acids and bases (chap 8) -olevel pure chem

what is an acid

an acid is a substance that produces hydrogen ions, H+, when dissolved in water

what are the properties of acids

1. acids have a sour taste

2. acids produce ions when dissolved in water. these ions allow the resulting aqueous solution to conduct electricity

3. acids turn blue litmus paper red

4. acids react with reactive metals

5. acids react with bases (metal oxides or hydroxides)

6. acids react with carbonates

what is the result of:

acid + base

acid + metal

acid + carbonate

acid + base —> salt + water

acid + metal —> salt + hydrogen

acid + carbonate —> salt + carbon dioxide + water

why does lead appear not to react with hydrochloric acid or sulfuric acid?

it forms an layer of lead chloride or lead sulfate around the metal which is both insoluble, preventing the metal from further reaction with the acid

what are some unreactive metals

copper

silver

gold

what is the difference between a strong and weak acid

strong acid- completely ionised in an aqueous solution

weak acid- partially ionised in an aqueous solution, reversible reaction

what is the difference between the strength of an acid and the concentration of an acid

strength of acid: its degree of ionisation

concentration of acid: the number of acid molecules present in a given volume of water

what is a base

any metal oxide or hydroxide

what is the differences between bases and alkalis

like acids, bases can also be strong or weak depending on their degree of ionisation

bases:

• mostly insoluble in water

alkali:

• produces OH- ions when dissolved in water

• soluble in water eg:

  • group 1 hydroxides

  • ammonium hydroxide

  • calcium hydroxide

what is the ionic equation for any neutralisation reaction

H+ (aq) + OH- (aq) —> H2O (l)

what are some properties of alkalis

1. alkalis taste bitter

2. alkalis feel slippery and soapy

3. alkalis dissolve in water to form solutions that conduct electricity

4. alkalis turn red litmus paper blue

5. alkalis react with acids

6. alkalis react with ammonium salts

   • alkali + ammonium salt —> salt + water + ammonia

what are the color changes of the following indicators

• methyl orange

• screened methyl orange

• litmus

• thymophthalein

• universal

1. methyl orange

   • acidic: red

   • alkaline: yellow

   • range where color changes: 3-5

2. screened methyl orange

   • acidic: violet

   • alkaline: green

   • range where color changes: 3-5

3. litmus

   • acidic: red

   • alkaline: blue

   • range where color changes: 5-8

4. thymophthalein

   • acidic: colorless

   • alkaline: blue

   • range where color changes: 9-10.5

5. universal

   • acidic: red-yellow

   • alkaline: green-violet

   • neutral: green

what is pH a measure of

pH is a measure of the concentration difference of H+ ions and OH- ions

why is fertilisers added to soil to control its pH

soil tends to be more acidic due to natural factors such as acid rain. most plants grow best when the soil is neutral, so fertiliser is added to neutralise the acidic soil and make it neutral so that the plant can grow optimally

what are some common elements for soil fertilisers

• nitrogen

• phosphorus

• potassium

• calcium hydroxide (slaked lime)

• ammonia

types of oxides