Salts

Seite 1

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

Ammonia

Neutralised with Nitric acid (HNO3) to make Fertiliser

Ammonia dissolves in water to make an alkline solution

When mixed with nitric acid you get a neutral salt - Ammonium nitrate

There is no water produced

Good fertiliser as there is lots of nitrogen

Plants 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

Electrolysis

Electrolysis 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

Electrolysis

Electroplating

Aluminium Extraction