Topic 3 - chemical change

Question 1

What is an acid?

Answer 1

A substance with a pH less than 7

Question 2

What ions do acids form in water?

Answer 2

H+ ions

Question 3

What is an alkali?

Answer 3

A base that is soluble in water. pH more than 7

Question 4

What ions do alkalis form in water?

Answer 4

OH- ions (Hydroxide ions)

Question 5

What is the pH of a neutral solution?

Answer 5

pH 7

Question 6

What is an indicator?

Answer 6

A dye that changes colour depending on whether it’s above or below a certain pH.

Question 7

Explain the effect of acidic, neutral and alkaline solutions on litmus

Answer 7

Red in acidic, purple in neutral, blue in alkaline

Question 8

Explain the effect of acidic, neutral and alkaline solutions on methyl orange.

Answer 8

Red in acidic, yellow in neutral and alkaline solutions

Question 9

Explain the effect of acidic, neutral and alkaline solutions on phenolphthalein

Answer 9

Colourless in acidic and neutral solutions, pink in alkaline

Question 10

What’s the effect of increasing the concentration of hydrogen ions in an acidic solution?

Answer 10

The solution becomes more acidic so the pH decreases

Question 11

What’s the effect of increasing the concentration of hydroxide ions in an alkaline solution?

Answer 11

The pH increases so becomes a stronger alkaline.

Question 12

What happens to the pH of a solution when hydrogen ion concentration is increased?

Answer 12

As hydrogen ion concentration increases by a factor of 10, the pH of the solution decreases by 1

Question 13

What does concentrated mean for an acid?

Answer 13

An acid with a large number of acid molecules compared to the volume of water

Question 14

What does dilute mean for an acid?

Answer 14

An acid with a small number of acid molecules compared to the volume of water.

Question 15

What are strong acids?

Answer 15

Acids that ionise almost completely in water ie. a large proportion of the acid molecules dissociate to release H+ ions.

Question 16

What are weak acids?

Answer 16

Acids that don’t fully ionise in solution ie. only a small proportion of the acid molecules dissociate to release H+ ions.

Question 17

What is a base?

Answer 17

Any substance that reacts with an acid to form a salt and water only.

Question 18

What is a neutralisation reaction?

Answer 18

A reaction between an acid and a base

Question 19

What is the chemical test for hydrogen?

Answer 19

Use a lighted splint and if hydrogen is present you will hear a squeaky pop due to hydrogen burning with oxygen in the air to form water.

Question 20

What is the chemical test for carbon dioxide using limewater?

Answer 20

To see if a gas is carbon dioxide bubble it through with limewater. If the gas is carbon dioxide the limewater will turn cloudy.

Question 21

What happens in an acid-alkali neutralisation reaction?

Answer 21

Hydrogen ions (H+) from the acid react with hydroxide ions (OH-) from the alkali to form water.

Question 22

Why must titration be used if soluble salts are prepared from an acid + soluble reactant?

Answer 22

because there is no insoluble excess reactant that could be removed by filtration

Question 23

What common substances are soluble in water?

Answer 23

All common sodium, potassium + ammonium salts
All nitrates
Most common chlorides
Most common sulphates

Question 24

What common substances are insoluble in water?

Answer 24

Silver + lead chlorides
Lead, barium + calcium sulfate
Most common carbonates + hydroxides except those of sodium, potassium + ammonium

Question 25

Why is excess of the reactant added when making soluble salts prepared from an acid + an insoluble reactant?

Answer 25

So you don’t have any leftover acid in your product

Question 26

Why is the excess reactant removed when making soluble salts prepared from an acid + an insoluble reactant?

Answer 26

To get a solution containing only the salt and water

Question 27

Why must the acid + soluble reactant be mixed in the correct proportions when soluble salts are prepared from an acid + and a soluble reactant?

Answer 27

Because the salt is soluble and would be contaminated with the excess alkali

Question 28

Describe the method used to prepare a pure, dry sample of an insoluble salt

Answer 28

1- mix two suitable solutions 2- use filtration to separate precipitate as a residue from solution 3- wash precipitate with distilled water while it’s in the filter funnel 4- leave washed precipitate aside or in warm oven to dry

Question 29

How is a salt formed?

Answer 29

During a neutralisation reaction (a reaction between an acid + base)

Question 30

What salts do the general acids produce?

Answer 30

Hydrochloric acid produces chloride salts Sulfuric acid produces sulfate salts Nitric acid produces nitrate salts

Question 31

Explain the general reactions of aqueous solutions of acids with metals

Answer 31

Acid + metal -> salt + hydrogen | Eg 2HCl + Mg -> MgCl2 + H2

Question 32

Explain the general reactions of aqueous solutions of acids with metal oxides

Answer 32

Acid + metal oxide -> salt + water | Eg 2HCl + CuO -> CuCl2 + H2O

Question 33

Explain the general reactions of aqueous solutions of acids with metal hydroxides

Answer 33

Acid + metal hydroxide -> salt + water | Eg HCl + NaOH -> NaCl + H2O

Question 34

Explain the general reactions of aqueous solutions of acids with metal carbonates

Answer 34

Acid + metal carbonate -> salt + water + carbon dioxide | Eg 2HCl + Na2CO3 -> 2NaCl + H2O + CO2