Dilution Of Acids And Alkalis

Question 1

Dilution of acids and alkalis

Answer 1

During dilution of a solution the number of particles (ions or molecules) of solute in every cm3 decreases.

When an acid is diluted by a factor of 10 the pH increases by a factor of 1

When an alkali is diluted by a factor of 10 the pH decreases by a factor of 1

Question 2

Dilution and water

Answer 2

Pure water is a very poor conductor of electricity. This shows water contains ions.

The very low conductivity shows water contains a very small number of ions

This shows that pure water contains a very small number of H+ and OH- ions

Acids contains more H+ ions than is present in pure water
Alkalis contain more OH- ions than his present in pure water
Diluting an acid or alkali decreases the concentration of H+ or OH- to bring them down to the same concentration as present in pure water

Question 3

Conductivity in water

Answer 3

The low conductivity of water shows very few molecules dissociate (break up) to form ions.
Pure water is neutral because there are equal numbers of H+ and OH- ions

This reaction is called the dissociation of water. This means all solutions contain small numbers of H+ and OH- ions

Question 4

Conductivity of acids

Answer 4

All acids conduct electricity meaning acidic solutions must be ionic
When they dissolve in water they dissociate into ions

All acids contain hydrogen and form hydrogen ions when dissolved in water

Hydrogen ions are positively charged meaning they are attracted to the negative electrode and form hydrogen gas

Question 5

Types of acids

Answer 5

Citric acid
Folic acid
Lactic acid
Tartaric acid
Ethanoic acid
Ascorbic acid
Amine acids
Fatty acids 

All acids contain the hydrogen ion

Question 6

Alkali ionic formulae

Answer 6

Metal hydroxides have ionic bonding
When an ionic compound is melted or in solution the ions are free to move the + is inserted between the ions in a formula to show they have moved apart

Question 7

Neutralisation

Answer 7

When an acid and alkali are mixed together they cancel each other out and the pH moves towards 7. This is called neutralisation.

A neutralisation reaction is one in which a base reacts with an acid to form a salt and water.

Question 8

Types of salt

Answer 8

Hydrochloric acid - chloride
Nitric acid - nitrate
Sulfuric acid - sulfate
Sulfurous acid - sulfite
Carbonic acid - carbonate 
Ethanoic acid - ethanoate