Quiz

QUIZ

1. Which reaction is considered a reduction reaction?

a. 2Mg + O2 leads to 2MgO b. 2MgO + Carbon leads to 2Mg + CO2 c. 2Cu + O2 leads to 2CuO2 d. 2Al + Fe2O3 leads to Al2O3 + 2Fe

Answer: b. Each of these is an oxidation reaction or a balanced redox reaction with the exception of the reaction in which MgO goes to magnesium solid, which is a true reduction reaction.

2. What is the best definition of an oxidation number?

a. The number of electrons the atom is sharing with other atoms in a covalent bond b. The number of oxygen atoms attached to a compound c. The number of hydrogen atoms lost from a compound d. The imagined charge that an atom would have if it were a 100 percent ionic compound

Answer: d. The oxidation number is the imagined charge on an atom if it were a 100 percent ionic compound. This makes it easier to determine whether something is oxidized or not.

3. What is the range of oxidation numbers for carbon as an atom in a reaction?

a. 0 to +4 b. -4 to 0 c. 0 to +4 d. -4 to +4

Answer: d. The range of oxidation numbers for carbon is -4 for methane (a fully reduced carbon atom) to +4 for CO2, which is a fully oxidized carbon atom).

4. Which number reflects the most reduced state or reduction of an atom?

a. -3 b. 0

c. +2 d. +4

Answer: a. The most reduced state of an atom is when it has an oxidation number as low as possible. This makes -3 the most reduced state of an atom.

5. In the reaction where calcium solid mixes with hydrogen gas goes to CaH2, which is the reducing agent?

a. Calcium b. Hydrogen gas c. CaH2 d. None of these

Answer: a. In this reaction, calcium gets oxidized to a theoretical +2 charge, meaning that it becomes the reducing agent to hydrogen, donating two electrons. Calcium is a (II)A atom, making it more likely to get oxidized than reduced.

6. What does the oxidation number of sodium change to when it mixes with

Chlorine gas to make sodium chloride?

a. -1 b. 0

c. +1 d. +2

Answer: c. In this case, sodium is a (I)A metal, meaning that it becomes positively charged. In such cases, this positive charge becomes its oxidation number.

7. The reaction of aluminum and sodium chloride going to aluminum chloride plus sodium does not occur. What does it say that the stronger oxidizing agent must be?

a. Aluminum chloride b. Sodium c. Sodium chloride d. Aluminum

Answer: a. Aluminum chloride must be the stronger oxidizing agent because it cannot be made from oxidizing aluminum with salt to make aluminum (III)chloride. Instead, it is reducible to make aluminum when mixed with sodium, which is a strong reducing agent.

8. Which atom is the strongest reducing agent?

a. Calcium b. Iron c. Aluminum d. Sodium

Answer: d. This can be predicted by looking at the periodic table. Sodium, being a (I)A metal is most reactive and is the strongest reducing agent of all of these elements. The weakest reducing agent in the list would be iron.

9. What is the chemical reaction that occurs when an iron pipe gets rusty?

a. It involves the oxidation of a solid metal b. It involves the reduction of a solid metal c. It involves the gain of electrons by solid metal d. It involves the gain of oxidation number of a metal oxide

Answer: a. The rusting of iron metal into metal oxide by its reaction with oxygen involves the oxidation of the solid metal.

10. Which organic chemical is most highly oxidized?

a. Alcohols b. Carboxylic acids c. Hydrocarbons d. Peroxides

Answer: d. Hydrogen peroxide is H2O2 and is highly oxidized—making peroxides the most oxidized of all of the listed organic chemicals.