[SEC 3] CHAPTER 1 - experimental chemistry

Question 1

common drying agents?

Answer 1

• concentrated sulfuric acid
• calcium oxide (quicklime)
• fused calcium chloride (heated calcium chloride)

footnote: drying agents should not react with the gas

Question 2

function of concentrated sulfuric acid (drying agent)

Answer 2

• dry neutral gases (e.g. hydrogen and oxygen)
• dry acidic gases (e.g. chlorine, hydrogen chloride and sulfur dioxide)
• cannot be used to try alkaline gases (eg. ammonia), will result in neutralisation

Question 3

function of calcium oxide (quicklime), drying agent

Answer 3

• absorbs moisture and carbon dioxide from the air (must be freshly heated before use)
• used to dry alkaline gases (eg. ammonia)
• cannot be used to dry acid gases (eg. carbon dioxide), will result in neutralisation)

Question 4

function of fused calcium chloride

Answer 4

• absorbs moisture from the air (must be freshly heated before use)
• usedd to dry gases (eg. hydrogen, nitrogen and carbon dioxide
• cannot be used to dry gases that react with calcium chloride (eg. ammonia)

Question 5

what is crystallisation used for?

Answer 5

• used to obtain a pure solid from its saturated solution
• used to obtain dissolved solids that decompose upon heating if evaporated to dryness (eg. sugar, copper(II) sulfate crystals)

Question 6

steps for crystallisation

Answer 6

1. heat the solution until it is saturated
2. allow the hot solution to cool. upon cooling, pure crystals will be formed
3. crystals are filtered out and collected as the resdiue
4. crystals are washed with cold distilled water and dried between layers of filter paper

Question 7

how to test for saturated solution?

Answer 7

dip a clean glass rod into the solution. if crystals form on the rod as the solution on the rod cools, the solution is saturated

Question 8

why must cold water enter from the bottom and out from the top in a condenser?

Answer 8

to ensure that the water jacket is completely filled with cold water to provide a more efficient cooling system

Question 9

what is Rf (retention factor)?

Answer 9

the ratio between the distance travelled by the substance and distance travelled by the solvent is constant

              distance travelled by solute Rf value = ---------------------------------------
               distance travelled by solvent