(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 wat...
Question 1 Report
(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:
\(\mathrm{NaHCO}_{3(aq)} + \mathrm{HCI}_{(aq)} \longrightarrow \mathrm{NaCl}_{(aq)} \mathrm{CO}_{2(g)} + \mathrm{H}_2\mathrm{O}_{(l)}\). 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.
\(\mathrm{NaHCO}_3 + \mathrm{HCI} \longrightarrow \mathrm{NaCI} + \mathrm{CO}_2 + \mathrm{H}_2\mathrm{O}\)
\(84\mathrm{g}\ \mathrm{NaHCO}_3 \longrightarrow 44\mathrm{g}\ \mathrm{CO}_2\)
\(X\mathrm{g} \longrightarrow 10\mathrm{g}\ \mathrm{CO}_2\)
\(X\mathrm{g} = \frac{84 \times 10}{44}\)
\(= 19.09\mathrm{g}\)
\(= 19.1\mathrm{g}.\)
(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.
Answer Details
(a)(i) I. Normal salt: a salt formed when all the replaceable hydrogen ions of an acid have been completely replaced by a metal ion (or the ammonium ion), for example \( Na_2SO_4 \). II. Acid salt: a salt formed when only part of the replaceable hydrogen ions of an acid has been replaced by a metal ion, so it still contains replaceable hydrogen, for example \( NaHSO_4 \).
(a)(ii)
I. Normal salt: \[ H_2SO_4 + 2NaOH \rightarrow Na_2SO_4 + 2H_2O \]
II. Acid salt: \[ H_2SO_4 + NaOH \rightarrow NaHSO_4 + H_2O \]
(b)(i) An acid-base indicator is a substance (usually a weak organic acid or base) that shows different colours in acidic and in basic media, and so is used to detect the end point of a titration.
(b)(ii) Completed table
| Indicator | Colour in acidic medium | Colour in basic medium |
|---|---|---|
| Methyl orange | Red (pink) | Yellow |
| Phenolphthalein | Colourless | Pink |
(b)(iii) I. Strong acid against strong base: methyl orange or phenolphthalein. II. Strong acid against weak base: methyl orange. III. Weak acid against strong base: phenolphthalein.
(c) Mass of baking soda producing 10 g of \( CO_2 \)
\[ NaHCO_3 + HCl \rightarrow NaCl + CO_2 + H_2O \]Molar mass of \( NaHCO_3 = 23 + 1 + 12 + (3 \times 16) = 84\ \text{g mol}^{-1} \); molar mass of \( CO_2 = 12 + 32 = 44\ \text{g mol}^{-1} \).
From the equation, \( 84\ g \) of \( NaHCO_3 \) gives \( 44\ g \) of \( CO_2 \). Let \( x \) be the mass needed for \( 10\ g \) of \( CO_2 \):
\[ x = \frac{84 \times 10}{44} = 19.09\ g \approx 19.1\ g \]Mass of baking soda = 19.1 g.
(d) A given mass of sodium hydroxide pellets cannot be used to prepare a standard solution because sodium hydroxide is deliquescent and also absorbs carbon(IV) oxide from the air; its mass therefore changes and is unreliable, so it is not a primary standard.
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