Chapter 11: Stoichiometry

The diagram shows the mass spectrum of a sample of naturally-occurring copper. What is the relative atomic mass of this copper?

• 63.3

• 63.5

• 63.6

• 64.0

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NGSS.HS-PS1-7

Which of these samples of gas contains the same number of atoms as 1g of hydrogen gas (H₂; Mr = 2)?

• 22 g of carbon dioxide (CO₂, Mr = 44)

• 8 g of methane (CH₄, Mr = 16)

• 20 g of neon (Ne, Ar = 20)

• 8 g of ozone (O₃, Mr = 48)

Most modern cars are fitted with airbags. These work by decomposing sodium azide to liberate nitrogen gas, which inflates the bag.

2NaN₃ → 3N₂ + 2Na

A typical driver’s airbag contains 50 g of sodium azide (Mr = 65). Calculate the volume of nitrogen this will produce at room temperature (at r.t.p molar volume is 24 dm³₎

• 9.2 dm³

• 13.9 dm³

• 27.7 dm³

• 72.0 dm³

A pure hydrocarbon is used in bottled gas for cooking and heating. When 10 cm³ of the hydrocarbon is burned in 70 cm³ of oxygen (an excess), the final gaseous mixture contains 30 cm³ of carbon dioxide and 20 cm³ of unreacted oxygen. All gaseous volumes were measured under identical conditions.

What is the formula of the hydrocarbon?

• C₂H₆

• C₃H₆

• C₃H₈

• C₄H₁₀

On collision, airbags in cars inflate rapidly due to the production of nitrogen. The nitrogen is formed according to the following equations.

2NaN₃ → 2Na + 3N₂

10Na + 2KNO₃ → K₂O + 5Na₂O + N₂

How many moles of nitrogen gas are produced from 1 mol of sodium azide, NaN₃?

• 1.5

• 1.6

• 3.2

• 4.0

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NGSS.HS-PS1-2

NGSS.HS-PS1-7

Oxides of nitrogen are pollutant gases which are emitted from car exhausts. In urban traffic, when a car travels one

kilometre, it releases 0.23 g of an oxide of nitrogen N_xO_y,

which occupies 120 cm³.

What are the values of x and y? (Assume 1 mol of gas molecules occupies 24.0 dm³.)

• x = 1, y = 1

• x = 1, y = 2

• x = 2, y = 1

• x = 2, y = 4

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NGSS.HS-PS1-1

NGSS.HS-PS1-2

The petrol additive tetraethyl-lead(IV), Pb(C₂H₅)₄, is now banned in many countries.

When it is completely burned in air, lead(II) oxide, CO₂ and H₂O are formed. How many moles of oxygen are required to burn one mole of Pb(C₂H₅)₄?

• 9.5

• 11

• 13.5

• 27

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NGSS.HS-PS1-2

A mixture of 10 cm³ of methane and 10 cm³

of ethane was sparked with an excess of oxygen. After cooling to room temperature, the residual gas was passed through aqueous potassium hydroxide. What volume of gas was absorbed by the alkali?

• 15 cm³

• 20 cm³

• 30 cm³

• 40 cm³

In the Basic Oxygen steel-making process the P₄O₁₀ impurity is removed by reacting it with calcium oxide. The only product of this reaction is the salt calcium phosphate, Ca₃(PO₄)₂.

In this reaction, how many moles of calcium oxide react with one mole of P₄O₁₀?

• 1

• 1.5

• 3

• 6

The foul smell that skunks spray is due to a number of thiols, one of which is methanethiol, CH₃SH, which burns as follows.

CH₃SH + 3O₂ → CO₂ + SO₂ + 2H₂O

A sample of 10 cm³ of methanethiol was exploded with 60 cm³ of oxygen. What would be the final volume of the resultant mixture of gases when cooled to room temperature?

• 20 cm³

• 30 cm³

• 50 cm³

• 70 cm³