Acids, bases and salts

Question 1

Describe the characteristic properties of acids as
reactions with metals, bases, carbonates and effect
on litmus

Answer 1

Properties:

• sour tasting, corrosive
• pH < 7
• are H+ ion (proton) donors
• turns litmus red
• acid + metal oxides/hydroxides -> salt + water
• acid + metal -> salt + hydrogen
• acid + carbonates -> salt + water + co2
• acid + base -> salt +water (neutralisation)

Question 2

Describe the characteristic properties of bases as
reactions with acids and with ammonium salts and
effect on litmus

Answer 2

Properties:

• corrosive, soapy
• pH > 7
• proton acceptors
• turns litmus blue
• base + ammonium salts -> salt + ammonia + water

Question 3

Describe the meaning of weak and strong

acids and bases

Answer 3

Strong acid/base:
- Fully ionised (donate/ accept all protons)
e.g. acid: HCl, H2SO4 (sulphuric), HNO3 (nitric)
        base: NaOH (sodium hydroxide)
Weak acid/base
- Partially ionised
e.g. acid: CH3COOH (ethanoic)
       base: NH3 (ammonia)

Question 4

Classify oxides as either acidic or basic, related to

metallic and non-metallic character. Further classify other oxides as neutral or amphoteric

Answer 4

• Metal oxides are basic. React with acid to form salt and water
• Most basic oxides do not react with water except for Group I and II metals to form metal hydroxide
• Non-metal oxides are acidic. Reacts with alkali to form salt and water. Formed direct reaction with oxygen
• React with water to form acidic solutions
• Neutral oxides do not react with acids or bases (N20, NO, CO)
• Amphetoric oxides have both acidic and bases properties and react with both of them

Question 5

Making salts: reacting a metal with acid

Answer 5

• Add metal to acid (metal is in excess)
• Warm the flask gently
• Filter off the excess metal. The filtrate is the solution of metal salt
• Put the filtrate in an evaporating dish and evaporate until crystallisation point is reached. Allow salt to crystallise
• Filter off the crystals and wash them with tiny amount of distilled water
• Dry it

Question 6

Making salts: titration method

Answer 6

• Measure the volume of alkali into flask using a volumetric pipette
• Add few drops of indicator solution to the alkali
• Fill a burette with acid
• Record the burette reading
• Open the burette tap and let acid flow. Swirl to make sure the alkali and acid mixe and react
• Stop adding when indicator changes colour
• Record the burette reading. Take final - initial
• Crystallisation

Question 7

Making salts: precipitation

Answer 7

• Making insoluble salts
• Done by mixing two soluble compounds (this is a precipitate)
• Filter off the precipitate
• Precipitate is washed with distilled water and dried

Question 8

Methods of collecting gas

Answer 8

• Downward displacement is for gas that is lighter than air: hydrogen, ammonia
• Upward displacement is for gas that is heavier than air: carbon dioxide, chlorine, hydrogen chlorine
• Downward displacement of water is used for gas that is insoluble in water: hydrogen, oxygen