Question

1. c is a mixture of two compounds. carry out the following exercises on c. record your observations and identify any gas(es) evolved. state the conclusions you draw from the results of each test.

(a) (i) put all of c into a beaker and add about 5 cm³ of distilled water. stir the mixture thoroughly and filter. keep both the filtrate and the residue.
(ii) test the filtrate with litmus papers.
(b) divide the filtrate into two portions.
(i) to the first portion, add naoh(aq) in drops, then in excess. allow the mixture to stand for about five minutes.
(ii) to the second portion, add a few drops of bacl₂(aq) followed by dilute hcl in excess.
(c) divide the residue into two portions.
(i) to the first portion, add about 5 cm³ of distilled water and boil.
(ii) to the second portion, add a few drops of iodine solution.
20 marks

Explanation:

Step1: Test with water and litmus

When C is mixed with distilled water, filtered and filtrate tested with litmus papers, we can determine if the solution is acidic or basic. If blue litmus turns red, it's acidic; if red litmus turns blue, it's basic.

Step2: React filtrate with NaOH

Adding NaOH in drops then in excess to the first portion of filtrate may form a precipitate which may dissolve in excess NaOH depending on the nature of the metal - ion present in the compound in C.

Step3: React filtrate with BaCl₂ and HCl

Adding BaCl₂ followed by excess HCl to the second portion of filtrate can test for the presence of sulfate ions. If a white precipitate (BaSO₄) forms which is insoluble in excess HCl, sulfate ions are present.

Step4: React residue with iodine

Adding iodine solution to the first portion of the residue can test for the presence of starch. If a blue - black color appears, starch is present.

Step5: Boil residue with water

Boiling the residue with water in the second part of (c) may dissolve some components which were not soluble in cold water and can be further tested for their identity.

Answer:

Based on the above tests, observations such as color - changes, precipitate formation or dissolution, and gas evolution need to be recorded to identify the components in the mixture C. For example, if blue litmus turns red in (a)(ii), the solution is acidic. If a white precipitate forms in (b)(ii) which is insoluble in excess HCl, sulfate ions are present. If a blue - black color appears in (c)(i), starch is present in the residue.