Chemistry GCSE Unit 3

Acids and Alkalis

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Strong acids

Completely ionise in water 100HCl molecules in water would ionise 100% to make H+ and Cl- ions Water has to be present

  • Hydrochloric acid 
  • Nitric acid
  • Sulphuric acid
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Weak acids

Partially ionise in water

Generally acids we eat

Formulas often end in COOH

Water has to be present

  • Ethanoic acid
  • Citric acid
  • Carbonic acid
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Bronsted lowry theory

A Bronsted Lowry acid is a proton donor

A Bronsted Lowry base is a proton acceptor

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Common acids

Water must be present for them to act as acids e.g dissolved

When added to water, the hydrogen ion dissociates from the rest of the acid and is hydrated by the water

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Common alkalis

Produce OH- ions in water

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Strong alkalis

Completely ionise in water

PH 11-14

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Weak alkalis

Partially ionise in water

E.g. ammonia

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Arrhenies' theory

An acid was a source of H+

An alkali was a source of OH-

This doesn't fit with ammonia

Theory replaced by Bronsted Lowry theory

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Measures the volume of acid and alkali needed to neutralise each other 

Indicator is added to the solution to observe when the reaction has occured


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Any strong acid with any strong alkali

Any weak acid and strong alkali

Colour in acid - colourless

Colour in alkali - pink

Methyl orange

Any strong acid and any strong alkali

Colour in acid - red

Colour in alkali - yellow

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Titration calculations

moles = vol (cm3) x conc


conc = moles /  vol


mass = moles x Mr

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Rosie McNally


really helpful thankyou!

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