chapter 11: acids and bases

Question 1

what is an acid?

Answer 1

it is a substance that dissociates in water to produce hydrogen ions
> hydrogen ions give rise to acidic properties

Question 2

what are the physical properties of an acid?

Answer 2

• it has a sour taste
• turns blue litmus paper red
• it dissolves in water to form solutions which conduct electricity

Question 3

what are the chemical properties of acids?

Answer 3

1. acids react with reactive metals to form salt and hydrogen gas
2. acids react with carbonates and hydrogen carbonates to form
   > a salt, water and carbon dioxide

3.acids react with metal oxides and hydroxides to form a salt and water only

Question 4

why do some metals not react with acids?

Answer 4

• unreactive metals such as copper or silver are added to dilute acids, there is no reaction
• lead appears not to react with dilute hydrochloric acid and dilute sulfuric acid
  > the initial reaction of lead and these acids form
  > lead (II) chloride and lead (II)sulfate which is insoluble
  > this forms a coating around the metal which prevents it from further reaction with the acid

Question 5

does solid and gaseous acids conduct electricity?

Answer 5

• NO
• since dissociation of the compound did not occur, there are no mobile ions to act as charge carriers

Question 6

what does the basicity of acids refer to?

Answer 6

• it refers to the number of hydrogen ions dissociated per molecule of acid when dissolved in water

eg.
monobasic acid: HCl
> one mole of hydrogen ion

dibasic acid: H₂SO₄
> two moles of hydrogen ions

tribasic acid: H3PO4
> three moles of hydrogen ions

Question 7

what does the strength of acids refer to?

Answer 7

• the extent of dissociation of an acid when dissolved in water

strong acid: an acid that completely dissociated in water to produce hydrogen ions

weak acid: an acid that partially dissociates in water to produce hydrogen ions

Question 8

what does the concentration of acids refer to?

Answer 8

• it refers the number of acid molecules that are dissolved in per unit volume of water

Question 9

what is a base?

Answer 9

• any metal oxide or hydroxide that reacts with an acid to produce a salt and water

Question 10

what is an alkali?

Answer 10

• it is a base that is soluble in water
• it is a substance that produces hydroxide ions when dissociated in water
  > alkalis are in aqueous state

Question 11

what are the physical properties of alkalis?

Answer 11

• bitter teste
  -soapy feel
• turns red litmus paper blue

Question 12

what are the chemical properties of alkalis?

Answer 12

• they produce OH¯ ions when dissolved in water
• they have a pH greater than 7
• they react with acids to form salt and water
  > neutralisation
• they react with ammonium salts to give off ammonia gas

Question 13

why should slaked lime NOT be added together with fertilisers containing ammonium salts?

Answer 13

• slaked lime ( calcium hydroxide) can react with ammonium salts to produce ammonia gas
  > this results in a loss of nitrogen content in the soil
  > nitrogen is important for plant growth

Question 14

what is quicklime and slaked lime?

Answer 14

quicklime: calcium oxide
slaked lime: calcium hydroxide

Question 15

what are metal oxides classified as?

Answer 15

BASIC
- eg. CuO, FeO, MgO
- displays basic properties
- react with acids to form salt and water

AMPHOTERIC
- ZnO, Al₂O₃, PbO
>ZAP
- displays both acidic and basic properties
> reacts with both acids and bases to form salt and water

Question 16

what are non metal oxides classified as?

Answer 16

ACIDIC
- SO₂, NO₂, CO2
> dioxides
- display acidic properties
- react with bases to form salt and water

NEUTRAL
- CO, NO, H2O
>monoxides
> no reaction