ACIDS, BASES & SALTS

Question 1

what is an acid?

Answer 1

a proton donor

Question 2

what is a base?

Answer 2

a proton acceptor

Question 3

what is an alkali?

Answer 3

a soluble base

Question 4

what is a neutral base?

Answer 4

one that is neither acidic nor alkaline

Question 5

types of acids

Answer 5

strong & weak acids

Question 6

what is a strong acid? + examples

Answer 6

one which completely ionizes in aqueous solution
- Nitric acid (HNO3)
- Hydrochloric acid (HCL)
- Sulfuric acid (H2SO4)

Question 7

what is a weak acid? + examples

Answer 7

one which is partially ionised in aqueous solution
- acetic acid
- phosphoric acid
- ethanoic acid
- lactic acid

Question 8

basicity of an acid

Answer 8

the number of moles of H+ ions that can be formed from 1 mole of an acid

Question 9

what is a strong base? + examples

Answer 9

one which is completely dissociated in aqueous solution
- Potassium hydroxide (KOH )
- Sodium hydroxide
(NaOH )
- Barium hydroxide (Ba(OH)2 )
- Calcium hydroxide (Ca(OH)2 )
- Lithium hydroxide (LiOH )

Question 10

what is a weak base? + examples

Answer 10

is one that is partially ionised in aqueous solution
- Ammonia (NH3)
- Aluminium hydroxide
( Al(OH)3)
- Lead hydroxide (Pb(OH)2)
- Copper hydroxide (Cu(OH)2)
- Zinc hydroxide (Zn(OH)2)

Question 11

effects of acids & alkalis in diff. indicators

Answer 11

litmus - red - blue
thymolphthalein - colourless - blue
methyl orange - red/orange - yellow

Question 12

properties of acids and bases

Answer 12

acid + metal =
salt + hydrogen
acid + base =
salt + water
acid + metal oxide =
salt + water
acid + ammonia =
ammonium salt
acid + carbonate =
salt + water + CO2
metal hydroxide + ammonium salt = (heat)
salt + water + ammonia

Question 13

guidelines for solubilities of substances

Answer 13

1. All group (I) and ammonium compounds are soluble in water.
2. All nitrates are soluble in water.
3. All carbonates are insoluble in water except group (I) carbonates and ammonium carbonates.
4. All chlorides, bromides and iodides are soluble in water except those of lead (II) and silver.
5. All sulfates are soluble in water except Barium sulfate and Lead (II) sulfate. Calcium sulfate is only sparingly soluble.
6. The oxides and hydroxides of group (II) are soluble. the rest are insoluble.

Question 14

basic oxides

Answer 14

oxides which react with acids to form a salt and water. This includes most of the metal oxides

Question 15

acidic oxides

Answer 15

oxides which react with alkalis to form a salt and water. This includes non-metallic oxides except monoxides

Question 16

neutral oxides

Answer 16

oxides which do not react with acids or bases. They are usually non-metallic monoxides

Question 17

amphoteric oxides

Answer 17

oxides which have both acidic and basic properties i.e. they form salts when they react with acids. They also react with alkalis to form complex salts

Question 18

hydrated and anhydrous substances

Answer 18

A hydrated substance is a substance that is chemically combined with water
An anhydrous substance is a substance containing no water

Question 19

water of crystallisation

Answer 19

the definite amount of water with which some substances chemically combine when they form crystals from their sol. in water

Question 20

saturated and super saturated solution

Answer 20

A saturated solution is one which cannot dissolve any more of the solute at that temperature in presence of an undissolved solute.

A supersaturated solution is one that cannot dissolve any more solute at any temperature in presence of an undissolved solute.

Question 21

solubility

Answer 21

Solubility of a solute in a solvent at a particular temperature is the number of grams of a solute required to saturate 100g of solvent at that temperature.

Question 22

Laboratory preparation of sodium chloride crystals

Answer 22

Procedure
1. Fill a clean burette with hydrochloric acid and fix it to the stand.
2. Pipette a fixed volume of sodium hydroxide into a conical flask and add a dew drops of an acid-base indicator e.g. methyl orange or thymolphthalein.
3. Run hydrochloric acid from the burette into the conical flask, while shaking the contents in the conical flask until the indicator changes colour and note the volume of acid used.
4. Mix the same volume of acid and alkali as used in the titration but without the indicator.
5. Pour the mixture in an evaporating dish and heat the mixture until the crystallisation point is reached
6. Allow the solution to cool so that crystals form. Filter off the crystals and dry them between filter papers.

NaOH (aq) + HCl (aq) = NaCl (aq) + H2O (l)

Question 23

Laboratory preparation of zinc sulfate crystals
starting from zinc metal

Answer 23

1. Put dilute sulfuric acid in a beaker and warm it gently until its hot.
2. Add zinc granules to the warm acid, a little at a time, while stirring, until in excess.
3. When effervescence has stopped, filter off the excess zinc metal.
4. Boil the filtrate until crystallisation point is reached or until saturation point is reached.
5. Allow the solution to cool by letting it stand for some time. Zinc sulfate crystals form as solution cools.
6. Filter off the crystals, wash them with cold pure distilled water and dry them in sunshine or between filter papers.

Question 24

Laboratory preparation of Lead (II) iodide.

Answer 24

Procedure
(Add water to both salts to make them solutions if they aren’t yet solutions)
1. Mix Lead (II) nitrate solution with potassium iodide solution in a test tube.
2. A yellow precipitate of Lead (II) iodide is formed.
3. The precipitate is then filtered off, washed and dried.

Pb(NO3)2 (aq)+2KI(aq)→ PbI2 (s)+2KNO3 (aq)

Ionically:

Pb2+(aq)+2I- → PbI2 (s)