Acids, bases and salts
Francine Taylor-Campbell, Contributor

Dr. Claude Packer, principal, welcoming new students to The Mico University College's dedication ceremony at St. Matthews Anglican Church, Weeville Gordon Road on Sunday, September 24. - Nathaniel Stewart/Freelance Photographer

SYLLABUS REQUIREMENTS

Students should be able to:

• Define acid, acid anhydride, base, alkali, salt, acidic, basic, amphoteric and neutral oxides.
  
  
• Relate acidity and alkalinity to the pH scale.
  
  
• Discuss the strength of acids and alkalis on the basis of the completeness of ionisation.
  
  
• Investigate the reactions of non-ionising acids with metals, carbonates, bases and hydrogen carbonates.

1. Which property does hydrochloric acid have?

A. It liberates ammonia from ammonium salts.
B. It reacts with any base to give a salt.
C. It reacts with any metal to give hydrogen.
D. It turns red litmus paper blue.

Ans: B. Acids react with bases to form salt and water. Alkalis liberate ammonia from ammonium salts. Although HCl is a strong acid, it will not liberate hydrogen when added to unreactive metals such as Cu, Ag (silver) and Au (gold). Finally, acids turn blue litmus paper red .

2. Which gas changes damp litmus paper from red to blue?

A. ammonia
B. carbon dioxide
C. chlorine
D. hydrogen chloride

Ans: A. Ammonia is the only alkaline gas of the group and so will turn red litmus to blue.

3. An aqueous solution has a pH value of 1. What information does this fact give about the ions in solution?

Concentration of H+ ions OH-

A. high none
B. high low
C. low low
D. low high

Ans: B. An acid has a low pH value. Generally, the smaller the pH value, the stronger the concentration of H+ ions in the solution. Thus, a value of 1 would indicate high concentration of H+ ions. Alkalis, on the other hand, would have pH values from 9-14.

4. Which element burns in air to form an oxide which when shaken with water gives a solution with a pH greater than 7?

A. carbon
B. hydrogen
C. magnesium
D. sulphur

Ans: C. Magnesium is the only metal of the group and so when it burns in air forms a metallic oxide, MgO, which is basic. This oxide dissolves slightly in water to form a slightly alkaline solution with pH greater than 7.

5. Which of the following reacts with dilute sulphuric acid to give a gas and water as two of the products?

A. zinc
B. zinc carbonate
C. zinc hydroxide
D. zinc

Ans: B. Zinc carbonate reacts with suphuric acid to form zinc sulphate, carbon dioxide and water.

ZnCO3 (s) + H2SO4 (aq) === ZnSO4 (aq) + CO4 (g) + H4O (l)

Only a gas, H2 is produced when zinc reacts with H2 SO4.

Zn (s) + H2SO4 (aq) === ZnSO4 (aq) + H2 (g)

The other reactions do not produce any gas, only the salt (ZnSO4) and water.