topic 3 - acids and alkalis

Question 1

What pH value indicates a very acidic solution?

Answer 1

pH 1

Question 2

What pH value indicates a very alkali solution?

Answer 2

pH 14

Question 3

What pH value indicates a neutral solution?

Answer 3

pH 7

Question 4

What color does litmus turn in acidic solutions?

Answer 4

Red

Question 5

What color does litmus turn in alkali solutions?

Answer 5

Blue

Question 6

What color does methyl orange turn in acidic solutions?

Answer 6

Red

Question 7

What color does methyl orange turn in alkali solutions?

Answer 7

Yellow

Question 8

What color does methyl orange turn in a neutral solution?

Answer 8

Orange

Question 9

What color does phenolphthalein turn in acidic solutions?

Answer 9

Colorless

Question 10

What color does phenolphthalein turn in alkali solutions?

Answer 10

Pink

Question 11

How does universal indicator differ from single indicators?

Answer 11

Universal indicator allows you to measure the pH by giving a range of colours.

Question 12

What type of ions are produced when an acid dissolves in water?

Answer 12

Hydrogen ions, H+

Question 13

What type of ions are produced when alkalis dissolve in water?

Answer 13

Hydroxide ions, OH-

Question 14

What is concentration?

Answer 14

The number of particles dissolved in a given volume of water.

Question 15

What is the equation to work out concentration?

Answer 15

Concentration (g/dm3) = mass (g) / Volume (dm3)

Or Concentration (mol/dm3) = moles (mol) / Volume (dm3)

Question 16

What happens to the pH when the hydrogen ion concentration increases?

Answer 16

It decreases.

Question 17

What happens to the hydrogen ion concentration when the pH decreases by 1?

Answer 17

It increases by a factor of 10 (x10).

Question 18

Define the term strong acid.

Answer 18

Hydrogen ions completely dissociate when the acid is dissolved in water.

Question 19

Give examples of strong acids.

Answer 19

HCl, HNO3, H2SO4

Question 20

What is a weak acid?

Answer 20

In a weak acid, the hydrogen ions partially dissociate.

Question 21

Give an example of a weak acid.

Answer 21

Ethanoic acid

Question 22

Why is the pH of a strong acid lower than that of a weak acid at the same concentration?

Answer 22

Strong acids completely ionise, producing a higher concentration of hydrogen ions in solution.

Question 23

What is a base?

Answer 23

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

Question 24

What is an alkali?

Answer 24

A soluble base.

Question 25

What is an acid?

Answer 25

A substance with a pH of less than 7 that releases hydrogen ions in water.

Question 26

What are the formulae for hydrochloric acid, nitric acid, and sulfuric acid?

Answer 26

a) HCl b) HNO3 c) H2SO4

Question 27

What type of reaction occurs when an acid reacts with a base?

Answer 27

Neutralisation

Question 28

What is the ionic equation for the neutralisation of an acid and an alkali?

Answer 28

H+ (aq) + OH- (aq) -> H2O (l)

Question 29

Describe how to test for carbon dioxide.

Answer 29

If carbon dioxide is bubbled through limewater, it turns from colourless to cloudy.

Question 30

What can be seen when an acid reacts with a metal or a carbonate?

Answer 30

Bubbles (effervescence)

Question 31

What is produced when hydrochloric acid reacts with ammonia?

Answer 31

Ammonium chloride (NH4Cl)

Question 32

How do you test for hydrogen gas?

Answer 32

A lit splint makes a 'pop' sound.

Question 33

What salts are formed when magnesium oxide reacts with hydrochloric acid, nitric acid, and sulfuric acid?

Answer 33

a) Magnesium chloride b) Magnesium nitrate c) Magnesium sulfate

Question 34

Explain acid-alkali neutralisation in terms of ions.

Answer 34

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

Question 35

Why is excess reactant added when preparing soluble salts from an acid and an insoluble reactant?

Answer 35

It ensures that the acid is completely reacted.

Question 36

Why is the excess reactant removed after the reaction?

Answer 36

To obtain a solution containing only salt and water via filtration.

Question 37

What is the result of the reaction when excess reactant is removed?

Answer 37

The solution remaining is only salt and water.

Question 38

Why must titration be used when preparing soluble salts from an acid and a soluble reactant?

Answer 38

To determine the exact point of neutralisation.

Question 39

What happens to the acid and soluble reactant during the reaction?

Answer 39

They are mixed in the correct proportions to ensure complete reaction.

Question 40

What is the result of the reaction after titration?

Answer 40

The solution remaining is only salt and water.

Question 41

Describe how to make a soluble salt using an acid and an insoluble base.

Answer 41

1. Add excess base to warm acid. 2. Filter the solution. 3. Heat to evaporate water. 4. Leave to cool and crystallise. 5. Dry in a warm oven.

Question 42

Describe how to use titration to make a soluble salt from an acid and an alkali.

Answer 42

1. Measure alkali into a conical flask. 2. Add indicator. 3. Slowly add alkali to acid until end-point is reached. 4. Repeat without indicator. 5. Evaporate water to crystallise.

Question 43

Describe how to make an insoluble salt from soluble reactants.

Answer 43

1. Mix and stir two aqueous solutions. 2. Filter the precipitate. 3. Rinse salt with distilled water. 4. Dry in a warm oven.

Question 44

What is the ionic equation for the reaction Mg(s) + 2HCl(aq)?

Answer 44

Mg (s) + 2H+ (aq) -> Mg2+ (aq) + H2 (g)

Question 45

What are spectator ions?

Answer 45

Ions that do not change during a chemical reaction.

Question 46

Explain why magnesium has been oxidised in terms of electrons.

Answer 46

A magnesium atom lost 2 electrons to form a magnesium ion.

Question 47

Define the term reduction.

Answer 47

Gain of electrons or loss of oxygen.

Question 48

Which chlorine salts are insoluble?

Answer 48

Silver chloride, Lead chloride

Question 49

Which sulfate salts are insoluble?

Answer 49

Lead sulfate, Barium sulfate, Calcium sulfate

Question 50

Which carbonates and hydroxides are soluble?

Answer 50

Sodium carbonate, Potassium carbonate, Ammonium carbonate