Q: Calculate the relative molecular mass ($$M_r) of $$sulfuric acid, $$\mathrm{H}_2\mathrm{SO}_4$$, using the following relative atomic masses: H = 1.0, S = 32.1, O = 16.0.

$$M_r = (2 \times 1.0) + 32.1 + (4 \times 16.0) = 98.1$$

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

A mole is the amount of substance that contains $$6.02 \times 10$$^{23}$$ particles.

Question 1

Which of the following best defines the term 'relative atomic mass' ($$A_r$$)?

Accepted Answer

The weighted mean mass of an atom of an element compared to $$\frac{1}{12} of $$the mass of an atom of $$^{12}\mathrm{C}.$$

Question 2

Calculate the relative molecular mass ($$M_r) of $$sulfuric acid, $$\mathrm{H}_2\mathrm{SO}_4$$, using the following relative atomic masses: H = 1.0, S = 32.1, O = 16.0.

Accepted Answer

$$M_r = (2 	imes 1.0) + 32.1 + (4 	imes 16.0) = 98.1$$

Question 3

A sample contains $$1.25\ \mathrm{g} of $$water ($$\mathrm{H}_2\mathrm{O}). $$How many molecules of water are present? ($$M = 18.0\ \mathrm{g\ $$mol^{-1}$$}$$, $$L = 6.02 	imes 10$$^{23}$$\ \mathrm{$$mol^{-1}$$})$$

Accepted Answer

$$4.18 	imes 10$$^{22}$$

Question 4

Which of the following statements about the mole is correct?

Accepted Answer

A mole is the amount of substance that contains $$6.02 	imes 10$$^{23}$$ particles.

Question 5

What is the mass of $$2.00 	imes 10$$^{22}$$ molecules of carbon dioxide ($$\mathrm{CO}_2$$)? (M = 44.0$$\ \mathrm{g\ $$mol^{-1}$$}$$, L = 6.02$$ 	imes $$10^{23}$$\ \mathrm{$$mol^{-1}$$}$$)

Accepted Answer

$$1.46\ \mathrm{g}$$

Question 6

A reaction is carried out: $$\mathrm{N}_2 + 3\mathrm{H}_2 \rightarrow 2\mathrm{NH}_3. If$$ $$28.0\ \mathrm{g} of$$ $$\mathrm{N}_2$$ reacts with excess $$\mathrm{H}_2$$, what mass of $$\mathrm{NH}_3 is $$formed? ($$M_{\mathrm{NH}_3$$} = 17.0\ \mathrm{g\ $$mol^{-1}$$}$$)

Accepted Answer

$$34.0\ \mathrm{g}$$

Question 7

A student decomposes $$5.78\ \mathrm{g} of $$copper(II) carbonate ($$\mathrm{CuCO}_3) to $$obtain copper(II) oxide ($$\mathrm{CuO}). $$What is the theoretical yield of $$\mathrm{CuO}$$? ($$M_{\mathrm{CuCO}_3$$} = 123.5\ \mathrm{g\ $$mol^{-1}$$}$$, M$$_{\mathrm{CuO}} = 79.5\ \mathrm{g\ $$mol^{-1}$$}$$)

Accepted Answer

$$3.72\ \mathrm{g}$$

Question 8

A manufacturer starts with $$75.0\ \mathrm{kg} of $$calcium carbonate ($$\mathrm{CaCO}_3) $$and obtains $$76.5\ \mathrm{kg} of $$sodium carbonate ($$\mathrm{Na}_2\mathrm{CO}_3) in $$the reaction $$\mathrm{CaCO}_3 + 2\mathrm{NaCl} \rightarrow \mathrm{Na}_2\mathrm{CO}_3 + \mathrm{CaCl}_2. $$What is the percentage yield? ($$M_{\mathrm{CaCO}_3$$} = 100.1\ \mathrm{g\ $$mol^{-1}$$}$$, M$$_{\mathrm{Na}$$_2\mathrm{CO}_3} = 106.0\ \mathrm{g\ $$mol^{-1}$$})$$

Accepted Answer

$$96.3\%$$

Question 9

Which of the following best describes 'atom economy'?

Accepted Answer

The percentage of reactant atoms that end up in the desired product.

Question 10

In the reaction $$2\mathrm{NH}_3 + \mathrm{NaOCl} \rightarrow \mathrm{N}_2\mathrm{H}_4 + \mathrm{NaCl} + \mathrm{H}_2\mathrm{O}$$, what is the atom economy for hydrazine ($$\mathrm{N}_2\mathrm{H}_4) $$production? ($$M_{\mathrm{N}_2$$\mathrm{H}_4} = 32.0$$, M$$_{\mathrm{NaCl}} = 58.5$$, M$$_{\mathrm{H}$$_2\mathrm{O}} = 18.0)$$

Accepted Answer

$$29.5\%$$

Question 11

A reaction has a theoretical yield of $$26.7$$ tonnes and an actual yield of $$18.5$$ tonnes. What is the percentage yield?

Accepted Answer

$$69.3\%$$

Question 12

Which of the following reactions has an atom economy of $$100\%$$?

Accepted Answer

$$\mathrm{C}_2\mathrm{H}_4 + \mathrm{H}_2\mathrm{O} \rightarrow \mathrm{C}_2\mathrm{H}_5\mathrm{OH}$$

Question 13

A chemist wants to maximize the atom economy of a process. Which type of reaction should they prefer?

Accepted Answer

Addition reactions

Question 14

A $$16.7\ \mathrm{g}$$ sample of $$\mathrm{Na}_2\mathrm{CO}_3\cdot 10\mathrm{H}_2\mathrm{O} is $$heated and produces $$3.15\ \mathrm{g} of $$water. What is the simplest ratio of moles of $$\mathrm{Na}_2\mathrm{CO}_3\cdot 10\mathrm{H}_2\mathrm{O} to$$ $$\mathrm{H}_2\mathrm{O}$$? ($$M_{\mathrm{Na}_2$$\mathrm{CO}_3\cdot 10\mathrm{H}_2\mathrm{O}} = 286.1$$, M$$_{\mathrm{H}$$_2\mathrm{O}} = 18.0)$$

Accepted Answer

1 : 3

Question 15

Which of the following is a reason why the actual yield of a reaction may be less than the theoretical yield?

Accepted Answer

The reaction is reversible and does not go to completion.

Question 16

A manufacturer uses $$4.32$$ tonnes of carbon monoxide ($$\mathrm{CO}) to $$produce methanol ($$\mathrm{CH}_3\mathrm{OH}) $$via $$\mathrm{CO} + 2\mathrm{H}_2 \rightarrow \mathrm{CH}_3\mathrm{OH}. If$$ $$4.07$$ tonnes of methanol are obtained, what is the percentage yield? ($$M_{\mathrm{CO}} = 28.0$$, $$M_{\mathrm{CH}_3$$\mathrm{OH}} = 32.0$$)

Accepted Answer

$$82.4\%$$

Question 17

Which of the following best describes the difference between percentage yield and atom economy?

Accepted Answer

Percentage yield measures how much product is obtained compared to the maximum possible, while atom economy measures how efficiently reactant atoms are incorporated into the desired product.

Question 18

A sample contains $$4.00\ \mathrm{g} of $$methane ($$\mathrm{CH}_4). $$How many molecules are present? ($$M = 16.0\ \mathrm{g\ $$mol^{-1}$$}$$, $$L = 6.02 	imes 10$$^{23}$$\ \mathrm{$$mol^{-1}$$})$$

Accepted Answer

$$1.51 	imes 10$$^{23}$$

Comparing Masses, Moles, and Reacting Quantities in Chemistry

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