AOS

Question 1

Define relative atomic mass

Answer 1

Ar= average mass of an atom of an element
1/12th the mass of a C12 atom

Question 2

Define Mr

Answer 2

Mr= average mass of one molecule
1/12th the mass of a c12 atom

Question 3

% yield

Answer 3

Actual yield/theoretical yield x 100

Question 4

Atom economy equation

Answer 4

Mass of desired product/ total. Mass of reactants x 100
Must use big numbers in equation

Question 5

Standard solution

Answer 5

Weigh the sample bottle containing the solid on a balance
Transfer to beaker and reweigh sample bottle
Record difference in mass
Add distilled water, stir with a glass rod until solid is dissolved
Transfer to volumetric flask using a funnel with washings
Make up to 250cm with distilled water
Invert or shake to mix

Question 6

percentage error

Answer 6

Error of equipment/ amount measured x 100

Question 7

Why remove bubbles from brunette tap

Answer 7

Volume of air bubble will be counted in the burette reading and increase the titre value.

Question 8

Why remove funnel

Answer 8

Solution drops could fall from the funnel into the burette and forget the reading

Question 9

Why swirl the concise flask with distilled water

Answer 9

Ensure all reagents react. Doesn’t change number of moles.

Question 10

Why not use a measuring cylinder

Answer 10

Volumetric pipettes has a lower percentage error, measuring cylinder is higher

Question 11

Why use 3-5v drops pf indicator

Answer 11

To not ruin or spoil the colour change at the end point

Question 12

Why not rinse the burette with water

Answer 12

Reactant will be diluted, titre volume will be higher

Question 13

Define empirical formula

Answer 13

Simplistic whole number ration of atoms of each element

Question 14

Why do boiling points increase with chain length?

Answer 14

As the molecules increase in size, and have more electrons, the size of the van der Waals forces between them also increases. Therefore, boiling point increases with increasing chain length since more energy is needed to overcome the greater forces.

Question 15

State whether branched or straight chain hydrocarbons have higher melting points and explain why.

Answer 15

Branched chain hydrocarbons have lower melting points than straight chain hydrocarbons. This is because straight chain hydrocarbons can pack together more closely and, therefore, the strength of van der Waals forces between molecules is stronger. Therefore more energy is needed to overcome the greater forces.

Question 16

Why are alkanes insoluble in polar solvents, such as water?

Answer 16

Alkanes only have van der Waals interactions with water molecules that are much weaker than the hydrogen bonds water forms between its molecules.

Question 17

Describe the reactivity of alkanes.

Answer 17

Alkanes are unreactive due to their highly non-polar nature.

Question 18

What is crude oil?

Answer 18

Crude oil is a mixture of hydrocarbons.

Question 19

What type of hydrocarbon does petroleum mainly contain?

Answer 19

Petroleum mainly contains saturated alkanes with roughly eight carbons.

Question 20

What is a fraction in relation to crude oil?

Answer 20

A mixture of hydrocarbons of similar chain length with a similar range of boiling points.

Question 21

Describe fractional distillation.

Answer 21

• Crude oil is heated (not burnt) until it vaporises.
• It is then passed into a tower that is hotter at the bottom than the top. The vapours rise until it condenses.
• Short chain hydrocarbons condense near the top, long chain hydrocarbons near the bottom.

Question 22

What bonds are broken when fractional distillation is carried out?

Answer 22

Fractional distillation is a physical process so no intramolecular covalent bonds are broken. Intermolecular van der Waals forces are instead overcome during vaporisation.

Question 23

What is cracking?

Answer 23

The breaking of covalent C-C bonds in long chain alkanes into shorter chain hydrocarbons, some of which are alkenes.

Question 24

What are the conditions of thermal cracking?

Answer 24

A temperature between 700 and 1200 K and a pressure of up to 7000 kPa.

Question 25

Why is the mixture only heated for a short time?

Answer 25

They are heated for short periods of time to avoid excess decomposition into carbon and hydrogen.

Question 26

Describe the chain length of products when thermal cracking is carried out at i) lower temperatures and ii) higher temperatures.

Answer 26

i) Lower temperature: The carbon chain breaks in the middle producing medium-sized alkanes and alkenes.
ii) Higher temperature: The carbon chain breaks near the end of the molecule producing a higher proportion of smaller alkenes.

Question 27

An alkane C18H38 is thermally cracked to produce ethene, an alkane containing eight carbons and one other hydrocarbon. Write an equation for this process.

Answer 27

C18H38 –> C2H4 + C8H18 + C8H16

Question 28

State the differences in temperature and pressure conditions between thermal cracking and catalytic cracking.

Answer 28

Temperature: less than 700 K for catalytic cracking, 700–1200 K for thermal cracking.
Pressure: slightly above atmospheric pressure for catalytic cracking, up to 7000 kPa for thermal cracking.

Question 29

Name two catalysts that can be used for catalytic cracking.

Answer 29

Zeolites and aluminium oxide

Question 30

Define fuel.

Answer 30

A fuel is a substance, which is burnt to release energy in the form of heat.

Question 31

Give three substances that can be used to remove sulfur dioxide from flue gases. What kind of reactions are these?

Answer 31

Calcium oxide, calcium hydroxide and calcium carbonate. They are neutralisation reactions because each calcium compound is a base and sulfur dioxide is acidic.

Question 32

What is a catalyst?

Answer 32

A catalyst is a substance that increases the rate of reaction of a process yet is not used up in the reaction.

Question 33

What does a catalytic converter do and why is it honeycomb shaped?

Answer 33

Removes pollutants from exhaust gases of internal combustion engine.
To increase surface area.

Question 34

Write an equation for the reaction of carbon monoxide and nitrogen monoxide to form nitrogen and carbon dioxide.

Answer 34

2CO + 2NO –> N2 + 2CO2

Question 35

Explain why nitrogen oxides only tend to form in car engines.

Answer 35

The N≡N covalent bond is so strong that only at the very high temperatures of an engine can it be broken.

Question 36

Outline the greenhouse effect and list three greenhouse gases

Answer 36

The effect where infrared radiation emitted by the Earth is absorbed and emitted by the atmosphere causing a heating effect (global warming). Common greenhouse gases are carbon dioxide, water and methane.