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Answers to Practise Questions (Basic) – Acids and Bases
Practise questions (Basic) are designed to ensure that students are aware of the basic
concepts of the topic. This should be the first step that students undertake while
revising for their chemistry examination. For the O Level examination, these basic
concepts will be tested although questions will not be straight forward and students
will need to be able to apply these concepts to solve the questions. For the chapter of
ammonia, there are fewer questions as this is a relatively small chapter and the scope
is much narrower.
(1): What is the difference between a strong acid and weak acid? Give two examples
each of strong and weak acid.
A strong acid dissociates fully in aqueous solution producing hydrogen ions. A weak
acid dissociates partially in aqueous solution producing hydrogen ions, most of it
exists as molecules.
Strong acid – nitric acid and sulfuric acid
Weak acid – ethanoic acid and citric acid
(2): What is the difference between a strong alkali and weak alkali? Give one
example each of a strong alkali and weak alkali
A strong alkali dissociates fully in aqueous solution producing hydroxide ions. . A
weak alkali dissociates partially in aqueous solution producing hydroxide ions, most
of it exists as molecules.
Strong alkali – sodium hydroxide
Weak alkali – aqueous ammonia
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(3): State the colour of universal indicator in the following solutions:
(i): Hydrochloric acid
Red
(ii): Acid from car battery
Red
(iii): Lemon juice
Orange
(iv): Milk of magnesia
Blue
(v): Baking soda
Green
(vi): Sodium hydroxide
Violet
(vii): Household bleach
Violet
(viii): Vinegar
Orange
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(ix): Ammonia
Blue
(4): What is the difference between bases and alkali
Bases are metal oxides or hydroxides that reacts with acid to produce salt and water.
Alkali is a base that is soluble in water.
(5): List down two uses of acids and two uses of alkali/bases
Sulfuric acid – Use in car batteries
Ethanoic acid – Use to preserve food
Sodium hydroxide – Use in the making of soap
Calcium hydroxide – Reduce the acidity in soil
(6): Write balanced chemical equations for the following reactions:
(i): Calcium carbonate + nitric acid
CaCO3 + 2HNO3  Ca(NO3)2 + CO2 + H2O
(ii): Zinc + sulfuric acid
Zn + H2SO4  ZnSO4 + H2
(iii): Magnesium oxide + hydrochloric acid
MgO + 2HCl  MgCl2 + H2O
(iv): Ammonium nitrate + sodium hydroxide
NH4NO3 + NaOH  NaNO3 + NH3 + H2O
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(v): Aluminium oxide + sulfuric acid
Al2O3 + 3H2SO4  Al2(SO4)3 + 3H2O
(7): Write ionic equations for the following reactions:
(i): Sodium + hydrochloric acid
2Na(s) + 2H+(aq)  2Na+(aq) + H2(g)
(ii): Calcium hydroxide + sulfuric acid
Ca2+(aq) + SO42-(aq)  CaSO4(s)
(iii): Ammonium chloride + sodium hydroxide
NH4+(aq) + OH-(aq)  NH3(g) + H2O(l)
(8): Explain why sulfuric acid is a dibasic acid. Give another example of a dibasic
acid.
Sulfuric acid is a dibasic acid as one mole of the acid dissociates in aqueous solution
to produce 2 mole of H+.
Another example of a dibasic acid is carbonic acid (H2CO3)
(9): State the formula of
(i): Slaked lime
Ca(OH)2
(ii): Quick lime
CaO
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(10): Explain why slaked lime is added to soil by farmers.
Slaked lime is alkaline and when added to soil it helps to neutralize the excess acid in
the soil.
(11): Give two examples each of acidic oxide, basic oxide and amphoteric oxide.
Acidic oxide - Carbon dioxide and sulfur dioxide
Basic oxide - Sodium oxide and calcium oxide
Amphoteric oxide - Aluminium oxide and zinc oxide
(12): Explain why sulfuric acid could be used to remove rust from metals.
Rust is alkaline (Iron (III) oxide) and thus sulfuric acid is able to neutralize it and thus
removing it in the process.
(13): Explain how does pH value indicates whether an unknown solution is a strong
acid, weak acid, strong alkali or weak alkali.
The lower the pH (as close to 0) the stronger is the acid and the higher the pH (as
close to 14) the stronger is the alkali.
A strong acid has a pH of around 0 to 1. A weak acid has a pH of more than 1 but less
than 7.
A strong alkali has a pH of close to14 and a weak alkali has a pH of more than 7 but
less than 14.
About Breeze Education:
Breeze Education offers chemistry tuition to O Level Students. Tuition classes are
conducted in small group with class size of not more than 3 students to facilitate
active discussion and consultation. Chemistry is taught in a way to facilitate easy
understanding of the topic. Students are also honed on their revision techniques so
that they can improve faster over a shorter period of time. Tuition sessions are
planned and taught by Dr Francis who has a PhD in Biomedical Science from
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National University of Singapore.
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