Question 1

Balance the following equation:

$\mathrm{C_8H_{18}O_3(l) + O_2(g) \rightarrow H_2O(g) + CO_2(g)}$

Which of the following is the correct balanced equation?

Accepted Answer

$\mathrm{C_8H_{18}O_3(l) + 11\ O_2(g) \rightarrow 9\ H_2O(g) + 8\ CO_2(g)}$

Question 2

A given element has two naturally occurring isotopes. One has mass $= 6.0151$ amu and abundance $7.5030\%$, and the other has mass $= 7.0160$ amu. What is the average atomic mass of this element?

Accepted Answer

6.9409 amu

Question 3

In a blast furnace, elemental iron is produced from a mixture of coke (C), iron ore ($\mathrm{Fe_3O_4}$), and other reactants. An important reaction sequence is:

$2\mathrm{C(s)} + \mathrm{O_2(g)} \rightarrow 2\mathrm{CO(g)}$

$\mathrm{Fe_3O_4(s)} + 4\mathrm{CO(g)} \rightarrow 3\mathrm{Fe(l)} + 4\mathrm{CO_2(g)}$

How many moles of iron can be formed in this sequence when $1.00$ mol of carbon, as coke, is consumed?

Accepted Answer

1.33 mol Fe

Question 4

Which of the following best describes the role of carbon monoxide ($\mathrm{CO}$) in the blast furnace process for iron production?

Accepted Answer

It acts as a reducing agent, converting $\mathrm{Fe_3O_4}$ to iron metal.

Question 5

If the abundance of the lighter isotope in the element from question 2 increases to $20\%$, what would happen to the average atomic mass?

Accepted Answer

It would decrease.

Question 6

Which of the following is a correct interpretation of the law of conservation of mass as applied to the combustion of $\mathrm{C_8H_{18}O_3}$?

Accepted Answer

The total mass of reactants equals the total mass of products.

Question 7

A student claims that doubling the amount of $\mathrm{C_8H_{18}O_3}$ in the combustion reaction will double the amount of $\mathrm{CO_2}$ produced. Is this correct?

Accepted Answer

Yes, because the reaction is stoichiometric and $\mathrm{CO_2}$ is directly proportional to $\mathrm{C_8H_{18}O_3}$.

Question 8

Which of the following best explains why isotopic abundance affects the average atomic mass of an element?

Accepted Answer

The average atomic mass is a weighted average based on the relative abundance of each isotope.

Question 9

If $2.00$ mol of $\mathrm{Fe_3O_4}$ reacts completely with excess $\mathrm{CO}$, how many moles of iron are produced according to the reaction: $\mathrm{Fe_3O_4(s) + 4CO(g) \rightarrow 3Fe(l) + 4CO_2(g)}$?

Accepted Answer

6.00 mol Fe

Question 10

Which of the following statements about the combustion of organic compounds is correct?

Accepted Answer

Combustion always produces $\mathrm{CO_2}$ and $\mathrm{H_2O}$ as products.

Question 11

A sample of $\mathrm{C_8H_{18}O_3}$ is combusted in excess oxygen. If $0.50$ mol of $\mathrm{C_8H_{18}O_3}$ is used, how many moles of $\mathrm{CO_2}$ are produced according to the balanced equation?

Accepted Answer

4.0 mol

Stoichiometry, Atomic Mass, and Chemical Equation Balancing Practice

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