The pH scale and what it measures, indicators, neutralisation as a reaction of hydrogen and hydroxide ions, and the difference between strong, weak, concentrated and dilute.
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1.What ion do all acids produce in solution?
Hydrogen ions, H+.
2.What ion do all alkalis produce in solution?
Hydroxide ions, OH-.
3.What is the pH range of the scale?
0 to 14.
4.What pH is an acid?
Below 7.
5.What pH is an alkali?
Above 7.
6.What pH is neutral?
Exactly 7.
7.What does the pH scale actually measure?
The concentration of hydrogen ions in the solution.
8.What is the difference between a base and an alkali?
A base neutralises an acid. An alkali is a base that is soluble in water.
9.Name two indicators used to measure pH.
Universal indicator, which gives a range of colours, and litmus, which shows red in acid and blue in alkali.
10.What is the advantage of a pH probe over an indicator?
It gives a precise numerical value rather than a colour that has to be judged by eye.
11.Write the ionic equation for neutralisation.
H+ + OH- gives H2O
12.What is always produced when an acid neutralises an alkali?
A salt and water.
13.What is a strong acid?
An acid that is completely ionised in aqueous solution, so every molecule releases its hydrogen ion.
14.Give three examples of strong acids.
Hydrochloric acid, sulfuric acid and nitric acid.
15.What is a weak acid?
An acid that is only partially ionised in aqueous solution, so only a small proportion of molecules release hydrogen ions.
16.Give three examples of weak acids.
Ethanoic acid, citric acid and carbonic acid.
17.What is the difference between concentrated and dilute?
Concentration is about how much acid is dissolved in a given volume. It says nothing about whether the acid is strong or weak.
18.Can a weak acid be concentrated?
Yes. Strength and concentration are completely separate ideas, so a weak acid can be concentrated and a strong acid can be dilute.
19.What happens to pH as hydrogen ion concentration increases by a factor of 10?
The pH decreases by 1.
20.A solution changes from pH 5 to pH 3. What happened to the hydrogen ion concentration?
It increased by a factor of 100, because the pH fell by 2.
21.Which has the lower pH, a strong acid or a weak acid at the same concentration?
The strong acid, because it produces far more hydrogen ions.
22.How could you compare the strength of two acids of equal concentration?
Measure the pH of each. The stronger acid has the lower pH. You could also compare their rates of reaction with a metal.
23.Why does a weak acid react more slowly with magnesium?
It has a lower concentration of hydrogen ions, so there are fewer collisions with the metal.
24.Name a common alkali.
Sodium hydroxide, potassium hydroxide or calcium hydroxide.
25.What colour is universal indicator in a strong acid and in a strong alkali?
Red in a strong acid, and purple in a strong alkali.
26.Why is neutralisation described as a reaction between ions?
The hydrogen ions from the acid and the hydroxide ions from the alkali combine to form water, which is what removes the acidity.
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