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A LEVEL CHEMISTRY PAPER 1 > Physical > Flashcards

Physical Flashcards

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1
Q

Hydrogen is used in the chemical industry.
Tungsten is extracted by passing hydrogen over heated tungsten oxide (WO3)
State the role of hydrogen in this reaction (1 mark)

A

Reducing agent

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2
Q

State a risk of using hydrogen gas in metal extractions

A

-Flammable/explosive

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3
Q

State why the electrode potential for the standard hydrogen electrode is equal to 0.00 V (1 mark)

A

By definition

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4
Q

Give one reason, other than cost, why the platinum electrodes are made by coating a
porous ceramic material with platinum rather than by using platinum rods. (1 mark)

A

Increases surface area.

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5
Q

Suggest why the e.m.f. of a hydrogen– oxygen fuel cell, operating in acidic conditions,
is exactly the same as that of an alkaline fuel cell. (1 mark)

A

Overall reaction is the same (2H2 + O2 → 2H2O)

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6
Q

Other than its lack of pollution, state briefly the main advantage of a fuel cell over a
re-chargeable cell such as the nickel– cadmium cell when used to provide power for an
electric motor that propels a vehicle. (1 mark)

A

Hydrogen and oxygen supplied continuously
OR
Can be operated without stopping to recharge

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7
Q

Hydrogen– oxygen fuel cells are sometimes regarded as a source of energy that is
carbon neutral. Give one reason why this may not be true. ( 1 mark)

A

Hydrogen may need to be made using an energy source that is not
‘carbon neutral’

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8
Q

Explain why the bond enthalpy of a Cl–Cl bond is greater than that of a Br–Br bond. (2 marks)

A
  • Bond is shorter or bonding pair closer to nucleus

- So attraction (between nucleus and) (to) bond pair is stronger

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9
Q

Suggest why the electron affinity of chlorine is an exothermic change.

A

Net attraction between the chlorine nucleus and the extra electron
OR
Allow Cl- ion more stable than Cl

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10
Q

Explain the meaning of the term perfect ionic model (1 mark)

A

Ions can be regarded as point charges (or perfect spheres)

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11
Q

Suggest why enthalpy lattice dissociated calculated from a born-haber cycle is GREATER than the theoretical value for enthalpy of lattice dissociation. (2 marks)

A
  • AgCl has covalent character

- Forces in the lattice are stronger than pure ionic attractions

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12
Q

Give the meaning of the term DYNAMIC in the context of a dynamic equilibrium

A

-Forward and reverse reactions occur at the same time/all of the time

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13
Q

Effect on time taken to reach equilibrium if pressure is increased: (3 marks)

A
  • Decrease in time taken
  • More particles in a given space
  • Therefore more successful collisions
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14
Q

What is the affect of doubling the pressure of a gas on the most probable energy in a maxwell-boltzmann distribution?

A

No effect

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15
Q

Write an overall equation to represent the decomposition of ozone into oxygen.

A

2O3—>3O2

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16
Q

Explain why dilute hydrochloric acid is not used to acidify the silver nitrate solution in
this test for iodide ions

A

-HCl would form a white ppt (which would interfere with test)

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17
Q

Give the formulas of the two different chlorine-containing compounds that are
formed when chlorine reacts with cold, dilute, aqueous sodium hydroxide

A
  • NaCl

- NaClO

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18
Q

Stereoisomers:

A

-Molecules with the same STRUCTURAL formula but with atoms and bonds arranged differently in space.

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19
Q

Why are you unable to measure enthalpy change using calorimetry for a hydrated salt reaction?

A

Not possible to prevent some dissolving so not accurate as it is soluble

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20
Q

Method to determine enthalpy of solution of an anhydrous salt (6);

A
  • Measure 10-200cm^3 of water USING measuring cylinder
  • Transfer into polystyrene cup
  • Add known mass of salt,
  • Weigh before and after

-Record a minimum of 2 INITIAL temps
-Record T at regular intervals until trend is seen and plot a T vs time graph
-Extrapolate line to when solid is added, to find initial and final t, getting /_\T. Use Q=MCAT. mol=mass/mr
Enthalpy of solution =-Q/mol

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21
Q

Why are major products formed in reactions:

A

Major product formed via more stable carbocation

-Due to positive inductive effect of alkyl groups (REASON: Due to having more alkyl groups than the minor)

22
Q

Conc Sulfuric acid with NaCl observation:

A

White steamy fumes

23
Q

Anti bumping granules purpose:

A

Prevents large bubbles from forming

24
Q

Reason to use electric heater in reaction rather than bunsen

A

Flammability

25
Q

Why is sodium benzoate soluble in cold water but benzoic acid isnt

A
  • Sodium benzoate soluble because ionic

- Benzoic acid has non polar benzene ring so not soluble

26
Q

Method to purify benzoic acid (General purification):

A
  • Dissolve crude product in hot water
  • Of minimum volume
  • Filter
  • Cool to recrystalise
  • Filter under reduced pressure
  • Wash (with cold water) and dry
27
Q

In terms of electrostatic forces suggest why electron affinity of fluorine has a negative value (2 mark)

A
  • Attraction from protons in nucleus to the (added) electrons
  • Energy released/exothermic reaction (when the electron is gained)
28
Q

A calculation of the enthalpy of lattice formation of silver iodide based on a perfect ionic model gives a smaller numerical galue than the value calculated in the cycle:
explain (2)

A

-AgI contains covalent character
-Forces/bonds holding lattice together are stronger
well

29
Q

Suggest a reagent used to indicate the presence of iodide ions in an aqueous solution, and describe the observation made: (2)

A

AgNO3

Would form a yellow ppt

30
Q

Describe a test you could carry out in a test tube, to distinguish between SODIUM OXIDE and PHOSPHOROUS OXIDE (3)

A
  • React with water
  • Add litmus paper
  • Litmus gives blue colour with NaO, red with P4O10
31
Q

Reaction of sulfur trioxide with potassium hydroxide

A

SO3 + 2KOH ——> K2SO4 + H2O

32
Q

Reaction with an excess of magnesium oxide with phosphoric acid

A

3MgO + H3PO4 —-> Mg3(PO4)2 + 3H2O

33
Q

Draw the displayed formula of the undissociated acid formed when sulfur dioxide reacts with water:

A 
H- O
        \
          S=O             (SO3H)+
        /
H - O
34
Q

State the type of bonding between oxygen and hydrogen in
[Cu(H2O)6]Cl2.

State why the chloride ions in this compound are not considered to be ligands

A

Covalent

Cl- NOT donating a lone pair to the Cu2+

35
Q

When Reagent D is added to [Cu(H2O)6]2+ , a yellow-green solution is formed. Identify D and write an ionic equation

A

HCl

[Cu(H2O)6]2+ + 4HCl —> [CuCl4]2- + 6H2O + 4H+

36
Q

Explain why colorimetry cannot be used to determine the concentration of solutions containing [CuCl2]-
In your answer refer to electron configuration (2 marks)

A
  • Full 3d orbital

- SO colourless

37
Q

Describe how a student could distinguish between aqueous solutions of KNO3 and Potassium sulfate using one simple test tube reaction (3)

A

Reagent: BaCl2

Observation with KNO3: No reaction

Observation with K2SO4: White ppt formed

38
Q

Describe how a student could distinguish between aqueous solutions of MgCl2 and AlCl3 using one simple test tube reaction (3)

A

Reagent: NaOH

Obs with MgCl2: White ppt

Obs with AlCl3: White ppt that dissolves in EXCESS NaOH

39
Q

When the complex ion [Cu(NH3)4(H2O)2]
2+ reacts with 1,2-diaminoethane, the
ammonia molecules but not the water molecules are replaced.
Write an equation for this reaction.

ii) Suggest why the enthalpy change for the reaction in Question 8.3 is approximately
zero. (2)

iii)Explain why the reaction in Question 8.3 occurs despite having an enthalpy change
that is approximately zero. (2)

A

[Cu(NH3)4(H2O)2]2+ + 2H2NCH2CH2NH2 ————[Cu(H2NCH2CH2NH2)2(H2O)2]
2+ + 4NH3

ii)-Cu–N bonds formed have similar enthalpy / energy to Cu–N bonds
broken
-And the same number of bonds broken and made

-3 particles form 5 particles / disorder increases because more
particles are formed / entropy change is positive

-Therefore, the free-energy change is negative

40
Q

A 5.00 g sample of potassium chloride was added to 50.0 g of water initially at
20.0 °C. The mixture was stirred and as the potassium chloride dissolved, the
temperature of the solution decreased.
Describe the steps you would take to determine an accurate minimum temperature
that is not influenced by heat from the surroundings.(4)

A
  • Start a clock when KCl is added to water
  • Record the temperature every subsequent minute for about 5 minutes
  • Plot a graph of temperature vs time
  • Extrapolate back to time of mixing = 0 and determine the temperature
41
Q

When chlorine gas dissolves in cold water a pale green solution is formed.
CL2(g) +H20(l) –> H+ + Cl- + HClO
Give the formula of the species responsible for the pale green colour in the solution of chlorine in water.

A

Cl2

42
Q

When chlorine reacts with water in BRIGHT sunlight, only two products are formed.
One is a colourless, odourless gas and the other is an acidic solution that reacts with silver nitrate solution to give a white precipitate.
Name the two products.

A

Colourless, odourless gas- O2

Acidic solution that reacts with silver nitrate - HCl

Cl2 + 2H20 –> HCl + O2

43
Q

Suggest why the concentration of sodium hydroxide in a solution slowly
decreases when left open to air

A

NaOH reacts with carbon dioxide (in the air)

44
Q

Mean bond enthalpy: (2 marks)

A
  • Enthalpy (energy required) needed in breaking a covalent bond
  • Averaged over a range of compounds
    (conditions: constant pressure)
45
Q

State the meaning of the term carbon-neutral

A

-No net/overall Carbon Dioxide emission to the atmosphere

46
Q

Rate of reaction definition:

A

The rate of reaction is defined as the change in concentration of a substance in unit time
Its usual unit is mol dm-3s
-1

47
Q

How to work out initial rate from a graph

A

Gradient of initial tangent=Initial rate

gradient of curve in general is the rate of reaction

48
Q

Maxwell boltzmann distribution higher conc

A

Graph is higher up

49
Q

Explain the function of the salt bridge. (2 marks)

A

-The ions in the ionic substance in the salt bridge move through the
salt bridge
-To complete the circuit

50
Q

There are two ways to use hydrogen as a fuel for cars. One way is in a fuel cell to
power an electric motor, the other is as a fuel in an internal combustion engine.
Suggest the major advantage of using the fuel cell.

A 
A fuel cell converts more of the available energy from combustion of
hydrogen into kinetic energy of the car / an internal combustion engine
wastes more (heat) energy
51
Q

Weak acid

A

partially dissociates

52
Q

Strong acid

A

Ionises completely in solution.

A LEVEL CHEMISTRY PAPER 1 (5 decks)

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