revision for salt, electrochemistry, carbon compounds , thermochemistry
DESCRIPTION
basic chemistry knowledgeTRANSCRIPT
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SELARAS 2 FORM 5 2011
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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
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b) Hydrochloric acid is a strong acid. Why?
HCl ionised completely in water toproduce high concentration of hydrogen ion
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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
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iii) Silver chloride is prepared by the precipitation method.Write the chemicalEquation to prepare silver chloride salt
33 NaNOAgClNaClAgNO
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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
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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
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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
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2.Diagram 2 shows the apparatus set up for two types of cells, P and Q
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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
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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
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d) State one observation at electrode zinc in cell Q
Zinc electrode becomes thinner
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e) Diagram 2.2 shows the apparatus set-up for the electrolysis of sodium chloride solution using carbon electrodes
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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-
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iii) Describe one chemical test to identify gas XPlace burning wooden splinter intomouth of test tube, ‘pop’ sound willbe produced
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Diagram 3 shows a series of reaction of compound P. Compound P and compound Q are shown in condensed structural formulae.
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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
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(a) Compound P is propene . State the homologous series of compound P
ALKENE
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(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
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(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
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(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.
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• 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.
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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.
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e) isomers of W.
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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)
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Draw labelled diagram of latex particle in water (2m)
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Explain why latex in the original form does not coagulate
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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
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The properties of natural rubber can be improved by treating it with sulphur.
Name this process (1m)
VULCANISATION
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State ONE use of the treated rubber above (1m)
TYRE GLOVE RUBBER HOSE
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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
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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
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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
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c. State one observation for the experiment • White precipitate forms or the containers become warm
1m
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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
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ii. The number of moles of barium sulphate formed
• Mole of BaSO4
= MV/1000 = 50 x 1.0 /1000 = 0.05 1m
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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
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e.Draw the energy level diagram for the precipitation of barium sulphate
Energy
2m
∆ H = -42 kJ mol-1
Ba 2+ + SO4 -2
BaSO4