(a) Give the reason in each case why it is necessary to:
(i) moisten a piece of litmus paper used in testing for the acidity or alkalinity of a gas.
(i) acidify the test solution with dilute hydrochloric acid in the confirmatory test for SO\(_4^2\)
(b)(i) List two gases that must not be prepared in the open laboratory
(ii) Mention one precaution that should be taken in the laboratory to prevent excessive inhalation of these gases during their preparation.
(iii) State one use of each of the following pieces of apparatus in the laboratory. I. Wash bottle II. Tripod stand
(c) State what would be observed when:
(i) Pb(NO\(_3\))\(_2\) is needed
(ii) concentrated HCI is added to MnO\(_2\)
(a) The dry gas does not contain H\(_3\)O\(^+\) or H\(^-\) or OH\(^+\) which changes the colour of litmus or the ions H\(_2\)O or H\(^+\) or OH\(^-\) are produced only in the presence of water.
(i) The reagent barium chloride can form a white precipitate with other ions if the solution is neutral. Addition of a mineral acid removes the interfering (CO\(_3^{2-}\), SO\(^{2-}_3\)) ions if they are present:
(b)(i) Chlorine, carbon (II) oxide, hydrogen sulphide, hydrogen chloride, sulphur (IV) oxide, nitrogen (V) oxide and ammonia.
(ii) They should be prepared in the fume chamber.
(I) For keeping solvents such as distilled water
(II) it is used as a support for flasks or beakers during heating
(C)(i) Pb(NO\(_3\))\(_2\) decomposes, brown fumes are given off, yellow residue or reddish-brown residue left.
(i) Greenish-yellow gas evolved.
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