4 Chemical Changes - Acids
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Define acid in terms of pH
A substance with a pH of less than 7
Define acids in terms of ions
A substance which releases H+ ions in solution
What does (aq) stand for?
Aqueous: when something is dissolved in water. E.g. NaCl(aq) is salt water
State the three common acids and give their formulae
Hydrochloric acid, HCl(aq), Sulphuric acid, H2SO4(aq), Nitric acid, HNO3
Which ions do the common acids form in solution?
HCl forms H+ and Cl-, H2SO4 forms 2H+ and SO4 2-, HNO3 forms H+ and NO3-
What is a neutral solution?
A solution with a pH of 7. Water is an example.
How do you measure pH?
With an indicator or pH probe.
What is a base?
A metal oxide, hydroxide or carbonate that will react with an acid. E.g. copper oxide
What is an alkali?
A soluble base. E.g. sodium hydroxide
Which ions are always present in a solution of an alkali?
OH?
What is a salt?
A compound formed when some or all of the hydrogen from an acid is replaced by a metal. E.g. CuSO?, copper sulphate, where copper has replaced H from H?SO?
What type of salts are formed by the three main acids?
Hydrochloric acid produces chlorides, sulphuric acid = sulphates, nitric acid = nitrates
What is a neutralisation reaction?
A reaction involving an acid that results in a neutral solution
Which ions always react together in a neutralization reactions between acids and alkalis?
H? and OH?
Write the equation showing the reaction between H? and OH? ions
H+ + OH- gives H2O
metal + acid ?
gives salt + hydrogen gas
metal hydroxide + acid ?
gives salt + water
metal oxide + acid ?
gives salt + water
metal carbonate + acid ?
gives salt + water + carbon dioxide
How do you make a soluble salt from an acid?
React the acid with a base. E.g. to make copper sulphate react copper oxide with sulphuric acid
If a salt is in solution, how do you extract it as a solid?
Allow the water to evaporate off and it will leave the salt behind as a solid.
What is a strong acid?
An acid which completely splits up into its ions in water. E.g. when HCl is in water all the HCl molecules split up into H? and Cl?
What is a weak acid?
An acid which will have some molecules which do not split up into their ions. E.g. in ethanoic acid only some of the molecules will have split up into the ethanoate ion and H? ions.
What is the relationship between the strength of an acid and its pH?
As an acid increases in strength the pH decreases.