chemistry salts etc

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  • Created by: natalie
  • Created on: 12-05-13 15:50

Oxides, Hydroxide, Neautralisation and Ammonia

Metal oxides and metal hydroxides are bases.

1) some metal oxides and metal hydroxides dissolve in water. These soluble compounds are alkalis.

2) even bases that won't dissolve in water still react with acids.

3) all metal oxides and metal hydroxides react with acids to form salt and water.

acid + metal oxide/hyrdoxide = salt + water

hydroxide ions make solutions alkaline. Hydrogen ions make solutions acidic, if dissolved in water.

Neutralisation: H+(aq) + OH-(aq) + H2O(l)

Ammonia can be neutralised with HNO3 to make fertiliser. Ammonia dissolves in water to make an alkaline solution. When it reacts with nitric acid, you get a neutral salt - ammonium nitrate. No water is produced. Ammonium nitrate is a good fertiliser because it has nitrogen from two sources - it has a double dose, and plants need nitrogen to make proteins. 

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Making soluble salts using a metal or insoluble ba

Most chloride, sulfates and nitrates are soluble in water (except lead chloride, lead sulfate and silver chloride). Most oxides and hydroxides are insoluble in water.

1) You need to pick the right acid and metal/insoluble base (a metal oxide or metal hydroxide). E.g. if you want to make copper chloride, mix hydrochloric acid and copper oxide.

2) You add the metal, metal oxide/hydroxide to the acid - the solid will dissolve in the acid as it reacts. You will know when all the acid has been neutralised because the excess solid will sink to the bottom of the flask.

3) Then filter out the excess metal, metal oxide/hydroxide to get the salt solution. To get pure, solid crystals of the salt, leave to evaporate - crystallisation

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Making soluble salts using an alkali

1)There is a different method for making soluble salts with alkalis (soluble bases) like sodium, potassium or ammonium hydroxides, because you can't tell if the reaction has finished in the other method.

2)You have to add the exact amount of alkali to just neutralise the acid - you need to use a ph indicator to show when the reaction is finished. Then repeat using the exact same amount volumes of alkali and acid so that the salt isn't contaminated with indicator.

3)Then evaporate off the water to crystallise the salt as normal.

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Making insoluble salts - precipitation reactions

1) If the salt you want to make is insoluble, you can use a precipitation reaction.

2) You just need to pick two solutions that contains the ions you need. E.g. to make lead chloride you need a solution which contains lead ions and one which contains chloride ions. So you can mix lead nitrate solution with sodium chloride solution ( all group 1 compounds are soluble).

3) Once the salt has precipitated out and is lying at the bottom of the flask, you filter it from the solution, wash it then dry it on the filter paper.

4) Precipitation reactions can be used to remove poisonus ions (e.g. lead) from drinking water. Calcium and magnesium ions can also be removed from water this way - they make water hard. 

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