Chp 2 Methods of Purification & Analysis

Which apparatus would be most suitable for measuring 45.00 cm³ of sodium hydroxide?

• beaker
• burette
• measuring cylinder
• pipette

A student has a sample of colourless liquid. Which of the following properties is the best way to check the purity of the colourless liquid?

• boiling point
• density
• melting point
• no residue left when evaporated

Which of the following methods is used to separate a mixture of iodine and iron?

• crystallisation
• magnetic attraction
• simple distillation
• sublimation

Which of the following must be true in order for two substances to be separated by paper chromatography?

• They have different colours.
• They have different densities.
• They have different boiling points.
• They are soluble in the same solvent.

You are given a mixture of hexane and a dilute solution of sodium chloride in water. Hexane boils at 69 ^oC and does not dissolve in water. To obtain samples of hexane and solid sodium chloride, which two techniques would you use?

• distillation followed by filtration
• evaporation to dryness followed by distillation
• filtration followed by crystallisation
• use a separating funnel followed by evaporation to dryness

Concentrated sulfuric acid is often used as a drying agent to obtain a dry sample of a moist gas. However, it is not suitable to dry a sample of ammonia gas. Why is this so?

• Ammonia is soluble in water.
• Ammonia is insoluble in water.
• Ammonia will react with sulfuric acid.
• The products formed will be too toxic.

Two groups of students conducted chromatography on the same sample of ink. The two chromatograms below show their results. Why were their chromatograms different?

• One group of students did not use enough sample.
• One group of students did not use enough solvent.
• The run time for the chromatograms were different.
• The two groups of students used different solvents.

Ethanol and water are miscible liquids. Ethanol boils at 78 °C while water boils at 100 °C. Which of the following methods can be used to separate a mixture of these two liquids?

• evaporation
• fractional distillation
• paper chromatography
• simple distillation

Order of following steps involved in crystallisation.

 

I      leave the solution to cool

II     heat the solution in an evaporating dish

III    filter the solution to collect the crystals, then wash and dry them

IV    test for saturation of the solution by dipping a clean glass rod into the solution

• I → III → IV → II
• II → I → IV → III
• II → IV → I → III
• IV → II → I → III

Sodium chloride is commonly known as table salt. At which temperature does a concentrated solution of sodium chloride begin to freeze?

• 4 ºC
• 1 ºC
• 0 ºC
• –4 ºC