Ch.10.acids and alkalis (3rd week)
Transcript of Ch.10.acids and alkalis (3rd week)
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Acids and AlkalisChapter 10Chemistry
3rd week
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Neutralisation
- When an acid reacts with an alkali
Neutralisation process occurs
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- Neutralisation reaction equation:
Acid + alkali salt + water
Some examples of neutralisation processes:
Hydrochloric acid
Sodium Hydroxide WaterSodium
Chloride+ +
Sulphuric acid + Potassium
HydroxidePotassium sulphate + Water
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Nitric acid Sodium Hydroxide WaterSodium
Nitrate+ +
- Sodium hydrogen carbonate (sodium bicarbonate) is a white solid.
- It is not an alkali, but, when dissolved in water it produces an alkaline solution.
Sodium hydrogen carbonate
Hydrochloric acid Water
Sodium Chlorid
e+ ++ Carbon
dioxide
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Using Neutralisation reactions
- Insect stings- Bee sting (acidic)
- Wasp sting (alkaline)
Neutralised by Soap (alkali)Neutralised by Vinegar (weak
acid)
Bee Wasp
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- Curing indigestion- Indigestion is caused by the stomach making too
much acid to digest food.
- Indigestion tablets contain sodium bicarbonate which dissolves to form an alkaline solution.
- This alkaline solution neutralises the stomach acid and cures indigestion.
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- Baking a cake- Baking powder contains a mixture of an acid and
sodium bicarbonate.
- When baking powder is mixed with water and flour to make a cake
- The CO₂ forms bubbles in the mixture making it rise and giving it the light texture.
Sodium bicarbonate solution
acid Water+ +Carbon dioxide
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- A model volcano- You used to make a model volcano using
vinegar and baking soda.
- This is actually a neutralisation reaction.
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- Fighting a fire- The soda-acid fire extinguisher contains a
bottle of sulphuric acid and a solution of sodium bicarbonate.
- When the plunger is struck or the extinguisher turned upside down, the acid and alkali react forming CO₂.
- The pressure of the CO₂ produced pushes the water out of the extinguisher.
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- Improving crop growth
- Acidity in the soil affects crops and make the produce less food.
- Lime (calcium hydroxide) is used to neutralise acidity in soil.
Fields appearing white after application of lime
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Acid rain
- Natural acid rain- CO₂ in the air dissolves in the water in
clouds forming Carbonic acid (weak acid)
- When this weak acid falls on limestone a reaction occurs and some of the limestone is washed away.
Cracks called grikes appear
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- In most of the places where most of the limestone surface is dissolved away, pinnacles of rock appear.
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- The acid rain sinks into the rock and forms underground streams.
- The water passing in the underground streams dissolves more rock and forming caves.
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- As the caves grow bigger the walls become weaker and collapse forming a gorge.
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Air pollution and acid rain- Fuels such as coals and oil contain
sulphur.
- When the fuel is burnt it reacts with the oxygen in the air to form sulphur dioxide.
- The sulphur dioxide reacts with the oxygen and water in the air to form sulphuric acid.
- Factories and cars also produce nitrogen oxides which produces nitric acid.
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The effect of acid rain
- When acid rain reaches the ground it dissolves some of the minerals in the soil and carries them away. This is called leaching.
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- Some of these minerals are needed for healthy growth of the plants