Analysis Of Ions And Gases

Question 1

Describe how to do a flame test.

Answer 1

1) Clean the end of the Nichrome wire by dipping into HCL, place in a roaring Bunsen. Repeat until wire no longer produces a colour.
2) Dip end of wire into fresh HCL and then into solid sample.
3) Place wire into non roaring, non luminous flame.
4) Record colour of the flame

Question 2

Flame test: Lithium

Li +

Answer 2

Pink/Red

Question 3

Flame test: Sodium

Na+

Answer 3

Orangey-yellow

Question 4

Flame test: Potassium

K+

Answer 4

Lilac

Question 5

Flame test: Copper (II)

Cu2+

Answer 5

Greeney-blue

Question 6

Flame test: Calcium

Ca2+

Answer 6

Brick red

Question 7

Describe how to work out the analysis of metal cations.

Answer 7

• Add NaOH a drop at a time to a solution of you cation.
• The OH- ions in the solution react with some positive metal ions in precipitation reactions to produce coloured insoluble metal hydroxide precipitates.

Question 8

Observation of Copper (II) and Sodium Hydroxide -

Answer 8

Blue precipitate formed

Question 9

Observations of Iron (II) and Sodium Hydroxide-

Answer 9

Green precipitate formed (murkyish)

Question 10

Observations of Iron (III) and Sodium Hydroxide -

Answer 10

Orangey-browny precipitate formed.

Question 11

Describe the analysis of ammonium (NH4+).

Answer 11

• Add 2cm3 of sodium hydroxide to the solid/solution under test.
• Warm the mixture, in a water bath.
• If ammonium ions are present, then ammonia gas (NH3) will be produced.
  - This is a pungent smelling gas, which turns damp red litmus paper blue.

Question 12

Describe the analysis of positive ions.

Answer 12

• Add small amount of NaOH to a solution of you +be ions.
  The OH- ions in the solution react with some positive metal ions in precipitation reactions to produce coloured insoluble metal hydroxide precipitates.

Question 13

How do you identify a carbonate?

Answer 13

• Add dilute HCl (2cm depth) to the solid carbonate or its aqueous solution.
• Use delivery tube to bubble the gas through lime water.

Question 14

Observations of Calcium Carbonate with dilute HCl

Answer 14

• Limewater turns cloudy

- Bubbles of gas

Question 15

How do you identify sulphates?

Answer 15

• Add dilute HCl (2cm depth) and Barium Chloride solution (2cm depth) to a solution of a sulphate (2cm depth).
• HCl is added first to remove any carbonate ions that might be present - would also produce the same observation, giving false positive test.

Question 16

Observations of Sodium Sulphate with dilute HCl and Barium Chloride -

Answer 16

Solution turns cloudy

Question 17

How do you identify Chlorides, Bromides and Iodides?

Answer 17

• Add dilute nitric acid (1cm depth) and silver nitrate solution (2cm depth) of chloride or a bromide or an iodide (2cm depth).
• Nitric acid reacts with any other ions that might give a confusing precipitate (produces nitrates, and all nitrates are soluble)

Question 18

Observation of chloride with dilute nitric acid and silver nitrate solution -

Answer 18

Forms a white precipitate.

Question 19

Observation of bromide with dilute nitric acid and silver nitrate -

Answer 19

Forms a cream precipitate.

Question 20

Observation of iodide with dilute nitric acid and silver nitrate -

Answer 20

Forms a yellow precipitate.

Question 21

When is upwards delivery used?

Answer 21

• For gases less dense than air e.g H2, NH3

Question 22

What happens in upwards delivery?

Answer 22

The gas produced pushes the air in the gas jar/test tube out the bottom

Question 23

When is downwards delivery used?

Answer 23

For gases more dense then air e.g CO2 and Cl2.

Question 24

What happens in downwards delivery?

Answer 24

The gas produced pushes the air in the gas jar/test tube out of the top.

Question 25

What happens when the gas is “over water” (displacement occurs)?

Answer 25

The gas produced in the reaction is bubbled through a trough of water into a upside down jar filled with water. The gas displaces the water, pushing it out the bottom. A ‘beehive shelf’ directs the gas into the gas jar.

Question 26

When is over water (displacement) used?

Answer 26

Only works for insoluble gases/slightly soluble gases.
H2 is insoluble, O2 and CO2 are only slightly soluble in water.
- Wouldn’t work for NH3 and Cl2 as they are soluble.

Question 27

When is a gas syringe used?

Answer 27

Can be used to collect any gas. For testing the gas must be transferred to a test tube using one of the first 3 methods.

Question 28

Test for chlorine and result

Answer 28

Damp blue litmus paper

• Will turn red
• Bleach it

Question 29

Test for hydrogen and result

Answer 29

Put a lit splint in a test tube

- squeaky pop

Question 30

Test for ammonia and result

Answer 30

Use damp red litmus paper

- Turns blue

Question 31

Test for Carbon Dioxide and result

Answer 31

Bubble gas through lime water

- Limewater turns cloudy/milky

Question 32

Test for oxygen and result

Answer 32

Put glowing splint in test tube

- Splint relighting

Question 33

Where should the preparation and testing of chlorine and ammonia occur? Why?

Answer 33

Both are toxic, therefore going to be released in the atmosphere.
Should be done in a fume cupboard.

Question 34

Chemical test for water

Answer 34

Water turns white anhydrous copper (II) sulphate BLUE.

- Only confirms water is present not pure.

Question 35

How to test if water is pure?

Answer 35

It should melt at 0ºC and boil at 100ºC.