Welcome to the most comprehensive wiki on Acids and Alkalis!
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Content:

1. Introduction on Acids and Alkalis
1.1. Properties of acids
1.2. Properties of alkalis
1.3. Indicators

2. Acids and Alkalis Explained
2.1. Types of acids
2.2. Bases or Alkalis
2.3. Uses of acids
2.4. Uses of alkalis

3. Effects of mixing acids or alkalis with other substances
3.1. Neutralisation
3.2. Reaction of acids with bases
3.3. Reaction of acids with metals
3.4. Naming salts

4. Videos on experiements
4.1. Video on Test for hydrogen gas
4.2. Video on Titration

5. Sources
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1. Introduction on Acids and Alkalis

Acids, bases, alkalis and metals are found in the laboratory and at home. They can be irritant or corrosive and must be handled carefully.
How acid or alkaline a chemical is can be measured on the pH scale, using indicators like litmus and universal indicator.
Acids and bases react together to form salts and other products too.

1.1. Properties of acidsexternal image corrosive.gifexternal image irritant.gif


Acids have a sour taste.
Acids turn moist blue litmus paper red.
Aqueous solutions of acids are good electrical conductor.
Acids react with metals to form salt and hydrogen gas.
Acids react with carbonates to form salt, carbon dioxide gas and water.
Concentrated acids are corrosive and can burn your skin or clothes.
Dilute acids can cause irritant to the skin.
Acids react with some reactive metals to give off hydrogen gas.
Acids react with carbonates to give off carbon dioxide gas.

1.2. Properties of alkalisexternal image produkty.jpg

Alkalis taste bitter and feel soapy.
Alkalis turn red litmus paper blue.
Alkalis are good electrical conductors.
Like acids, alkalis are usually very corrosive and can attack metals and destroy skin if spilled, but many people do not realise this.
Neutral solutions do not cause litmus papers to change colour.


1.3. Indicators

Indicators are used to determine how acidic or alkaline an solution is. When mixed with a solution, the indicator changes colour according to whether the solution is acidic or alkaline.

Some of the common indicators are:
1. Red and blue litmus paper
2. pH scale


2. Explaining acids and alkalis

2.1. Types of acids

Laboratory acids are too dangerous to taste, but dilute weak acids which are safe to use in food can be tasted.
Here are some of the acids you can find at home.
Sources
Acid
Vinegar
Ethanoic acid
Fizzy drinks
Carbonic acid
Tea
Tannic acid
Vitamin C
Ascorbic acid
Citrus fruits (oranges,lemons and limes)
Citric acid
Fermented milk products (yoghurt)
Lactic acid
Ants and bees
Formic acid

2.2. Bases or Alkalisexternal image bases_alkali.gif

Alkalis belong to a larger class of chemicals known as bases.
Alkalis are soluble bases.
Bases are insoluble in water.

Here are two examples:
1. Copper oxide is a base because it will react with acids and neutralise them, but it is not an alkali because it does not dissolve in water.
2. Sodium hydroxide is a base because it will react with acids and neutralise them. It's also an alkali because it dissolves in water.

2.3. Uses of acids

Hydrochloric acid is used to remove rust on iron and steel.
Sulphuric acid is used in car batteries.
Nitric acid is used to manufacture fertilisers.

2.4. Uses of alkalis

Ammonia solution is used to make fertilisers.
Sodium hydroxide (Caustic soda) is used for making soaps and detergents.
Calcium hydroxide (Slaked lime/limewater) is used to reduce acidity of soil in agriculture.

3. Effects of mixing acids or alkalis with other substances

3.1. Neutralisationexternal image neutralisation2.jpg

Neutralisation is a reaction caused when an acid is mixed with an alkali.
Mixing an acid with an alkali produces salt and water only.
Example: Mixing sodium hydroxide with hydrochloric acid produces sodium chloride and water.

The general word equation to represent the reaction of an alkali with an acid is:
Acid + Alkali ----> Salt + Water

Some everyday uses of neutralisation:

1. Many face cleansers are alkaline and may cause skin to become dry. Toners are used to neutralise acidity and restore skin to its normal level of acidity.

2. Shampoos usually contain a mild alkali which causes strands of hair to become entangled easily. Hair conditioners contain a mild acid that neutralises the alkali which makes your hair feel smoother and easier to manage.

3. Food that remains on your teeth decays and produces an acid that causes tooth decay. Using toothpaste, an alkaline, to brush your teeth neutralises the acid.

3.2. Reaction of acid with bases

Metal oxides and metal hydroxides are two types of bases. For example copper oxide and sodium hydroxide.
Here are general word equations for what happens in their neutralisation reactions with acids.
Metal oxide + acida salt + water
Metal hydroxide + acida salt + water
A salt and water is always produced.

Carbonates and hydrogen carbonates are two other types of base. They also make a salt and water when we neutralise them with acid. But this time we get carbon dioxide gas too.
The reaction fizzes as bubbles of carbon dioxide are given off. This is easy to remember because we see the word 'carbonate' in the chemical names.
These are the general word equations for what happens:
Acid + metal carbonatea salt + water + carbon dioxide
Acid + metal hydrogen carbonatea salt + water + carbon dioxide

3.3. Reaction of acids with metals

Acids react with most metals and a salt is produced. But unlike the reaction between acids and bases we don't get any water. Instead we get hydrogen gas.
This is the general word equation for the reaction:
Metal + acidsalt + hydrogen

The salt produced depends upon the metal and the acid. Here are two examples:
Zinc + sulphuric acidzinc sulphate + hydrogen
Magnesium + hydrochloric acidmagnesium chloride + hydrogen
It doesn't matter which metal or acid is used, if there is a reaction we always get hydrogen gas as well as the salt.

All acids contain hydrogen atoms. Apart from hydrochloric acid, this is not clear from their names, but you can tell they contain hydrogen from their chemical formulae. Remember that the chemical symbol for hydrogen is H.

Name of acid
Chemical formula of an acid
Hydrochloric acid
HCl
Nitric acid
HNO3
Sulphuric acid
H2SO4
Carbonic acid
H2CO3
Phosphoric acid
H3PO4

3.4. Naming salts

A salt is always made when an acid is neutralised by a base. But the exact salt made depends upon which acid and base were used.
The name of a salt has two parts:
1. The first part comes from the metal in the base used
2. The second part comes from the acid that was used

Example: Where does the name potassium nitrate come from?


external image potassium_nitrate_text.gif

Here are some examples on naming salts:
1. Copper oxide + sulphuric acid → copper sulphate + water
2. Copper carbonate + sulphuric acid copper sulphate + water + carbon dioxide
3. Sodium hydroxide + hydrochloric acid → sodium chloride + water
4. Sodium hydrogen carbonate + hydrochloric acid → sodium chloride + water + carbon dioxide

4. Videos on experiments

4.1. Video on Test for hydrogen gas



4.2. Video on Titration
(The process, operation, or method of determining the concentration of a substance in solution by adding to it a standard reagent of known concentration in carefully measured amounts until a reaction of definite and known proportion is completed, as shown by a color change or by electrical measurement, and then calculating the unknown concentration.)



A titration experiment is used to calculate an unknown concentration of acid (or alkali) using a neutralisation reaction.

In this titration an alkali (with a known concentration) is carefully added to the acid (of unknown concentration) using a burette. The volume of alkali used in the experiment is needed in order to perform a calculation to work out the concentration of the acid.

The acid used in this titration is hydrochloric acid (HCl, 25ml volume, unknown concentration) and the alkali used is sodium hydroxide (NaOH, 0.1M concentration).


Useful equations to calculate the unknown concentration of acid:

number of moles = concentration x volume

concentration = number of moles ÷ volume

Concentration is measured in moles per litre (moldm-3)
Volume is measured in litres (decimetre cubed: dm3)


The equation for this reaction is:
hydrochloric acid + sodium hydroxide ---- sodium chloride + water

HCl + NaOH ---- NaCl + H2O
(using subscript for the 2 in H2O)

5. Sources
http://www.bbc.co.uk/schools/ks3bitesize/science/chemical_material_behaviour/acids_bases_metals/revise1.shtml
http://www.youtube.com/watch?v=8UiuE7Xx5l8&hd=1
http://sciencelinkcafe.com/year_7_acids_alkalis.html
http://www.albertina-labelling.com/index.asp?menu=784
http://www.ssc.education.ed.ac.uk/bsl/chemistry/neutralisationd.html
http://www.youtube.com/watch?v=uMSduJHe_Fo&hd=1
http://www.answers.com/topic/titration

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