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GCSE Chemistry (C3) > Analysis and Synthesis > Flashcards

Analysis and Synthesis Flashcards

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1
Q

Which metals can be identified using flame tests?

A

Group 1 and 2 metals

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2
Q

What colours do different metals turn the flame in a flame test?

A
  • Lithium - Crimson red
  • Sodium - Yellow
  • Potassium - Lilac
  • Calcium - Red
  • Barium - Green
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3
Q

Which types of metal hydroxides are insoluble in water?

A

Those of most metals that have ions with 2+ and 3+ charges

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4
Q

What happens when sodium hydroxide is added to solutions of metals ions with 2+ and 3+ charges?

A

A precipitate of the metal hydroxide forms

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5
Q

Which metals form white precipitates?

A

Aluminium, calcium, and magnesium

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6
Q

What happens when excess sodium hydroxide solution is added to the precipitate/solution of aluminium hydroxide?

A

It dissolves

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7
Q

State the colours of:

Copper(II) hydroxide

Iron(II) hydroxide

Iron(III) hydroxide

A
  • Copper(II) hydroxide is blue
  • Iron(II) hydroxide is green
  • Iron(III) hydroxide is brown
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8
Q

Why might you test lithium and calcium ions with sodium hydroxide solution as well as a flame test?

A

They both produce red flames which can be difficult to tell apart from a single test

Calcium ions form a white precipitate when sodium hydroxide is added but lithium does not

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9
Q

Write an equation for testing Iron(III) with sodium hydroxide

A

Fe3+(aq) + 3OH- → Fe(OH)3(s)

This is a balances ionic equation (i.e. don’t include the sodium)

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10
Q

What are the three types of negative ions you might test for?

A
  • Carbonate ions
  • Halide ions
  • Sulfate ions
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11
Q

How would you test for carbonate ions?

A

Add dilute hydrochloric acid to the substance to see if it fizzes

If it does and the substance produced turns limewater milky, the substance contains carbonate ions

This is because a salt, water, and CO2 are produced

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12
Q

How would you test for halide ions?

A

Add dilute nitric acid and then silver nitrate solution

  • Chlorine ions give a white precipitate
  • Bromine ions give a cream precipitate
  • Iodine ions give a yellow precipitate

AgNO3(aq) + NaCl(aq) → AgCl(s) + NaNO3(s)

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13
Q

How would you test for sulfate ions?

A

Add dilute hydrochloric acid and then barium chloride solution

If a white precipitate forms, sulfate ions are present

BaCl2(aq) + MgSO4(aq) → BaSO4(s) + MgCl2(aq)

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14
Q

What is a titration?

A

A method for measuring the volumes of two solutions that react together

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15
Q

What is the end-point?

A

The point at which an acid-base/neutralisation reaction is complete

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16
Q

How would you perform a titration?

A
  • Use a pipette to accurately measure the volume of alkali into a conical flask
  • Add an indicator to the alkali
  • Fill a burette with acid
  • Use the burette to gradully add the acid to the alkali. Stop when the idicator changes colour (at the end point)
  • Take the burette reading
  • Repeat this several times
17
Q

What is concentration measured in?

A

g/dm3 or mol/dm3

18
Q

How much is 1dm3 in cm3?

A

1000cm3

1 X 10 X 10 X 10

1dm3 = 1L

19
Q
A
20
Q

Why have large databases of the results of analyses been built up? (What are they used for)

A
  • To identify substances in samples
  • To identify individuals
  • To monitor the cganges in amounts of substances over time
21
Q

What is equilibrium?

A

The point in a reversible reaction in which the forward and backward rates of reaction are the same

Therefore, the amounts of substances remains constant but not the same

Both reactions continue to occur, but the amounts of products + reactants remains the same

22
Q

What conditions must there be for equilibrium to be achieved?

A

The reversible reaction must happen in a closed system

This means no products can escape

23
Q

How can the amounts of reactants and products in a reversible reaction be changed?

A

By changing the reaction conditions

Think of equilibrium as a see-saw, if you take something off one side, the other side will try and make more of it to balance the see-saw!

24
Q

If the forward reaction produces more molecules of gas, what effect does changing the pressure of the reaction have?

A

An increase in pressure decreases the amount of products formed

A decrease in pressure increases the amount of products formed

25
Q

If the forward reaction produces fewer molecules of gas, what effect does changing the pressure of the reaction have?

A

An increase in pressure increases the amount of products formed

A decrease in pressure decreases the amount of products formed

26
Q

If the forward reaction is exothermic, what effect with temperature have on the amount of products formed?

A

An increase in temperature decreases the amount of product formed

A decrease in temperature increases the amount of product formed

27
Q

If the forward reaction is endothermic, what effect with temperature have on the amount of products formed?

A

An increase in temperature increases the amount of product formed

A decrease in temperature decreases the amount of product formed

28
Q

Which type of reaction does increasing the temperature favour?

A

Endothermic

29
Q

Which type of reaction does decreasing the temperature favour?

A

Exothermic

30
Q

What happens if the pressure is increased?

A

The position of equilibrium will shift to try and reduce the pressure

31
Q

What is the Haber process used to manufacture and what can this be used to make?

A

Ammonia

This can be used to make fertilisers and other chemicals

32
Q

Describe the Haber process

A
  • Nitrogen from the air and hydrogen (usually from natural gas) are purified and mixed in the correct proportions
  • The gases are passed over an iron catalyst at a temperature of 450°C and a pressure of 200 atmospheres
  • Some ammonia produced breaks down into nitrogen and hydrogen, so the yield of ammonia is only about 15%
  • The gases that come out of the reactor are cooled so the ammonia condenses
  • The liquid ammonia is seperated from the unreacted gases. These are then recycled so they are not wasted
33
Q

What is the equation for the Haber process?

A

N2(g) + 3H2(g) ⇌ 2NH3(g)

34
Q

Why is a pressure of 200 atmospheres used in the Haber process?

A
  • The products have fewer molecules of gas than the reactants, so the higher the pressure the greater the yield of ammonia
  • However, the higher the pressure, the more energy is needed to compress the gas.
  • Higher pressures also need stronger reaction vessels and pipes which increase costs
  • 200 atmospheres is a compromise
35
Q

Why is a temperature of 450°C used in the Haber process?

A
  • The forward reaction is exothermic, so the lower the temperature the greater the yield of ammonia
  • However, the reaction rate decreases as the temperature is lowered
  • The iron catalyst also becomes ineffective so it would take longer to produce any ammonia
  • A compromise temperature of 450°C is used to give a reasonable yield in a short time

GCSE Chemistry (C3) (5 decks)

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