Q: Which of the following best describes Avogadro's number, and what is its value?

The number of atoms in one mole of a substance; $$6.022 \times 10$$^{23}$$

Q: A sample contains $$4.5$$ grams of helium gas ($$He). $$Given that the molar mass of helium is $$4.0 g/$$mol, how many atoms of helium are present in the sample?

$$1.13 \times 10$$^{24}$$ atoms

Q: Which of the following statements about the mole is correct?

A mole is $$6.022 \times 10$$^{23}$$ particles of a substance.

Q: Which of the following best describes the relationship between mass, moles, and molar mass?

$$\text{Moles} = \dfrac{\text{Mass (g)}}{\text{Molar Mass (g/mol)}}$$

Question 1

Which of the following best describes Avogadro's number, and what is its value?

Accepted Answer

The number of atoms in one mole of a substance; $$6.022 	imes 10$$^{23}$$

Question 2

A sample contains $$4.5$$ grams of helium gas ($$He). $$Given that the molar mass of helium is $$4.0 g/$$mol, how many atoms of helium are present in the sample?

Accepted Answer

$$1.13 	imes 10$$^{24}$$ atoms

Question 3

Which of the following statements about the mole is correct?

Accepted Answer

A mole is $$6.022 	imes 10$$^{23}$$ particles of a substance.

Question 4

If you have $$22.4$$ liters of oxygen gas ($$O_2) at $$standard temperature and pressure (STP), how many moles of $$O_2 do $$you have?

Accepted Answer

$$1$$ mole

Question 5

A student dissolves $$53$$ grams of sodium chloride ($$NaCl) in $$water. The molar mass of $$NaCl is$$ $$58.5 g/$$mol. How many moles of $$NaCl$$ are present?

Accepted Answer

$$0.91$$ moles

Question 6

Which of the following best explains why the atomic mass of chlorine is approximately $$35.5 u ($$atomic mass units)?

Accepted Answer

It is the average of the masses of all isotopes of chlorine, weighted by their natural abundance.

Question 7

A chemical reaction requires $$2.0$$ liters of a $$1.0 M $$solution of hydrochloric acid ($$HCl). $$How many grams of $$HCl$$ are needed to prepare this solution? (Molar mass of $$HCl = 36.5 g/$$mol)

Accepted Answer

$$73$$ grams

Question 8

Which of the following is the correct balanced chemical equation for the combustion of methane ($$CH_4) in $$oxygen?

Accepted Answer

$$CH_4 + 2O_2$$ \rightarrow $$CO_2 + 2H_2O$

Question 9

A patient receives an intravenous solution containing $$0.9\%$$ sodium chloride ($$NaCl) by $$mass. If the patient receives $$500 mL of $$this solution, how many grams of $$NaCl$$ does the patient receive?

Accepted Answer

$$4.5$$ grams

Question 10

Which of the following best describes the relationship between mass, moles, and molar mass?

Accepted Answer

$$	ext{Moles} = \dfrac{	ext{Mass (g)}}{	ext{Molar Mass (g/mol)}}$$

Question 11

A balloon contains $$2.0$$ moles of nitrogen gas ($$N_2) at $$STP. What is the volume of the gas in liters?

Accepted Answer

$$44.8 L$$

Question 12

Which of the following is a correct statement about isotopes?

Accepted Answer

Isotopes of an element have the same number of protons but different numbers of neutrons.

Question 13

A chemist needs to prepare $$250 mL of a$$ $$0.5 M $$solution of potassium chloride ($$KCl). $$What mass of $$KCl ($$molar mass $$= 74.5 g/$$mol) is required?

Accepted Answer

Question 14

Which of the following best explains why $$CO_2 is $$considered a compound and not a mixture?

Accepted Answer

Because $$CO_2$$ consists of two or more elements chemically bonded in a fixed ratio.

Question 15

A $$2.0 L $$solution contains $$0.5$$ moles of glucose ($$C_6H_{12}O_6$). What is the molarity of the solution?

Accepted Answer

$$0.25 M$$

Question 16

Which of the following is the correct electron configuration for a neutral neon atom ($$Ne$$, atomic number $$= 10$$)?

Accepted Answer

$$1s^2$$ $$2s^2$$ $$2p^6$$

Question 17

A reaction produces $$4.9 	imes 10$$^{22}$$ molecules of water (H_2O$). How many moles of water is this?

Accepted Answer

$$0.081$$ moles

Question 18

Which of the following best describes a chemical change?

Accepted Answer

A process in which new substances with different properties are formed.

Question 19

A $$45 g $$sample of a compound contains $$15 g of $$carbon, $$5 g of $$hydrogen, and $$25 g of $$oxygen. What is the percent by mass of oxygen in the compound?

Accepted Answer

$$55.6\%$$

Question 20

Which of the following is a physical property of matter?

Accepted Answer

Melting point

Atoms, Elements, and Chemical Quantities: Key Concepts and Calculations

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