F4-C6- Salts, Acids and alkali

Question 1

What is an acid

Answer 1

A substance which dissolve and ionise in water to produce hydrogen ions.

Question 2

All alkalis are bases. True or False?

Answer 2

True. Alkalis are bases which are soluble in water

Question 3

Explain the reaction when ammonia is added into tetrachloromethane

Answer 3

• Ammonia can dissolve but cannot ionise in tetrachloromethane to form hydroxide ions.
• Ammonia exists as neutral covalent molecules in tetrachloromethane
• Ammonia cannot show its alkalinity without the presence of water.
• No effect towards red litmus paper

Question 4

What is the colour of mthyl orange when in acidic, neutral and alkali condition?

Answer 4

acidic: red
neutral : orange
alkali : yellow

Question 5

Define degree of ionisation of acids and alkalis

Answer 5

A measurement of the percentage of the total number of acid/ alkali molecules that will ionise when dissolved in water.

Question 6

Explain phosphoric acid as a weak acid.

Answer 6

• Phosphoric acid dissolve and ionise partially in water to produce a low concentration of hydroxide ions.
• Most of the phosphocic acid still exists as covalent molecules and only a small number of the acid ionises to form hydrogen ions.

Question 7

Why is totthpaste used to clean teeth?

Answer 7

• Totthpaste which is alkali can neutralise the lactic acid produced by bacteria in mouth

Question 8

Name 2 examples of salts used in agriculture

Answer 8

• Fertilizers : ammonium sulphate, potassium chloride, ammonium nitrate
• Pesticides : copper (II) sulphate, iron(II) sulphate

Question 9

What is the use of barium sulphate?

Answer 9

• used in medical field

- Patients drink before taking x-ray

Question 10

NAme 2 examples of slats used is industry.

Answer 10

• Silver chloride/bromide to make photochromic glass

- Sodium carbonate to make soda lime glass

Question 11

Is barium hydroxide soluble in water?

Answer 11

duhhh of coz

Question 12

Is HgCl soluble in water?

Answer 12

noooh

Question 13

Why does effervesence occur when mg powder added to aqueous hcl but no obersavtion is seen when mg powder is added to hcl dissolved in methylbenzene?

Answer 13

In aqeous HCL

• HCl dissolve and ionise in water to produce hydrogen ions and chloride ions.
• presence of hydrogen ions causes solution to be acidic
• Thus, HCL reacts with magnesium powder to produce hyrogen gas which causes effervescence

In HCL dissolved in methylbenzene

• HCl is a covalent compound
• HCl can dissolve but cannot ionise in methylbenzene to form hydrogen ions.
• No observation occurs because HCl cannot react with magnesium powder

Question 14

During titration, why does the burette need to be rinsed with sulphuric acid after rising it with water.

Answer 14

ensure water droplets in the inner wall of the burette does not dilute the concentration of the acid used.

Question 15

How to test for anion in potassium chloride solution

Answer 15

Anion: chloride ion

• add dilute HNO3
• add silver nitrate
• white precipitate forms indiciating prescence of chloride ions

Question 16

in a solution,dilute hydrochloric acid and barium chloride is added. A white precipitate is formed indicating the presence of ______ anion

Answer 16

sulphate ion

Question 17

How to test for presence of nitrate ion in salt solution?

Answer 17

dilute H2So4 + iron (II) sulphate + concentrated H2So4

- brown ring is formed

Question 18

A colourless solution added with sodium hydroxide solution forms a white precipitate. In excess NaOh , it dissolves to form a colourless solution. What cation might be present

Answer 18

Zinc, aluminium, lead(II) ions

Question 19

A colourless solution added with NH3 solution forms a white precipitate which remains incoluble in excess Nh3. What cation might be present?

Answer 19

Aluminium, Lead(II) or Magnesium ions

Question 20

A solid is heated strongly and produces a brown gas with pungent smell. The residue is yellow when hot and white when cold. What inference can be made?

Answer 20

• Nitrogen dioxide gas is produced

- ZInc oxide is produced

Question 21

When dilute HNO3 is added into a solution, bubbles of colourless gas are produced. The gas turns limewater milky indicating the presence of ___?

Answer 21

co2 gas

Question 22

What is the use of Nessler reagent?

Answer 22

To comfirm the presence of Ammonium ion

Question 23

When a solution is added with ammonia solution until in excess, what are the observations shown if copper (II) ion ins present?

Answer 23

• A blue precipitate is produced and dissolves in excess ammonia to form a dark blue solution

Question 24

A BROWN solution is poured into a test tube and added with potassium thiocynate solution to determine the cation present. What observation and inference can be made?

Answer 24

• A blood red colouration is formed

- Iron (III) ions are present