Acids and alkalis
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What is an acid?
A substance with a pH lower than 7 that dissolves some metals and has a sour taste
What is a base?
a substance with a pH above 7 that has a bitter taste
What is an alkali?
a soluble base that effervesces acids
What does neutral mean?
a substance with a pH of 7
What is a solvent?
a liquid that dissolves a solute
What is a solute?
a substance that dissolves in a solvent
What does aqueous mean?
a substance that has water as its solvent
What does dilute mean?
A solution that contains little dissolved solute
What does concentrated mean?
A solution that contains a lot of dissolved solute
What is a chemical indicator?
An indicator that changes colour to identify a solution’s pH
What is neutralisation?
A chemical reaction between an acid and a base, that makes a chemical neutral (pH7) producing salt and water
List the chemical indicators:
-universal indicator -litmus paper -phenolphthalein -methyl red/orange -bromothymol blue -cresol red -red cabbage indicator
What is the pH scale range?
1-14
What is the range of a strong acid
1-3 (red)
What is the range of a weak acid
4-6 (orange/yellow)
What is a neutral substance’s pH?
pH 7 (green)
What is the range of a weak alkali?
8-10 (light/dark blue)
What is the range of a strong alkali?
11-14 (purple)
What happens to litmus paper in an acid, an alkali or a neutral substance?
in an acid, blue litmus paper turns red and red litmus paper stays red. in an alkali, blue litmus paper stays blue and red litmus paper turns blue a neutral substance has no effect on litmus paper, so blue litmus paper stays blue and red litmus paper stays red
What is the word equation for neutralisation?
Base + acid → salt + water (pH 7)
How can we tell if something is an alkali? (by the substance’s name)
anything that has ‘hydroxide’ in it is an alkali
Give the formulas and pH of these substances: Sulfuric acid Hydrochloric acid Nitric acid Hydrofluoric acid Ethanoic acid Sodium chloride (salt) Ammonium hydroxide Calcium hydroxide Potassium hydroxide
H2SO4 (pH1) HCl (pH2) HNO3 (pH3) HF (pH3) CH3COOH (pH4) NaCl (pH7) NH4OH (pH8-10) Ca(OH)2 (pH9-11.5) KOH (pH12.5)
What colour is the colour of ethanoic acid in universal indicator, what is its pH number, and is it an acid, an alkali or a neutral substance?
it’s orange in universal indicator, it has a pH of 4, and it is a weak acid
What colour is the colour of distilled water in universal indicator, what is its pH number, and is it an acid, an alkali or a neutral substance?
it’s green in universal indicator, it has a pH of 7, and it is a neutral substance