Chemical analysis

Question 1

Test for chlorine

Answer 1

Damp, blue litmus paper (blue to white)

Question 2

Test for oxygen

Answer 2

Glowing splint (splint will be relit)

Question 3

Test for hydrogen

Answer 3

Squeeky pop (lit splint)

Question 4

Test for carbon dioxide

Answer 4

Limewater (turns cloudy)

Question 5

Test for carbonates

Answer 5

Add dilute HCl, then check for CO2 (using limewater)

Question 6

Test for sulfates

Answer 6

Add dilute HCl, add barium chloride, white PPT formed

Question 7

Test for halides

Answer 7

Add dilute nitric acid, add silver nitrate, different halides = different ppt
Chloride ions = white ppt
Bromide ions = cream ppt
Iodide ions = yellow ppt

Question 8

What colour flame is a Lithium ion?

Answer 8

Crimson

Question 9

What colour flame is a Sodium ion?

Answer 9

Yellow

Question 10

What colour flame is a Potassium ion?

Answer 10

Lilac

Question 11

What colour flame is a Calcium ion?

Answer 11

Orange - red

Question 12

What colour flame is a Copper ion?

Answer 12

Green

Question 13

What ppt does Calcium form?

Answer 13

White ppt (reacted with sodium hydroxide)

Question 14

What ppt does iron II form?

Answer 14

Green ppt (reacted with sodium hydroxide)

Question 15

What ppt does iron III form?

Answer 15

Brown ppt (reacted with sodium hydroxide)

Question 16

What ppt does magnesium form?

Answer 16

White ppt (reacted with sodium hydroxide)

Question 17

What ppt does copper form?

Answer 17

Blue ppt (reacted with sodium hydroxide)

Question 18

Test for aluminium ions?

Answer 18

• Mix with sodium hydroxide
• White ppt will be formed
• Dissolves in excess to form colourless solution

Question 19

How to differentiate between aluminium, magnesium and calcium ions?

Answer 19

• All form white ppt in sodium hydroxide
• Aluminium dissolves in excess to form colourless solution, magnesium and calcium remain undissolved
• Clacium has orange-red flame when burned

Question 20

How to prepare a flame test

Answer 20

• Dip inoculating loop into dilute hydrochloric acid
• Hold loop over blue flame in bunsen burner until there is no colour change
• This has cleaned the wire loop to avoid contamination

Question 21

Why must we clean the inoculating loop in flame tests?

Answer 21

• Test will only work with one type of ion present
• Two or more ions means the colour will mix, leading to an erroneous result

Question 22

What is a pure substance?

Answer 22

• A substance that only contains one type of compound or element

Question 23

Pure vs impure substances

Answer 23

• Pure substances melt and boil at specific temperatures
• Impure substances melt and boil over a range of temperatures

Question 24

What is paper chromatorgraphy used for?

Answer 24

• Used to separate different inks in a dye

Question 25

Steps of chromatorgaphy

Answer 25

• Draw the baseline at the bottom of the chromatography paper in pencil
• Place a dot(s) of the ink you want to separate on the baseline
• Fill a beaker with a solvent (water or ethanol) and place paper in it
• Make sure the baseline is above the solvent
• Place lid on top to prevent solvent from evaporating
• All soluble dyes in the ink will move up the paper at different rates and separate. Insoluble dyes will stay at the bottom

Question 26

What is the mobile phase?

Answer 26

• The substance in which the molecules are able to move
• In chromatorgaphy this is the solvent

Question 27

What is the stationary phase?

Answer 27

• The substance in which the molecules cannot move
• In chromatography this is the chromatography paper

Question 28

What determines how far a substance travels up the chromatography paper?

Answer 28

• The more soluble the substance is in the solvent, the more time it will spend in the mobile phase and therefore will carried further up the paper

Question 29

How to calculate Rf value and what does it help us do?

Answer 29

• Distance travelled by substance / distance travelled by solvent
• Allows scientists to compare the Rf value of the unkown substance with that of known substances under the same conditions (type of paper and solvent) to find out what substance it is