Chemical analysis

Question 1

what are the differences between mixtures and compounds

Answer 1

mixtures:
- no fixed composition
- elements are separated more easily
- no chemical bonds

Compounds:
- fixed composition
- need chemical reactions to separate elements
- chemical bonds between atoms

Question 2

What is the use of filtration

Answer 2

used to separate substances that are insoluble in a particular solvent from those that are soluble

Question 3

use of distillation

Answer 3

used to separate a liquid from a soluble solid from a solution

Question 4

use of crystallisation

Answer 4

used to separate a dissolved solid from a solution when the solid is much more soluble

Question 5

steps of distillation

Answer 5

• solution is heated and boiled to evaporate the solvent
• the vapour given off is then cooled and condensed back into a liquid for collection
• dissolved solids remain in the heated flask

Question 6

steps of crystallisation

Answer 6

• water is evaporated from solution by heating an evaporating dish on a water bath
• heating should be stopped when the solution is at the point of crystallisation -> when small crystals first appear around the edge of the solution
• rest of water is then left to evaporate off the saturated solution at room temperature

Question 7

what is a mixture

Answer 7

made up of two or more elements or compound which are not chemically combined together

Question 8

what is the use of paper chromatography

Answer 8

used to separate different substances and provide information to help identify them, components of the substance have different solubilities

Question 9

why should you use a pencil in paper chromatography

Answer 9

pencil is insoluble and wont interfere with the separation of the mixture

Question 10

what is the formula of Rf (retention factor)

Answer 10

Rf = distance moved by substance / distance moved by solvent

Question 11

what is the stationary phase

Answer 11

fixed material or surface that the mobile phase passes through

Question 12

what is the mobile phase

Answer 12

the liquid solvent that moves the mixture

Question 13

How does chromatography separate mixtures

Answer 13

different substances have different solubilities so they will travel at different rates causing the substance to spread apart

Question 14

what colour flame will Lithium have

Answer 14

crimson

Question 15

what colour flame will Barium have

Answer 15

green

Question 16

what colour flame will Sodium have

Answer 16

yellow

Question 17

what colour flame will Potassium have

Answer 17

lilac

Question 18

what colour flame will calcium have

Answer 18

red

Question 19

what are the steps of a flame test

Answer 19

• small amount of compound is tested in a nichrome wire loop
• hold the loop in the blue flame of the bunsen burner
• colour of the bunsen flame is used to identify the metal ion

Question 20

what is the test for hydrogen

Answer 20

squeak pop test, a lighted splint pops

Question 21

what is the test for oxygen

Answer 21

glowing splint, glowing splint relights

Question 22

what is the test for carbon dioxide

Answer 22

limewater turns cloudy

Question 23

what is the test for ammonia

Answer 23

damp red litmus paper turns blue

Question 24

what is the test for chlorine

Answer 24

damp red litmus paper turns blue then white (as it bleaches)

Question 25

how to test for positive ions

Answer 25

adding sodium hydroxide solution to substances

Question 26

what are the elements that a white precipitate forming could mean

Answer 26

Aluminium ion, Calcium ions, and Magnesium ions

Question 27

How to test if its an aluminium ion

Answer 27

add excess sodium hydroxide until is dissolves

Question 28

how to test if the white precipitate formed from sodium hydroxide is calcium or magnesium

Answer 28

if the flame is brick-red, its calcium. if the flame has no colour, its magnesium

Question 29

what happens if you add sodium hydroxide solution to copper (Cu3+) ions

Answer 29

blue precipitate is formed

Question 30

what happens if you add sodium hydroxide solution to iron (Fe2+) ions

Answer 30

Green precipitate is formed

Question 31

what happens if you add sodium hydroxide solution to iron (Fe3+) ions

Answer 31

Brown precipitate is formed

Question 32

How to test is a substance is a carbonate

Answer 32

by adding dilute acid, and checking to see if it fizzes producing carbon dioxide

Question 33

How to check is a substance has halide ions

Answer 33

add dilute nitric acid and then silver nitrate solution, if a precipitate forms halide ions are present

Question 34

What colour are the precipitates made by Iodide ions (I-) after adding dilute nitric acid and silver nitrate solution

Answer 34

Yellow precipitate

Question 35

What colour are the precipitates made by Chloride ions (Cl-) after adding dilute nitric acid and silver nitrate solution

Answer 35

white precipitate

Question 36

What colour are the precipitates made by Bromide ions (Br-) after adding dilute nitric acid and silver nitrate solution

Answer 36

Cream precipitate

Question 37

How to test for sulfates

Answer 37

adding dilute hydrochloric acid and barium chloride solution, if a white precipitate forms sulfate ions are present