Elements of the Sea

Question 1

Explain what is meant by the term dynamic equilibrium.

Answer 1

rate of forward reaction = rate of back reaction and
concentrations of reactants and products remain
constant

Question 2

Give the colour of the silver chloride precipitate

Answer 2

White

Question 3

The seawater contains sulfate ions. These react with silver ions, forming silver sulfate. Give the formula of silver sulfate.

Answer 3

Ag2SO4

Question 4

Explain, in terms of intermolecular bonds, why chloromethane has a lower boiling point than water.

Answer 4

The intermolecular bonds in chloromethane are weaker

Question 5

Chloromethane is slightly soluble in water. Give the strongest type of intermolecular bond that could form between molecules of chloromethane and water.

Answer 5

Permanent dipole - permanent dipole

Question 6

State the oxidation numbers of the elements in H2S

Answer 6

H +1x2

S -2

Question 7

Name the piece of apparatus that one would use to add an alkali solution to acid during a titration

Answer 7

Burette

Question 8

Explain, in terms of intermolecular bonds, why chlorine is a gas at room temperature and pressure but bromine is a liquid under the same conditions.

Answer 8

instantaneous – induced dipole bonds are formed by electron movements in the molecules create an uneven
distribution of charge. This induces a dipole in a neighbouring molecule leading to attraction between the molecules. The intermolecular bonds are stronger in bromine as bromine has more electrons therefore
more energy is needed to break its
intermolecular bonds

Question 9

Describe how hydrogen bonds are formed

Answer 9

The lone pair on the oxygen is attracted to hydrogens with a positive charge

Question 10

Bromine can be made from a concentrated solution of bromide ions (derived from sea water) by passing chlorine through the solution. What would you expect to see as the reaction takes place? Explain your answer.

Answer 10

Solution goes brown as bromine is produced

Question 11

Suggest how chlorine is manfactured

Answer 11

Electrolysis of brine/seawater

Question 12

State two safety precautions needed when handling bromine industrially.

Answer 12

Protective clothing and prevent breathing of vapour

Question 13

State large-scale uses of bromine or of one of its compounds.

Answer 13

Photography and medicine

Question 14

Copper and nickel compounds often have similar reactions. In which block of the Periodic Table are copper and nickel both found

Answer 14

d block

Question 15

Give instructions that would be necessary for someone to carry out a titration to obtain an accurate value for the amount of acid being tested

Answer 15

Add an indicator 
do several titrations 
proceed drop by drop near end-point
do a rough titration first
use a white tile to notice colour change quickly