts d... | {
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(ii)An acid salt is formed when part/portion the ionizable /replaceable hydrogen in an acid is replaced by a metal or metallic /ammonium radical. Table showing normal and acid salts derived from common acids Acid name Chemical formula Basicity Normal salt Acid salt Hydrochloric acid HCl Monobasic Chloride(Cl-) None Nit... | {
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Table showing normal and acid salts derived from common acids Acid name Chemical formula Basicity Normal salt Acid salt Hydrochloric acid HCl Monobasic Chloride(Cl-) None Nitric(V)acid HNO3 Monobasic Nitrate(V)(NO3-) None Nitric(III)acid HNO2 Monobasic Nitrate(III)(NO2-) None Sulphuric(VI)acid H2SO4 Dibasic Sulphate(VI... | {
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e.g. CuCO3 (s) -> CuO(s) + CO2(g) CaCO3 (s) -> CaO(s) + CO2(g) PbCO3 (s) -> PbO(s) + CO2(g) FeCO3 (s) -> FeO(s) + CO2(g) ZnCO3 (s) -> ZnO(s) + CO2(g) (iii)Sodium hydrogen carbonate(IV) and Potassium hydrogen carbonate(IV)decompose on heating to give the corresponding carbonate (IV) and form water and carbon(IV)oxide ga... | {
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Both sodium/potassium hydroxide solutions are precipitating reagents. The alkalis produce unique colour of a precipitate/suspension when a few/three drops is added and then excess alkali is added to unknown salt/compound solution. NB: Potassium hydroxide is not commonly used because it is more expensive than sodium hyd... | {
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Add three
drops of 2M sodium hydroxide solution then excess (2/3 the length of a standard test tube). Observation Inference Explanation No white precipitate Na+ and K+ Both Na+ and K+ ions react with OH- from 2M sodium hydroxide solution to form soluble colourless solutions Na+(aq) + OH-(aq) -> NaOH(aq) K+(aq) + OH-(aq... | {
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Observation Inference Explanation No white precipitate Na+ and K+ Both Na+ and K+ ions react with OH- from 2M sodium hydroxide solution to form soluble colourless solutions Na+(aq) + OH-(aq) -> NaOH(aq) K+(aq) + OH-(aq) -> KOH(aq) No white precipitate then pungent smell of ammonia /urine NH4+ ions NH4+ ions react with ... | {
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Ba2+(aq) + 2OH-(aq) -> Ba(OH) 2(s) Ca2+(aq) + 2OH-(aq) -> Ca(OH) 2(s) Mg2+(aq) + 2OH-(aq) -> Mg(OH) 2(s) White precipitate soluble in excess Zn2+ ,Pb2+, Al3+ ions Pb2+ ,Zn2+ and Al3+ ions react with OH- from 2M sodium hydroxide solution to form insoluble white precipitate of their hydroxides. Zn2+(aq) + 2OH-(aq) -> Zn(... | {
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Zn2+(aq) + 2OH-(aq) -> Zn(OH) 2(s) Pb2+(aq) + 2OH-(aq) -> Pb(OH) 2(s) Al3+(aq) + 3OH-(aq) -> Al(OH) 3(s)
The hydroxides formed react with more OH- ions to form complex salts/ions. Zn(OH) 2(s) + 2OH(aq) -> [ Zn(OH) 4]2-(aq) Pb(OH) 2(s) + 2OH(aq) -> [ Pb(OH) 4]2-(aq) Al(OH) 3(s) + OH(aq) -> [ Al(OH) 4]-(aq) Blue precipit... | {
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Fe2+(aq) + 2OH-(aq) -> Fe(OH) 2(s) Hydrogen peroxide is an oxidizing agent that oxidizes green Fe2+ oxidized to brown Fe3+ Fe(OH) 2(s) + 2H+ -> Fe(OH) 3(aq) Brown precipitate insoluble in excess Fe3+ Fe3+ ions react with OH- from 2M sodium hydroxide solution to form insoluble brown precipitate of Iron(II) hydroxide. Fe... | {
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Procedure Put about 2cm3 of MgCl2, CaCl2, AlCl3, NaCl, KCl, FeSO4, Fe2(SO4) 3, CuSO4, ZnSO4NH4NO3, Pb(NO3) 2, Ba(NO3) 2 each into separate test tubes. Add three drops of 2M aqueous ammonia then excess (2/3 the length of a standard test tube). Observation Inference Explanation No white precipitate Na+ and K+ NH4+,Na+ an... | {
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Observation Inference Explanation No white precipitate Na+ and K+ NH4+,Na+ and K+ ions react with OH- from 2M aqueous ammonia to form soluble colourless solutions NH4+ (aq) + OH-(aq) -> NH4+OH(aq) Na+(aq) + OH-(aq) -> NaOH(aq) K+(aq) + OH-(aq) -> KOH(aq) White precipitate insoluble in excess Ba2+ ,Ca2+, Mg2+ ,Pb2+, Al3... | {
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Zn2+(aq) + 2OH-(aq) -> Zn(OH) 2(s) The Zinc hydroxides formed react NH3(aq) to form a complex salts/ions. Zn(OH) 2(s) + 4NH3(aq) ->[ Zn(NH3) 4]2+(aq)+ 2OH-(aq) Blue precipitate Cu2+ Cu2+ ions react with OH- from 2M aqueous
that dissolves in excess ammonia solution to form a deep/royal blue solution ammonia to form blue... | {
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Fe2+(aq) + 2OH-(aq) -> Fe(OH) 2(s) Hydrogen peroxide is an oxidizing agent that oxidizes green Fe2+ oxidized to brown Fe3+ Fe(OH) 2(s) + 2H+ -> Fe(OH) 3(aq) Brown precipitate insoluble in excess Fe3+ Fe3+ ions react with OH- from 2M aqueous ammonia to form insoluble brown precipitate of Iron(II) hydroxide. Fe3+(aq) + 3... | {
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Observation Inference Explanation (i)White precipitate does not dissolve on heating Ag+ ions Ag+ ions reacts with Cl- ions from a soluble chloride salt to form a white precipitate of AgCl (ii)White precipitate dissolve on heating Pb2+ ions Pb2+ ions reacts with Cl- ions from a soluble chloride salt to form a white prec... | {
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Add six drops of sulphuric(VI)acid /sodium sulphate(VI)/ammonium sulphate(VI)solution. Repeat with six drops of sodium sulphate(IV). Observation Inference Explanation White Ca2+, Ba2+, CaSO3 and CaSO4 do not form a thick precipitate as
precipitate Pb2+ ions they are sparingly soluble. Ca2+(aq)+ SO32-(aq) -> CaSO3(s) Ca... | {
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Cu2+(aq)+ CO32-(aq) -> CuCO3(s) Fe2+(aq)+ CO32-(aq) -> FeCO3(s) When sodium carbonate(IV)is added to CuCO3(s) the CO32-(aq) ions are first hydrolysed to produce CO2(g) and OH(aq)ions. CO32-(aq) + H2O (l) -> CO2 (g) + 2OH- (aq) The OH-(aq) ions further react to form basic copper(II) carbonate(IV). Basic copper(II) carbo... | {
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When bubbled/directed into orange acidified potassium dichromate(VI) solution, it turns to green/decolorizes acidified potassium manganate(VII). (f) Reaction of cation with sulphide / S2- ions All sulphides are insoluble black solids/precipitates except sodium sulphide/ Na2S/ potassium sulphide/K2S.When a few/3drops of... | {
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Shake thoroughly. Divide the mixture into five portions. Observation Inference (1mark) Solid dissolves to form Polar soluble compound a colourless solution Cu2+ , Fe2+ ,Fe3+ absent (i)To the first portion, add three drops of sodium hydroxide then add excess of the alkali. Observation Inference (1mark) White ppt, solubl... | {
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e.g. “SO4-2” is wrong, “sO42-” is wrong, “cu2+” is wrong. Sample solutions of salt were labeled as I,II, III and IV. The actual solutions, not in that order are lead nitrate, zinc sulphate potassium chloride and calcium chloride. a)When aqueous sodium carbonate was added to each sample separately, a white precipitate w... | {
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For some salts, on heating, more of the salt/solid/solute dissolve in the saturated solution to form a super saturated solution. The solubility of a salt is thus calculated from the formula Solubility = Mass of solute/salt/solid x 100 Mass/volume of water/solvent Practice examples (a)Calculate the solubility of potassi... | {
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Mass of solute/salt/solid = Solubility x Mass/volume of water/solvent 100 => 72 x 25 = 18.0g of KClO3 dissolve/saturate 100 (e) 22g of potassium nitrate(V) was dissolved in 40.0g of water at 10oC. Calculate the solubility of potassium nitrate(V) at 10oC. Solubility = Mass of solute/salt/solid x 100 =>( 22 x 100 ) = 55.... | {
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(vii) An area above the solubility curve of the salt shows a saturated /supersaturated solution. (viii) An area below the solubility curve of the salt shows an unsaturated solution. 19.(a) For salts whose solubility increases with increase in temperature, crystals form when the salt solution at higher temperatures is c... | {
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A salt solution has a mass of 65g containing 5g of solute. The solubility of this salt is 25g per 100g water at 20oC. 60g of the salt are added to the solution at 20oC.Calculate the mass of the solute that remain undissolved. Mass of solvent at 20oC = mass of solution – mass of solute => 65 - 5 = 60g Solubility before ... | {
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10.0 g of hydrated potassium carbonate (IV) K2CO3.xH2O on heating leave 7.93 of the hydrate. (a)Calculate the mass of anhydrous salt obtained. Hydrated on heating leave anhydrous = 7.93 g (b)Calculate the mass of water of crystallization in the hydrated salt Mass of water of crystallization = hydrated – anhydrous => 10... | {
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Temperature(oC) 5.0 10.0 15.0 30.0 40.0 50.0 60.0 mass KNO3/ 100g water 15.0 20.0 25.0 50.0 65.0 90.0 120.0 (a)Plot a graph of mass of in 100g water(y-axis) against temperature in oC
(b)From the graph show and determine (i)the mass of KNO3 dissolved at: I. 20oC From a correctly plotted graph = 32g II. 35oC From a corre... | {
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35oC Solubility before heating = 180 g Less Solubility after heating(from the graph) = 58 g Mass of KNO3crystals = 122 g III. 55oC
Solubility before heating = 180 g Less Solubility after heating(from the graph) = 102 g Mass of KNO3crystals = 78 g 7. The table below shows the solubility of salts A and B at various tempe... | {
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(d)What happens when the mixture in (c) above is then cooled from 50oC to 20oC. Method I. Total mass before cooling at 50oC = 100.0 g (From graph) Solubility/mass after cooling at 20oC = 32.0 g Mass of crystals deposited 68.0 g Method II. Mass of soluble salt crystals at 50oC added = 100 g (From graph)Solubility/mass b... | {
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Method I. Total mass before cooling at 50oC = 100.0 g (From graph) Solubility/mass after cooling at 20oC = 32.0 g Mass of crystals deposited 68.0 g Method II. Mass of soluble salt crystals at 50oC added = 100 g (From graph)Solubility/mass before cooling at 50oC = 85.0 g Mass of crystals that cannot dissolve at 50oC 15.... | {
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Total mass before cooling at 50oC = 100.0 g (From graph) Solubility/mass after cooling at 20oC = 32.0 g Mass of crystals deposited 68.0 g Method II. Mass of soluble salt crystals at 50oC added = 100 g (From graph)Solubility/mass before cooling at 50oC = 85.0 g Mass of crystals that cannot dissolve at 50oC 15.0 g (From ... | {
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Mass of soluble salt crystals at 50oC added = 100 g (From graph)Solubility/mass before cooling at 50oC = 85.0 g Mass of crystals that cannot dissolve at 50oC 15.0 g (From graph) Solubility/mass before cooling at 50oC = 85.0 g (From graph) Solubility/mass after cooling at 20oC = 32.0 g Mass of crystals deposited after c... | {
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