Q: How many atoms of copper are in a penny weighing 3.10 g, assuming the penny is pure copper? (Molar mass of Cu = 63.55 g/mol, $$1 \text{ mol} = 6.022 \times 10$$^{23}$$ atoms)

$$2.94 \times 10$$^{22}$$ atoms

Q: How many molecules are in a 22.5 g sample of dry ice (solid $$CO_2$$)? (Molar mass of $$CO_2 = 44.01$ g/mol, 1$$ \text{ mol} = 6.022 \times $$10^{23}$$ molecules)

$$3.08 \times 10$$^{23}$$ molecules

Q: Which of the following best describes the relationship between grams, moles, and number of atoms for an element?

$$\text{grams} \rightarrow \text{moles} \rightarrow \text{atoms}$$

Q: Which of the following is the correct formula to calculate the mass percent of an element X in a compound?

$$\text{Mass percent of X} = \frac{\text{molar mass X (moles of X)}}{\text{molar mass of compound}} \times 100\%$$

Q: Which of the following statements about molar mass is correct?

$$\text{The molar mass of a compound is the mass of 1 \text{ mol} of molecules or formula units of that compound.}$$

Question 1

A sample of pencil lead contains 0.0265 g of pure carbon. How many moles of carbon are present in the sample? (Molar mass of C = 12.01 g/mol)

Accepted Answer

$$0.00221$$ moles

Question 2

How many atoms of copper are in a penny weighing 3.10 g, assuming the penny is pure copper? (Molar mass of Cu = 63.55 g/mol, $$1 	ext{ mol} = 6.022 	imes 10$$^{23}$$ atoms)

Accepted Answer

$$2.94 	imes 10$$^{22}$$ atoms

Question 3

Calculate the mass in grams of 2.78 mol of sulfur. (Molar mass of S = 32.06 g/mol)

Accepted Answer

$$89.1 g$$

Question 4

How many molecules are in a 22.5 g sample of dry ice (solid $$CO_2$$)? (Molar mass of $$CO_2 = 44.01$ g/mol, 1$$ 	ext{ mol} = 6.022 	imes $$10^{23}$$ molecules)

Accepted Answer

$$3.08 	imes 10$$^{23}$$ molecules

Question 5

A chemist has $$4.78 	imes 10$$^{24}$$ molecules of NO_2$. What is the mass of this sample? (Molar mass of NO_2$ = 46.01 g/$$mol, $$1 	ext{ mol} = 6.022 	imes 10$$^{23}$$ molecules)

Accepted Answer

$$365 g$$

Question 6

How many moles of oxygen are in 3.7 mol of $$CaCO_3$$?

Accepted Answer

$$11.1$$ mol

Question 7

A 0.358 g sample of chromium reacts with oxygen to form 0.523 g of metal oxide. What is the mass percent of chromium in the sample?

Accepted Answer

$$68.5\%$$

Question 8

If the FDA recommends consuming less than 2.4 g of sodium per day, how much table salt ($$NaCl) $$does this correspond to? (Molar mass of Na = 22.99 g/mol, NaCl = 58.44 g/mol, 1 mol NaCl contains 1 mol Na)

Accepted Answer

$$6.1 g$$

Question 9

What is the mass percent of chlorine in Freon-112 ($$C_2Cl_4F_2$$)? (Molar mass Cl = 35.45 g/mol, Molar mass $$C_2Cl_4F_2 = 203.8 g/$$mol)

Accepted Answer

$$69.58\%$$

Question 10

A 55.4 g sample of $$C_{10}H$$_{14}$$O$$ contains how many grams of carbon? (Molar mass $$C_{10}H$$_{14}$$O = 150.2 g/$$mol, 10 mol C per 1 mol $$C_{10}H$$_{14}$$O$, Molar mass C = 12.01 g/mol)

Accepted Answer

$$44.3 g$$

Question 11

Which of the following best describes the relationship between grams, moles, and number of atoms for an element?

Accepted Answer

$$	ext{grams} ightarrow 	ext{moles} ightarrow 	ext{atoms}$$

Question 12

A compound contains 79.2% carbon by mass. What mass of the compound contains 19.8 g of carbon?

Accepted Answer

$$25.0 g$$

Question 13

How many moles of phosphorus are in 4.49 g of $$Ca_3$$($$PO_4)_2$? (Molar mass Ca_3$(PO_4$)_2 = 310.18 g/$$mol, 2 mol P per 1 mol $$Ca_3$$($$PO_4)_2$)

Accepted Answer

$$0.0290$$ mol

Question 14

Which of the following is the correct formula to calculate the mass percent of an element X in a compound?

Accepted Answer

$$	ext{Mass percent of X} = \frac{	ext{molar mass X (moles of X)}}{	ext{molar mass of compound}} 	imes 100\%$$

Question 15

A 5.8 g sample of sodium bicarbonate ($$NaHCO_3) $$contains how many grams of oxygen? (Molar mass $$NaHCO_3 = 84.001$ g/mol, 3 mol O per 1 mol $$NaHCO_3$$, Molar mass O = 15.9994 g/mol)

Accepted Answer

$$3.3 g$$

Question 16

Which of the following statements about molar mass is correct?

Accepted Answer

$$	ext{The molar mass of a compound is the mass of 1 	ext{ mol} of molecules or formula units of that compound.}$$

Chemical Composition and Quantitative Relationships in Chemistry

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