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Counting Particles by Mass: The Mole · Paper 2 — Free Chemistry HL Practice Questions

1ChallengeSAQ-LDefinition of the mole and Avogadro's constant10 marksPaper 2~15 min

Data

M(\text{Ti}) = 47.9\,\text{g mol}^{-1}

M(\text{O}) = 16.0\,\text{g mol}^{-1}

N_A = 6.02 \times 10^{23}\,\text{mol}^{-1}

A sample of pure titanium(IV) oxide,

\text{TiO}_2

, used as a white pigment in paint, has a mass of

7.99\,\text{g}

(a)

Show that the molar mass of

\text{TiO}_2

79.9\,\text{g mol}^{-1}

, and hence determine the number of moles of

\text{TiO}_2

in the

7.99\,\text{g}

sample. [2 marks]

(b)

Calculate the number of titanium atoms in the

7.99\,\text{g}

sample of

\text{TiO}_2

. [2 marks]

(c)

The mole is described as a "bridge" between the atomic scale and the macroscopic scale. Using the relationship between the mass of one

\text{TiO}_2

formula unit in atomic mass units and the molar mass of

\text{TiO}_2

in grams, explain what this bridging role means and why it is necessary for quantitative chemistry. [3 marks]

(d)

A student claims that a

7.99\,\text{g}

sample of pure titanium metal contains more atoms than the

7.99\,\text{g}

sample of

\text{TiO}_2

. Evaluate this claim using calculations, and explain why any difference arises in terms of molar mass. [3 marks]

Solutions

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