revision for salt, electrochemistry, carbon compounds , thermochemistry

SELARAS 2 FORM 5 2011

Question 1a) Write the formula of the following substances:i) Hydrochloric acid – ii) Sulphuric acid – iii) Barium hydroxide – iv) Barium sulphate –

HCl

H2SO4

Ba(OH)2

BaSO4

b) Hydrochloric acid is a strong acid. Why?

HCl ionised completely in water toproduce high concentration of hydrogen ion

c)Silver chloride and copper (II)sulphateare two salts that are required to be prepared in the lab

i) Which one is the soluble salt?

ii) State the name of acid needed to prepare copper (II) sulphate

Copper (II) sulphate

Sulphuric acid

iii) Silver chloride is prepared by the precipitation method.Write the chemicalEquation to prepare silver chloride salt

33 NaNOAgClNaClAgNO

d) Calculate the following:i) What is the concentration of 50 cm3

NaOH solution needed to neutralise 100 cm3 0.5 moldm-3 H2SO4?

b

VM

a

VM

OHSONaSOHNaOH

2211

24242 22

Where M1 = molarity of acidV1 = volume of acidM2 = Molarity of alkaliV2 = volume of alkalia = no. of mol of acid in the equatnb = no. of mol of alkali in the equatn

3

2

2

2211

24242

2

50/21005.02

50

1

1005.0

22

moldmM

xxM

xMxb

VM

a

VM

OHSONaSOHNaOH

NaOH

Where M1 = molarity of acidV1 = volume of acidM2 = Molarity of alkaliV2 = volume of alkalia = no. of mol of acid in the equatnb = no. of mol of alkali in the equatn

i) How much water is needed to form asolution of 1.0moldm-3 NaOH solutionfrom a solution of 50cm3 sodium hydroxide 2.0moldm-3

3

2

2

2211

5050100

100

)(1)50(2

2

cm

Volume

V

V

VMVM

OH

Where

M1 = molarity of original solutionV1 = volume of original solutionM2 = Molarity of diluted solution V2 = total volume of diluted solution

2.Diagram 2 shows the apparatus set up for two types of cells, P and Q

a) State one difference in energy change between cell P and cell Q:

In cell P energy change is from electrical energy to chemical energy

 In cell Q energy change is from

chemical energy to electrical energy

b) What is the product at the anode in cell P?

Oxygen gas

c) Write the half equation for the discharge of cation in cell P

CueCu 22

d) State one observation at electrode zinc in cell Q

Zinc electrode becomes thinner

e) Diagram 2.2 shows the apparatus set-up for the electrolysis of sodium chloride solution using carbon electrodes

i) State all ions attracted towards electrode P and Q

Electrode P Electrode Q

Na+ , H+ Cl- , OH-

ii) State which ion discharge at electrode Q. Explain whyChloride ion because the concentration of Cl- is higher than concentration of OH-

iii) Describe one chemical test to identify gas XPlace burning wooden splinter intomouth of test tube, ‘pop’ sound willbe produced

Diagram 3 shows a series of reaction of compound P. Compound P and compound Q are shown in condensed structural formulae.

Diagram 3

Steam and

Phosphoric acid

Compound Q

CH3CH2 CH3

Compound P

CH2=CHCH3

Compound R

Compound S

CO2 + H2O

I

II

III

Combustion

+ Ethanoic acid

+ concentrated sulphuric acid

(a) Compound P is propene . State the homologous series of compound P

ALKENE

(b)Compound Q is used as a cooking

gas. • i) State the molecular formula of

compound Q

ii) Write a chemical equation for the combustion of compound Q to produce carbon dioxide and water

C3H8

C3H8 + 5O2 3CO2 + 4H2O

(C) Compound P can be changed to compound R which is an alcohol through process II.

• Name process II

• State the general formula for alcohol

HYDRATION

CnH2n+1OH

(d) Explain briefly how compound S can be prepared from compound R in laboratory.

In your answer include the appropriate reagents and condition for the preparation.

• Add absolute propanol and glacial ethanoic acid into a beaker.

• Add slowly concentrated H2SO4.

• Heat under reflux for 6 hours• Distill the mixture to get the

products.

e) An organic compound W has a molecular formula of C4 H8 . Compound W has 3 isomers. Draw two structural formulae of two isomers of W.

e) isomers of W.

4) Natural rubber is a polymer, where the monomer is isoprene or 2- methylbuta-1,3-diene. Natural rubber is obtained from latex, which is a colloid made up of rubber particles and water.Draw Structural formula of isoprene (1m)

Draw labelled diagram of latex particle in water (2m)

Explain why latex in the original form does not coagulate

However when latex is exposed to air or when acid is added, coagulation of latex occur. Explain(3m)

• Air contains bacteria that acts on latex to produce lactic acid

The properties of natural rubber can be improved by treating it with sulphur.

Name this process (1m)

VULCANISATION

State ONE use of the treated rubber above (1m)

TYRE GLOVE RUBBER HOSE

QUESTION 5

50 cm3 of 1.0 mol dm-3 Potassium sulphate solution

50 cm3 of 1.0 mol dm-3

Barium Chloride solution

Initial temperature of both solutions = 29.5 o CHighest temp of the mixture = 34.5 o C

a. What is meant by the heat of precipitation of barium sulphate? • Heat change when 1 mole of

barium sulphate is formed from barium ion and sulphate ion in aqueous solution 1m

b. Write an ionic equation for the reaction

• Ba 2+ + SO4 -2 BaSO4 1m

Method:First, write the formula of the precipitate on the right side of the equationSecond, write the ions of the precipitate on the left side of equation

c. State one observation for the experiment • White precipitate forms or the containers become warm

1m

d. Calculate i. The heat released in the experiment. [Specific heat capacity of water = 4.2 Jg-1oC-1, Density of water = 1.0 g cm-3]

Heat release = mc =100x4.2x(34.5- 29.5)J = 2100J 2m

ii. The number of moles of barium sulphate formed

• Mole of BaSO4

= MV/1000 = 50 x 1.0 /1000 = 0.05 1m

iii. The heat of precipitation of barium sulphate

0.05 mole BaSO4 produce heat 2100 J

1 mole BaSO4 2100 / 0.05 J

= 42000 J ∆ H = - 42 kJ mol-1

e.Draw the energy level diagram for the precipitation of barium sulphate

Energy

2m

∆ H = -42 kJ mol-1

Ba 2+ + SO4 -2

BaSO4