Salts

Question 0

Salts can exist in which forms at room temp?

Answer 0

1. Dissolved
   - aqueous solution
2. Solid crystals
   - hydrated salt
3. Solid powder
   - anhydrous salt

Question 1

What is a salt?

Answer 1

Ionic compound which is formed when a metallic ion or an ammonium ion replaces one or more hydrogen ions in an acid.

Question 2

How can we obtain an anhydrous salt?

Answer 2

Heating till dryness in an evaporating dish.

Question 3

Which nitrates(NO3 -) are soluble?

Answer 3

ALL NITRATES ARE SOLUBLE.

Question 4

Describe the solubility of halides? (Chlorides, iodides)

Answer 4

ALL SOLUBLE Except Lead(II) and silver.

Question 5

Describe the solubility of sulfates. (SO4 2-)

Answer 5

ALL SOLUBLE except Calcium, barium and lead(II)

Question 6

Describe the solubility of bases. (Hydroxides, oxides)

Answer 6

ALL INSOLUBLE except sodium, ammonium, calcium, potassium, barium.

Question 7

Describe the solubility of carbonates. (CO3 2-)

Answer 7

ALL INSOLUBLE except sodium , ammonium, potassium.

Question 8

What are hydrated salts?

Answer 8

Salts which combine with water to form aqueous solutions.

Question 9

What happens when hydrated salts are heated gently?

Answer 9

They form anhydrous salts and water is given off.

Question 10

When is titration used?

Answer 10

When salt is soluble, and it is either a sodium, ammonium or potassium salt.

Question 11

Which salts are soluble?

Answer 11

Sodium, potassium and ammonium salts.

Question 12

When is precipitation used?

Answer 12

For ALL INSOLUBLE SALTS.

Question 13

Describe the precipitation process

Answer 13

1. Mix the 2 solutions in beaker. Stir with glass rod. Precipitate of salt would have been formed.
2. Filter out precipitate using funnel and filter paper.
3. Wash residue by running distilled water through it.
4. Allow salt to dry between sheets of filter paper.

Question 14

When is reaction of an acid with an insoluble reactant used ?

Answer 14

1. All soluble salts except SAP.
2. Base, carbonate or metal must be insoluble(the cation)
3. Copper and silver metal cannot be used.

Question 15

Describe the process of the reaction of an acid with an insoluble reactant.

Answer 15

1. Add excess carbonate/metal/ base to warm acid until no further acid.
2. Filter mixture to remove unreacted solid.
3. Heat filtrate in evaporating dish till saturated.
4. Cool solution to obtain salt.
5. Dry salts between sheets of filter paper.

Question 16

Why is reaction of acid with insoluble reactant only suitable for soluble salts?

Answer 16

If this method were to be used to prepare an insoluble salt, insoluble salt produced will form a ‘protective layer’ over insoluble reactant, preventing any further reaction and hence a lower yield.

Question 17

Why must an excess of insoluble reactant be added for RAIR?

Answer 17

Ensure all acid completely reacted, prevent any excess acid which will contaminate the aqueous salt formed. Excess reactant on the other hand can be removed easily though filtration.

Question 18

Suggest why group I salts may not be prepared through RAIR with an excess of a group I base or carbonate.

Answer 18

They are all soluble in water, hence any excess reactant will not be able to be removed through filtration.

Question 19

Suggest why group I salts may not be prepared through RAIR with excess of group I metals.

Answer 19

They are very reactive, hence react violently with acids, causing experiment to be too dangerous to perform.

Question 20

Suggest why titration needs to be repeated a second time without using an indicator.

Answer 20

During first titration, salt sample produced has been contaminated by indicator added. Repeating without indicator will produce pure salt sample without contamination.

Question 21

Why an alkali or carbonate must be used in titration, instead of a metal salt?

Answer 21

Only by product is water for alkali and carbonate. If metal salt used, by product will contaminate salt.

Question 22

Describe the process of titration.

Answer 22

1. Meade out fixed volume of acid using pipettes. Transfer this solution into comical flask.
2. Add few drops of indicator.
3. Add alkali/carbonate drop by drop until indicator changes color using burette.
4. Note down volume of alkali/carbonate required for complete neutralization.
5. Repeat titration without indicator. Stop burette when reading reached same level as earlier noted.