1.1. Until recently, arsenic poisoning, either deliberate or accidental, has been a frequent cause of death. The symptoms of arsenic poisoning are identical with those of a common illness, cholera. A reliable test was needed to prove the presence of arsenic in a body.

In 1840, Marsh devised a reliable test for arsenic

Hydrogen is formed in this reaction. Any arsenic compound reacts with this hydrogen to form arsine which is arsenic hydride, AsH₃.

i) The mixture of hydrogen and arsine is burnt at the jet and arsenic forms as a black stain on the glass. Write an equation for the reaction which forms hydrogen.

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ii) Draw a diagram which shows the arrangement of the outer electrons in one molecule of the covalent compound arsine. The electron distribution of arsenic is 2 + 8 + 18 + 5. Use x to represent an electron from an arsenic atom. Use o to represent an electron from a hydrogen atom.

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1.2. Separate: Chemistry and Extended Only

Another hydride of arsenic has the composition below.

arsenic 97.4% hydrogen 2.6%

i) Calculate the empirical formula of this hydride from the above data. Show your working.

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ii) The mass of one mole of this hydride is 154 g. What is its molecular formula?

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iii) Deduce the structural formula of this hydride.

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1.3. Separate: Chemistry and Extended Only

In the 19th Century, a bright green pigment, copper(II) arsenate(V) was used to kill rats and insects. In damp conditions, micro-organisms can act on this compound to produce the very poisonous gas, arsine.

i) Suggest a reason why it is necessary to include the oxidation states in the name of the compound.

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ii) The formula for the arsenate(V) ion is AsO₄^3–.

Complete the ionic equation for the formation of copper(II) arsenate(V).

......Cu²⁺ + ......AsO₄^3– → ..................................

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