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Acids and bases
What you need to know
Reflections and Exam tips
Acids and bases
The pH scale tells us the acidity or alkalinity of a solution.
The scale shows that acids have a pH value of below seven.
Alkalis have pH values greater than seven, and anything with a pH value of exactly seven is neutral.
pH is defined as the negative logarithm of the hydrogen ion concentration pH = – log [H+], [H+] = 10-pH and provides a measurement of the hydrogen ion concentration, [H+].
An INDICATOR is a dye which changes colour according to whether it is in an acidic, neutral or alkaline solution.
Acids are compounds that produce hydrogen (H+) ions in solution.
Alkalis are substances that produce hydroxide (OH-) ions in solution.
A neutralisation reaction is where an acid reacts with a base to produce a neutral solution of a salt and water.
A salt is a compound made when the hydrogen in an acid is replaced by a metal.
Neutralising sulphuric acid produces salts called SULPHATES. Sulphuric acid (aq) has the formula H2SO4 and contains two H+ ions and one SO42-.
Neutralising nitric acid produces salts called NITRATES. Nitric acid (aq) has the formula HNO3 and contains the ions H+ and NO3-.
Neutralising hydrochloric acid produces salts called CHLORIDES. Hydrochloric acid(aq) has the formula HCl and contains the ions H+ and Cl-.
When two aqueous solutions are mixed, they may react to form a product that is insoluble in water. The solid is called a precipitate and the reaction is called a precipitation reaction.
Soluble salts from bases
What you want to achieve:
Understand the difference between a base and an alkali
Be able to define and give an ionic equation for the process of neutralisation
Give ionic equations to show substances acting as acids and alkalis
Be able to explain the difference between weak and strong acids
Be able to explain why certain steps are taken in the synthesis of a salt
Be able to write ionic equations to show the formation of insoluble salts
Be able to write ionic equations to show the formation of ammonium ions and hydroxide ions in water