atomic structure (basics)

Question 1

What is a compound?

Answer 1

Two or more elements combined chemically in fixed proportions which can be represented by formulae

Question 2

What is a mixture?

Answer 2

A mixture consists of two or more elements or compounds not chemically combined together; it does have the same chemical properties

Question 3

What are the methods through

which mixtures can be separated

Answer 3

• Filtration
• crystallisation
• simple distillation
• fractional distillation
• chromatography

Question 4

Describe and explain simple

distillation.

Answer 4

Simple distillation is used to separate liquid from a solution

• the liquid boils off and condenses in the condenser.
• The thermometer will read the boiling point of the pure liquid.

we get to keep the liquid.

Question 5

Describe and explain

crystallisation

Answer 5

Crystallisation is used to separate a SOLUABLE solid from a liquid.

• remove some of the solvent by evaporation to form a saturated solution
• Then, we cool down the solution.
• As we do it, the solid starts to crystallise, as it becomes less soluble at lower temperatures.
• The crystals can be collected and separated from the solvent via filtration.

Question 6

Describe and explain fractional distillation

Answer 6

technique for separation of a mixture of liquids.

• It works when liquids have different boiling points.
• additional fractionating column placed on top of the heated flask.
• The fractionating column contains glass beads. It helps to separate the compounds.
• In industry, mixtures are repeatedly condensed and vapourised. The column is hot at the bottom and cold at the top. The liquids will condense at different heights of the column.

Question 7

Describe and explain filtration

Answer 7

Filtration is used to separate an INSOLUABLE solid suspended in a liquid.
The insoluble solid (called a residue) gets caught in the filter paper, because the particles are too big to fit through the holes in the paper.
The filtrate is the substance that comes through the filter paper.
Apparatus: filter paper + funnel.

Question 8

Describe and explain

chromatography

Answer 8

Chromatography is used to separate a mixture of substances dissolved in a solvent.
Chemical in mixture will be attracted to the stationary phase to a different extent, so chemicals strongly attracted to the stationary phase won’t move very far, weakly attracted ones will move further up the paper
- piece of chromatography paper with pencil line along bottom
- put a dot of the first colour on the line, and the next.
- place bottom of paper in a beaker with some solvent.
- The bottom of the paper has to be in contact with the solvent.
- The solvent level will slowly start to rise, dissolving the ink in the dots, thus separating the spot
- carries ink up the paper
- paper - stationary
- solvent - mobile phase, does move
- one spot - pure, two/ more spots - mixture

Question 9

Describe and explain simple distillation

Answer 9

• used to separate a liquid from a solid if we want to keep the liquid
• evaporate liquid by heating
• condense vapour by cooling
• place solution with liquid and solid in a flask, which is connected to a continuous glass tube. (tube surrounded by condenser jacket, cold water continuously runs through condenser, keeps internal glass tube cold)
• heat solution, starts evaporating and turns into a vapour and rises up tube.
• vapour passes into cold condenser, then condenses back into a liquid as it passes through
• collect liquid in a beaker, solid is left as crystals in the original flask