Q: Which of the following is the correct formula for calculating percent yield?

$\frac{\text{actual yield}}{\text{theoretical yield}} \times 100\%$

Question 1

Which of the following best explains why coefficients, rather than subscripts, are changed when balancing chemical equations?

Accepted Answer

Changing subscripts changes the chemical identity of the compounds, while changing coefficients only adjusts the number of molecules.

Question 2

A sample of glucose ($C_6H_{12}O_6$) weighing 18.0 g is completely combusted in oxygen. How many grams of $CO_2$ are produced? (Molar masses: $C_6H_{12}O_6 = 180.0$ g/mol, $CO_2 = 44.0$ g/mol)

Accepted Answer

$26.4$ g

Question 3

Which of the following is the correct balanced equation for the reaction of aluminum hydroxide with hydrochloric acid?

Accepted Answer

$Al(OH)_3(s) + 3HCl(aq) \rightarrow AlCl_3(aq) + 3H_2O(l)$

Question 4

A compound is found to contain 40.0% carbon, 6.7% hydrogen, and 53.3% oxygen by mass. What is its empirical formula?

Accepted Answer

$CH_2O$

Question 5

Which of the following statements about combustion reactions is correct?

Accepted Answer

Combustion reactions typically involve a hydrocarbon reacting with $O_2$ to produce $CO_2$ and $H_2O$.

Question 6

A 0.1005 g sample of menthol is combusted, producing 0.2829 g of $CO_2$ and 0.1159 g of $H_2O$. If menthol contains only C, H, and O, what is the empirical formula of menthol?

Accepted Answer

$C_{10}H_{20}O$

Question 7

Which of the following best describes a decomposition reaction?

Accepted Answer

A single compound breaks down into two or more simpler substances.

Question 8

What is the percent by mass of oxygen in sulfuric acid, $H_2SO_4$? (Molar mass: $H_2SO_4 = 98.1$ g/mol)

Accepted Answer

$65.0\%$

Question 9

A sample of aspartame ($C_{14}H_{18}N_2O_5$) has a mass of 1.00 mg. How many hydrogen atoms are present in this sample? (Molar mass = 294 g/mol, Avogadro's number $= 6.02 	imes 10^{23}$)

Accepted Answer

$3.68 	imes 10^{19}$

Question 10

Which of the following is the correct formula for calculating percent yield?

Accepted Answer

$\frac{	ext{actual yield}}{	ext{theoretical yield}} 	imes 100\%$

Question 11

If 30.0 g of benzene ($C_6H_6$) reacts with 65.0 g of bromine ($Br_2$) to form bromobenzene ($C_6H_5Br$), what is the theoretical yield of bromobenzene? (Molar masses: $C_6H_6 = 78.0$ g/mol, $Br_2 = 160.0$ g/mol, $C_6H_5Br = 157.0$ g/mol)

Accepted Answer

$58.5$ g

Question 12

Which of the following is the correct mole ratio of $H_2$ to $O_2$ in the balanced equation $2H_2(g) + O_2(g) \rightarrow 2H_2O(l)$?

Accepted Answer

$2:1$

Question 13

A 1.00 g sample of sodium bicarbonate ($NaHCO_3$) reacts with 1.00 g of citric acid ($H_3C_6H_5O_7$). Which is the limiting reactant? (Molar masses: $NaHCO_3 = 84.0$ g/mol, $H_3C_6H_5O_7 = 192.0$ g/mol)

Accepted Answer

Citric acid

Question 14

Which of the following best describes Avogadro's number?

Accepted Answer

The number of atoms in 12 grams of carbon-12

Question 15

A metal carbonate decomposes upon heating to form a metal oxide and carbon dioxide. Which of the following is a correct example of this reaction?

Accepted Answer

$CaCO_3(s) \rightarrow CaO(s) + CO_2(g)$

Question 16

If the empirical formula of a compound is $CH_2$ and its molar mass is 56 g/mol, what is its molecular formula?

Accepted Answer

$C_4H_8$

Question 17

Which of the following is NOT a correct statement about stoichiometry?

Accepted Answer

Stoichiometry is only applicable to reactions involving gases.

Question 18

A reaction has a theoretical yield of 50.0 g, but only 42.0 g of product is actually obtained. What is the percent yield?

Accepted Answer

$84.0\%$

Question 19

Which of the following is the correct sequence of steps to determine the empirical formula from percent composition?

Accepted Answer

Convert percent to grams, convert grams to moles, divide by smallest number of moles

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