Definition of a Base
Specification Point 3.9:
Recall that a base is any substance that reacts with an acid to form a salt and water only.
- Bases have pH values of above 7.
- A base which is water soluble is referred to as an alkali.
- Bases are substances which can neutralise an acid, forming a salt and water only.
Definition of an Alkali
Specification Point 3.10:
Recall that alkalis are soluble bases.
- Many bases are insoluble in water but the ones that do dissolve in water are called alkalis.
- They thus form an alkaline solution.
- Examples of alkalis are soluble metal hydroxides such as NaOH and Ca(OH)2.
Reactions of Acids
Specification Point 3.11:
Explain the general reactions of aqueous solutions of acids with:
b) metal oxides
c) metal hydroxides
d) metal carbonates to produce salts
- A salt is a compound that is formed when the hydrogen atom in an acid is replaced by a metal.
- For example if we replace the H in HCl with a potassium atom, then the salt potassium chloride is formed, KCl.
- Salts are an important branch of chemistry due to the varied and important uses of this class of compounds.
- These uses include fertilisers, batteries, cleaning products, healthcare products and fungicides.
- The name of a salt has two parts.
- The first part comes from the metal, metal oxide or metal carbonate used in the reaction.
- The second part comes from the acid.
- The name of the salt can be determined by looking at the reactants
- For example hydrochloric acid always produces salts that end in chloride and contain the chloride ion, Cl–.
- Other examples:
- Sodium hydroxide reacts with hydrochloric acid to produce sodium chloride.
- Zinc oxide reacts with sulfuric acid to produce zinc sulfate.
Reactions of Acids and Metals
- Only metals above hydrogen in the reactivity series will react with dilute acids.
- When acids react with metals they form a salt and hydrogen gas:
Reactions of Acids with Metal Oxides and Metal Hydroxides
- Metal oxides and metal hydroxides act as bases.
- When they react with acid, a neutralisation reaction occurs.
- In all acid-base neutralisation reactions, salt and water are produced.
Reactions of Acids with Metal Carbonates
- Acids will react with metal carbonates to form the corresponding metal salt, carbon dioxide and water.
Edexcel GCSE Chemistry Notes
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Morgan’s passion for the Periodic Table begun on his 10th birthday when he received his first Chemistry set. After studying the subject at university he went on to become a fully fledged Chemistry teacher, and now works in an international school in Madrid! In his spare time he helps create our fantastic resources to help you ace your exams.
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