Separating mixtures and evaporation

Section 1 from the Edexcel IGCSE Chemistry Specification - principles of chemistry

Fill in the blank

Temperature doesn't rise until all of the ____ substance has been melted.

pure

Fill in the blank

______ substances melt/boil over a range of temperatures.

impure

To separate salt and water (but the water still escapes), what can you do?

evaporation

To separate a salt-water solution to get both the salt and water back, what can you do?

simple distillation

What is the term given to when a liquid turns into a gas at the surface of the liquid?

hint - this can happen at any temperature, even when cold

evaporation

The rate of evaporation increases as....

Temperature increases

What is NaCl or sodium chloride?

Table salt

What is a risk of heating to dryness?

When it has lost a lot of solvent, the solution spits drops of very hot liquid

The safety flame is…

• Easily visible

• Not as hot

The blue flame is….

• Hotter than the safety flame

• Not easily visible

What is the boiling point of water?

100°C

What is the name of the technique used to separate substances dissolved in a mixture as different coloured dyes?

Chromatography

List 3 pure substances made up only one coloured dye.

Blue

Red

Yellow

Why do the pigments level up the paper at different speeds in paper chromatography?

• Some are more soluble

• Some stick to the paper more

"The chroma prefix in ''chromatography'' means black and white."

True or false?

False

"Water is a common solvent for paper chromatography."

True or false?

True

"Inks can be mixtures of different substances."

True or false?

True

"Chromatography separates solids from liquids."

True or false?

False

How many centimetres should you draw a pencil line from the chromatography paper?

2 cm

Why can't you draw the starting-point line on the chromatography paper in pen?

The ink will smudge and interfere with results

What is the name for the paper with the end result?

chromatogram