1. Which solution has greater hydrogen-ion concentration: pH 2 or pH 5?
- pH 5
- They are equal
- pH 2
Check the answer and reasoning
pH 2
Lower pH indicates greater aqueous hydrogen-ion concentration.
CHEM / IGCSE
Acids, bases, salts and chemical analysis
Acids produce hydrogen ions in aqueous solution; alkalis provide hydroxide ions. Neutralisation forms water and a salt, while carbonate reactions also release carbon dioxide.
Learning objectives
- Explain acids, bases, salts and chemical analysis using a concrete example.
- Apply the worked method and justify each step.
- Recognise the limitation described in the final check.
The big idea
Acids produce hydrogen ions in aqueous solution; alkalis provide hydroxide ions. Neutralisation forms water and a salt, while carbonate reactions also release carbon dioxide.
Choose crystallisation, precipitation or titration to prepare a salt according to its solubility. Chromatography and characteristic gas, flame and ion tests provide evidence; observations must be combined rather than overinterpreted.
Equations and relationships
Net ionic neutralisation.
Worked example
Which gas forms when an acid reacts with a carbonate?
Follow the solution
Hydrogen ions react with carbonate to form water and CO₂; the remaining ions form a salt.
Investigate and explain
Predict the worked result before calculating. Change one input, record the new result, and explain which assumptions still hold.
Related interactive model. Compare its assumptions with the explanation; it is not a complete syllabus lesson.
Check your understanding
2. Which gas forms when an acid reacts with a carbonate?
- Carbon dioxide
- Hydrogen
- Oxygen
Check the answer and reasoning
Carbon dioxide
Hydrogen ions react with carbonate to form water and CO₂; the remaining ions form a salt.
3. Which method separates coloured soluble mixture components?
- Filtration alone
- Chromatography
- A magnet
Check the answer and reasoning
Chromatography
Components move differently between stationary and mobile phases.