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IGCSE Chemistry > Acids, Bases and Salts > Flashcards

Acids, Bases and Salts Flashcards

(i) The characteristic properties of acids and bases (ii) Types of oxides (iii) Preparation of salts (iv) Identification of ions and gases

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1
Q

Describe the characteristics of acids in terms of the following:

  1. effect on litmus
  2. pH
  3. taste
  4. ions
  5. proton transfer
A
  1. Turns litmus red
  2. pH < 7
  3. sour taste
  4. contain H+ ions
  5. proton donors
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2
Q

Describe the characteristics of bases in terms of the following:

  1. effect on litmus
  2. pH
  3. taste
  4. ions
  5. proton transfer
A
  1. turns litmus blue
  2. pH > 7
  3. bitter taste
  4. contain OH- ions
  5. proton acceptors
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3
Q

What colours do the following indicators turn in acids and bases?

  1. litmus
  2. phenolphthalein
  3. methyl orange
  4. universal indicator (UI)
A
  1. litmus: acid - red, alkali - blue (purple solution in neutral)
  2. phenolphthalein: acid - colourless, blue - pink
  3. methyl orange: acid - red, alkali - yellow
  4. UI: acid - red-yellow, alkali - dark green-purple (green in neutral)
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4
Q

What determines the strength of an acid or base?

A

The concentration of H+ or OH- ions when an acid or alkali dissolves (respectively) determines the strength of the acid or alkali. This is called ionisation or dissociation.

completely ionised/dissociated → strong

partially ionised/dissociated → weak

note: The stronger the acid/base, the higher its conductivity.

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5
Q

Describe the dissociation of weak acids or and weak alkalis.

A

For weak acids and alkalis, the process of dissociation is reversible, and a dynamic equilibrium is reached.

The position of the equilibrium lies well over to the left-hand side because the concentration of molecules is much greater than the concentration of ions.

e.g. CH3COOH (aq) ⇔ H+ (aq) + CH3COO- (aq)

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6
Q

What are the reactions of acids with metals, bases, oxides and carbonates?

A

acid + metal → salt + hydrogen

acid + base → salt + water

acid + metal oxide → salt + water

(metal must be more reactive than hydrogen)

acid + metal carbonate → salt + carbon dioxide + water

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7
Q

What are the reactions of bases with acids and ammonium salts?

A

acid + base → salt + water

base + ammonium salt → salt + water + ammonia

e.g. Ca(OH)2 (s) + 2NH4Cl (s) → CaCl2 (s) + 2H2O (l) + 2NH3 (g)

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8
Q

Define

neutralisation

A

A reaction between an acid an alkali giving salt and water.

note: reactions of acids with metals are not neutralisations as water is not produced

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9
Q

What is the importance of controlling acidity in soil?

A

Soil may be acidic due to the type of rock it was formed from, rotting vegetation or heavy use of fertilisers. Soil that is too acidic or basic can affect the growth of plants.

To reduce acidity, the soil is neutralised with crushed limestone (calcium carbonate), lime (calcium oxide), or slaked lime (calcium hydroxide).

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10
Q

How can you test if a substance is an acid or a base? (without using an indicator)

A

acid:

  1. react with metal carbonate
  2. bubble gas through limewater
  3. if acid, CO2 effervescence should turn limewater milky

base:

  1. react with ammonium salt
  2. test gas with damp litmus paper
  3. ammonia gas turns damp red litmus paper blue
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11
Q

Which oxides are acidic?

What exceptions are there?

A

Non-metal oxides are acidic.

e. g. SO2, NO2, CO2
* They are gases

Exceptions: (neutral oxides)

N2O dinitrogen oxide

CO carbon monoxide

H2O water

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12
Q

Which oxides are basic?

What exceptions are there?

A

Metal oxides are basic

e.g. MgO, Na2O

  • They are solids
  • They are insoluble in water except group 1 metal oxides.

Exceptions: amphoteric oxides (react with both acids and bases)

Al2O3 aluminium oxide

ZnO zinc oxide

lead

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13
Q

List the steps in the preparation of a salt using an acid and a metal, metal oxide or metal carbonate.

A
  1. Add an excess of metal/oxide/carbonate to the acid
  2. Wait until (i) no more dissolves (ii) no more gas is given off (for metal or carbonate only) (iii) the temperature stops rising or (iv) the solution becomes neutral.
  3. Filter off the excess solid
  4. Recrystallise by heating salt solution
  5. Wash and dry
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14
Q

List the steps used to prepare a salt using an acid and alkali.

A

Titration method:

  1. Add known quantity of alkali to conical flask
  2. Add phenolphthalein to alkali (turns pink)
  3. Add acid to flask using a burette to measure
  4. Neutralisation complete when indicator turns colourless. Note down volumes used.
  5. Repeat with known volumes without indicator
  6. Recrystallise by heating salt solution
  7. Wash and dry
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15
Q

List the steps involved when making an insoluble salt.

A
  1. Add a solution of the +ve ion to a solution of the -ve ion. A precipitate forms.
  2. Filter the mixture using a funel and filter paper
  3. Wash and dry the crystals (warm oven)
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16
Q

Which salts are soluble/insoluble?

A
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17
Q

How do you test for the following gases?

  1. hydrogen
  2. oxygen
  3. carbon dioxide
  4. ammonia
  5. chlorine
A
  1. place lighted splint, squeaky pop heard
  2. place glowing splint, relights
  3. bubble through limewater, turns milky
  4. damp red litmus, turns blue OR place near concentrated HCl fumes, NH4Cl forms, pungent smell
  5. damp blue litmus, turns red then bleaches white
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18
Q

Which method should you use to prepare a soluble salt for each of the metals in the reactivity series?

A
19
Q

How do you test for the following aqueuous cation?

Aluminium: Al3+

A

Add a few drops of NaOH: white precipitate forms

Precipitate dissolves in excess NaOH but not in aqueous ammonia

20
Q

Which aqueous cation is present?

Add a few drops of NaOH: white precipitate forms

Precipitate dissolves in excess NaOH but not in aqueous ammonia

A

Aluminium: Al3+

21
Q

How do you test for the following aqueous cation?

Ammonium: NH4+

A

Add NaOH, may need gentle warming

Test gas given off with damp red litmus: turns blue

22
Q

Which aqueous cation is present?

Add NaOH, may need gentle warming

Test gas given off with damp red litmus: turns blue

A

Ammonium: NH4+

23
Q

How do you test for the following aqueous cation?

Calcium: Ca2+

A

Add a few drops of NaOH: white precipitate forms

Doesn’t dissolve in excess NaOH or aqeuous ammonia

24
Q

Which aqueous cation is present?

Add a few drops of NaOH: white precipitate forms

Doesn’t dissolve in excess NaOH or aqeuous ammonia

A

Calcium: Ca2+

25
Q

How do you test for the following aqueous cation?

Copper(II): Cu2+

A

Add NaOH: pale blue precipitate formed

26
Q

Which aqueous cation is present?

Add NaOH: pale blue precipitate formed

A

Copper(II): Cu2+

27
Q

How do you test for the following aqueous cation?

Iron(II): Fe2+

A

Add NaOH: dirty green precipitate formed

Remember: two e’s in green

28
Q

Which aqueous cation is present?

Add NaOH: dirty green precipitate formed

Remember: two e’s in green

A

Iron(II): Fe2+

29
Q

How do you test for the following aqueous cation?

Iron(III): Fe3+

A

Add NaOH: rusty brown precipitate formed

30
Q

Which aqueous cation is present?

Add NaOH: rusty brown precipitate formed

A

Iron(III): Fe3+

31
Q

How do you test for the following aqueous cation?

Zinc: Zn2+

A

Add NaOH: white precipitate forms

Dissolves in both excess NaOH and aqueous ammonia

32
Q

Which aqueous cation is present?

Add NaOH: white precipitate forms

Dissolves in both excess NaOH and aqueous ammonia

A

Zinc: Zn2+

33
Q

How do you test for the following anion?

Carbonate: CO32-

A

React with dilute acid (e.g. HCl): gas given off

Bubble gas through limewater: turns milky

34
Q

Which anion is present?

React with dilute acid (e.g. HCl): gas given off

Bubble gas through limewater: turns milky

A

Carbonate: CO32-

35
Q

How do you test for the following anion?

Bromide: Br-

A

Reaction under acidic conditions with aqueous silver nitrate, i.e. add small amounts of aqueous silver nitrate to anions dissolved in dilute nitric acid

cream precipitate formed

36
Q

Which anion is present?

Reaction under acidic conditions with aqueous silver nitrate, i.e. add small amounts of aqueous silver nitrate to anions dissolved in dilute nitric acid

cream precipitate formed

A

Bromide: Br-

37
Q

How do you test for the following anion?

Chloride: Cl-

A

Reaction under acidic conditions with aqueous silver nitrate, i.e. add small amounts of aqueous silver nitrate to anions dissolved in dilute nitric acid

white precipitate formed

38
Q

Which anion is present?

Reaction under acidic conditions with aqueous silver nitrate, i.e. add small amounts of aqueous silver nitrate to anions dissolved in dilute nitric acid

white precipitate formed

A

Chloride: Cl-

39
Q

How do you test for the following anion?

Iodide: I-

A

Reaction under acidic conditions with aqueous silver nitrate, i.e. add small amounts of aqueous silver nitrate to anions dissolved in dilute nitric acid

pale yellow precipitate formed

40
Q

Which anion is present?

Reaction under acidic conditions with aqueous silver nitrate, i.e. add small amounts of aqueous silver nitrate to anions dissolved in dilute nitric acid

pale yellow precipitate formed

A

Iodide: I-

41
Q

How do you test for the following anion?

Nitrate: NO3-

A

Add NaOH and aluminium: anion gets reduced, ammonia given off (test for ammonia gas)

42
Q

Which anion is present?

Add NaOH and aluminium: anion gets reduced, ammonia given off (test for ammonia gas)

A

Nitrate: NO3-

43
Q

How do you test for the following anion?

Sulphate: SO42-

A

Reaction under acidic conditions with aqueous barium ions, i.e. add barium chloride to anions dissolved in dilute HCl

white precipitate forms

44
Q

Which anion is present?

Reaction under acidic conditions with aqueous barium ions, i.e. add barium chloride to anions dissolved in dilute HCl

white precipitate forms

A

Sulphate: SO42-

IGCSE Chemistry (15 decks)

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