Properties of acids & bases
1. Give the equation for the reaction between dilute hydrochloric acid, HCl(aq), and:
(a) potassium hydroxide solution, KOH(aq).
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(b) ammonia, NH3(aq).
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(c) copper(II) oxide, CuO(s).
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(d) sodium hydrogen carbonate, NaHCO3(s).
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(e) calcium carbonate, CaCO3(s).
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(f) zinc metal, Zn(s).
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2. Distinguish between the terms base and alkali.
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3. Describe two different test-tube reactions to illustrate that a solution of sodium hydroxide, NaOH(aq)
is basic.
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4. Give the equation for the reaction which occurs when solid ammonium chloride, NH4Cl(s) is heated
with potassium hydroxide solution, KOH(aq).
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5. The image below shows the colour of universal indicator paper at different pH values.
(a) Deduce the approximate colour when a strip of the indicator paper is placed in a dilute solution of
ammonia.
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(b) If nitric acid is added in excess to this solution how would you expect the colour of the indicator
paper to change?
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6. State the equation for the reaction between magnesium oxide, MgO(s) and sulfuric acid, H2SO4(aq).
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Answers
1. (a) HCl(aq) + KOH(aq) → KCl(aq) + H2O(l) or H+(aq) + OH–(aq) → H2O(l).
(b) HCl(aq) + NH3(aq) → NH4Cl(aq) or H+(aq) + NH3(aq) → NH4+(aq)
(c) 2HCl(aq) + CuO(s) → CuCl2(aq) + H2O(l)
(d) HCl(aq) + NaHCO3(s) → NaCl(aq) + CO2(g) + H2O(l)
or H+(aq) + HCO3–(aq) → CO2(g) + H2O(l)
(e) 2HCl(aq) + CaCO3(s) → CaCl2(aq) + CO2(g) + H2O(l)
or 2H+(aq) + CO32–(aq) → CO2(g) + H2O(l)
(f) 2HCl(aq) + Zn(s) → ZnCl2(aq) + H2(g) or 2H+(aq) + Zn(s) → Zn2+(aq) + H2(g)
2. A base is a substance than can neutralise an acid. An alkali is a soluble base.
3. (i) Add a dilute acid, such as hydrochloric acid, to the sodium hydroxide solution. Universal indicator
paper (or another indicator such as phenolphthalein) or a pH meter can be used to show the pH moves
from above 7 to below 7 as the sodium hydroxide solution is first neutralised then the acid is present is
excess.
(ii) Add the sodium hydroxide solution to solid ammonium chloride and warm. The smell of ammonia
being evolved will be noticed.
4. NH4Cl(s) + KOH(aq) → KCl(aq) + NH3(g) + H2O(l) or NH4+(s) + OH–(aq) → NH3(g) + H2O(l)
5. (a) Green/blue as the pH will be about 8-10 depending upon the concentration of the ammonia.
(b) Change to red/pink as the pH will drop to about 3 or slightly less depending upon the
concentration of the acid.
6. MgO(s) + H2SO4(aq) → MgSO4(s) + H2O(l)