Q: A sample contains $$0.500$$ mol of magnesium. How many magnesium atoms are present in the sample?

$$3.01 \times 10$$^{23}$$ atoms

Q: How many molecules are present in $$2.25 g of $$fluorine gas ($$\mathrm{F_2$}$$)? (Molar mass of $$\mathrm{F_2$}$$ = $$38.00 g/$$mol)

$$3.57 \times 10$$^{22}$$ molecules

Q: How many molecules of argon gas occupy $$0.430 L at $$STP?

$$1.15 \times 10$$^{22}$$ molecules

Question 1

Which of the following best describes Avogadro’s number?

Accepted Answer

The number of atoms in 12.01 grams of carbon.

Question 2

A sample contains $$0.500$$ mol of magnesium. How many magnesium atoms are present in the sample?

Accepted Answer

$$3.01 	imes 10$$^{23}$$ atoms

Question 3

What is the molar mass of copper(II) nitrite, $$\mathrm{Cu(NO_2$)_2}$$?

Accepted Answer

$$187.56 g/$$mol

Question 4

How many moles of aluminum are in $$54.0$$ grams of aluminum? (Molar mass of Al = $$26.98 g/$$mol)

Accepted Answer

$$2.00$$ mol

Question 5

A balloon contains $$44.8 L of $$oxygen gas at STP. How many moles of oxygen gas are present?

Accepted Answer

$$2.00$$ mol

Question 6

What is the density of ammonia gas ($$\mathrm{NH_3$}) at $$STP? (Molar mass of $$\mathrm{NH_3$}$$ = $$17.03 g/$$mol)

Accepted Answer

$$0.760 g/L$$

Question 7

How many molecules are present in $$2.25 g of $$fluorine gas ($$\mathrm{F_2$}$$)? (Molar mass of $$\mathrm{F_2$}$$ = $$38.00 g/$$mol)

Accepted Answer

$$3.57 	imes 10$$^{22}$$ molecules

Question 8

A gas sample has a mass of $$4.29 g $$and occupies $$1.50 L at $$STP. What is the molar mass of the gas?

Accepted Answer

$$64.0 g/$$mol

Question 9

What is the percent composition by mass of hydrogen in water ($$\mathrm{H_2O}$$)? (Molar mass of H = $$1.01 g/$$mol, O = $$16.00 g/$$mol)

Accepted Answer

$$11.2\%$$

Question 10

A $$1.640 g $$sample of radium metal reacts to form $$1.755 g of $$radium oxide. What is the empirical formula of the oxide? (Molar mass: Ra = $$226 g/$$mol, O = $$16.00 g/$$mol)

Accepted Answer

$$\mathrm{RaO}$$

Question 11

Acetylene is $$92.2\%$$ carbon and $$7.83\%$$ hydrogen by mass. What is its empirical formula?

Accepted Answer

$$\mathrm{CH}$$

Question 12

If the empirical formula of a compound is $$\mathrm{CH}$$ and its molar mass is $$26.0 g/$$mol, what is its molecular formula?

Accepted Answer

$$\mathrm{C_2H_2}$$

Question 13

How many molecules of argon gas occupy $$0.430 L at $$STP?

Accepted Answer

$$1.15 	imes 10$$^{22}$$ molecules

Question 14

What is the mass of $$3.36 L of $$ozone gas ($$\mathrm{O_3$}) at $$STP? (Molar mass of $$\mathrm{O_3$}$$ = $$48.00 g/$$mol)

Accepted Answer

$$7.20 g$$

Question 15

Which of the following is NOT a correct interpretation of the mole?

Accepted Answer

1 mol = 1 gram of any element

Question 16

Which step is first in the unit analysis method for solving chemistry problems?

Accepted Answer

Write down the unit asked for in the answer.

Question 17

A single molecule of sulfur dioxide ($$\mathrm{SO_2$}) $$has what mass? (Molar mass of $$\mathrm{SO_2$}$$ = $$64.07 g/$$mol)

Accepted Answer

$$1.06 	imes 10$$^{-22}$$ g

Question 18

Which of the following best explains why gases have much lower densities than liquids?

Accepted Answer

Gas particles are much farther apart than in liquids.

Question 19

A sample of methane gas occupies $$4.50 L at $$STP. How many moles of methane are present?

Accepted Answer

$$0.201$$ mol

Question 20

Which of the following is the correct percent composition by mass of oxygen in water ($$\mathrm{H_2O}$$)?

Accepted Answer

$$88.8\%$$

The Mole Concept and Chemical Quantities: Study Notes for General Chemistry

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