Topic 3 – Relative Atomic Mass and The Mole

Topic TestName: ___________________________

Teacher: ___________________________

Reading time: 5 minutesWriting time: 45 minutes

Section A. Multiple Choice

Question 1Which of the following statements is CORRECT?

A. All atoms contain protons, neutrons and electrons.

B. The neutron must be present in an atom for it to be electrically neutral.

C. Isotopes of a particular element have the same electronic configuration when neutral.

D. The isotope of carbon that has an atomic number of 6 and a mass number of 12 must

have twice as many neutrons as protons.

Question 2In a mass spectrometer, isotopes of an element are separated based upon:

A. Mass only

B. Charge only

C. Mass and charge

D. Atomic radius

Question 3Silver has a relative atomic mass of 107.87, based on two isotopes of masses 107 and 109.

The percentage of the lighter isotope occurring naturally is about:

A. 40 %

B. 45 %

C. 50 %

D. 55 %

Question 4The molar mass of Ca(HCO3)2 is:

A. 101.1 g.mol–1

B. 102.1 g.mol–1

C. 149.1 g.mol–1

D. 162.1 g.mol–1

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Question 5Twelve grams of pure carbon-12 contains:

A. 6.02 1023 atoms of carbon-12.

B. 1 mole of carbon atoms with a relative atomic mass of 12.

C. the same number of atoms as 16 grams of oxygen-16.

D. All of the above.

Question 6Anne Bonny used a balance to find the mass of three 24-carat gold coins. She then

calculated the number of gold atoms in the coins. Ideally, the number of significant figures in

her final answer should be determined by:

A. the precision of her balance.

B. Avogadro’s number.

C. the number of gold coins.

D. the number of decimal places displayed on her calculator.

Question 7The molecular formula of a compound is X4Y8Z2, which provides the information that

A. the ratio of moles of X to Y to Z in any sample of the compound is 2:4:1.

B. in any sample of the compound the mass of X is two times the mass of Z.

C. the mass of element Y is less than the mass of element X.

D. each molecule of this compound contains one atom of element Z, two

atoms of element X and four atoms of element Y.

Question 8A particular hydrocarbon has a molar mass of 70 g.mol–1. Which of the following could be the

empirical formula of the hydrocarbon?

A. CH

B. CH2

C. CH3

D. C2H3

[8 1 = 8 marks]

Section B. Short Answer

In order to get full marks for any calculations, you must show all your working and include any relevant units in your final answer. Each missing unit is penalised 0.5 marks to a maximum of 1 marks. Each answer expressed with the incorrect number of significant figures (1

significant figure is acceptable) is penalised 0.5 marks to a maximum of 1 marks.

Question 1Element X has three naturally occurring isotopes each with the following % abundance.

Isotope 20X

21X 22X

Ir 19.992 20.994 21.991

% Abundance 90.48 0.270 9.25

a. Calculate the relative atomic mass of Element X.

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b. What is the identity of Element X?

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[2 +1 = 3 marks]

Question 2A New Zealander by the name of Ernest Rutherford fired alpha particles at a delicate piece

of gold foil (as shown in the diagram below).

a. Fill in the gaps.

Rutherford was able to conclude that, for

such a large number of the alpha particles

to pass straight through the gold foil, most

of the volume of an atom must be

___________ ____________. Most of the

mass of an atom, and all of the

____________ charge, was located in a tiny central region.

b. One piece of foil used contained 1.65 x 10-3 moles of gold.

i. How many gold atoms were in the piece of gold foil?

ii. What was the mass of the piece of gold foil?

[1 + 2 + 2 = 5 marks]

Question 3Once upon a time there was a bulldog named Rufus. Rufus had an insatiable (large)

appetite and would eat just about anything. One day, upon finding the pantry (kitchen

cupboard) door ajar (open), Rufus ate a whole box of baking powder, NaHCO3.

The baking powder reacted with the dilute hydrochloric acid, HCl, in his stomach, to produce

a salt, water and carbon dioxide gas.

Rufus gave three loud burps and trotted off in search of a slipper to chew on.

a. Baking powder is a common or trivial name for NaHCO3. Give the systematic name for

NaHCO3?

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b. Is baking powder a metallic, ionic or covalent substance?

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c. Write a balanced chemical equation, including state symbols, for the reaction that

occurred in Rufus’s stomach.

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d. Rufus ate 25.38 grams of baking powder.

i. How many moles of NaHCO3 did he eat?

ii. How many moles of oxygen atoms did he eat (as part of the baking powder)?

iii. How many sodium atoms did he eat?

[1 + 1 + 2 + 2 + 1 + 2 = 9 marks]

Question 4The hormone epinephrine, also known as adrenaline, is responsible for the ‘flight or fight’ response, and has the molecular formula C9H13NO3. Calculate:

a. the molar mass of adrenaline

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b. its percentage composition by mass of each element in the compound

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[1 + 4 = 5 marks]

Question 5a. A compound, that is commonly used to give artificial pineapple flavouring, contains 62.0

% carbon and 10.4 % hydrogen, the rest being oxygen. Determine the empirical formula of this molecule.

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b. The relative molecular mass of the compound is 116.2 g/mol. What is the molecular formula of this molecule?

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[4 + 2 = 6 marks]