Chemistry Ionic equations, precipitation, strong and weak acids

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  • Created by: Lydia1
  • Created on: 05-11-12 17:35

Strong and weak acids

  • An acid ionises in water to produce H+ ions
  • Strong acids fully ionise in water- e.g Hydrochloric Acid (HCL)

strong acid---->hydrogen ions +other ions

  • Strong acids have lots of H+ ions so they do seem very acidic.This means lots of collisions occur and the reaction is quick.
  • Weak Acids only partially ionise and form an equilibrium mixture-e.g Ethanoic acid (CH3COOH)

weak acid reversible reaction hydrogen ions + other ions

  • Weak acids do not have as many H+ ions so it doesn't seem to be as acidic. The smaller amount of H+ ions also means that there will be fewer collisions so the reaction is slower.
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Strong and weak acids

  • Acid Strength- a measure of the degree of ionisation of the acid
  • Acid concentration- the number of moles in an acid
  • High concentration of H+ions- Strong acid- Low pH number
  • Low concentration of H+ ions- Weak acid- High pH number

Strong acids ionise completely in water:  HCl---->H+ +Cl

In Weak acids not all of the molecule ions so the concentration of H+ ions is low:               CH3COOH reversible reaction H+ +CH3COO[-

Ethanoic acid reacts slower than hydrochloric acid:                                                  -fewer hydrogen ions                                                                                                  -fewer collisiosions between hydrogen ions and reactant particles

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Ionic Equations and Precipitation

  • A precipitation reaction is when two solutions react to form an insoluble precipitate/solid is forms. There is a high collision frquency between the ions of both solutions which is why the reaction is extremely quick.
  • Ionic Lattices are formed by Ionis substances.

- In a solid material, the lattices hold the ions in a fixed position so they can not move.       -In water the ionic substances and lattices break away so the ions can move.                    -In precipitation reactions, the reactant ions can move in solution but must collide to react.

To get a dry sample of insoluble compound by precipitation you must:

  • Mix solutions of reactants
  • Filter
  • Wash- with distilled water 
  • Dry

Spectator ions-are ions that do not directly take part in a reaction

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Ionic Equations and Precipitation

Testing for Halide Ions:

1) Add some dilute nitric acid to the test sample.

2) Then add 10 drops of silver nitrate solution.

3) If halide ions are present a precipitate will form:

  • Chloride ions will form white precipitate
  • Bromide ions will produce a cream precipitate 
  • Iodide ions will produce a pale yellow precipitate.


Example of simple preipitation reaction:                                                            barium chloride+sodium sulphate-->barium sulphate + sodium chloride

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