Mastery Questions - Acids

Question 1

Identify substances as acidic or alkaline using the pH scale

Answer 1

Substances with a pH below 7 are acidic

Substances with a pH above 7 are alkaline

Question 2

Recall different indicators and their colour changes

Answer 2

Litmus = Acidic: Red | Alkaline: Blue
Methyl Orange = Acidic: Red | Alkaline: Yellow
Phenolphthalein = Acidic: Colourless | Alkaline: Pink

Question 3

Explain what pH is a measure of

Answer 3

pH scale measures acidity 
(H+ ion concentration)
- Each pH level below 7 shows a 
x10 increase in H+ ion 
concentration
- Each pH level above 7 shows a 
x10 increase in OH- ion 
concentration

Question 4

Explain what a strong acid is

Answer 4

Strong acids completely dissociate into their ions in water

Question 5

Describe alkalis in terms of ions

Answer 5

Acids produce an excess of hydrogen ions (H+) in water

Alkalis produce an excess of hydroxide ions (OH-) in water

Question 6

Explain neutralisation in terms of ions

Answer 6

A neutralisation reaction is a reaction between an acid and a base.
Acids produce hydrogen ions, H+
Alkalis produce hydroxide ions, OH-
Hydrogen ions react with hydroxide ions to form water:
H+(aq) + OH-(aq) → H2O(l)

Question 7

State the products of the following reactions with acids:

Answer 7

Acid + Metal → salt + hydrogen
Acid + Metal Oxide → salt + water
Acid + Metal Hydroxide → salt + water
Acid + Metal Carbonate → salt + water + carbon dioxide

Question 8

Describe the test for hydrogen gas

Answer 8

Lit splints

Squeaky pop sound

Question 9

Describe the test for carbon dioxide

Answer 9

Bubble through lime water

Lime water turns cloudy

Question 10

Describe how to measure the change in pH by calcium oxide (or hydroxide) to hydrochloric acid

Answer 10

Find pH of acid by dipping glass rod into solution then touching to indicator paper (or use pH probe)
Add 0.3g calcium oxide and stir
Touch glass rod to indicator paper
Repeat until there is no further 
change in pH

Question 11

Describe how to identify soluble substances (F)

Answer 11

SPAN - sodium, potassium, ammonium or nitrate - soluble
Chlorides – soluble (except silver chloride and lead chloride)
Sulfates – soluble (except lead, barium and calcium)
Carbonates and Hydroxides – insoluble (except sodium, potassium, ammonium)

Question 12

Describe how you use titration to determine the volume of acid needed to neutralise a know volume of an alkali (F)

Answer 12

Measure out 25cm3 of alkali into a conical flask using a pipette.
Add a few drops of indicator.
Fill a burette with acid.
Slowly add acid using a burette, swirling the flask as you go
until you reach the end point (indicator just changes colour)
Record volume of acid used