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Higher Chemistry > HC Prelim > Flashcards

HC Prelim Flashcards

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1
Q

Electrolysis of magnesium chloride takes place. Suggest why this is carried out at a temperature of 750 degrees

A

Below 750 degrees, they are solids and electrolysis must take place between liquids

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2
Q

Why is sulphuric acid added to a reaction?

A

To add hydrogen ions

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3
Q

State the term for the unstable arrangement of atoms formed at the top of the curve on the potential energy diagram

A

Activated complex

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4
Q

State what is meant by the term electronegativity

A

Electronegativity is the measure
of attraction an atom has
for the electrons in a bond

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5
Q

Enthalpy

A

Energy change for a chemical reaction or physical change

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6
Q

Activation energy

A

Minimum kinetic energy required for a reaction to occur
OR minimum kinetic energy required by colliding molecules to form an activated complex

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7
Q

Enthalpy of combustion

A

Enthalpy change when one mole of a substance burns completely in oxygen

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8
Q

Enthalpy of solution

A

Enthalpy change when one mole of a substance dissolve completely in water

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9
Q

Enthalpy of neutralisation

A

Enthalpy change per mole of water formed when an acid is neutralised by an alkali

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10
Q

Enthalpy of formation

A

Energy needed to make one mole of a compound from its elements in their standard state

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11
Q

Equilibrium

A
  • rate of forward reaction and reverse reactions are equal
  • conc of reactants and products remain constant but not necessarily equal
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12
Q

Explain fully why the boiling points of the halogens increase going down
group 7.
In your answer you should name the intermolecular forces involved

A

(Intermolecular) forces/bonds
increase (going down the group).
(1)

LDFs are the forces (broken)
between the molecules. (1)

The more electrons the stronger the
LDFs.

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13
Q

Silicon tetrachloride can be used to make silicon nitride (Si3N4), a
compound found in many cutting tools.
(i) Silicon nitride has a melting point of 1900 °C and does not conduct
electricity when molten.
Explain fully, in terms of structure and bonding, why silicon nitride
has a high melting point.

A

Silicon nitride is a (covalent)
network

(Strong) covalent bonds are broken

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14
Q

Explain why the aluminium foil needs to be heated at the start of
the preparation, despite the reaction being highly exothermic

A

To provide (initial) activation
energy/(sufficient) energy to form activated (activation) complex.

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15
Q

Suggest a reason why there is a small test tube filled with cold water in
the neck of the tube containing the reaction mixture.

A

Condense reactants or products/acts
as a condenser/to prevent escape of
(volatile/gaseous) reactants or
products/to prevent the escape of gas(es)

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16
Q

Name a reagent which could be used to distinguish between
3-methylbutanal and a ketone

A

Acidified dichromate solution

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17
Q

3-Methylbutanal is found in olive oil.
Explain fully what can happen to 3-methylbutanal that will cause the
olive oil to develop an unpleasant taste.

A

Will react with oxygen/undergo
oxidation. (1)
Forming a carboxylic acid (which has unpleasant taste).

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18
Q

Explain why step 1 is described as a condensation reaction.

A

Because it has two molecules joining together with the loss of a
small/water molecule

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19
Q

Describe how free radicals are formed.

A

Bond breaking by UV

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20
Q

State how free radical scavengers prevent further chain reactions

A

Can react with free radicals forming
stable molecules/free radicals (and
prevent chain reactions).
OR
Donates electron(s).
OR
Acting as a reducing agent.

21
Q

Ethene is an important feed stock for the production of plastics. Which type of reaction is involved in converting ethane to ethene?

A

Alkenes made from alkanes from cracking

22
Q

The chemical indicator in a breathe test kit turns from orange to green when a motorist is over the legal alcohol limit. Which indicator is used:
- acidified potassium dichromate
- benedicts solution
- fehlings solution
- tollens reagent

A

acidified potassium dichromate

23
Q

Which one is not a raw material in chemical industry?
- iron ore
- sodium chloride
- water
- ammonia

A

Ammonia

24
Q

On descending group 1 from Lithium to Caesium, the electronegativity of the elements decreases. Explain why this happens

A

Greater shielding effect as more shells as you go down therefore attraction nucleus has for electrons in bond decreases

25
Q

Homogeneous and heterogeneous

A

Homogeneous: catalyst and reactants are same state

26
Q

Covalent radius

A

Half the distance between two neighboring atoms if they were to form a covalent bond

27
Q

Ionisation energy

A

Energy required to remove one mole of electrons from one mole of atoms in a gaseous state

28
Q

Difference in mean bond enthalpy and bond enthalpy

A

Bond enthalpy is an exact value as bond is only in one type of compound whereas mean bond enthalpy is an average as bond is in different types of compounds

29
Q

Polar covalent bond

A

Unequal sharing of electrons between two atoms

30
Q

Enzyme

A

Biological catalyst

31
Q

Standard solution

A

A solution of accurately known concentration

32
Q

Condensation reaction

A

Reaction where two molecules join with the loss of a small molecule (usually water)

33
Q

Why do some titrations not need an indicator

A

Because the reaction if self indicating

34
Q

Molar volume

A

Volume occupied by one mole of gas at a certain temp and pressure

35
Q

Activated complex

A

Unstable arrangement of atoms formed at the maximum of the potential energy barrier during a reaction

36
Q

Temperature

A

Measure of average kinetic energy of the particles in a substance

37
Q

Enthalpy

A

Measure of the energy stored in a chemical

38
Q

Hess’s law

A

Enthalpy change for any particular chemical reaction is the same regardless of the chemical route taken

39
Q

Molar bond enthalpy

A

Energy required to break one mole of bonds in a diatomic molecule

40
Q

Mean molar bond enthalpy

A

Average energy required to break one mole of bonds, for a bond that occurs in a number of compounds

41
Q

Dynamic equilibrium

A

Rates of forward and reverse reactions are equal

42
Q

Titration used

A

To accurately determine the volume of solution to reach the end point of a reaction

43
Q

Explain fully the cleaning action of a soap

A

(Compound C) has an ionic/hydrophilic
part and a non polar/hydrophobic part (or
alternative wording/diagram showing
knowledge of these parts of the molecule)
(1)
Correctly identifies the part of the
molecule/head/COO- dissolves in water/
is hydrophilic and the part of the
molecule/tail/hydrocarbon chain dissolves
in oil/hydrophobic. (1)
Agitation separates oil from the
surface/cause small oil droplets to form
OR
The (negatively-charged) ball-like
structures repel each other (and the oil or
grease is kept suspended in the water)
OR
Soaps/compound C allow(s) emulsions to
form or break(s) oil into micelles. (1)

44
Q

How are free radicals formed

A

Bond breaking by UV (light) or
example of initiation reaction
(equation or diagram).
eg chlorine splitting to give two free
radicals is accepted, provided UV is
shown.

45
Q

State how free radical scavengers prevent further chain reactions

A

Can react with free radicals forming
stable molecules/free radicals (and
prevent chain reactions).
OR
Donates electron(s).
OR
Acting as a reducing agent.
OR
Provide electrons to pair with an
unpaired electron.

46
Q

Explain why antioxidants are added to food

A

To prevent unwanted oxidation

47
Q

Free radical

A

Species (atoms/molecules/particles)
with unpaired electrons

48
Q
A

Higher Chemistry (1 decks)

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