The Edexcel core practical: adding calcium hydroxide or calcium oxide to dilute hydrochloric acid a little at a time, measuring the pH, and explaining the shape of the graph.
What you will learn
- Name the variables and write a 6-mark method for the practical
- Read where the acid was neutralised from a table of pH against mass
- Explain why the pH levels off at about 12
- Calculate the mass of base needed to neutralise the acid (Higher)
What happens
Calcium hydroxide and calcium oxide are bases.
Each neutralises hydrochloric acid to make calcium chloride, a salt.
- Ca(OH)₂ + 2HCl → CaCl₂ + 2H₂O
- CaO + 2HCl → CaCl₂ + H₂O
- in both: H⁺ + OH⁻ → H₂O (calcium oxide makes OH⁻ ions when it meets water)
You add the powder a little at a time to a fixed volume of acid and measure the pH after each portion.
- Independent variable: the total mass of base added.
- Dependent variable: the pH.
- Control variables: the volume and concentration of the acid, the size of each portion, the temperature at the start.
The rest of this lesson and its 9 practice questions are locked.
In this lesson
- What happens
- The method
- The shape of the graph
- Try it: The chemistry first
9 practice questions, marked as you go; about 20 minutes in all.
Key terms
Fixed volume
In this unit: Chemical changes: reactivity, acids and electrolysis
The reactivity series and metal extraction, oxidation and reduction, acids, salts and pH, titrations, and electrolysis of melts and solutions.