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Class 10 Acids, Bases and Salts: cheat sheet
CBSE Science. Acids, bases and salts: how indicators and the pH scale tell them apart, how they react, and the salts used every day.
Key ideas
- Acids give H⁺ ions in water; bases that dissolve in water (alkalis) give OH⁻ ions.
- Litmus: acids turn blue litmus red, bases turn red litmus blue. Phenolphthalein is pink in a base and colourless in an acid.
- pH runs from 0 to 14: below 7 is acidic, 7 is neutral, above 7 is basic. The lower the pH, the stronger the acid.
- Acid + base → salt + water (neutralisation).
- Acid + metal → salt + hydrogen gas. Acid + metal carbonate → salt + carbon dioxide + water.
- When diluting, add the acid slowly to water, never water to acid: the mixing gives out a lot of heat.
- Some salts hold water of crystallisation: blue copper sulphate crystals turn white when heated as the water leaves.
Remember
| Neutralisation | NaOH + HCl → NaCl + H₂O |
| Common salt | NaCl |
| Baking soda | NaHCO₃ |
| Washing soda | Na₂CO₃·10H₂O |
| Bleaching powder | CaOCl₂ |
| Plaster of Paris | CaSO₄·½H₂O |
Watch out
- Thinking pH 2 is weaker than pH 5 (a lower pH is more acidic).
- Adding water to concentrated acid.
- Expecting phenolphthalein to turn pink in an acid (it stays colourless).
Worked example
Zinc carbonate reacts with dilute nitric acid. Name the gas given off and write the balanced equation.
Working: carbonate + acid → salt + water + carbon dioxide
Answer: Carbon dioxide; ZnCO₃ + 2HNO₃ → Zn(NO₃)₂ + H₂O + CO₂
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