Tests for ions

Question 1

How do you carry out a flame test?

Answer 1

Dip a nichrome wire loop in concentrated hydrochloride acid and then dip it into the unknown compound

Question 2

What colour will the flame for Ca2+ be?

Answer 2

Brick red

Question 3

What is a flame test used for?

Answer 3

To identify positive ions of group 2 elements

Question 4

What colour will the flame for Sr2+ be?

Answer 4

Red

Question 5

What colour will the flame for Ba2+ be?

Answer 5

pale green

Question 6

What can you use to test for ammonium ions? Why is this possible?

Answer 6

Red litmus paper

It is an alkaline

Question 7

What colour change will occur with litmus paper if ammonium ions are present?

Answer 7

Red to blue

Question 8

What reaction can you use to test whether a substance contains ammonium ions?

Answer 8

Add dilute hydroxide solution to the mystery sample
If ammonia gas is given off and there is a colour change with the red litmus paper then there must be ammonium ions present in the sample

Question 9

What is the equation for the reaction of hydroxide solution with a solution containing ammonium ions?

Answer 9

NH4+(aq) + OH- (aq) -> NH3 (g) + H2O (l)

Question 10

How do you test for a negative sulphate ion?

Answer 10

Add dilute hydrochloric acid followed by barium chloride solution (BaCl2).
If a white precipitate of barium sulphate forms, the original compound contained a sulphate

Question 11

What is the ionic equation for the reaction between a sulfate ion and barium chloride?

Answer 11

Ba 2+ (aq) + SO4 2- (aq) -> BaSO4(s)

Question 12

What do hydroxide solutions do to solutions?

Answer 12

Turn them alkaline

Question 13

What can be used to test if a solution has hydroxide ions?

Answer 13

A pH indicator test

Red litmus will turn blue

Question 14

What test is used for halide ions?

Answer 14

Add dilute nitric acid (HNO3) followed by silver nitrate solution (AgNO3)

Question 15

What result will chloride ions give if they are present?

Answer 15

They will form a white precipitate of silver chloride

Question 16

What result will bromide ions give if they are present?

Answer 16

They will form a cream precipitate of silver bromide

Question 17

What result will iodide ions give if they are present?

Answer 17

They will form a yellow precipitate of silver iodide

Question 18

What will silver chloride dissolve in? (further test for confirmation)

Answer 18

Dilute ammonia solution

Question 19

What will silver bromide dissolve in? (further test for confirmation)

Answer 19

Concentrated ammonia solution

Question 20

What will silver iodide dissolve in? (further test for confirmation)

Answer 20

It wont dissolve in either ammonia solution

Question 21

What test can be used for carbonate ions?

Answer 21

Add an acid

If present, fizzing will occur (effervescence)

Question 22

What equation shows the reaction of carbonate ions with an acid?

Answer 22

CO3 2- (aq) + 2H+(aq) -> CO2 (g) + H2O(l)

Question 23

How can you do further testing to make sure that the gas produced is actually CO2?

Answer 23

Bubble the gas through limewater and it will turn it cloudy if it is.