Acids, Bases and Salts 2

Question 1

Describe the solubility of the following ions.
1: NO3 ^-
2: SO4 ^2-
3: CO3 ^2-
4: O ^2-
5: OH ^-
6: PO4 ^3-
7: Cl ^-
8: Br ^-
9: I ^-
10: sodium salts
11: potassium salts
12: ammonium salts

Answer 1

1: All nitrates are soluble.
2: All sulfates are soluble except lead sulfate (Pb ^2+), barium sulfate (Ba ^2+), and calcium sulfate (Ca ^2+).
3: All carbonates are insoluble except Na+, K+ and NH4+.
4: All oxides are insoluble except Na+ and K+.
5: All hydroxides are insoluble except Na+ and K+. Ba ^2+ and Ca ^2+ are slightly soluble.
6: All phosphates are insoluble except Na+, K+ and NH4+.
7: All chlorides are soluble except Ag+ and Pb 2+.
8: All bromides are soluble except Ag+ and Pb 2+.
9: All iodides are soluble except Ag+ and Pb 2+.
10: All sodium salts are soluble.
11: All potassium salts are soluble.
12: All ammonium salts are soluble.

Question 2

Briefly describe how a salt is formed.

Answer 2

A salt is the compound formed when a metallic ion or an ammonium ion replaces one or more hydrogen ions of an acid.

Question 3

State a difference between hydrated salts and anhydrous salts.

Answer 3

Hydrated salts contain water of crystallisation, while anhydrous salts do not contain water of crystallisation.

Question 4

State one use for each of the following salts below:
1: ammonium chloride
2: ammonium nitrate
3: calcium carbonate
4: calcium chloride
5: calcium sulfate
6: iron sulfate
7: magnesium sulfate
8: potassium nitrate
9: silver bromide
10: sodium carbonate
11: sodium chloride
12: sodium stearate
13: tin fluoride

Answer 4

1: torch batteries
2: fertilisers
3: making of cement and glass
4: extraction of sodium / drying agent
5: making of plasters
6: in ‘iron’ tablets
7: medicines
8: fertilisers
9: in film photography
10: making of glass / washing powders
11: food flavouring
12: soaps
13: toothpaste

Question 5

State the 3 types of salt preparation.

Answer 5

Precipitation method, filtration method, titration method

Question 6

What type of salts can the precipitation method prepare?

Answer 6

All insoluble salts can be prepared by the precipitation method.

Question 7

What type of salts should be mixed when preparing an insoluble salt in the precipitation method?

Answer 7

Mix a soluble salt that contains its cations with another soluble salt that contains its anions.

Question 8

Describe the precipitation method in detail.

Answer 8

(1) Add an excess of one solution to the other.
(2) Stir thoroughly until no more precipitate forms.
(3) Filter the liquid to separate the precipitate.
(4) Wash the precipitate with deionised water to remove unwanted reactants.
(5) Dry the crystals by pressing them between sheets of filter paper.

Question 9

Suggest the reagents required to prepare the following insoluble salts.
1: silver iodide
2: lead (II) sulfate
3: copper (II) carbonate
4: lead (II) iodide

Answer 9

1: AgNO3 (aq), KI (aq)
2: Pb(NO3)2 (aq), Na2SO4 (aq) or H2SO4 (aq)
3: Cu(NO3)2 (aq), Na2CO3 (aq)
4: Pb(NO3)2 (aq), NaCl (aq)

Question 10

Describe the method, in detail, for making soluble salts by filtration.

Answer 10

(1) Add excess metal / insoluble base / insoluble carbonate to warm dilute acid and stir until no more reacts. (2) Filter the mixture to obtain the filtrate.
(3) Heat the filtrate till the point of saturation.
(4) Test for saturation by dipping a glass rod into the solution.
(5) Cool the filtrate to allow crystals to form.
(6) Filter to obtain the crystals.
(7) Wash with a small amount of cold deionised water.
(8) Dry the crystals between pieces of filter paper.

Question 11

Name 2 types of metals that are unsuitable for making soluble salts through filtration. Explain why.

Answer 11

Unreactive metals such as lead and copper. They do not react with dilute acids.
Very reactive metals such as sodium, potassium and calcium. Their reactions with acids are too vigorous.

Question 12

Which of the following metals react with oxygen to form oxides?
1: magnesium
2: zinc
3: iron
4: calcium
5: copper
6: aluminium
7; lead

Answer 12

1, 2, 3, 4, 6, 7

Question 13

Which of the following metals react with water?
1: magnesium
2: zinc
3: iron
4: calcium
5: copper
6: aluminium
7; lead

Answer 13

1, 4, 6

Question 14

Which of the following metals react with acids?
1: magnesium
2: zinc
3: iron
4: calcium
5: copper
6: aluminium
7; lead

Answer 14

1, 2, 3, 4, 6, 7

Question 15

When preparing soluble salts by filtration, what should be done if the metal used is non-reactive?

Answer 15

The metal oxide, hydroxide or carbonate should be used to react with an acid to form the salt.

Question 16

Suggest the reagents required to prepare the following soluble salts.
1: iron chloride
2: aluminium sulfate
3: zinc nitrate

Answer 16

1: HCl(aq), Fe(s) OR FeO(s) OR FeCO3(s)
2: H2SO4(aq), Al2O3(s)
no such thing as aluminium carbonate!
3: HNO3(aq), Zn(s) OR ZnO(s) OR ZnCO3(s)

Question 17

What type of salts can be prepared using the titration method?

Answer 17

Soluble salts containing group 1 or ammonium cations

Question 18

Describe the method, in detail, for preparing sodium nitrate, NaNO3 using titration method.

Answer 18

(1) Pipette 25.0cm^3 of aqueous NaOH into a conical flask.
(2) Add 2 to 3 drops of methyl orange / phenolphthalein into the conical flask.
(3) Using a burette filled with dilute HNO3, titrate NaOH with the acid until the endpoint is reached, where one drop of the acid causes the indicator to change colour permanently.
(4) Record the volume of HNO3 used.
(5) Repeat the titration without the indicator by adding the same volume of HNO3 from the burette as in the previous titration.
(6) Transfer the aqueous NaNO3 solution to a crucible and heat the solution to evaporate the water, forming a saturated solution. Test for saturation by dipping a glass rod into the solution and if crystals are formed on the cool rod, no further heating is required.
(7) Cool the saturated solution to room temperature for the sodium nitrate salt to crystallise.
(8) Filter the solution to obtain the sodium nitrate crystals and rinse them with a small amount of cold deionised water.
(9) Dry the sodium nitrate crystals between sheets of filter paper.

Question 19

Suggest the reagents required to prepare the following soluble salts.
1: lithium chloride
2: sodium ethanoate
3: potassium phosphate

Answer 19

1: HCl(aq), LiOH(aq)
2: CH3CO2H(aq), NaOH(aq)
3: H3PO4(aq), KOH(aq)

Question 20

Describe the procedure to obtain aluminium nitrate salt as a solid. State the 2 reagents that are used.

Answer 20

Reagents used: aluminium oxide, dilute nitric acid
Add excess aluminium oxide to warm dilute nitric acid and stir until no more reacts. Filter the mixture to obtain the aqueous aluminium nitrate as filtrate. Heat the filtrate till the point of saturation. Test for saturation by dipping a glass rod into the solution. Cool the filtrate to allow aluminium nitrate crystals to form. Filter to obtain the aluminium nitrate crystals. Wash with a small amount of cold deionised water. Dry the aluminium nitrate crystals between pieces of filter paper.

Question 21

Describe the procedure to obtain silver iodide salt as a solid. State the 2 reagents that are used.

Answer 21

Reagents used: aqueous silver nitrate, aqueous potassium iodide
Pour 25cm^3 of aqueous silver nitrate into a beaker and add aqueous potassium iodide in excess. Stir throughly until no more silver iodide precipitate forms. Filter the mixture. The residue is impure silver iodide. Rinse the precipitate of silver iodide with deionised water. Dry the silver iodide crystals between sheets of filter paper.

Question 22

Describe the procedure to obtain potassium sulfate salt as a solid. State the 2 reagents that are used.

Answer 22

Reagents used: aqueous potassium hydroxide, dilute sulfuric acid
Pipette 25.0cm^3 of dilute sulfuric acid into a conical flask. Add 2 to 3 drops of methyl orange / phenolphthalein into the conical flask. Using a burette filled with aqueous potassium hydroxide, titrate the sulfuric acid with the potassium hydroxide until the endpoint is reached, where one drop of the alkali causes the colour of the indicator to change colour permanently. Record the volume of the aqueous potassium hydroxide used. Repeat the titration without the indicator by adding the same volume of potassium hydroxide from the burette as in the previous titration. Transfer the aqueous potassium sulfate solution to a crucible and heat the solution to evaporate the water, forming a saturated solution. Test for saturation by dipping a glass rod into the solution and if crystals form on the cool rod, no further heating is required. Cool the hot saturated solution to room temperature for the potassium sulfate salt to crystallise. Filter the solution to obtain the potassium sulfate crystals and rinse them with a small amount of deionised water. Dry the potassium sulfate crystals between sheets of filter paper.

Question 23

When hydrogen chloride is bubbled through aqueous silver nitrate, a chemical reaction and a salt is formed.
a) Write the ionic equation for the reaction.
b) What is the name given to this type of reaction used in the production of salts?

Answer 23

a) Ag^+(aq) + Cl^-(aq) -> AgCl(s)
b) Precipitation