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aqa a level chemistry > Chemystery > Flashcards

Chemystery Flashcards

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1
Q

Explain the process of electrospray ionisation (2 marks)

A
  • Sample is dissolved in a polar solvent and passed through a positive terminal with a high voltage
  • Molecules gain a proton
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2
Q

Define relative atomic mass - Ar (2 marks)

A 
  1/12th mass of one atom of 12C
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3
Q

Define relative molecular mass - Mr (2 marks)

A

1/12th mass of one atom of 12C

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4
Q

Define relative isotopic mass - Ar (2 marks)

A 
  1/12th mass of one atom of 12C
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5
Q

State and explain how the enthalpy of formation of liquid water would differ to the enthalpy of formation of gaseous water (2 mark)

A
  • More negative (more exothermic)

- As heat energy is released when water vapour condenses

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6
Q

Suggest why a catalyst may need to be heated during a reaction (1 mark)

A
  • To overcome the activation energy
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7
Q

A reagent which is miscible in water is added to a hydrated compound then allowed to dry. Suggest two reasons why adding this reagent is an effective method for producing a pure, dry precipitate (2 marks)

A
  • The reagent will evaporate

- Removing water from the precipitate

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8
Q

In terms of atomic structure, explain why the van der Waals’ forces in liquid argon are very weak (2 marks)

A
  • Argon particles are single atoms with electrons closer to nucleus
  • Cannot easily be polarised (or electron cloud not easily distorted)
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9
Q

Explain why sulfur has a relatively high melting point (2 marks)

A
  • Strong van der waals forces

- So a lot of energy required to LOOSEN these forces

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10
Q

Explain why silicon has a very high melting point (3 marks)

A
  • Giant macromolecular structure
  • With many strong covalent bonds
  • A lot of energy required to BREAK these bonds
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11
Q

Explain how metals conduct electricity (2 marks)

A
  • Delocalised electrons

- Move / flow in a given direction (NOT CARRY CHARGE)

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12
Q

Explain the meaning of the term periodicity (2 marks)

A
  • Pattern in the change in the properties of a row of elements OR trend in the properties of elements across a period
  • Repeated in the next row
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13
Q

P is an element in period 3. Oxide P is a solid with a high melting point. It does not conduct electricity when solid but does conduct when molten or when dissolved in water. Oxide P reacts with water forming a solution with a high pH. Identify P. State the type of bonding present in P and explain its electrical conductivity. Write an equation for the reaction of P with water (5 marks)

A
  • Ionic
  • Ions not free to move in the solid state
  • Ions free to move when molten or in aqueous solution
  • Identity of P: Na2O or sodium oxide
  • Equation: Na2O + H2O → 2 NaOH
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14
Q

Q is an element in period 3. Oxide Q is a colourless gas at room temperature. It dissolves in water to give a solution with a low pH. Identify Q. State the type of bonding present in Q and explain why it is a gas at room temperature. Write an equation for the reaction of Q with water (4 marks)

A
  • Covalent
  • Intermolecular forces are weak or van der Waals forces,
  • Identity of Q: SO2
  • Equation: SO2 + H2O → H2SO3
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15
Q

Write the equation for the reaction between aluminium hydroxide and NaOH (1 mark)

A

Al(OH)3 + NaOH → NaAl(OH)4

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16
Q

Explain why aluminium hydroxide is insoluble in water (3 marks)

A

Strong covalent bonds

17
Q

Explain why increasing the concentration of acid increases the rate of reaction at an increasing rate (3 marks)

A
  • As concentration increases, amount of heat given out increases
  • More successful collisions in a given time
  • So this increases the rate of reaction
18
Q

State the product formed when magnesium reactions with steam (1 mark)

A

MgO

19
Q

State the product formed when magnesium reactions with water (1 mark)

A

Mg(OH)2

20
Q

Define rate of reaction (1 mark)

A

Amount of substance formed per unit time

21
Q

Mechanism for catalytic cracking (1 mark)

A

Heterolytic fission

22
Q

The pollutant gas NO is found in the exhaust gases from petrol engines. Explain why NO is formed in petrol engines but is not readily formed when petrol burns in the open air (3 marks)

A
  • NO formed by reaction between N2 and O2
  • from the air
    OR N2 +O2 → 2NO
  • High combustion temperature or spark in engine provides EA or sufficient heat / energy to break triple N bond
23
Q

The pollutant gas CO is also found in the exhaust gases from petrol engines. Explain how CO and NO are removed from the exhaust gases and why the removal of each of them is desirable (9 marks)

A
  • Need to remove NO as forms acid rain or toxic product or causes respiratory problems
  • 2NO + O2 → 2NO2
  • 4NO2 + O2 + 2H2O → 4HNO3
  • Need to remove CO as it is poisonous
  • Catalytic converter
  • uses Pt / Rh / Pd / Ir
  • Provides active sites / reduces EA
  • Forms N2 + CO2
  • 2NO + 2CO → N2 + 2CO2
24
Q

State the observation when aqueous aluminium solution reacts with carbonate ions (1 mark)

A

Effervescence

25
Q

State what must be done to maintain the EMF of a fuel cell (1 mark)

A
  • Keep the concentration of reactants constant
26
Q

Outline briefly why chromatography is able to separate a mixture of compounds (3 marks)

A
  • Phase or solvent (or named solvent) is moving or mobile
  • Stationary phase - solid or alumina/silica/resin
  • Separation of molecules depends on balance between solubility or affinity

aqa a level chemistry (18 decks)

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