RP4 - Simple test-tube reactions

Question 1

Testing for halide ions

Question 2

How would we test for halide ions, what solution would we need?

Answer 2

• Add 2cm3 of dilute nitric acid, followed by 2cm3 of silver nitrate to each sample
• shake gently

Question 3

presence of chloride ions is show by…?
Presence of Bromide ions is shown by…?
Presence of iodide ions is shown by..?

Answer 3

Chloride = white precipitate
Bromide = cream precipitate
Iodide = yellow precipitate

Question 4

Why do we add dilute ammonia to each precipitate?

Answer 4

because it is hard to distinguish between the colours sometimes

Question 5

When we add dilute ammonia to each test tube what will happen?

Answer 5

• Dilute ammonia will cause the white precipitate of ammonia to become colourless
• No change with dilute ammonia for Bromide ions and Iodide ions

Question 6

What happens when we add Concentrated ammonia to each of the test tubes?

Answer 6

• Bromide ion dissolves to form a colourless solution
• The iodide remains

Question 7

What do we need to make sure when working with concentrated ammonia?

Answer 7

working in a fume cupboard

Question 8

Testing for Sulphate ions

Question 9

What is the test for sulphate ions

Answer 9

Acidified barium chloride

Question 10

Describe how the test would be carried out?

Answer 10

• using a dropping pipette add equal volumes of Hydrochloric acid and Barium chloride to the sample

Question 11

What would a positive result show?

Answer 11

A positive result would show a white precipitate of barium sulphate, sulphate ions are present

Question 12

What are some safety procedure we must follow?

Answer 12

Wear gloves and lab coat because barium chloride is harmful

Question 13

Testing for Carbonate ions

Question 14

what is the test for carbonate ions?

Answer 14

Adding HCL and bubble through limewater

Question 15

Describe how this test would be carried out?

Answer 15

• Add dilute HCL to sodium carbonate solution
• be careful not to touch the sides of the tube with the dropping pipette
• using a a clean pipette collect the gas produced and bubble it through limewater
• place a bung and shake gently from side to side

Question 16

What is a positive result?

Answer 16

cloudy white mixture

Question 17

Testing for Ammonium Ions

Question 18

solutions containing ammonium ions are usually what colour?

Answer 18

They are usually colourless

Question 19

How would you carry out test to identify ammonium ions?

Answer 19

1. Place 10 drops of ammonium chloride into a clean test tube. Add about 10 drops of sodium hydroxide solution. Shake the mixture.
2. Warm the mixture in the test tube gently using a water bath. (necessary because ammonia gas is very soluble)
3. Test the fumes released from the mixture by using forceps to hold a piece of damp red litmus paper in the mouth of the test tube.
4. Make sure the sides of the red litmus paper does not touch the sides of the test tube

Question 20

What is the observation made?

Answer 20

The red litmus paper turns blue

Question 21

Why do we mix at the start?

Answer 21

Shaking ensure the reactant
combine properly.

Question 22

Why is a water bath preferred over a flame?

Answer 22

A water bath is more gentle than using a flame.

Question 23

Testing for Group 2 ions

Question 24

What is the test for group 2?

Answer 24

Sodium hydroxide solution

Question 25

How is the test carried out?

Answer 25

1. sodium hydroxide is added to test tubes containing Magnesium, Calcium, Strontium and Barium Chloride

Question 26

What are the results?

Answer 26

Magnesium forms a Slight white ppt in little NaOH and a white precipitate in excess NaOH
Calcium forms a Slight white ppt
Strontium forms a slight white precipitate
Barium forms a colourless solution with NaOH

Question 27

Done!!