Note by juliasutton, updated more than 1 year ago
Created by juliasutton over 6 years ago


GCSE Chemistry (C2b) Note on Salts, created by juliasutton on 04/15/2014.

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The more reactive the metal the faster the reaction Copper doesn't react with dilute acids because it's less reactive than hydrogen The speed of the reaction is indicated by the speed at which bubbles are given off The hydrogen is confirmed by the burning splint test and the 'pop' The name of the salt depends on the metal used

Hydrochloric acid will produce chloride salts Sulphuric acid will produce sulphate salts Nitric acid will produce Nitrate salts

Metal Oxides and Metal Hydroxides are Bases

The combination of Metal and Acid descides the salt

AmmoniaNeutralised with Nitric acid (HNO3) to make FertiliserAmmonia dissolves in water to make an alkline solutionWhen mixed with nitric acid you get a neutral salt - Ammonium nitrateThere is no water producedGood fertiliser as there is lots of nitrogenPlants use nitrgen to make proteins

Making Soluable Salts

Using a Metal or Insoluble base Need to pick right acid, metal or insoluble base Ass the metal, metal oxide or hydroxide to the acid The solid will dissolve It will be neutralised when the excess solid falls to the bottom Filter out the excess metal, metal oxide or hydroxide To get the salt solution Evaporate the water to get pure salt crystals Evaporate it to make it more concentrated Leave the rest to evaporate slowly Crystalisation

Using an Alkali You can't use the reaction above as you can't tell when the reaction has finished You have to know exactly the right amount of alkali needed to neutralise the acid Need to use an indicator Then repeat using the same volumes but without the indicator Then just evaporate to remove the water

Making Insoluble Salts

Precipitation Reactions 2 solutions that contain the ions you need Need lead ions to lead chloride Once the salt has precipitated out (lying at the bottom of the flask) Filter it from the solution Wash it Dry it on filter paper Can be used to remove poisonous ions from drinking water Calcium and magnesium can be removed this way They make water hard Can be used fro treating sewage

ElectrolysisElectrolysis is the process by which ionic substances are broken down into simpler substances using electricity

If you pass a electric current through a substance that is molten r in a solution It breaks down the elements it's made of Needs a liquid to conduct electricity- the electrolyte Electrolytes contain free ions Usual molten or dissolved in the substance It's the free ions tat conduct electricity Electrons are taken from the positive electrode and given to the ions t the negative electrode As ions loose or gain electrons they become atoms r molecules

Oxidation Gain of oxygen The loss of electrons Doesn't have to involve oxygen

Reduction Loss of oxygen Gin of electrons Doesn't have to involve oxygen

Here is what happens during electrolysis: Positively charged ions move to the negative electrode during electrolysis. They receive electrons and are reduced. Negatively charged ions move to the positive electrode during electrolysis. They lose electrons and are oxidised. The substance that is broken down is called the electrolyte.

Electroplating Electrolysis is used to electroplate objects This is useful for coating a cheaper metal with a more expensive one, such as copper or silver

How it works The negative electrode should be the object that is to be electroplated The positive electrode should be the metal that you want to coat the object with The electrolyte should be a solution of the coating metal, such as its metal nitrate or sulfate

Electroplating with copper The object to be plated, such as a metal pan, is connected to the negative terminal of the power supply A piece of copper is connected to the positive terminal The electrolyte is coppersulfate solution This arrangement can also be used to purify copper during copper manufacture In this case, both electrodes are made from copper The negative electrode gradually gets coated with pure copper as the positive electrode gradually disappears

Aluminium is common (abundant- found everywhere, naturally in compounds) it is expensive due to the extraction process. Aluminium ore is called bauxite The bauxite is purified to aluminium oxide - from which aluminium can be extracted. The extraction is done by electrolysis aluminium oxide must be melted so that electricity can pass through it Aluminium oxide has a very high melting point (over 2000°C)  Too expensive to melt it it is dissolved in moltencryolite - an aluminium compound with a lower melting point than aluminium oxide The use of cryolite reduces some of the energy costs involved in extracting aluminium

Reactivity Sometimes there are more than 2 free ions in the electrode e.g a salt dissolved in water will have H+ and OH- At the negative electrode, if metal ions and H+ ions exist metal ions will stay in solution if they are more reactive than hydrogen Because the more reactive element is keener to stay as ions Hydrogen is produced if the metal is more reactive At the positive electrode if OH- ions and halide ions are present (Cl-, Br-, I-) are present Molecules of chlorine, bromine and iodine will be forms If no halide is present oxygen is formed

Half Equations show reactions at electrodes Make sure number of electrons is the same for both Write the formulae of the reactant and product Adjust the number of ions Count the number of charges Add enough electrons so that both sides have the same total number of charges e.g. Al3+ + e– → Al to Al3+ + 3e– → Al

The three products of electrolysis The three products of the electrolysis of concentrated sodium chloride solution have important uses in the chemical industry: Hydrogen is used as a fuel and for making ammonia Chlorine is used to kill bacteria in water, and to make bleach and plastics Sodium hydroxide is used to make soap and bleach

Aluminium Extraction

The diagram shows an aluminium oxide electrolysis tank. Both the negative electrode (cathode) and positive electrode (anode) are made of graphite, a form of carbon. Aluminium metal forms at the negative electrode and sinks to the bottom of the tank, where it is tapped off. Oxygen forms at the positive electrodes. This oxygen reacts with the carbon of the positive electrodes, forming carbon dioxide, and they gradually burn away As a result, the positive electrodes have to be replaced frequently This adds to the cost of the process

Uses:Decoration: Silver is attractive But expensive It is cheaper to plate a cheaper material with it Conduction: Metals like copper conduct electricity well used to plate for electronic circuits and computers

Oxides, Hydroxides and Ammonia

Making Salts



Aluminium Extraction

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