Topic 4 - chemical changes (topics from Jan assessments)

Question 1

What is the range of the PH scale?

Answer 1

0-14

Question 2

What is the ph scale a measure of?

Answer 2

How acidity or alkalinity

Question 3

The lower the ph of a solution …

Answer 3

the more acidic it is

Question 4

The higher the ph of a solution…

Answer 4

the more alkaline it is

Question 5

A substance of ph7 is …

Answer 5

neutral

Question 6

What is the ph of a neutral substance?

Answer 6

7

Question 7

What two things can be used to measure ph?

Answer 7

• universal indicator
• ph probe

Question 8

What is the ph of aqueous solutions of acids?

Answer 8

ph values less than 7

Question 9

What is the ph of aqueous solutions of alkalis?

Answer 9

• ph values greater than 7

Question 10

What happens in a neutralisation reaction between an acid and an alkali?

Answer 10

hydrogen ions react with hydroxide ions to produce water

Question 11

What ion is contained in aqueous solutions of alkalis?

Answer 11

hydroxide ions

Question 12

What do acids produce in aqueous solutions?

Answer 12

hydrogen ions

Question 13

What is an indicator?

Answer 13

a dye that changes colour depending on whether it is above or below a certain ph?

Question 14

Why do some indicators contain a mixture of dyes?

Answer 14

So they gradually change colour over a broad range of ph

Question 15

What is the name for indicators that contain a mixture of dyes?
What are these useful for?

Answer 15

a wide range indicator
they are useful for estimating the ph of a solution

Question 16

Give an example of a wide range indicator?

Answer 16

universal indicator

Question 17

How is a ph probe used?
How is it more useful than an indicator?

Answer 17

• A ph probe attached to a ph meter can be used to measure ph electronically
• the probe is placed into the solution you are measuring and the ph is given as a numerical value on a digital display - meaning it is more useful than an indicator

Question 18

Acids and bases ………….. each other?

Answer 18

neutralise

Question 19

What neutalises an acid?

Answer 19

A base

Question 20

What neutralises a base?

Answer 20

an acid

Question 21

What is an acid? -2

Answer 21

an acid is a substance that forms aqueous solutions of a pH less than 7
Acids form H+ (hydrogen) ions in water
- they are also proton donors

Question 22

What is a base?

Answer 22

a base is a subsance with a pH greater than 7

Question 23

What is an alkali?-2`

Answer 23

a soluble base that dissolves in waterto form a soution of a pH hreater than 7
for OH- (hydroxide) ions in water

Question 24

What is the ph of the products of a neutralisation reaction?

Answer 24

when an acid and base neutralise each other, the producst are neutral (pH 7)
- an indicator can be used to show a neutralisation rection is over

Question 25

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

Answer 25

the concentration of an acid or alkali by titration

Question 26

Some metal oxides and metal hydroxides react with water? What are these soluble compounds called?

Answer 26

alkalis (also bases)

Question 27

Will bases that don't dissolve in water (insoluble) still take part in neutralisaton reactions with acids?

Answer 27

they will

Question 27

When reacting a metal oxide/hydroxide, what two things determine the salt that is produced?

Answer 27

- the acid - the metal ion in the oxide or hydroxide

Question 28

What do you get when you react an acid with a metal oxide?

Answer 28

a salt + water

Question 29

What do you get when you react an acid with a metal hydroxide?

Answer 29

a salt + water

Question 30

What do you get when you react an acid with a metal carbonate?

Answer 30

a salt +water + carbon dioxide

Question 31

What are metal carbonates? What do they produce when they react wth an acid?

Answer 31

bases a salt + water + carbon dioxide

Question 32

What are metal oxides and metal hydroxides that dissolve in water? What are metal carbonates?

Answer 32

- alkalis (also bases) - bases

Question 33

How can soluble salts be made from acids?

Answer 33

By reacting then with solid insoluble substances (such as metals, metal oxides, hydroxides or carbonates)

Question 34

How can you produce solid salts from salt solutions?

Answer 34

they can be crystallised

Question 35

What do acids do in aqueous solutions?

Answer 35

- they ionise in aqueous solutions (they produce hydrogen ions H+) - they produce protons in water (a hydrogen ion is just a proton)

Question 36

What is a hydrogen ion, H+?

Answer 36

a proton

Question 37

Why is hydrochloric acidic but hydrogen chloride gas isn't?

Answer 37

acids don't produce hydrogen ions until they meet water

Question 38

Give 3 examples of strong acids?

Answer 38

- sulfuric acid - hydrochloric acid - nitric acid

Question 39

What are strong acids?

Answer 39

acids that ionise completely in water (all acid particles dissociate to release H+ ions)

Question 40

What happens to strong acids in water?

Answer 40

- they ionise completely - all acid particles dissociate to release H+ ions

Question 41

What are 3 examples of weak acids?

Answer 41

- ethanoic acid - citric acid - carbonic acid

Question 42

What are weak acids?

Answer 42

- acids that do not fully ionise in solution - only a small proportion of acid particles dissociate to release H+ ions

Question 43

What happens to weak acids in solution (water)?

Answer 43

- it does not fully ionise - only a small proportion of acid particles dissociate to release H+ ions

Question 44

What do reactions of acids involve/ what will always happen?

Answer 44

the H+ (hydrogen ions) react with other substances

Question 45

What do stronger acids have a higher concentration of?

Answer 45

H+, hydrogen ions

Question 46

Explain why a strong acids will be more reactive than a weak acid of the same concentration?

Answer 46

- the concentration of H+ ions is higher - the rate of reaction will be faster (reactions of acids involve the H+ ions reacting with other substances)

Question 47

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

Answer 47

the concentration of H+ ions in the solution

Question 48

What happens to the concentration of H+ ions in a solution for every decrease of 1 on the ph scale?

Answer 48

concentration of H+ ions increases by a factor of 10

Question 49

How does the concentration of H+ ions compare for an acis of pH4 and an acid of pH5?

Answer 49

the acid of pH4 has 10 times the H+ ions than an acid of pH5

Question 50

For a decrease of 2 on the ph scale, what does the concentration of H+ ions increase by?

Answer 50

a factor of 100

Question 51

When at the same concentration, how will the pH of a strong acid compare to that of a weak acid?

Answer 51

- the pH of a strong acid is always less than that of a weaker acid if they have the same concentration

Question 52

What does acid strength tell you?

Answer 52

(i.e. strong or weak) tells you what proportion of the acid molecules ionise in water

Question 53

REMEMBER: The concentration of an acid is NOT the same as its strength

Question 54

What is the concentration of an acid?

Answer 54

concentration measures how much acid there is for a certain volume of water (basically how watered down your acid is) Remember: concentration describes the total number of dissolved acid molecules- not the number of molecules that are ionised to produce hydrogen ions at any given moment

Question 55

Increasing the amount of acid in a certain volume of liquid will...

Answer 55

increase the concentration of the acid

Question 56

REMEMBER: - you can have a dilute but strong acid - or a concentrated but weak acid

Answer 56

;)

Question 57

How does pH of an acid change with increasing acid concentration?

Answer 57

pH will decrease with increasing acid concentration regardless of whether it's a strong or weak acid