Topic 3 Acids and Alkalis

Question 1

Name some natural sources of indicators

Answer 1

red cabbage,
red rose petals,
beetroot,
red onion skin

Question 2

What happens to red and blue litmus paper when placed in acid?

Answer 2

red paper remains red, blue litmus turns red

Question 3

What happens to red and blue litmus paper when placed in alkali?

Answer 3

blue litmus remains blue, red litmus turns blue

Question 4

What happens to red and blue litmus paper when placed in a neutral solution?

Answer 4

remain unchanged

Question 5

Why is universal indicator better than litmus?

Answer 5

Litmus only tells if something is acid, alkali or neutral. Universal indicator indicates the strength of an acid or alkali.

Question 6

What is pH and what should you remember?

Answer 6

pH is a measure of how acidic or alkaline a substance is. Remember it is small p capital H.

Question 7

What pH do acids have?

Answer 7

Less than 7

Question 8

What pH do neutral substance have?

Answer 8

7

Question 9

What pH do alkalis have?

Answer 9

More than 7

Question 10

What pH do strong acids have?

Answer 10

1-2 (low)

Question 11

What pH do weak acids have?

Answer 11

3-6

Question 12

What pH do neutral substances have?

Answer 12

7

Question 13

What pH do weak alkalis have?

Answer 13

8-11

Question 14

What pH do strong alkalis have?

Answer 14

12-14 (high)

Question 15

What colour do strong acids turn universal indicator?

Answer 15

red

Question 16

What colour do strong alkalis turn universal indicator?

Answer 16

purple

Question 17

What colour do weak acids turn universal indicator?

Answer 17

orange at pH 3 to yellow at pH 6

Question 18

What colour do weak alkalis turn universal indicator?

Answer 18

turquoise at pH 8 to blue at pH 11

Question 19

What colour do neutral substances turn universal indicator?

Answer 19

green

Question 20

Name some strong acids

Answer 20

stomach acid which is hydrochloric acid

Question 21

Name some weak acids

Answer 21

lemon juice, vinegar, acid rain

Question 22

Name a neutral substance

Answer 22

water

Question 23

Name some weak alkalis

Answer 23

ammonia, toothpaste

Question 24

Name some strong alkalis

Answer 24

oven cleaner, sodium hydroxide

Question 25

What does too much stomach acid cause?

Answer 25

indigestion

Question 26

How would you make a concentrated acid/alkali less hazardous

Answer 26

add it to water

Question 27

Strong acids and alkalis can be…

Answer 27

corrosive

Question 28

Alkalis feel…

Answer 28

soapy

Question 29

Weak acids, like vinegar and lemon juice, taste…

Answer 29

sour

Question 30

Acids are neutralised by…

Answer 30

alkalis

Question 31

Alkalis are neutralised by…

Answer 31

acids

Question 32

What is the name given to the reaction of an acid with an alkali and what is produced?

Answer 32

Neutralisation, neutral water is produced

Question 33

Give some examples of neutralisation reactions

Answer 33

Treating (i) indigestion with an antacid, (ii) acid produced by mouth bacteria from sugary foods with tooth paste (alkali), (iii) nettle stings (acid) with juice of a dock leave (alkali), (iv) treating bee stings (acid) with baking soda (alkali), (v) treating wasp stings (alkali) with vinegar/lemon juice (acid)

Question 34

What is universal indicator made from?

Answer 34

A mixture of dyes

Question 35

What is an indicator?

Answer 35

A dye that changes colour depending on whether it is in an acid or alkali.

Question 36

Describe how you would make an indicator solution from red cabbage.

Answer 36

Half fill a beaker of water and add some red cabbage.
Place the mixture on a tripod and gauze and heat using a Bunsen burner.
Boil for about 5 min then allow to cool.
Filter the cooled mixture, collecting the liquid in a conical flask.
The liquid can be used a an indicator.