samples/texts_merged/1789294.md

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Information: Oxygen and Oxidation

You have probably heard of antioxidants, which are substances (often vitamins) taken to prevent the oxidation of cells. When iron rusts we say that the iron has oxidized. What is oxidation?

Let's look at the chemical reaction for separating iron from iron ore:

$$2{\text{Fe}}_2{\text{O}}_3+3\text{C}\rightleftharpoons 4\text{Fe}+3{\text{CO}}_{2}2\; \backslash text\{Fe\}\_2\backslash text\{O\}\_3\; +\; 3\backslash text\{C\}\; \backslash rightleftharpoons\; 4\; \backslash text\{Fe\}\; +\; 3\; \backslash text\{CO\}\_2$$

$$+\to +\backslash underset\{\backslash text\{Iron\; ore\}\}\{\backslash text\{2\; Fe\}\_2\backslash text\{O\}\_3\}\; +\; \backslash underset\{\backslash text\{Iron\; metal\}\}\{3\backslash text\{C\}\}\; \backslash rightarrow\; \backslash underset\{\backslash text\{4\; Fe\}\}\{\backslash text\{4\; FeO\}\}\; +\; \backslash underset\{\backslash text\{3\; CO\}\_2\}\{\backslash text\{3\; CO\}\}$$

Critical Thinking Questions

1. In Equation 1 above carbon is “oxidized” and iron ore is “reduced.” Define each of the terms using the concept of gaining or losing oxygen.

Oxidizing:

Reducing:

2. In the following reaction, is magnesium oxidized or reduced? Explain.

$$2\text{Mg}+{\text{O}}_2\to 2\text{MgO}2\; \backslash text\{Mg\}\; +\; \backslash text\{O\}\_2\; \backslash rightarrow\; 2\; \backslash text\{MgO\}$$

3. Which substance is reduced in the following reaction? (Note: When answering a question like this we are always talking about which reactant is reduced, not which product.)

$$\text{CaO}+2\text{Na}\to {\text{Na}}_2\text{O}+\text{Ca}\backslash text\{CaO\}\; +\; 2\; \backslash text\{Na\}\; \backslash rightarrow\; \backslash text\{Na\}\_2\backslash text\{O\}\; +\; \backslash text\{Ca\}$$

Information: Oxidation States

The term “oxidation state” is a fancy term for “charge.” The charge, or oxidation state, of any atom by itself or in its natural state is zero. Here are some examples of substances that have an oxidation state of zero: Mg, Na, Cl₂, S, O₂, or any substance by itself or any normally diatomic substance.

When a substance is bonded we can often find its oxidation state from the periodic table:

$$2\text{Na}+{\text{Cl}}_2\to 2\text{NaCl}2\; \backslash text\{Na\}\; +\; \backslash text\{Cl\}\_2\; \backslash rightarrow\; 2\; \backslash text\{NaCl\}$$ ---PAGE_BREAK---

Critical Thinking Questions

4. Assign oxidation numbers to each atom in the following chemical reactions:

$$\text{a) Li}+{\text{CaCl}}_2\to \text{Ca}+\text{LiCl}\backslash text\{a)\; \}\; \backslash text\{Li\}\; +\; \backslash text\{CaCl\}\_2\; \backslash rightarrow\; \backslash text\{Ca\}\; +\; \backslash text\{LiCl\}$$

$$\text{b) }\mathrm{A}\mathrm{l}+\mathrm{C}\mathrm{a}\mathrm{O}\to {\mathrm{A}\mathrm{l}}_2{\mathrm{O}}_3+\mathrm{C}\mathrm{a}\backslash text\{b)\; \}\; \backslash mathrm\{Al\}\; +\; \backslash mathrm\{CaO\}\; \backslash rightarrow\; \backslash mathrm\{Al\}\_\{2\}\backslash mathrm\{O\}\_\{3\}\; +\; \backslash mathrm\{Ca\}$$

5. Sometimes it is difficult to determine from the periodic table. For example, Consider SO₂.

a) Both sulfur and oxygen are in the same column of the periodic table and we could predict the same oxidation state (or charge) of ______ for each of them when they are bonded ionically.
what number? (include + or -)

b) What about in SO₂? They both can't have the exact same oxidation state. Here's a rule: Oxygen almost always has a -2 oxidation state when it is bonded. You'll have to figure out the S, by first assuming oxygen is -2. Treat S like an unknown “x”: XO₂. Verify that the oxidation state for S is +4 in SO₂.

6. Find the oxidation state for each atom bonded to oxygen below:

a) NO

b) $ClO_3$

c) $S_2O_3$

d) $NO_3^{-1}$ (Note: the total of all charges must equal -1)

7. Assign oxidation states to each atom in the following reactions:

$$\text{a) }2\text{Mg}+{\text{O}}_2\to 2\text{MgO}\backslash text\{a)\; \}\; 2\; \backslash text\{Mg\}\; +\; \backslash text\{O\}\_2\; \backslash rightarrow\; 2\; \backslash text\{MgO\}$$

$$\text{b) }\mathrm{C}\mathrm{u}\mathrm{O}+\mathrm{P}\to {\mathrm{C}\mathrm{u}}_3{\mathrm{P}}_2+{\mathrm{O}}_2\backslash text\{b)\; \}\; \backslash mathrm\{CuO\}\; +\; \backslash mathrm\{P\}\; \backslash rightarrow\; \backslash mathrm\{Cu\}\_3\backslash mathrm\{P\}\_2\; +\; \backslash mathrm\{O\}\_2$$

$$\text{c) }{\mathrm{S}\mathrm{O}}_2{\mathrm{C}\mathrm{l}}_2\to {\mathrm{S}\mathrm{O}}_2+{\mathrm{C}\mathrm{l}}_2(\text{note: Cl’s column is almost always -1 when bonded like in }{\mathrm{S}\mathrm{O}}_2{\mathrm{C}\mathrm{l}}_2)\backslash text\{c)\; \}\; \backslash mathrm\{SO\}\_2\backslash mathrm\{Cl\}\_2\; \backslash rightarrow\; \backslash mathrm\{SO\}\_2\; +\; \backslash mathrm\{Cl\}\_2\; \backslash \; (\backslash text\{note:\; Cl\text{'}s\; column\; is\; almost\; always\; -1\; when\; bonded\; like\; in\; \}\; \backslash mathrm\{SO\}\_2\backslash mathrm\{Cl\}\_2)$$

8. A positive ion is formed when an atom __________ electrons. gains OR loses?

9. A negative ion is formed an atom __________ electrons. gains OR loses? ---PAGE_BREAK---

10. Consider again the isolation of iron from iron ore: $2\text{Fe}_2\text{O}_3 + 3\text{C} \rightarrow 4\text{Fe} + 3\text{CO}_2$.

a) Which substance—iron or carbon—has an oxidation number that decreases during the reaction?

b) Which substance—iron or carbon—has an oxidation number that increases during the reaction?

c) For a substance to become more positive it must gain OR lose electrons.

d) For a substance to become more negative it must gain OR lose electrons.

Information: Electrons and Oxidation/Reduction

As you found out in question 10a, iron has its oxidation number decreased during the reaction in question 10. Its oxidation number gets reduced from +3 to 0.

Likewise, carbon's oxidation number gets increased from 0 to +4.

Earlier we defined oxidation and reduction in terms of gaining or losing oxygen. Now, let's formulate a definition for oxidation and reduction in terms of gaining or losing electrons.

Critical Thinking Questions

11. Define oxidation and reduction in terms of gaining or losing electrons:

Oxidation:

Reduction:

12. In question 7c, __________ was oxidized and __________ was reduced. oxygen, sulfur, OR chlorine

oxygen, sulfur, OR chlorine

13. Consider the following reaction:

$${\mathrm{H}\mathrm{N}\mathrm{O}}_3+{\mathrm{H}}_3{\mathrm{P}\mathrm{O}}_3\to \mathrm{N}\mathrm{O}+{\mathrm{H}}_3{\mathrm{P}\mathrm{O}}_4\backslash mathrm\{HNO\}\_\{3\}+\backslash mathrm\{H\}\_\{3\}\backslash mathrm\{PO\}\_\{3\}\; \backslash rightarrow\; \backslash mathrm\{NO\}+\backslash mathrm\{H\}\_\{3\}\backslash mathrm\{PO\}\_\{4\}$$

a) Assign oxidation numbers to every atom. (A hint: just like oxygen is always -2 when bonded, so also hydrogen is +1 when bonded.)

b) Which atom is oxidized?

c) Which atom is reduced? ---PAGE_BREAK---

Information: Oxidizing and Reducing Agents

A chemical reaction that has oxidation and reduction going on is referred to as a redox reaction. The substance that gets reduced causes the other substance to be oxidized. Therefore, the substance that gets reduced is called the “oxidizing agent.” It is an agent that causes something else to be oxidized.

You can think of a reducing agent similarly. The substance that gets oxidized will cause the other substance to be reduced. Reducing agents get oxidized by causing something else to get reduced.

Critical Thinking Questions

14. Consider question 13 again. __________ is the reducing agent and __________ is the oxidizing agent. nitrogen OR phosphorus nitrogen OR phosphorus

15. Consider the following reaction: $4 \text{Al} + 3 \text{O}_2 \rightarrow 2 \text{Al}_2\text{O}_3$

a) Which atom is oxidized?

b) Which atom is reduced?

c) Which atom is the oxidizing agent?

d) Which atom is the reducing agent?