Properties of acids and bases, proton transfer
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The teaching part (2 min) is free to watch. A free account opens the whole lecture: 1 worked example, 4 practice questions, 2 real past-paper questions with the answers explained, the mistakes that lose marks, the full-marks tip, a one-card summary and a quick quiz.
What this lecture covers
- Lemon juice and soap
- Acids
- Bases and alkalis
- Acid + metal
- Acid + base
- Acid + carbonate
Read the transcript of the teaching part
Last time
Before we start: last time, in Making soluble and insoluble salts, hydrated salts, you learned these points. Here they are again on one card. Keep them in mind, because today builds on them.
Lemon juice and soap
Lemon juice tastes sour. Soap feels slippery. One is an acid and the other is an alkali, and they have opposite properties. In this lesson you will learn what acids and bases do, and then find the one idea behind all of it: a proton moves.
Acids
An acid is a substance that forms hydrogen ions, H plus, in water. Examples are hydrochloric, sulfuric and nitric acid. Acids turn blue litmus red and have a pH below 7. They are corrosive when concentrated, so wear eye protection.
Bases and alkalis
A base is a substance that reacts with an acid and neutralises it. Metal oxides and metal hydroxides are bases. An alkali is a base that dissolves in water. Sodium hydroxide is an alkali. Copper oxide is a base but not an alkali. Alkalis turn red litmus blue and have a pH above 7.
Acid + metal
An acid reacts with a reactive metal to make a salt and hydrogen. For example: magnesium plus two HCl gives magnesium chloride plus hydrogen. The test for hydrogen is a squeaky pop with a lighted splint.
Acid + base
An acid reacts with a base to make a salt and water. This is neutralisation. Copper oxide plus sulfuric acid gives copper sulfate plus water. With an alkali: sodium hydroxide plus hydrochloric acid gives sodium chloride plus water.
Acid + carbonate
An acid reacts with a carbonate to make a salt, water and carbon dioxide. Calcium carbonate plus two HCl gives calcium chloride, water and carbon dioxide. It fizzes. The gas turns limewater milky.
How often it comes up
How often Cambridge has asked each part, counted by ExamYard from every past paper in its question bank: Properties of acids and bases.
The whole chapter: Acids, Bases and Salts, Acids, Bases and Salts.
Chapter 7: Acids, bases and salts
- Properties of acids and bases, proton transfer 5 min
- The pH scale, indicators, strong and weak acids 6 min
- Neutralisation and oxides 6 min
- Making soluble and insoluble salts, hydrated salts 6 min
Also for IGCSE Chemistry 0620
Which topics come up most in IGCSE Chemistry 0620 past papers, counted from every paper since 2004.