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GCSE - Chemistry > Topic 5 - Separate Chemistry 1 > Flashcards

Topic 5 - Separate Chemistry 1 Flashcards

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1
Q

What are the typical properties of transition metals?

A

High melting pt
High density
Form coloured compounds
Transition metals and their compounds can be used as catalysts

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2
Q

Which transition metal is used as a catalyst in the Haber process?

A

Iron

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3
Q

What causes metals to corrode

A

Oxygen reacts with the metal to form a metal oxide

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4
Q

Why is corrosion of a metal a redox reaction?

A

The metal loses electrons so is oxidised

Oxygen gains electrons so is reduced

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5
Q

What is rusting

A

Rusting is the name specifically given to the corrosion of iron when it reacts to oxygen and water in the air

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6
Q

What 2 substances need to be excluded to prevent rusting

A

Oxygen (O₂)

Water (H₂O)

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7
Q

How can water and oxygen be excluded to prevent iron rusting?

A

Paint the metal
Coat the metal in oil/grease
Cover the metal in plastic
Keep the metal in a vacuum container

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8
Q

What is sacrificial protection? How does it prevent corrosion?

A

When the metal being protected from corroding is galvanised with a more reactive metal. The outer metal will corrode first and will prevent corrosion of inner metal.

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9
Q

Which metal is used in the sacrificial protection of iron?

A

Zinc

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10
Q

What is electroplating?

A

A process in which a metal is coated with a layer of another metal

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11
Q

What are 2 reasons for using electroplating?

A

To make a metal more resistant to corrosion

To improve the appearance of a metal

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12
Q

Explain how the process of electroplating works

A

The metal being coated is the cathode. The metal that will form the exterior layer is the anode. The electrolyte solution must contain ions of the mtal which will form the outer coating. A power supply is connected to botn electrodes.

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13
Q

Why are pure metals generally very malleable?

A

The atoms lie in uniform rows which are able to slide over one another

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14
Q

What is an alloy?

A

An alloy is a mixture of 2 or more metals or a metal and another element

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15
Q

A pure metal can be converted into an allow. How does this increase the stength of the product?

A

Alloys contain several metals which will have different sized atoms. This distorts the regukar arrangement of the atoms so the layers are unable to slide over one another very easily

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16
Q

Why is iron alloyed with other metals to produce alloy steels?

A

Iron is relatively brittle so is combined with other elements such as carbon and produces a material with more desirable qualities.
Low carbon steel: malleable (used for sheeting)
High carbon stel: hard (used for cutting tools)
Stainless steel: corrosion resistant so used for cutlery

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17
Q

What property of copper makes it suitable to be used in electrical cables?

A

Very good electrical conductor

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18
Q

What property of aluminium makes it suitable for use in aircrafts?

A

Low density

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19
Q

What is a key property fpof gold that makes it suitable for use in jewellery?

A

Very unreactive so resist to corrosion

Jewellery appearance will not be affected over time

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20
Q

What is magnalium? What is it used for?

A

Magnalium is an allow of magnesium and aluminium.

It is lighter and stronger than aluminium and more resistant to corrosion. Its used for cars and aircrafts

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21
Q

What is brass? Whats it used for?

A

An alloy of copper and zinc.

Is hard and resistant to corrosion. Is used for decorative hardware such as plumbing fittings

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22
Q

How do you calculate the concentration of a solution in mol dm⁻³ ?

A

Concentration = moles / volume (dm³)

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23
Q

How can you convert concentration in g dm⁻³ to mol dm⁻³ ?

A

Concentration (mol dm⁻³) = concentration (g dm⁻³) / Mr

Mr = molecular mass

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24
Q

Describe how to carry out an acid-alkali titration to find the concentration of an alkali

A
  1. Rinse pipette with solution of unknown concentration (alkali) and use to add known volume of alkali to conical flask
  2. Add few drops of indicator
  3. Rinse and fill burette with acid
  4. Gradually add acid to conical flask
  5. Record volume in burettebwhen indicator changes colour
  6. Repeat until you have concordant results
  7. Use results to calculate a mean litre and the concentration of alkali
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25
Q

If you know the volume of acid required to neutralise an alkali, how could you calcukate the concentration of the acid, given the alkali concentration and volume?

A
  • Calculate number of moles of alkali using known volume and concentration (moles=concentration x vol)
  • Use chemical equation to work out ratio of acid and alkali that react and work out how many moles of acid have reacted
  • Divide moles of acid by volume used in neutralisation to find concentration
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26
Q

What is meant by the term theoretical yield?

A

The amount of product that would be collected under perfect reaction conditions

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27
Q

How do you calculate percentage yield?

A

Percentage yield = (actual yield / theoretical yield) x 100

28
Q

Whats the percentage yield of NH₃ if 40.5g is produced from 20mol H₂ and excess N₂ ?

A

Equation: N₂ + 3H₂ -> 2NH₃
Moles of ammonia = 20/1.5 = 13.3 moles
Mass of ammonia = 13.3 x (14+1+1+1) = 227g
Percentage yield = (40.5/227)x100 = 17.8%

29
Q

Why could the actual yield of product be less than expected?

A

Incomplete reaction
Competing unwanted side reactions
Practical losses, eg some solid may get lost when being transferred between beakers

30
Q

What is the atom economy of a reaction?

A

Atom economy is a measure of the efficiency of the reaction. It looks at the amount of reactants that get turned into useful products.

31
Q

How can atom economy be calculated?

A

Atom economy = (Mr of desired product / Mr of reactants) x 100
Mr = molecular mass

32
Q

The ________ the atom economy, the more sustainable and efficient the process

A

Higher

33
Q

Why might one reaction pathway be chosen over another?

A

Higher atom economy
Higher yield
Faster rate
Equilibrium position favours products more
By-products are more useful / less harmful

34
Q

What does Avogadro’s Law state about gas volumes?

A

At the same temp and pressure, equal amounts of gas will occupy the same volume

35
Q

What is the molecular volume of a gas?

A

The volume occupied by one mole of molecules of any gas at room temp and pressure

36
Q

What is RTP?

A

room temperature and pressure
20°C
1 atmosphere

37
Q

How can the molar volume of a gas be calculated? Units included

A

Molar volume = volume (dm³) / moles of gas

Units: dm³ mol⁻¹

38
Q

Whats the Haber process

A

A reversible reaction that forms ammonia from nitrogen and hydrogen

39
Q

Describe the steps that are carried out during the Haber process

A
  1. Reactants are obtained (hydrogen from natural gas, nitrogen from air)
  2. The gases are compressed to 200 arm and heated to 450°C before being pumped into a tank containing layers of catalytic iron beads
  3. Ammonia forms
  4. Ammonia and unreacted hydrogen and nitrogen pass into a cooling tank where the ammonia is collected as a liquid
  5. The unreacted hydrogen and nitrogen are recycled back into the tank
40
Q

Whats meant by the term dynamic equilibrium

A

The rate of the forward reaction equals the rate of the backwards reaction. The concentration of reactants and products are constant.

41
Q

Whats the chemical equation for the formation of ammonia from hydrogen and nitrogen?

A

N ₂ + 3H ₂ <=> 2NH ₃

42
Q

What are the ideal conditions for the Haber process?

A

450°C temp
200 atm pressure
Iron catalyst

43
Q

How is the rate of attainment of equilibrium affected by temperature

A

A higher temp means equilibrium is reached quicker. This is because the reacting particles have more KE so there are more frequent successful collisions

44
Q

How is the ratebof attainment of equilibrium affected by a catalyst?

A

Equilibrium is reached faster when a catalyst is used because the catalyst provides an alternative reaction pathway with a lower activation energy.

45
Q

How is the rate of attainment of equilibrium affected by pressure?

A

Equilibrium is reached faster with a higher pressure. This is bc there are more particles in the same volume (or same no of particles in a smaller vol) so more collisions between reacting particles

46
Q

How is the rate of attainment of equilibrium affected by concentration?

A

Equilibrium is reached faster at a higher concentration. This is because there are more particles in the same volume so more collisions between the reacting particles

47
Q

Why are the conditions used in the Haber process a compromise?

A
  • A high temp increases rate of reaction but will favour reverse reaction, decreasing yield. Compromise of 450°C is used to obtain sufficient rate and yield
  • High pressure speeds up rate and favours forward reaction (increasing yield). High pressures can be dangerous and require expensive machinery so a compromise of 200atm is used.
48
Q

Why is a catalyst used in the Haber process?

A

To increase the rate of reaction so more product is produced within the same time frame

49
Q

What factors should be considered before deciding the conditions for an indistrial reaction?

A
  • availability and cost of raw materials
  • energy requirements
  • optimum temp and pressure for high yield and fast rate of reaction
  • need for a catalyst
50
Q

Whats the purpose of fertilisers?

A

Promote plant growth

51
Q

What chemical compounds might fertilisers contain?

A

Nitrogen, phsophorus and potassium compounds

52
Q

What compounds are found in NPK fertilisers?

A

A combination of all three fertiliser compounds: nitrogen, phosphorus and potassium compounds

53
Q

Which parts of plant growth do the compounds nitrogen, potassium and phosphorus help with?

A

Nitrogen: healthy leaves
Phosphorus: healthy roots
Potassium: growth and healthy fruit/flowers

54
Q

Which ammonium salt is most commonly used in fertilisers?

A

Ammonium nitrate

55
Q

How is the salt ammonium nitrate formed? Write a chemical equation for the reaction taking place

A

React ammonia with nitric acid

NH₃ + HNO₃ -> NH₄NO₃

56
Q

Whats the chemical equation for the formation of ammonium salfate from ammonia and sulfuric acid?

A

2NH₃ + H₂SO₄ -> (NH₄)₂SO₄

57
Q

How can ammonium sulfate be prepared in a laboratory

A

Titration between ammonia and sulfuric acid:

  • exact volume of NH₃ added to conical flask using pipette
  • add few drops of indicator
  • add H₂SO₄ from burette drop by drop. Stop when indicator changes colour
  • repeat adding exact same volumes of reactants without the indicator (as its an impurity)
  • remove the water by evaporation and crystallisation, leaving pure crystals
58
Q

How can ammonium sulfate be produced on an industrial scale?

A

Raw materials obtained from Haber process (ammonia) and the contact process (sulfuric acid). A large reactor chamber is filled with ammonia gas. Sukfuric acid is sprayed into the chamber from above. Ammonium sulfate crystals are produced

59
Q

Compare the laboratory method of producing ammonium sulafte with the industrial process

A

Lab - faster rate of reaction, small reactant quantities easily bought, room temp and pressure, simple equipment, very small yield
Industrial - v expensive and complex, continuous process so continuous yield, large volumes of product, slow rate of reaction, high energy requirement, other industrial processes required to obtain reactants

60
Q

How is a voltage produced from a chemical cell

A

2 metals of dofferent reactivities are placed in an electrolyte
The more reactive metal releases electrons, becoming positively charged. The electrons flow to the other electrode which becomes negatively charged. The difference in the ability of each electrode to release electrons causes a voltage to be produced

61
Q

When will a chemical cell stop producing a voltage

A

When one of the reactants has been used up

62
Q

What is a fuel cell

A

A cell that continually produces a voltage as long as it is supplied with oxygen and a fuel (like hydrogen)

63
Q

What is the only product of a hydrogen-oxygen fuel cell?

A

Water

64
Q

How does a hydrogen-oxygen fuel cell work?

A

Hydrogen and oxygen are pumped through porous electrodes. The electrolyte is often an acid such as phosphoric acid.
Hydrogen and oxygen react, producing electricity and water

65
Q

Write an equation for the overall reaction that takes place in a hydrogen-oxygen fuel cell

A

2H₂ + O ₂ -> 2H₂O

66
Q

What are the advantages of using fuel cells?

A

No pollution produced
Produce more energy than an alternative fuel like petrol
Continuous process as long as fuel is supplied

67
Q

What are the disadvantages of using fuel cells

A

Materials used to make them are expensive
High pressure tanks required to store oxygen and fuels like hydrogen
Hydrogen is expensive and hard to store
Efficiency is affected by temperature

GCSE - Chemistry (8 decks)

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