Q: A sample of chlorine gas ($$\mathrm{Cl}_2) $$contains 1.204 $$\times$$ $$10^{24}$$ atoms of chlorine. How many molecules of $$\mathrm{Cl}_2$$ are present in the sample?

$$6.022 \times 10$$^{23}$$ molecules

Q: A ring of pure silver ($$\mathrm{Ag}) $$weighs 22.25 g. How many atoms of silver are in the ring? (Atomic weight of Ag = 107.9 g/mol)

$$1.242 \times 10$$^{23}$$ atoms

Q: Which of the following best describes Avogadro's number?

The number of atoms in one mole of any element, $$6.022 \times 10$$^{23}$$

Q: A penny has a mass of 3.10 g and is made of pure copper ($$\mathrm{Cu}$$, atomic weight = 63.55 g/mol). How many atoms of copper are in the penny?

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

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

$$\frac{\text{(# moles of element)} \times \text{atomic mass of element} \times 100}{\text{molar mass of compound}}$$

Q: A sample of $$\mathrm{CuSO}_4 \cdot 5\mathrm{H}_2\mathrm{O}$$ weighing 13.58 g contains how many hydrogen atoms? (Molar mass = 185.66 g/mol, 10 H atoms per molecule)

$$4.41 \times 10$$^{23}$$ atoms

Question 1

Which of the following statements best describes the definition of one atomic mass unit (amu)?

Accepted Answer

It is exactly equal to 1/12 the mass of one $$^{12}\mathrm{C}$$ atom.

Question 2

A sample of chlorine gas ($$\mathrm{Cl}_2) $$contains 1.204 $$	imes$$ $$10^{24}$$ atoms of chlorine. How many molecules of $$\mathrm{Cl}_2$$ are present in the sample?

Accepted Answer

$$6.022 	imes 10$$^{23}$$ molecules

Question 3

Copper has two naturally occurring isotopes: $$^{63}\mathrm{Cu} (62.9 $$amu, 69.1% abundance) and $$^{65}\mathrm{Cu} ($$unknown mass, 30.9% abundance). If the average atomic mass of copper is 63.5 amu, what is the mass of $$^{65}\mathrm{Cu}$$?

Accepted Answer

64.8 amu

Question 4

How many moles of sodium chloride ($$\mathrm{NaCl}) $$are present in 233.772 g of the compound? (Molar mass = 58.443 g/mol)

Accepted Answer

4.000 moles

Question 5

A ring of pure silver ($$\mathrm{Ag}) $$weighs 22.25 g. How many atoms of silver are in the ring? (Atomic weight of Ag = 107.9 g/mol)

Accepted Answer

$$1.242 	imes 10$$^{23}$$ atoms

Question 6

Which equation correctly relates mass ($$m$$), moles ($$n$$), and molar mass ($$M$$)?

Accepted Answer

$$n = \frac{m}{M}$$

Question 7

A compound has the following percent composition: 35.51% C, 4.77% H, 37.85% O, 8.29% N, and 13.60% Na. What is the empirical formula of the compound?

Accepted Answer

$$\mathrm{C}_5\mathrm{H}_8\mathrm{N}\mathrm{Na}\mathrm{O}_4$$

Question 8

Calculate the molecular mass (in amu) of $$\mathrm{C}_9\mathrm{H}_{16}\mathrm{O}_3.$$

Accepted Answer

173.12 amu

Question 9

Which of the following best describes Avogadro's number?

Accepted Answer

The number of atoms in one mole of any element, $$6.022 	imes 10$$^{23}$$

Question 10

A sample contains $$2.25 	imes 10$$^{22}$$ tungsten (W) atoms. What is the mass of this sample? (Atomic weight of W = 183.9 g/mol)

Accepted Answer

6.87 g

Question 11

Which process is used to determine the relative abundance of isotopes in a sample?

Accepted Answer

Mass spectrometry

Question 12

Calculate the percent composition of carbon in $$\mathrm{C}_7\mathrm{H}_{12}\mathrm{O}_2 ($$molar mass = 128.173 g/mol).

Accepted Answer

65.60%

Question 13

A penny has a mass of 3.10 g and is made of pure copper ($$\mathrm{Cu}$$, atomic weight = 63.55 g/mol). How many atoms of copper are in the penny?

Accepted Answer

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

Question 14

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

Accepted Answer

$$\frac{	ext{(# moles of element)} 	imes 	ext{atomic mass of element} 	imes 100}{	ext{molar mass of compound}}$$

Question 15

A sample of $$\mathrm{CuSO}_4 \cdot 5\mathrm{H}_2\mathrm{O}$$ weighing 13.58 g contains how many hydrogen atoms? (Molar mass = 185.66 g/mol, 10 H atoms per molecule)

Accepted Answer

$$4.41 	imes 10$$^{23}$$ atoms

Question 16

Which of the following statements about molar mass is correct?

Accepted Answer

The molar mass in grams is numerically equal to the molecular mass in amu.

Question 17

A sphere of aluminum contains $$8.55 	imes 10$$^{22}$$ atoms. If the density of aluminum is 2.70 g/cm^3$, what is the mass of the sphere? (Atomic weight of Al = 26.98 g/mol)

Accepted Answer

3.83 g

Question 18

Which of the following best explains why the average atomic mass of carbon is 12.011 amu, not exactly 12.00 amu?

Accepted Answer

Carbon has more than one naturally occurring isotope.

Question 19

If you have 0.215 mole of $$\mathrm{MgCl}_2 ($$molar mass = 95.216 g/mol), how many grams of magnesium (Mg) are present? (Atomic weight of Mg = 24.305 g/mol)

Accepted Answer

5.24 g

Question 20

Which of the following is NOT a correct application of Avogadro's number?

Accepted Answer

The number of atoms in one gram of carbon is $$6.022 	imes 10$$^{23}$$.

chapter 3 lec 1

Guida di studio - Domande di pratica

Study guide - Flashcard