2018 waec chemistry answer
CHEMISTRY OBJ:
1-10: ABDCBCABAC
11-20: DACBBACCAA
21-30: CBCDCAAACB
31-40: AACACBABAA
41-50: DBBDDBDCDB
.
Chemistry THEORY :
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1 a )
Fermentation is the chemical breakdown of a substance by bacteria , yeasts , or other microorganisms , typically involving effervescence and the giving off of heat.
1 aii )
disastase
1 b )
i ) colour change
ii ) end point
1 c )
1 mole
c = n / v = 1 . 0 moldm ^ – 3
V = 10 cm ^ 3 = 0 . 01 dm ^ 3
n = cv= 1 . 0 moldm ^ – 3 * 0 . 01 dm ^ 3
n = 0 . 01 mol of H 2 SO 4
x – – – > 0 . 01 mol of H 2 SO 4
x = 56 * 0 . 01 / 1 = 0 . 56 g
mass unreacted = ( 5 – 0 . 56 ) g = 4 . 44 g
1 di )
copper ( ii ) tetraoxsulphate ( iv)
1 dii)
dyes
============================
2 ai )
collision theory state that for a reaction to occur it is necessary for the reacting species ( atoms or molecules ) to come together or collide with one another .
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1-10: ABDCBCABAC
11-20: DACBBACCAA
21-30: CBCDCAAACB
31-40: AACACBABAA
41-50: DBBDDBDCDB
.
Chemistry THEORY :
=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
1 a )
Fermentation is the chemical breakdown of a substance by bacteria , yeasts , or other microorganisms , typically involving effervescence and the giving off of heat.
1 aii )
disastase
1 b )
i ) colour change
ii ) end point
1 c )
1 mole
c = n / v = 1 . 0 moldm ^ – 3
V = 10 cm ^ 3 = 0 . 01 dm ^ 3
n = cv= 1 . 0 moldm ^ – 3 * 0 . 01 dm ^ 3
n = 0 . 01 mol of H 2 SO 4
x – – – > 0 . 01 mol of H 2 SO 4
x = 56 * 0 . 01 / 1 = 0 . 56 g
mass unreacted = ( 5 – 0 . 56 ) g = 4 . 44 g
1 di )
copper ( ii ) tetraoxsulphate ( iv)
1 dii)
dyes
============================
2 ai )
collision theory state that for a reaction to occur it is necessary for the reacting species ( atoms or molecules ) to come together or collide with one another .
(2aii)
When the rate of collision increases, the rate at which molecules collide with each other will also increase thereby making the kinetic energy of the molecules to also increase. The temperature will also increase because temperature is a measure of average kinetic energy.
(2bi)
Draw your diagram
(2bii)
C2H5OH + 3O2 —->2CO2 + 3H2O
1mole of ethanol = 3moles of O2
2.5moles of ethanol will require 3 × 2.5/1 = 7.5moles of O2.
but 1 mole of gas = 22.4dm3
7.5moles = 7.5 × 22.4 = 168dm3 of O2.
(2Ci)
Esterification is the formation of an Ester by the reaction between Alkanol and an acid.
(2cii) Two uses of alkanols
(i) They are used as solvents for cellulose
(ii) They are uses in making perfumes and cosmetics.
(iii) They are used for quick drying of paints and nail varnishes.
(2ciii)
Sodium Ethanoate
(2di)
Tin
(2dii )
This is because the galvanized plate is corrosion-resistant. It has a protective coating which prevents further oxidation of the metal.
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4ai)
4aii)
Na2SO3(aq) + 2HCl(aq)—–>2Nacl(aq)+H2O(s)+SO2(q)
4aiii)
dry the gas evolved by passing it through H2SO4 and collect it by downward delivery
4aiv)
because it is denser than air
4bi)
Dalton’s law of partial pressure states that in a mixture of gases, which do not react chemically together, a gas will exert a partial pressure, which is the pressure, it will exert if it is kept alone in the vessel.
4bii)
T1=12degree = 285k
P1=690mm Hg
V1=30cm^3
T2=273k
P2=760mmhg
V2=?
Using the general gas law
V1P1/T1 = V2P2/T2
V2=30 690273/285*760
V2=261cm^3
V2=26cm^3
4ci)
Cl2(q)+H2O(i)——>HCL(aq)+HOCL(aq)
4cii)
litmus turn red because of the presence of the acid HCL.
4di)
chlorine bromine iodine/increasing boiling point.
4dii)
because water has two(2)ion pairs of electrons as compared to ammonia which has one.
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(5ai )
Na2S2O3 ===> 2+2x+6=0
2x=6-2=4
X=4/2
X=2
The oxidation number of sulphur is 2
(5aii)
Rhombic & monoclinic
(5aiii )
-Both are tetravalent
-both are allotrope of carbon.
(5bi)
CO2 & Chloroflorocarbon.
(5bii)
There is increase in sun radiation reaching the
earths surface ie Global warming
(5biii )
ThunderStorm.
(5iv)
I 2KNo3 —-> 2KNO3 + O2
II AgNo3 —> 2Ag + 2NO
(5ci)
Calcium chloride in a solution can give rise to
crystal using filteration & evaporation to dryness .
The sol is filtered into filtrate & residue b4
evaporation to dryness takes place.
(5cii)
– Because of presence of hydrogen bonding in
NH3
-Because Iodine as higher molecular mass than
chlorine
(5di)
Mol of Nacl = Mass/MM
= 5.85/58.01
= 0.1mol
From the equation
2mol of Nacl gives 2mol of HCL, 0.1mol of Nacl
gives 0.1mol of Hcl
Vol of Hcl = 0.1 x 22.4 = 2.24mol/dm^3
Typing…..
When the rate of collision increases, the rate at which molecules collide with each other will also increase thereby making the kinetic energy of the molecules to also increase. The temperature will also increase because temperature is a measure of average kinetic energy.
(2bi)
Draw your diagram
(2bii)
C2H5OH + 3O2 —->2CO2 + 3H2O
1mole of ethanol = 3moles of O2
2.5moles of ethanol will require 3 × 2.5/1 = 7.5moles of O2.
but 1 mole of gas = 22.4dm3
7.5moles = 7.5 × 22.4 = 168dm3 of O2.
(2Ci)
Esterification is the formation of an Ester by the reaction between Alkanol and an acid.
(2cii) Two uses of alkanols
(i) They are used as solvents for cellulose
(ii) They are uses in making perfumes and cosmetics.
(iii) They are used for quick drying of paints and nail varnishes.
(2ciii)
Sodium Ethanoate
(2di)
Tin
(2dii )
This is because the galvanized plate is corrosion-resistant. It has a protective coating which prevents further oxidation of the metal.
-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
4ai)
4aii)
Na2SO3(aq) + 2HCl(aq)—–>2Nacl(aq)+H2O(s)+SO2(q)
4aiii)
dry the gas evolved by passing it through H2SO4 and collect it by downward delivery
4aiv)
because it is denser than air
4bi)
Dalton’s law of partial pressure states that in a mixture of gases, which do not react chemically together, a gas will exert a partial pressure, which is the pressure, it will exert if it is kept alone in the vessel.
4bii)
T1=12degree = 285k
P1=690mm Hg
V1=30cm^3
T2=273k
P2=760mmhg
V2=?
Using the general gas law
V1P1/T1 = V2P2/T2
V2=30 690273/285*760
V2=261cm^3
V2=26cm^3
4ci)
Cl2(q)+H2O(i)——>HCL(aq)+HOCL(aq)
4cii)
litmus turn red because of the presence of the acid HCL.
4di)
chlorine bromine iodine/increasing boiling point.
4dii)
because water has two(2)ion pairs of electrons as compared to ammonia which has one.
==================
(5ai )
Na2S2O3 ===> 2+2x+6=0
2x=6-2=4
X=4/2
X=2
The oxidation number of sulphur is 2
(5aii)
Rhombic & monoclinic
(5aiii )
-Both are tetravalent
-both are allotrope of carbon.
(5bi)
CO2 & Chloroflorocarbon.
(5bii)
There is increase in sun radiation reaching the
earths surface ie Global warming
(5biii )
ThunderStorm.
(5iv)
I 2KNo3 —-> 2KNO3 + O2
II AgNo3 —> 2Ag + 2NO
(5ci)
Calcium chloride in a solution can give rise to
crystal using filteration & evaporation to dryness .
The sol is filtered into filtrate & residue b4
evaporation to dryness takes place.
(5cii)
– Because of presence of hydrogen bonding in
NH3
-Because Iodine as higher molecular mass than
chlorine
(5di)
Mol of Nacl = Mass/MM
= 5.85/58.01
= 0.1mol
From the equation
2mol of Nacl gives 2mol of HCL, 0.1mol of Nacl
gives 0.1mol of Hcl
Vol of Hcl = 0.1 x 22.4 = 2.24mol/dm^3
Typing…..
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