Chemistry 0620 · IGCSE · Relative masses of atoms and molecules

Relative masses of atoms and molecules — practice question

Lead is a metallic element in Group IV. Galena is one of its ores and it is an impure form of lead(II) sulfide, PbS. Another lead ore is cerussite, which contains lead(II) carbonate, PbCO$_3$.
(a)[1]

Calculate the relative formula mass, $M_r$, for PbCO$_3$.

(b)[1]

Calculate what percentage of the mass of PbS is lead.

(c)[1]

Use this information together with your answer to (b) to suggest whether lead should be extracted from PbCO$_3$ or PbS. Give a reason for your choice.

(d)[1]

When lead(II) carbonate is heated, it breaks down into lead(II) oxide, PbO, and carbon dioxide. Write a chemical equation for this reaction.

(e)[2]

Write a chemical equation for this reaction.

(f(i))[2]

Complete the diagram so that it shows the electron arrangement in one CO$_2$ molecule. Include only the outer electrons.

(f(ii))[3]

Use your knowledge of structure and bonding to explain why lead(II) oxide has a much higher melting point than carbon dioxide. Your answer should mention the types of particles involved and compare the strength of the attractive forces between them.

(g)[2]

Write an ionic equation for any reaction that happens in each experiment. If no reaction happens, write 'no reaction'.

(h(i))[2]

Describe a test for oxygen, including both the test and the observation.

(h(ii))[1]

Name the other gaseous product.

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