Measurements

Structured Question Worked Solutions

1. Select from the following list, one method by which each of the following may be separated from the stated mixture. You may use a method once, more than once, or not at all.

chromatography

precipitation

filtration

distillation

sublimation

electrolysis

crystallisation

reduction

oxidation

synthesis

a. red dye from a mixture of red and blue dyes in solution

b. oxygen from liquid air

c. barium sulphate from a mixture of barium sulphate and water

d. ammonium chloride from a mixture of ammonium chloride and sodium chloride

e. amino acids from a mixture obtained by the hydrolysis of a protein

Solution

1a. chromatography

1b. distillation

1c. filtration

1d. sublimation

1e. chromatography

2. Name the apparatus that is most suitable for

a. measuring exactly 23.4cm³ of liquid

b. mixing 100cm³ of two liquids

c. measuring about 20cm³ of liquid

d. measuring exactly 10cm³ of liquid

Solution

2a. Burette

2b. Beaker

2c. Measuring cylinder

2d. Pipette

3. Given a mole of ammonia gas and carbon dioxide, arrange in ascending order the mass and density of ammonia gas, carbon dioxide and air.

Solution

For 1 mole of NH₃, CO₂ and air (79% N₂ and 21% O₂) at fixed volume,

mass of NH₃ = 14 + 3(1) = 17g

mass of CO₂ = 12 + 2(16) = 44g

mass of air = 0.79[2(14)] + 0.21[2(16)] = 28.8g

Therefore, arrange in ascending order of mass and density: NH₃, air, CO₂.