(a) State how you would carry out the following procedures in the laboratory:
(i) Remove the sediment in sample of water;
(ii) Soften temporarily hard water without heating it,
(iii) Obtain pure water from muddy water;
(iv) Remove oxygen and moisture from a sample of air
(b)(i) What type of salts are alums?
(ii) State the function of alum in water treatment plants.
(iii) State and explain how rain water that hac passed through limestone deposits will react with soap solution.
(c)(i) Write an equation for the laboratory preparation of chlorine
(ii) List the products of the reaction of chlorine with hot concentrated sodium hydroxide solution
(iii) What is observed when moist blue litmus paper comes in contact with chlorine?
(iv) Calculate the volume of chlorine at s.t.p. that would be required to react completely with 3.70g of dry slaked lime according to the following equation:
Ca(OH)\(_{2(s)}\) + Cl\(_{2(g)}\) –> CaOCl\(_{2}\). H\(_2\)O\(_{(s)}\) [H = 1, O = 16, Ca = 40, 1 mole of gas occupies 22.4 dm\(^3\) at s.t.p.]
(d)(i) State what is observed on warming ammonium trioxonitrate (V) with sodium hydroxide solution
(ii) Explain why ammonium trioxocarbonate (IV) leaves no residue on being heated.
Explanation
(a)(i) The sediment is a sample of water can be removed by filtration, decantation or centrifuging.
(ii) Add washing soda Na\(_2\)CO\(_3\) or pass it through an ion exchange resin or add calculated amount of Ca(OH)\(_2\).
(iii) To obtain water from muddy water, distill it.
(iv) Bubble the air through alkaline pyrogallol or pass it over burning phosphorus or hot copper (I). To remove moisture from air, pass it through a U - tube containing concentrated H\(_2\)SO\(_4\) or fused CaCl\(_2\) or silica gel or P\(_2\)O\(_5\) or Quicklime.
(b)(i) Alums are double salts.
(ii) Alum is used for coagulation of fine / colloidal particles in water treatment plants.
(iii) It will not form lather readily with soap. The reason is that the CO\(_2\) present in the atmosphere and in the rain water react with the limestone and convert it to Ca(HCO\(_3\))\(_2\) which renders the water temporarily hard. OR CaCO\(_3\) + H\(_2\)O + CO\(_2\) -> Ca(HCO\(_3\))\(_2\)
(c)(i) MnO\(_2\) + 4HCI -> MnCl\(_2\) + Cl\(_2\) + 2H\(_2\)O.
OR 2KMnO\(_4\) + 16HCI \(\to\) 2MnCl\(_2\) + 2KCI + 8H\(_2\)O + 5Cl\(_2\)
(ii) The products of the reaction of chlorine with hot concentrated NaOH are NaCI, NaCl and water i.e (sodium chloride, sodium chlorate or sodium trioxochlorate (V).
(iii) The paper turns red or pink and turns white (bleached)
(iv) Ca(OH)\(_2\) + Cl\(_2\) -.> CaOCl\(_2\). H\(_2\)O. From equation 22.4 dm\(^3\) of Cl\(_2\) at STP reacts completely with 1 mole of Ca(OH)\(_2\).
Molar mass of Ca(OH)\(_2\) is 40 + (2 x 16) + (2 x 1) g = 74g
Vol. of CI\(_2\) that will react with 3.7g of slaked lime = \(\frac{22.4 \times 3.7}{74}\) = 1.12 dm\(^3\)
(d)(i) On warming NH\(_4\)NO, with NaOH, a colourless gas, with choking or pungent smell is evolved.
(ii) (NH\(_4\))\(_2\) CO\(_3\) leaves no residue on being heated strongly because it decomposes into gaseous (NH\(_4\))\(_2\) CO\(_3\) -> 2NH\(_3\) + CO\(_2\) + H\(_2\)O.