Topic 9 Chemical Analysis

Question 1

Element

Answer 1

A substance that consists of only one type of atom and it cannot be broken down into anything simpler by chemical means

Question 2

Compound

Answer 2

A substance that consists of two or more (different) elements chemically bonded together

Question 3

Pure substance

Answer 3

A single element or compound not mixed with any other substance

Question 4

Melting and boiling point of pure elements

Answer 4

Melt and boil at specific temperatures and melting and boiling point can be used to distinguish pure substances from mixtures

Question 5

Formulation

Answer 5

A mixture that has been designed as a useful product

Question 6

How are formulations formed?

Answer 6

Mixing together several different substances in carefully measured quantities to ensure the product has the required properties

Question 7

Examples of formulations

Answer 7

Alloys, medicines, fertilisers

Question 8

Soluble

Answer 8

Dissolves in water

Question 9

Insoluble

Answer 9

Does not dissolve in water

Question 10

Solute

Answer 10

A (soluble) substance which dissolves

Question 11

Solvent

Answer 11

The liquid in which the solute dissolves

Question 12

Solution

Answer 12

The mixture of solute dissolved in a solvent

Question 13

Miscible

Answer 13

Liquids which mix

Question 14

Immiscible

Answer 14

Liquids which do not mix eg water and oil

Question 15

Filtrate

Answer 15

The filtered solution

Question 16

Residue

Answer 16

The solid which remains on the filter paper

Question 17

Separation techniques

Answer 17

Filtration, evaporation, crystallisation, chromatography, simple distillation and fractional distillation

Question 18

Filtration

Answer 18

• separates an insoluble substance and a liquid eg sand and water

Question 19

Evaporation

Answer 19

• seperates a solute from a solvent eg salt and water

Question 20

Crystallisation

Answer 20

• sometimes only some of the solvent is evaporated to leave a hot saturated solution
• as the solution cools the solute becomes less soluble and crystallises out of the solution
• these crystals can then be filtered off

Question 21

Simple distillation

Answer 21

• desperate solvent from a solution eg water and salt water
• the substance collected is called the distillate

Question 22

Fractional distillation

Answer 22

• separates 2 or more miscible liquids eg ethanol and water
• the distillate collected at each temperature is called a fraction
• the the chemical with the lowest boiling temperature separates first

Question 23

Chromatography

Answer 23

• separates two or more substances in a solution eg food dyes, inks or drugs
• the substances must be soluble to some extent
• each substance in the mixture moves at a different rate depending on its relative attraction to the stationary or mobile phase
• the colours separate out because they dissolve, to different extents, in the solvent
• a substance will always travel the same distance (in the same solvent or same conditions)

Question 24

How to calculate Rf values

Answer 24

Rf = distance moved by solute (ink)/ distance moved by solvent (water)

Question 25

Why is the base line of a chromatography graph drawn in pencil?

Answer 25

If a pen were used the ink of the pen would interfere with the results, and a pencil is insoluble