Test for Ions

Question 1

What acid is used to detect carbonates?

Answer 1

A dilute acid such as hydrochloric acid.

Question 2

What will happen if a dilute acid is added to a carbonate?

Answer 2

Carbon dioxide will be released as bubbles or fizz.

Question 3

How do you test for carbon dioxide?

Answer 3

Limewater will turn cloudy in the presence of CO2.

Question 4

How do you use the limewater to test for CO2?

Answer 4

Bubble the gas released through a test tube of limewater.

Question 5

What is the equation for the reaction of a carbonate and an acid?

Answer 5

CO3^3-(s) + 2H+(aq) = CO2(g) + H2O(l)

Question 6

How do you test for sulfates?

Answer 6

Add dilute HCl followed by barium chloride solution.

Question 7

Which sulfate is insoluble in water?

Answer 7

Barium sulfate

Question 8

What will happen if a sulfate is present?

Answer 8

You will get a white precipitate.

Question 9

What sulfate is the white precipitate?

Answer 9

Barium sulfate

Question 10

What tells you that a sulfate is present?

Answer 10

Barium sulfate.

Question 11

What is the equation for the reaction producing barium sulfate?

Answer 11

Ba2+(aq) +SO4^2-(aq) = BaSO4(s)

Question 12

What is used to test for halides?

Answer 12

Add nitric acid and then silver nitrate solution.

Question 13

What will happen in the halide test if chloride, bromide or iodide is present?

Answer 13

A precipitate will form.

Question 14

What colour precipitate is formed if chloride is present?

Answer 14

A yellow precipitate of silver chloride.

Question 15

What colour precipitate is formed if bromide is present?

Answer 15

A cream precipitate of silver bromide.

Question 16

What colour precipitate is formed of iodide is present?

Answer 16

A yellow precipitate of silver iodide.

Question 17

Why does fluoride give no precipitate when testing for halides?

Answer 17

Silver fluoride is soluble.

Question 18

How do you tell the ppts of halides apart?

Answer 18

Test their solubility in ammonia.

Question 19

Does AgCl dissolve in dilute NH3?

Answer 19

Yes

Question 20

Does AgCl dissolve in concentrated NH3?

Answer 20

Yes

Question 21

Does AgBr dissolve in dilute NH3?

Answer 21

No

Question 22

Does AgBr dissolve in concentrated NH3?

Answer 22

Yes

Question 23

Does AgI dissolve in dilute NH3?

Answer 23

No

Question 24

Does AgI dissolve in concentrated NH3?

Answer 24

No

Question 25

How do you test for ammonium compounds?

Answer 25

Use NaOH and damp litmus paper?

Question 26

Why does the litmus paper have to be damp when testing for ammonia?

Answer 26

This is so that the ammonia gas can dissolve and make the colour change.

Question 27

What colour litmus paper should be used to test for ammonium gas?

Answer 27

Red

Question 28

What colour will the ammonium gas turn the litmus paper?

Answer 28

It will turn it blue.

Question 29

Is ammonium gas acid or alkaline?

Answer 29

It is alkaline.

Question 30

What does the NaOH and litmus paper test tell you about a compound?

Answer 30

It tells you whether or not a substance contains ammonium ions.

Question 31

How do you carry out the test for ammonium compounds?

Answer 31

Add some sodium hydroxide to the test tube containing the sample and warm the mixture. If ammonia gas is given off, there are ammonium ions in the substance.

Question 32

What is the equation for testing for ammonium compounds?

Answer 32

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

Question 33

What three compounds are insoluble?

Answer 33

Barium sulfate, barium carbonate and barium sulfite.

Question 34

What is important when testing for sulfates?

Answer 34

You must make sure that no carbonate ions or sulfite are present first.

Question 35

Why do you need to test for sulfate ions before halides?

Answer 35

This is because both sulfate and halide ions will produce ppts with silver nitrate.

Question 36

What will adding dilute acid do to the test solution?

Answer 36

It will remove anions.

Question 37

Which tests test for anions?

Answer 37

Carbonate, sulfate and halide tests.

Question 38

Which test tests for cations?

Answer 38

NaOH and litmus paper

Question 39

In what order should you test for anions?

Answer 39

Carbonates then sulfates then halides.