Question 1

Which of the following best describes the reason why chemical equations must be balanced?

Accepted Answer

Because atoms are neither created nor destroyed during a chemical reaction.

Question 2

Balance the following equation: $$\mathrm{P_4O_{10}(s) + H_2O(l) \rightarrow H_3PO_4(aq)}. $$What are the correct coefficients?

Accepted Answer

$$\mathrm{P_4O_{10}(s) + 4H_2O(l) \rightarrow 4H_3PO_4(aq)}$$

Question 3

What is the oxidation number of manganese in $$\mathrm{$$MnO_4$$^-}$$?

Accepted Answer

+7

Question 4

In the reaction $$\mathrm{2Al + 6HCl \rightarrow 2AlCl_3 + 3H_2}$$, which element is oxidized?

Accepted Answer

Aluminium

Question 5

Assign the oxidation number to the underlined element in $$\mathrm{C_6H_6} ($$benzene).

Accepted Answer

0

Question 6

Which rule is used to determine the oxidation number of hydrogen in $$\mathrm{LiH}$$?

Accepted Answer

Hydrogen is +1 when combined with non-metals and -1 when combined with metals.

Question 7

What is the sum of the oxidation numbers in a neutral molecule?

Accepted Answer

It equals zero.

Question 8

Which of the following is the correct balanced equation for the reaction of calcium carbonate with hydrochloric acid?

Accepted Answer

$$\mathrm{$$CaCO_3$$(s) + 2HCl(aq) \rightarrow $$CaCl_2$$(aq) + H_2O(l) + CO_2$(g)}$$

Question 9

Which statement about oxidation numbers is FALSE?

Accepted Answer

The oxidation number of oxygen is always -2, even in peroxides.

Question 10

In the half-reaction $$\mathrm{Fe$$^{3+}$$ + e^- \rightarrow Fe$$^{2+}$$}$$, what change occurs to the oxidation number of iron?

Accepted Answer

It decreases from +3 to +2.

Question 11

Which of the following best describes a redox reaction?

Accepted Answer

A reaction involving the transfer of electrons, resulting in changes in oxidation numbers.

Question 12

What is the oxidation number of aluminium in $$\mathrm{$$AlH_3$$}$$?

Accepted Answer

+3

Question 13

Which of the following is the correct balanced equation for the reaction: Aluminium + Hydrochloric Acid $$\rightarrow$$ Aluminium Chloride + Hydrogen?

Accepted Answer

$$\mathrm{2Al + 6HCl \rightarrow 2AlCl_3 + 3H_2}$$

Question 14

Which element is ALWAYS assigned an oxidation number of -1 in its compounds?

Accepted Answer

Fluorine

Question 15

In the half-reaction $$\mathrm{$$MnO_4$$^- + 8H^+ + 5e^- \rightarrow Mn$$^{2+}$$ + 4H_2O}$$, what is the change in oxidation number for manganese?

Accepted Answer

It decreases from +7 to +2.

Question 16

Which of the following is a correct statement about balancing redox equations?

Accepted Answer

Both atoms and charges must be balanced.

Question 17

A student attempts to balance the equation $$\mathrm{Al + HCl \rightarrow $$AlCl_3$$ + H_2$} by $$multiplying $$\mathrm{HCl} by 3. $$What is the next step to fully balance the equation?

Accepted Answer

Multiply $$\mathrm{$$AlCl_3$$} by 2 $$and $$\mathrm{Al} by 2.$$

Question 18

Which of the following is the correct oxidation number for oxygen in most compounds?

Accepted Answer

-2

Question 19

In the reaction $$\mathrm{Fe$$^{3+}$$ + e^- \rightarrow Fe$$^{2+}$$}$$, what process is occurring?

Accepted Answer

Reduction

Balancing Chemical Equations and Oxidation Numbers

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