Topic 4

Question 1

m When is the pH solution more acidic?

Answer 1

the lower the pH

Question 2

When is the pH solution more alkaline?

Answer 2

the higher the pH solution

Question 3

At what pH is the substance neutral?

Answer 3

pH 7

Question 4

What is an indicator?

Answer 4

An indicator is a dye that changes colour depending on whether it’s above or below a certain pH

Question 5

What are wide range indicators and what are they useful for?

Answer 5

Indicators that contain a mixture of dyes that means they gradually change colour over a broad range of pH. They’re useful for estimating the pH of a solution

Question 6

What can a pH probe attached to a pH meter be used for?

Answer 6

A pH probe attached to a pH meter can be used to measure pH electronically. The probe is placed in the solution you are measuring and the pH is given on a digital display as a numerical value, meaning it’s more accurate than an indicator.

Question 7

What is an acid?

Answer 7

An acid is a substance that forms aqueous solutions with a pH of less than 7

Question 8

What do acids form in water?

Answer 8

H+ ions

Question 9

What is a base?

Answer 9

A substance with pH greater greater than 7

Question 10

What is an alkali?

Answer 10

A base that dissolves in water to form a solution with a pH greater than 7.

Question 11

What do alkalis form in water?

Answer 11

OH- ions in water

Question 12

What is the neutralisation reaction?

Answer 12

acid + base —-> salt + water

Question 13

What is the neutralisation reaction in terms of H+ and OH- ions?

Answer 13

H+ + OH- —-> H2O

Question 14

What happens when an acid neutralises a base (or vice versa)?

Answer 14

the products are neutral

Question 15

What can neutralisation reactions of strong acids and alkalis be used to calculate?

Answer 15

The concentration of an acid or alkali by titrations

Question 16

Why do you need to use a single indicator in a titration?

Answer 16

To see a sudden colour change at the end-point.

Question 17

What do acids produce in water?

Answer 17

ionise to produce protons and hydrogen ions

Question 18

What happens to strong acids in water?

Answer 18

ionise completely in water

Question 19

What happens to weak acids in water?

Answer 19

do not fully ionise in solutions

Question 20

What is the difference between ionisation of weak and strong acids?

Answer 20

ionisation of weak acids is a reversible reaction, which sets up an equilibrium between the undissociated and dissociated acid

Question 21

What if the concentration of H+ ions is higher then the rate of reaction?

Answer 21

the rate of reaction will be faster, so strong acids will be more reactive than weak acids of the same concentration.

Question 22

What is the pH of an acid or alkali a measure of?

Answer 22

The pH of an acid or alkali is a measure of the concentration of H+ ions in the solution

Question 23

What happens to the concentration of hydrogen ions as you decrease the pH scale by one?

Answer 23

The concentration of hydrogen ions increases by a factor of x10 so an acid that has a pH of 4 has 10 times the concentration of hydrogen ions of an acid with pH 5.

Question 24

What does the concentration of an acid tell you?

Answer 24

tells you what proportion of the acid molecules ionise in water.

Question 25

What does the concentration of an acid measure?

Answer 25

Concentration measures how much acid there is in a certain volume of water ( so how watered down your acid is ).

Question 26

How does the amount of acid in a certain volume of liquid affect the concentration?

Answer 26

The larger the amount of acid in a certain volume of liquid, the more concentrated the acid. So you can have a dilute but strong acid, or a concentrated but weak acid. The pH will decrease with increasing acid concentration regardless of whether it's a strong or weak acid.

Question 27

What are metal oxides and metal hydroxides examples of?

Answer 27

Bases

Question 28

When metal oxides or metal hydroxides react with acids what do they form?

Answer 28

a salt and water

Question 29

When acids and metal carbonates react what do they form?

Answer 29

a salt, water and carbon dioxide

Question 30

Are metal carbonates a base?

Answer 30

yes

Question 31

List the reactivity series from most to least reactive.

Answer 31

Potassium -K Sodium -Na Lithium -Li Calcium -Ca Magnesium -Mg Carbon -C Zinc -Zn Iron -Fe Hydrogen -H Copper -Cu

Question 32

For metals what does their reactivity determine?

Answer 32

How easily they lose electrons to form positive ions. The higher up the reactivity series a metal is, the more easily they form positive ions.

Question 33

What happens when metals react with water or acid?

Answer 33

They loose electrons and form positive ions. So the higher a metal is in the reactivity series, the more easily it reacts with water or acid.

Question 34

When acids and metals react what do they form?

Answer 34

salt and hydrogen gas

Question 35

What is the speed of reaction indicated by?

Answer 35

The rate at which the bubbles of hydrogen are given off

Question 36

How do you investigate the reactivity of metals?

Answer 36

By measuring the temperature change of the reaction with an acid or water over a set time period. If you use the same mass and surface area of metal each time, then the more reactive the metal, the greater the temperature change should be.

Question 37

When metals and water react what do they form?

Answer 37

metal hydroxide and hydrogen less reactive metals like zinc, iron and copper won't react with water but the metals potassium, sodium, lithium and calcium will react with water.

Question 38

What is oxidation of metals?

Answer 38

the gain of electrons

Question 39

What is reduction of metals?

Answer 39

the loss of electrons.