Q: How many molecules are present in 6.00 mol of a molecular compound?

$$3.613 \times 10$$^{24}$$ molecules

Q: A rare gold coin (24 karat, 100% gold) has a mass of 25.54 g. How many atoms of gold are present in this coin? (Molar mass of Au = 196.97 g/mol, Avogadro's number = $$6.022 \times 10$$^{23}$$)

$$7.806 \times 10$$^{22}$$ atoms

Q: A sample of $$\mathrm{N_2O}$$ has a mass of 5.70 g. How many molecules are present in this sample? (Molar mass $$\mathrm{N_2O} = 44.01 g/$$mol, Avogadro's number = $$6.022 \times 10$$^{23}$$)

$$7.80 \times 10$$^{22}$$ molecules

Q: A 117 kg sample of water contains how many molecules? (Molar mass $$\mathrm{H_2O} = 18.02 g/$$mol, Avogadro's number = $$6.022 \times 10$$^{23}$$)

$$3.91 \times 10$$^{27}$$ molecules

Question 1

Which of the following best describes the mass of 1 mole of atoms for an element?

Accepted Answer

It is equal to the molar mass of the element.

Question 2

How many molecules are present in 6.00 mol of a molecular compound?

Accepted Answer

$$3.613 	imes 10$$^{24}$$ molecules

Question 3

What is the molar mass of dichloromethane ($$\mathrm{CH_2Cl_2}$$)?

Accepted Answer

$$84.93\ \mathrm{g/mol}$$

Question 4

For the compound sucrose ($$\mathrm{C$$_{12}$$H_{22}O$$_{11}}$), what is the correct conversion factor between moles of the compound and moles of hydrogen atoms?

Accepted Answer

1 mole $$\mathrm{C$$_{12}$$H_{22}O$$_{11}}$ = 22 moles H atoms

Question 5

A jeweler has 10.0 g of platinum. How many moles of platinum does this represent? (Molar mass of Pt = 195.08 g/mol)

Accepted Answer

$$0.0513\ \mathrm{mol}$$

Question 6

A rare gold coin (24 karat, 100% gold) has a mass of 25.54 g. How many atoms of gold are present in this coin? (Molar mass of Au = 196.97 g/mol, Avogadro's number = $$6.022 	imes 10$$^{23}$$)

Accepted Answer

$$7.806 	imes 10$$^{22}$$ atoms

Question 7

Which sample contains the greatest number of moles of oxygen atoms?

Accepted Answer

0.5 mol $$\mathrm{Ca(NO_3$)_2}$$

Question 8

A food additive contains 2.20 g of sodium chloride ($$\mathrm{NaCl}). $$How many grams of sodium are present in this sample? (Molar mass: Na = 22.99 g/mol, NaCl = 58.44 g/mol)

Accepted Answer

0.865 g

Question 9

Calculate the mass percent of carbon in $$\mathrm{C_4H_8O_2} ($$Molar mass: C = 12.01 g/mol, H = 1.008 g/mol, O = 16.00 g/mol).

Accepted Answer

54.53%

Question 10

A compound containing nitrogen and oxygen is decomposed and produces 1.78 g of nitrogen and 4.05 g of oxygen. What is the empirical formula of the compound?

Accepted Answer

$$\mathrm{NO_2$}$$

Question 11

An oxide of phosphorus consists of 56.34% phosphorus by mass. What is the empirical formula for this compound?

Accepted Answer

$$\mathrm{P_2O_3}$$

Question 12

A compound containing selenium and fluorine is decomposed and produces 2.231 g of selenium and 3.221 g of fluorine. What is the empirical formula of the compound? (Molar mass: Se = 78.96 g/mol, F = 19.00 g/mol)

Accepted Answer

$$\mathrm{$$SeF_6$$}$$

Question 13

A compound has an empirical formula of $$\mathrm{CCl}$$ and a molar mass of 284.77 g/mol. What is its molecular formula? (C = 12.01 g/mol, Cl = 35.45 g/mol)

Accepted Answer

$$\mathrm{C_6Cl_6}$$

Question 14

A sample of $$\mathrm{N_2O}$$ has a mass of 5.70 g. How many molecules are present in this sample? (Molar mass $$\mathrm{N_2O} = 44.01 g/$$mol, Avogadro's number = $$6.022 	imes 10$$^{23}$$)

Accepted Answer

$$7.80 	imes 10$$^{22}$$ molecules

Question 15

Which of the following best explains why the mass percent composition is important in real-world chemical analysis?

Accepted Answer

It allows chemists to determine the purity and identity of substances in mixtures, such as in pharmaceuticals or food products.

Question 16

A compound has an empirical formula of $$\mathrm{C_2HCl_3}$$ and a molar mass of 131.39 g/mol. What is its molecular formula?

Accepted Answer

$$\mathrm{C_2HCl_3}$$

Question 17

A 117 kg sample of water contains how many molecules? (Molar mass $$\mathrm{H_2O} = 18.02 g/$$mol, Avogadro's number = $$6.022 	imes 10$$^{23}$$)

Accepted Answer

$$3.91 	imes 10$$^{27}$$ molecules

Question 18

Which of the following is the correct mass percent composition of oxygen in $$\mathrm{CH_2O_2}$$? (C = 12.01 g/mol, H = 1.008 g/mol, O = 16.00 g/mol)

Accepted Answer

69.52%

Question 19

A compound has an empirical formula of $$\mathrm{C_2HCl}$$ and a molar mass of 181.44 g/mol. What is its molecular formula? (C = 12.01 g/mol, H = 1.008 g/mol, Cl = 35.45 g/mol)

Accepted Answer

$$\mathrm{C_6H_3Cl_3}$$

Introduction to Chemistry: Moles, Molar Mass, Empirical & Molecular Formulas Study Guide

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