Topic 2 Methods Of Seperating And Purifying Substances

Question 1

What is the difference between a pure substance and a mixture?

Answer 1

A pure substance consists of either 1 single element or 1 types of molecule
A mixture has multiple different elements and/or molecule, and all are not chemically bonded

Question 2

Melting points of mixtures

Answer 2

Have multiple melting points due to the different substances melt at different temperatures

Question 3

At pure substance’s melting point

Answer 3

The atoms vibrate more as they gain more energy and move apart slightly

Question 4

Filtration can separate what mixtures

Answer 4

Mixtures with solids and liquids, e.g. sand in water

Question 5

Crystallisation can separate what substances?

Answer 5

(Evaporation)separates liquids and solid which have been dissolved into the water, e.g. salt or sugar dissolved in water

Question 6

How are substances separated by filtration?

Answer 6

There are small holes in filter paper, which allows the liquids through, but not the larger

Question 7

Solvent

Answer 7

The liquid in a locution

Question 8

Solute

Answer 8

The solid dissolved in a solution

Question 9

How does crystallisation work?

Answer 9

As the solvent is evaporated, the solution becomes more concentrated until the saturated solution starts to deposit the solute and slowly more solute is attached to the crystals and they grow larger

Question 10

What mixtures can be separated by chromatography?

Answer 10

Pigments in solutions such as ink can be separated by chromatography

Question 11

What do pure substances look like on chromatography paper?

Answer 11

Pure substances have 1 dot with 1 pigment

Question 12

What do mixtures look like on chromatography

Answer 12

Mixtures contain multiple different pigments which appear as different dots on the paper

Question 13

How are substances separated in chromatography?

Answer 13

Different substances are separated because they have different amounts of solubility, which allows them to move further up the sheet with the water

Question 14

How to calculate Rf value?

Answer 14

Distance travelled by solute/distance traveled by water

Question 15

What is simple distillation?

Answer 15

Simple distillation is used to separate a single solvent from a solute in a solution, such as taking the water from saline water

Question 16

What is fractional distillation?

Answer 16

Fractional distillation is used to separate multiple liquids from a mixture to separate crude oil

Question 17

How does fractional distillation work?

Answer 17

Fractional distillation works because all of the liquids have different boiling points and so in the fractioning columns there are sections at different temperatures where the different substances will condense and be seperated

Question 18

Why must water used in chemical analysis not contain dissolved salts

Answer 18

The salts could react with other chemicals being used an change the reaction

Question 19

How can fresh water be produced from sea water?

Answer 19

Sea water can be distilled to get fresh water and salt

Question 20

What are the steps needed to make fresh water suitable for drinking(3 main steps)

Answer 20

Reservoir, so the large bits can settle or float to the top, the water is extracted toward the bottom but up a bit so logs float to the top and larger silt sinks to the bottom
Filtration through sand then gravel, to remove smaller particles
Chlorination, to remove bacteria