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Measurements



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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.
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