Experimental Chemisty

Question 1

State the ways to perform crystallisation.

Answer 1

1. Heat the solution (to evaporate most of the water) to obtain a saturated solution
2. Cool the saturated solution to allow the crystals to form
3. Filter the mixture to obtain crystals as residue and diluted solution as filtrate
4. Wash the crytals with cold distilled water to remove impurities
5. Dry crystals between few sheets of filter paper

Question 2

What is used to dry acidic gases?

Answer 2

• ## Concentrated Sulfuric Acid

Question 3

What is used to dry alkaline gases?

Answer 3

• Fused Calcium Chloride (Cannot dry Ammonia)
• Calcium Oxide (Quick Lime)

Question 4

What does impurities do to the m.p and b.p?

Answer 4

• Impurities lower the melting point of a solid and **increase the boiling point of a liquid. **
• Impurities causes melting and boiling to take place over a range of temperatures

Question 5

How does a separating funnel work?

Answer 5

• When the mixture is placed in the separating funnel, the mixture separates into different layers based on density differences
• When a heterogenous mixture is left to settle into layers, each component is separated by opening the tap at the bottom and collecting each component in separate flask / beaker.

Question 6

What is the purpose of boiling chips?

Answer 6

Boiling stones / chips are added into the mixture in the flask to ensure smooth boiling.

Question 7

What are the purpose of thermometers in distillation setups?

Answer 7

This is to measure the temperature of the vapour entering the condenser so as to identify the distillate.

Question 8

Why is cold water entering from bottom in condensers in distillation setups?

Answer 8

• to ensure that the condenser is completely filled with cold running water
• to ensure the part of the condenser near the collection of distillate is cool

Question 9

What is the purpose of fractionating column?

Answer 9

The fractionating column is to increase surface area for condensation of vapour with the highest boiling point back into the round bottom flask so that a pure distillate (with lower boiling point) could be obtained.

Question 10

Why do start lines in chromatography always written in pencil?

Answer 10

• The start line must be drawn in pencil because pencil lead is insoluble in water while ink contains a mixture of dyes which will dissolve in the solvent and will be separated.
• This will interfere with the chromatogram of the sample to be analysed.

Question 11

Why is start line always above the solvent level in chromatography?

Answer 11

The start line must be above the solvent level to prevent the sample dots to dissolve into the solvent in the beaker instead of traveling up the chromatogram

Question 12

Why is it important for barrel to be able to freely move in the syringe?

Answer 12

Any friction would result in a pressure build- up in the syringe and would lead to an inaccurate measurement, that is, a smaller volume of gaswould be recorded than what it should have been.