Q: A sample of chloroform ($$\text{CHCl}_3) $$has a molecular mass of $$119.37$$ amu. Which calculation below correctly determines the molecular mass?

$$1 \times 12.01 + 1 \times 1.008 + 3 \times 35.45$$

Q: Which of the following is the correct sequence for determining the empirical formula from combustion analysis?

Weigh sample, weigh $$\text{CO}_2$$ and $$\text{H}_2\text{O}$$, calculate moles of C and H, calculate C:H mole ratio, calculate empirical formula

Q: Which of the following is the correct formula for calculating percent composition by mass of an element in a compound?

$$\frac{\text{mass of element in compound}}{\text{molar mass of compound}} \times 100$$

Question 1

Which of the following statements best explains why subscripts in chemical formulas must not be changed when balancing chemical equations?

Accepted Answer

Changing subscripts alters the identity of the substance, resulting in a different chemical compound.

Question 2

Given the balanced equation $$2 	ext{H}_2 + 	ext{O}_2 ightarrow 2 	ext{H}_2	ext{O}$$, how many moles of water are produced from 5 moles of $$	ext{O}_2$$ and excess $$	ext{H}_2$$?

Accepted Answer

$$10$$ moles

Question 3

A sample of chloroform ($$	ext{CHCl}_3) $$has a molecular mass of $$119.37$$ amu. Which calculation below correctly determines the molecular mass?

Accepted Answer

$$1 	imes 12.01 + 1 	imes 1.008 + 3 	imes 35.45$$

Question 4

Which of the following best describes the difference between molecular mass and formula mass?

Accepted Answer

Molecular mass refers to covalent compounds, while formula mass refers to ionic compounds.

Question 5

How many grams of $$	ext{NaCl}$$ are present in $$2.00$$ moles of $$	ext{NaCl}$$? (Molar mass of $$	ext{NaCl} = 58.44 g/$$mol)

Accepted Answer

$$116.88 g$$

Question 6

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

Accepted Answer

$$84.0\%$$

Question 7

Which of the following is the correct sequence for determining the empirical formula from combustion analysis?

Accepted Answer

Weigh sample, weigh $$	ext{CO}_2$$ and $$	ext{H}_2	ext{O}$$, calculate moles of C and H, calculate C:H mole ratio, calculate empirical formula

Question 8

If $$3.00$$ moles of ethylene oxide react with $$5.00$$ moles of water according to the reaction $$3 	ext{C}_2	ext{H}_4	ext{O} + 5 	ext{H}_2	ext{O} ightarrow 3 	ext{C}_2	ext{H}_6	ext{O}_2 + 2 	ext{H}_2	ext{O}$$, which reactant is limiting?

Accepted Answer

Ethylene oxide

Question 9

A compound is found to contain $$40.0\% C$$, $$6.7\% H$$, and $$53.3\% O by $$mass. What is its empirical formula?

Accepted Answer

$$	ext{CH}_2	ext{O}$$

Question 10

Which of the following best describes the symbolic level of chemical representation?

Accepted Answer

It uses chemical formulas and equations to represent reactions.

Question 11

Given the reaction $$2 	ext{CH}_3	ext{OH} (l) + 3 	ext{O}_2 (g) ightarrow 2 	ext{CO}_2 (g) + 4 	ext{H}_2	ext{O} (l)$$, how many grams of $$	ext{O}_2$$ are required to completely react with $$50.0 g of$$ $$	ext{CH}_3	ext{OH}$$? (Molar mass $$	ext{CH}_3	ext{OH} = 32.04 g/$$mol, $$	ext{O}_2 = 32.00 g/$$mol)

Accepted Answer

$$74.9 g$$

Question 12

A compound has an empirical formula mass of $$57.1$$ amu and a molecular mass of $$114.2$$ amu. What is the molecular formula if the empirical formula is $$	ext{C}_4	ext{H}_9$$?

Accepted Answer

$$	ext{C}_8	ext{H}_{18}$$

Question 13

Which of the following is the correct formula for calculating percent composition by mass of an element in a compound?

Accepted Answer

$$\frac{	ext{mass of element in compound}}{	ext{molar mass of compound}} 	imes 100$$

Question 14

Which of the following best describes the role of a limiting reactant in a chemical reaction?

Accepted Answer

It determines the maximum amount of product that can be formed.

Question 15

If $$35.8 g of$$ $$	ext{CH}_3	ext{OH}$$ reacts with excess $$	ext{O}_2$$ and the percent yield of water is $$76.6\%$$, how many grams of $$	ext{H}_2	ext{O}$$ are actually produced? ($$	ext{CH}_3	ext{OH}$$ molar mass = $$32.04 g/$$mol, $$	ext{H}_2	ext{O}$$ molar mass = $$18.02 g/$$mol)

Accepted Answer

$$30.7 g$$

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