2.f - Acids, Alkalis and Titrations

Question 1

what does the pH scale tell you

Answer 1

how acidic or alkaline a solution is

Question 2

what does the pH scale range from

Answer 2

0-14

0 = strongest acid
14 = strongest alkali

Question 3

what does a pH of 0-3 mean

Answer 3

strongly acidic

Question 4

what is the pH of something weakly acidic

Answer 4

4-6

Question 5

what does neutral substance (eg.water ) have a pH of

Answer 5

7

Question 6

what does a pH of 8-10 mean

Answer 6

weakly alkaline

Question 7

what is the pH of something strongly alkaline

Answer 7

11-14

Question 8

what colours does pH range from ( in terms of universal indicator

Answer 8

Red to Purple (colours of rainbow )

red= strongest acid
green = neutral 
purple = strongly alkaline

Question 9

what colours for blue litmus paper in acid and alkali

Answer 9

blue litmus = acidic = red
blue litmus = alkali = blue
blue litmus = neutral = blue

Question 10

what are the colours for red litmus paper

Answer 10

red litmus = alkali = blue
red litmus = acidic = red
red litmus = neutral = red

Question 11

what are the colours for neutral litmus paper

Answer 11

acidic = red
alkali = blue 
neutral = purple

Question 12

what colours for phenolphthalein in acid and alkali

Answer 12

acidic = colourless 
alkali = bright pink

Question 13

what colours for methyl orange in acid and alkali

Answer 13

acidic = red
alkali = yellow

Question 14

what are acids in aqueous solution a source of

Answer 14

hydrogen ions = H+ ions

Question 15

what are alkalis in aqueous solution a source of

Answer 15

hydroxide ions = OH- ions

Question 16

what is the name of reaction between acid + alkali

Answer 16

neutralisation reaction ( acid- base reaction )

Question 17

what do titrations do

Answer 17

allow you to find out exactly how much acid is need to neutralise an alkali ( or vice versa )

Question 18

PAPER 2

describe how to carry out an acid- alkali titration

Answer 18

1. using pipette add (25cm3) alkali ( sodium hydroxide ) to a conical flask
2. add 2 to 3 drops of indicator eg phenolphthalein / methyl orange
3. fill a burette with acid
4. using burette add acid to alkali a bit at a time - giving conical flask regular swirl ( go really slow when think near colour change )
5. indicator changes colour when all alkali has be neutralised ( in this case pink -> colourless )
6. record volume of acid used to neutralise the alkali
7. repeat + take average