Chapter 6 - Chemical Equations : Tests For Anions

Question 0

What is added to the chloride salt?

Answer 0

Silver nitrate solution AgNO3

Question 1

To detect the presence of chloride ions in aqueous solution

Chemicals required?

Answer 1

Any chloride salt such as NaCl or KCl

Silver nitrate solution

Dilute ammonia solution

Deionised water

Question 2

What is observed when AgNO3 is added to the chloride

Answer 2

A white precipitate - silver chloride

Ag+ and Cl- —-> AgCl arrow pointing down for precipitate

Question 3

What is used to confirm the white precipitate is silver chloride?

Answer 3

Dilute ammonia solution

The white precipitate disappears

Question 4

To detect the presence of sulfate ions ( SO4 2- ) and sulfite ions ( SO3 2- ) in aqueous solution

Chemicals required?

Answer 4

Any soluble sulfate salt - Na2SO4 K2SO4

Any soluble sulfite salt - Na2SO3 K2SO3

Barium chloride BaCl2 solution

Dilute HCl

Deionised water

Question 5

What is added to the sulfate solution?

Answer 5

Barium chloride solution

Question 6

What is observed when barium chloride is added to the sulfate and then to sulfite?

Answer 6

A white cloudy solid material settles out

Materials formed are barium sulfate and barium sulfite

Question 7

Write the equations for the barium sulfate and sulfite

Answer 7

Ba 2+ and SO4 2- —-> BaSO4 white precipitate

Ba 2 + and SO3 2- —-> BaS03 white precipitate

Question 8

What is done to distinguish between the sulfate and sulfite? What is observed?

Answer 8

Dilute HCl is added

Barium sulfate is insoluble in dilute HCl

Barium sulfite is soluble in dilute HCl and so the precipitate disappears

Question 9

Write the equation for barium sulfate using the ions

Answer 9

SO4 2- + H+ —-> no reaction

Question 10

Write the equation from barium sulphite using the ions

Answer 10

So3 2- + 2H+ —-> So2 + H20

Question 11

To detect the presence of carbonate ions ( Co3 2-) and hydrogencarbonate ions ( HCO3-) in aqueous solution

Chemicals required?

Answer 11

Any soluble carbonate salt - Na2CO3 or K2Co3

Any soluble hydrogencarbonate salt - NaHCO3 , KHCO3

Dilute HCl

Limewater

Magnesium sulfate solution

Deionised water

Question 12

What procedure is done to the carbonate salt?

Answer 12

Placed in a boiling tube

Insert a one holed rubber tuber into the boiling tube

Question 13

What is added to the carbonate salt in the boiling tube? What happens?

Answer 13

Dilute HCl

Fizzing as acid comes in contact with carbonate

Question 14

Equation for carbonate ions reacting with the acid to liberate carbon dioxide

Answer 14

CO3 2- + 2H+ —-> CO2 + H2O

Question 15

What happens to the limewater with the carbonate?

Answer 15

The co2 turns it milky due to the formation of calcium carbonate

Question 16

Equation for Calcium carbonate formation

Answer 16

ca(OH)2 + Co2 —-> CaCo3 white precipitate + H20

Question 17

What happens if you continue to bubble co2 through the carbonate solution?

Answer 17

It goes from milky to colourless

Soluble calcium hydrogencarbonate is formed

Question 18

Equation for when excess Co2 is bubbled into calcium carbonate limewater

Answer 18

CaCO3 + CO2 + H2O —-> Ca(HCO3)2

Insoluble Soluble

Question 19

What happens when hydrogencarbonate is mixed with HCL?

Answer 19

Co2 is also liberated

Question 20

Equation for Hydrogencarbonate with dilute HCl

Answer 20

Hco3 - + H+ —-> Co2 + H20

Question 21

To distinguish between carbonate and hydrogencarbonate ions what is added?

Answer 21

Magnesium sulfate MgSo4

Question 22

What is observed when magnesium sulphate is added to carbonate?

Answer 22

A white precipitate of insoluble magnesium carbonate

Question 23

Equation for magnesium carbonate formation

Answer 23

Mg2+ + C03 2- —-> MgCo3 white precipitate

Insoluble

Question 24

What is observed when magnesium carbonate is added to hydrogencarbonate ions?

Answer 24

No precipitate is formed as magnesium hydrogencarbonate is soluble in water

Question 25

Equation for when magnesium hydrogencarbonate is added to hydrogencarbonate ions

Answer 25

Mg2+ + 2HCO3- ----> Mg(HCO3)2 | Soluble

Question 26

Brown ring test - to detect the presence of nitrate ions in aqueous solution Chemicals required?

Answer 26

Any nitrate salt such as NaNo3 or KNO3 Iron(II) sulfate solution Concentrated sulphuric acid Deionised water

Question 27

What is first added to the nitrate salt solution?

Answer 27

Iron(II) sulfate solution

Question 28

What is added to the nitrate salt solution after adding the Iron(II) sulfate solution. What happens o this solution in the test tube?

Answer 28

Concentrated sulphuric acid is added down the angled side using a dropper It is dense so it settles to the bottom

Question 29

What forms at the junction of the sulphuric acid layer and the solution of nitrate ions layer?

Answer 29

A brown ring. It is formed as a result of nitrate ions being present Brown colour is due to the formation of the substance FeSO4.NO

Question 30

To detect the presence of phosphate ions aqueous solution Chemicals required?

Answer 30

Any soluble phosphate salt such as Na2HPO4 Ammonium molybdate solution Concentrated nitric acid Deionised water

Question 31

What is first added to the phosphate salt solution?

Answer 31

Ammonium molybdate solution

Question 32

What is next added to the phosphate salt and molybdate solution?

Answer 32

5 drops of Concentrated nitric acid

Question 33

What forms when the nitric acid is added to the phosphate salt and ammonium molybdate solution?

Answer 33

A yellow precipitate

Question 34

What should you do with the yellow precipitate does not form and phosphate ions solution?

Answer 34

Place the test tube in warm water

Question 35

What is the name of the yellow precipitate formed unconcentrated nitric acid is added to a solution containing phosphate ions and ammonium Molybdate?

Answer 35

Ammonium phosphomolybdate