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Edexcel Chemsitry > Topic 5: Separate Chemistry 1 > Flashcards

Topic 5: Separate Chemistry 1 Flashcards

1
Q

5.1 What are most metals?

A

Transition metals, found between groups 2 and 3

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2
Q

5.1 What are the typical properties of transition metals?

A
  • High melting/boiling point and densities compared to other metals
  • Form different coloured compounds, other metal compounds white or colourless
  • Malleable and ductile
  • Good conductors
  • Shiny when polished
  • Show catalytic activity alone or as compounds- i.e. Iron is used as one in the Haber process
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3
Q

5.1 Why do transition metals form different coloured compounds?

A

Most have variable ions/ oxidation states which form different coloured compounds- eg Fe 2+ forms Fe(OH)2 (pale green) but Fe3+ forms Fe(OH)3 (orange-brown)

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4
Q

5.2C How is corrosion caused?

A

Oxidation of metals
eg
Sodium + Oxygen -> Sodium Oxide
4Na(s) + O2(g) -> 2Na2O(s)

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5
Q

5.3C How is rusting caused?

A

Corrosion of iron or steel when it reacts with oxygen and water
eg
Iron + oxygen + water -> hydrated iron (III) sulfate

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6
Q

5.3C Explain how rusting of iron or steel can be prevented

A
  • Exclusion of oxygen by storing metal in unreactive nitrogen/argon atmosphere
  • Exclusion of water by using desiccants that absorb it
    -> Exclusion of both with painting, plastic coating, oiling and greasing
  • Sacrificial protection by attaching more reactive magnesium or zinc to iron so oxidises instead
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7
Q

5.4C What is electroplating?

A

The coating of the surface of one metal with a thin layer of another via electrolysis

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8
Q

5.4C Describe the electroplating of a copper ring with silver

A
  1. Plating metal (silver) anode
  2. Metal object to be plated (copper) cathode
  3. Both electrodes in electrolyte of ions of plating material (silver)
  4. Silver atoms lose electrons and become ions that go into the electrolyte
  5. Silver ions in electrolyte move to negatively charged copper ring, gaining electrons and deposited as silver atoms
  6. Longer current flows = thicker silver layer
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9
Q

5.4C Write the half equations that occur during electroplatingof a copper ring with silver

A
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10
Q

5.4C Explain how electroplating can be used

A
  • Improve the appearance of metal objects
  • Make eg gold object more cheaply using gold layer on cheap base
  • Improve the resistance to corrosion of metal objects, eg use of chromium to plate vehicle parts to stop rusting of steel below
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11
Q

5.4C Describe galvanising

A

Used to protect iron or steel from rusting by coating in zinc, stopping water from reaching it as a sacrificial metal even if damaged
Carried out through electroplating or dipping into molten zinc

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12
Q

5.4C Describe tin plating

A

Used to protect steel food cans from rusting by electroplating with tin that doesn’t react with air or water at room temperature, but not sacrificial metal as less reactive than iron so effectiveness reduced with damage

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13
Q

5.5C What is an alloy?

A

Mixture of a metal element with one or more usually metal elements

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14
Q

5.5C Explain, using models, why converting pure metals into alloys often increases the strength of the product

A
  • In a solid, pure metal atoms are all the same size in regular layered arrangements that move past eachother with force making them malleable
  • In an alloy, atoms of different elements may be different sizes making it harder for layers to move past eachother and so stronger though still malleable
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15
Q

5.6C Explain why iron is alloyed with other metals to produce alloy steels

A

Alloy steels can have enhanced properties-
- Stainless steels contain chromium that resist rusting by forming Cr2O3 protecting metal below but thin enough to be transparent and reacting to replace the layer if damaged
- ‘Tough’ steels contain tungsten and molybdenum to increase strength. Higher carbon content in steel also helps.

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16
Q

5.7C Explain how the uses of metals are related to their properties (and vice versa), including aluminium, copper and gold

A

All resist corrosion but:
- Aluminium worse conductor than copper, but stronger, cheaper and less dense so used for overhead electrical cables
- Copper and gold malleable, ductile and very good conductors but copper much cheaper so used for most wiring and gold for microprocessors and memory chips in tiny amounts

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17
Q

5.7C Explain how the uses of metals are related to their properties (and vice versa) and their alloys including magnalium and brass

A
  • Brass is copper and zinc; copper + brass resist corrosion, copper better conductor but brass stronger so used in plug pins
  • Magnalium 95% aluminium and 5% magnesium- denser than magnesium but twice as strong and better corrosion resistance so used in lightweight aircraft parts
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18
Q

5.8C Calculate the concentration of solutions in g dm-3

A

mass / volume

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19
Q

5.8C Convert concentration in g dm-3 into mol dm-3 and vice versa

A

concentration / relative formula mass of solute

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20
Q

5.9C Core Practical: Carry out an accurate acid-alkali titration, using burette, pipette and a suitable indicator

A
  1. BURETTE washed with acid and jet filled by running some out.
  2. Initial reading recorded on burette
  3. Conical flask filled with 25cm3 of alkali using PIPETTE placed on white tile under burette
  4. Indicator added to alkali and acid slowly added to alkali
  5. END-POINT occurs when indicator changes to indicate neutralisation
  6. Repeat titration without initial washing until concordant results obtained
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21
Q

5.9C What are concordant results?

A

Within 0.2cm3 of eachother

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22
Q

5.10C how to calculate an unknown concentration from titration results?

A

1) write balanced equation
2) add data given in question under reactants in equation
3) calculate amount in mol of reactant with all data given
4) use balanced equation to determine amount in mol of other reactant
5) calculate unknown concentration of reactant

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23
Q

5.11C What is the theoretical yield?

A

Maximum mass of a product that can be formed from a reactant

24
Q

5.11C What is the actual yield?

A

Actual mass of a product formed from a reactant when a reaction is carried out

25
Q

5.11C Calculate the percentage yield of a reaction from the actual yield and the theoretical yield

A

(Actual yield / theoretical yield) x 100

26
Q

5.12C How do the actual and theoretical yields compare?

A

Actual usually less than theoretical

27
Q

5.12C Why is the actual yield usually less than the theoretical one?

A
  • Incomplete reactions if a reaction reaches equilibrium or hasn’t been left long enough so some limiting reactant remains
  • Practical losses if eg liquid remains on the walls of a container when moving to another or a precipitate is formed and some left behind when filtered
  • Competing side reactions where reactants may react to make unwanted products alongside the one intended- eg alkanes can form CO or C during combustion when incomplete
28
Q

5.13C Recall the atom economy of a reaction forming a desired product

A

Shows efficiency of a reaction at using atoms in its reactants- percentage by mass of useful products

29
Q

5.14C How do you calculate the atom economy of a reaction forming a desired product?

A

(Relative formula mass of useful produce / sum of relative formula masses of all reactants) x 100

30
Q

5.15C Explain why a particular reaction pathway is chosen to produce a specified product

A
  • Higher yield and atom economy with conceivable conditions for it, causing less wastage eg by finding uses of by products
  • Rate of reaction, controlled by equilibrium position
  • Availability and cost of raw materials & energy supplies
31
Q

5.16C Describe molar volume

A

Volume occupied by one mole of molecules of any gas at room temperature and pressure

32
Q

5.16C What is the value of molar volume?

A

24 dm3 or 24000 cm3

33
Q

5.17C Use the molar volume and balanced equations in calculations involving the masses of solids and volumes of gases

A

molar volume = volume of gas / number of moles

34
Q

5.18C Use Avogadro’s law to calculate volumes of gases involved in a gaseous reaction, given the relevant equation,
eg volume of ammonia produced if 100cm3 nitrogen used N2(g) + 3H2(g) → 2NH3(g)

A

If temperature and pressure are the same equal volumes of different gases have an equal number of molecules
Nitrogen to ammonia ratio 1:2 so ammonia is 200cm3

35
Q

5.19C Describe the Haber process

A

Reversible reaction between nitrogen and hydrogen to form ammonia
N2(g) + 3H2(g) ⇌ 2NH3 (g)

36
Q

5.20C Predict how the rate of attainment of equilibrium is affected by changes in temperature

A

Higher temperature makes molecules move faster, so more frequent collisions, so more reactions in a given time, so equilibrium reached faster

37
Q

5.20C Predict how the rate of attainment of equilibrium is affected by changes in pressure

A

Higher pressure increases concentration of gases, so more frequent collisions, so more reactions in a given time, so equilibrium reached faster

38
Q

5.21C Explain how in industrial reactions, including the Haber process, conditions used are related to: a the availability and cost of raw materials and energy supplies

A
  • Nitrogen and hydrogen fairly cheap and plentiful from air and natural gas respectively
  • Pressure of 200 atmospheres compromise to keep yield high without too much cost
39
Q

5.20C Predict how the rate of attainment of equilibrium is affected by use of a catalyst

A

If a catalyst is added equilibrium position is unchanged as forwards and backwards reactions sped up to the same extent, but rate of attainment of equilibrium increases

40
Q

5.20C Predict how the rate of attainment of equilibrium is affected by changes in concentration

A

Excess reactant/product increases concentration of this reactant/product so more frequent collisions between this reactant/product and other particles, so more reactions in given time, so equilibrium reached faster

41
Q

5.21C Explain how, in industrial reactions, including the Haber process, conditions used are related to the control of temperature, pressure and catalyst used produce an acceptable yield in an acceptable time

A
  • Increased temperature moves equilibrium to the left, but low temperatures reduce rate so 450C compromise gives acceptable yield of ammonia in an acceptable time
  • Pressure of 200 atmospheres compromise to keep yield high without too much cost
  • Iron catalyst doesn’t change position of equilibrium but increases rate of reaction
42
Q

5.22C What do fertilisers usually contain?

A
  • Nitrogen, phosphorus and potassium compounds
  • Plants need these mineral ions to promote growth by preventing deficiency diseases like stunted growth and discolouring, which they can take up through the soil and gradually use up
  • Must be provided as soluble compounds because root hair cells only absorb dissolved ions
43
Q

5.23C Describe how ammonia reacts with nitric acid

A
  • To produce Ammonium nitrate salt that is used as a fertiliser with ammonia SOLUTION and DILUTE nitric acid
    ammonia + nitric acid → ammonium nitrate
    NH3(aq) + HNO3(aq) → NH4NO3(aq)
44
Q

5.23C How is nitric acid manufactured?

A
  • From ammonia
    ammonia + oxygen → nitric acid + water
    NH3(g) + 2O2(g) → HNO3(aq) + H2O(l)
45
Q

5.24C Describe Ammonium sulfate

A

A nitrogenous fertiliser, just like Ammonium nitrate

46
Q

5.24C Describe the laboratory preparation of ammonium sulfate

A

Uses pre bought ammonia solution and dilute sulfuric acid on a small scale via titration
ammonia + sulfuric acid → ammonium sulfate
2NH3(aq) + H2SO4(aq) → (NH4)2SO4(aq)

47
Q

5.24C Describe the industrial production of ammonium sulfate

A

Involved making ammonia solution and dilute sulfuric acid on a large scale with raw materials in several stages

48
Q

5.24C Compare the laboratory and industrial preparation of ammonium sulfate

A
  • Small scale in labs, large scale in industrial production
  • Ammonia solution and dilute sulfuric acid pre-bought in labs, raw materials used to make it in industrial production
  • Uses titration in labs but several stages in industrial production
  • Batch production in labs where a small amount made manually, apparatus cleaned and another is made, but continuous automated production in industry as reactants constantly fed into reactants and products removed- cleaning rare
49
Q

5.25C Describe a chemical cell

A
  • Two different metals each dipped in a solution of one of their salts
  • A ‘salt bridge’- usually potassium nitrate solution- is a strip of filter paper soaked in a salt- letting dissolved ions and so charge pass from one solution to another completing circuit so current can flow
50
Q

5.25C Describe how a chemical cell functions

A
  1. An exothermic reaction occurs but energy is transferred mainly by electricity than heating
  2. Voltage is produced between the two metals which is greater the further apart they are in the reactivity series until one of the reactants is used up,- battery goes flat/ car needs recharging
  3. A current flows if the cell is connected to an external circuit
51
Q

5.25C What is a battery?

A

Two or more electrical cells joined together

52
Q

5.25C Describe the reaction that occurs when copper and zinc are used in a chemical cell

A

zinc + copper sulfate → zinc sulfate + copper
Zn(s) + CuSO4(aq) → ZnSO4(aq) + Cu(s)

Zinc produces electrons because zinc metal goes into zinc solution to form zinc ions and give up two electrons, that travel into copper sulfate solution where copper ions will pick up two electrons to form copper
Flow of electrons can thus be measured on a voltmeter

53
Q

5.26C Describe a fuel cell

A
  • 2 platinum electrodes connected to a motor that catalyse reactions in cell
  • Membrane inbetween electrodes
  • Hydrogen fuel in/ excess out on one side, oxygen in/waste water out on other
54
Q

5.26C Describe how a fuel cell functions, eg hydrogen-oxygen fuel cell

A
  1. Negative platinum electrode supplied with hydrogen gas fuel where hydrogen ions and electrons form, catalysed by electrode
  2. Electrons flow through external circuit through motor and hydrogen ions through membrane to positive platinum electrode
  3. Hydrogen ions gain electrons and react with oxygen supplied to positive platinum electrode to form water, catalysed by electrode
  4. Any unreacted hydrogen (left) and waste water (right) is taken out of the bottom
55
Q

5.26C Describe the reaction that occurs in a hydrogen-oxygen fuel cell

A

hydrogen and oxygen are used to produce a voltage and water is the only product
Hydrogen oxidised because loses electrons
Oxygen reduced because gains electrons

56
Q

5.27C Evaluate the strengths and weaknesses of fuel cells for given uses (6)

A
  • Chemical cells store all reactants, fuel cells must be supplied with fuel and oxygen from outside
  • No combustion takes place in either, and energy produced from both is converted into electrical energy
  • Fuel cells produce voltage as long as a continuous supply of fuel and oxygen is provided, don’t go ‘flat’ like batteries in chemical cells
  • Neither directly produce greenhouse gases, but most hydrogen manufactured by reaction of steam + coal/natural gas that releases carbon dioxide anyway
  • Platinum electrode in hydrogen cells expensive, but don’t need to be replaced
  • Motor in fuel cell much quieter and low maintenance than petrol/diesel engine (no moving parts) but hydrogen still needs to be stored, but few hydrogen stations for refuelling unlike electrical outlets to recharge a battery
57
Q
A

Edexcel Chemsitry (9 decks)

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