(a)(i) Define each of the following terms: I. normal salt. II. acid salt.
(ii) Tetraoxosulphate (VI) acid and sodium hydroxide react to produce salt and water. Write a balanced chemical equation fir the formation of: I. a normal salt; II. an acid salt.
(b)(i) Explain briefly the term acid-base indicator.
(ii) Copy and complete the following table.
|
Indicator |
, Colour in acidic medium |
, Colour in basic medium |
|
Methyl orange |
||
|
Phenolphthalein |
(iii) For each of the following titrations, state the most suitable indicator: I. strong acid against strong base; II. strong acid against weak base; iii. weak acid against strong base.
(c) Baking soda and hydrochloric acid react according to the following equation:
NaHCO\(_{3(aq)}\) + HCI\(_{(aq)}\) —> NaCl\(_{(aq)}\) CO\(_{2(g)}\) + H\(_2\)O\(_{(l)}\). Calculate the mass of baking soda that would produce 10g of ccrbon (IV) oxide. [H = 1.00, C = 12.0, 0 = 16.0, Na = 23.0]
(d) Give a reason why a given mass of sodium hydroxide pellets cannot be used to prepare a standard solution.
NaHCO\(_3\) + HCI –> NaCI + CO\(_2\) + H\(_2\)O
84g NaHCO\(_3\) –> 44g CO\(_2\)
Xg –> 10g CO\(_2\)
Xg = \(\frac{84 \times 10}{44}\)
= 19.09g
= 19.1g.
(d) give a reason why a given mass of sodium hydroxide pellets cannot be used to prepare a standard solution: Sodium hydroxide absorbs water/deliquescent and absorbs carbon IV oxide from air/and this would make mass taken unreliable/add to its mass.
Explanation
(a)(i) Define each of the following terms:
I. Normal salt: Salt formed when all the replaceable hydrogen ions/replaceable hydrogen atoms of an acid are replaced by a metal/ammonium ion. Or a salt formed when all the OH\(^-\) of the alkali are replaced by an ionic group of an acid.
II. Acid salt: Salt formed when only some part of the (replaceable) hydrogen ions/atoms of an acid are replace a metal.
(ii) Tetraoxosulphate VI acid and sodium hydroxide react to produce s d water. Write a balanced chemical equation for the formation of:
I. A normal salt: 2NaOH + H\(_2\)SO\(_4\) \(\to\) Na\(_2\)SO\(_4\) + 2H\(_2\)O.
II. An acid salt: NaOH + H\(_2\)SO\(_4\) \(\to\) NaHSO\(_4\) + H\(_2\)O.
(b)(i) Explain briefly the term acid-base indicator: It is either a weak acid or weak base which gives different colour in acid alkaline medium/depending on pH of the solution.
(ii) Copy and complete the following table:
(ii) Copy and complete the following table.
|
Indicator |
, Colour in acidic medium |
, Colour in basic medium |
|
Methyl orange |
Red/Pink | Yellow |
|
Phenolphthalein |
Colourless | Pink/Red |
(iii) For each of the following titrations, state the most suitable indicator:-
I. Strong acid against strong base – Methyl orange/methyl red/litmus/bromocresol blue or red.
II. Strong acid against weak base – Methyl orange.
III. Weak acid against strong base – Phenolphthalein.
(c) Baking soda and hydrochloric acid react according to the following equation:
NaHCO\(_{3(aq)}\) + HCl\(_{(aq)}\) \(\to\) NaCl\(_{aq}\) + CO\(_{2(aq)}\) + H\(_2\)O
Calculate the mass of baking soda that would produce 10g of carbon(iv)oxide. [ H = 1, C = 12, O = 16, Na = 23 ]
Relative molar mass (CO\(_2\)) = 12 + (2 x 16) = 44.
Relative molar mass (NaHCO\(_3\)) = 23 + 1 + 12 + (3 x 16) = 84