Download - Unit 3 Redox
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Unit 3 Redox
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a. 4
b. 3
c. 2
d. 1
Cr2O7 2- (aq) + 14H+ + 6e 2Cr 3+ (aq) + 7H2O (l)
I2 (aq) + 2e- 2I - (aq)
How many moles of I2 are reduced by 1 mole of Cr2O7 2- ions?
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1st hintThe number of electrons on both sides of the redox equation must balance.
a hint!!!!
2nd hintHow many more moles of Iodine are now needed?
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Ans: b. 3
How many moles of I2 are reduced by 1 mole of Cr2O7 2- ions?
Correct because…..
The number of electrons lost and gained must be equal.
Cr2O7 2- (aq) + 14H+ + 6e 2Cr 3+ (aq) + 7H2O (l)
I2 (aq) + 2e- 2I- (aq) X 3
Cr2O7 2- (aq) + 14H+ (aq) + 3I2 (aq) 2Cr 3+ (aq) + 7H2O (l) + 6I- (aq)
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Which of the following is not a redox reaction.
a. Mg (s) + 2HCl (aq) MgCl2 (aq) + H2 (g)
b. CuCO3 (s) + H2SO4 (aq) CuSO4(aq) + CO2 (g) + H2O (l)
c. Zn(NO3)2 (aq) + 2Ag 2AgNO3 (aq) + 2Zn (s)
d. H2 (g) + Cl2 (g) HCl (g)
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Which reaction does not involve the formation of ions.?
a hint!!!!
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Which of the following is not a redox reaction.
Correct because……
A redox reaction involves the transfer of electronsbetween reactants.
a. Mg (s) + 2HCl (aq) MgCl2 (aq) + H2 (g)Mg 2+ + 2H+ Mg 2+ + H2
b. CuCO3 (s) + H2SO4 (aq) CuSO4(aq) + CO2 (g) + H2O (l)2H+ + CO3
2- CO2 + H2O
c. Zn(NO3)2 (aq) + 2Ag 2AgNO3 (aq) + 2Zn (s) Zn 2+ + 2Ag 2Ag + + Zn
Ans: d. H2 (g) + Cl2 (g) HCl (g)
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In order to balance this ion-equation
I – to IO 3 –
You need to
a.
b.
c.
d.
Number H + Number of e-
6 3
3 6
3 3
6 6
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1st hintBalance the oxygen by adding water.
a hint!!!!
2nd hintBalance the hydrogen by adding H+ ions.
3rd hintBalance the charges by adding electrons
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In order to balance this ion-equation
I – to IO 3 –
Correct because………
1st balance the water moleculesI – + 3H2O IO 3 –
2nd balance the H using H+ ions.I – + 3H2O IO 3 – + 6H+
3rd balance the charges by adding electronsI – + 3H2O IO 3 – + 6H+ + 6e-
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The balanced redox equation for the two ion-equationsbelow is (you will need to look a you data book, page 11)
a. 2Fe (s) + 3SO4 2- (aq) 2Fe 3+ (aq) + 3SO3 2- (aq)
b. 2Fe (s) + 3SO4 2- (aq) + 6H+ (aq) 2Fe 3+ (aq) + 3SO3 2- (aq) + 3H2 (g)
c. 2Fe (s) + 3SO4 2- (aq) + 6H+ (aq) 2Fe 3+ (aq) + 3SO3 2- (aq) + 3H2O (l)
d. 3Fe (s) + SO4 2- (aq) + 6H+ (aq) Fe 3+ (aq) + SO3 2- (aq) + 3H2O (l)
SO4 2- (aq) SO3 2- (aq)
Fe (s) Fe 3+ (aq)
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a hint!!!!
1st hintSO4 2- (aq) + 2H + (aq) + 2e- SO3 2- (aq) + H2O (l)
2nd hintFe (s) Fe 3+ (aq) + 3e-
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The balanced redox equation for the two ion-equationsbelow is (you will need to look a you data book, page 11)
SO4 2- (aq) SO3 2- (aq)
Fe (s) Fe 3+ (aq)
SO4 2- (aq) + 2H + (aq) + 2e- SO3 2- (aq) + H2O (l)
Correct because……
Fe (s) Fe 3+ (aq) + 3e- X 2
3SO4 2-(aq) + 6H +(aq) + 2Fe(s) 3SO3 2-
(aq) + 3H2O(l) + 2Fe 3+ (aq)
X 3
Ans: C
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What colour change takes place during this reaction?
a. Blue to colourless
b. Colourless to purple
c. Colourless to blue
d. Purple to colourless
5 Fe 2+ (aq) + 8H+ (aq) + MnO4- (aq) 5 Fe 3+ (aq) + Mn 2+ (aq) + 4H2O(l)
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a hint!!!!
The permanganate ion is purple.
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What colour change takes place during this reaction?
Correct because………..
The MnO4- (aq) ion is purple,
while the Mn 2+ (aq) ion is colourless.
5 Fe 2+ (aq) + 8H+ (aq) + MnO4- (aq) 5 Fe 3+ (aq) + Mn 2+ (aq) + 4H2O(l)
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25 cm 3 of 0.200 mol –1 potassium permanganate was titrated against a solution of Fe 2+ ions. The concentration of Fe 2+ ions was?
5 Fe 2+ (aq) + 8H+ (aq) + MnO4- (aq) 5 Fe 3+ (aq) + Mn 2+ (aq) + 4H2O(l)
Titration results, 20.5 cm3, 20.1 cm3 and 20.0 cm 3
a. 1.25 mol 1-
b. 1.24 mol 1-
c. 0.250 mol 1-
d. 1.00 mol 1-
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Have you used concordant titration results?
a hint!!!!
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n = V x C and a 5:1 ratio of mol of Fe 2+ to MnO4 -
a hint!!!!
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a hint!!!!
V x x C x
n x
= V y x C y
n y
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25 cm 3 of 0.200 mol –1 potassium permanganate was titrated against a solution of Fe 2+ ions. The concentration of Fe 2+ ions was?
5 Fe 2+ (aq) + 8H+ (aq) + MnO4- (aq) 5 Fe 3+ (aq) + Mn 2+ (aq) + 4H2O(l)
Titration results, 20.5 cm3, 20.1 cm3 and 20.0 cm 3
V x x C x
n x
= V y x C y
n y
X = MnO4- Y = Fe 3+
(20.1+20.0)/2 + Y 25 x 0.200
1 5=
Ans : b. 1.24 mol 1-
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The production of Aluminium during the electrolysisof aluminium oxide can be represented by
a. 96,500 C
b. 19300 C
c. 57,900 C
d. 193,000
What is the quantity of electricity needed to produce 0.2 mol of Al?
Al 3+ + 3e Al
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1st hintHow many moles of electrons are needed to deposit 1 molof Al?
a hint!!!!
2nd hintThe charge on a mole of electrons is 96,500C?
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The production of Aluminium during the electrolysisof aluminium oxide can be represented by
What is the quantity of electricity needed to produce 0.2 mol of Al?
Correct because……..
To produce 1 mole of aluminium, 3 moles of electrons are needed. i.e. 96,500 C x 3 = 289500 C needed.
Al 3+ + 3e Al
1 mole Al = 289500 C0.2 mole Al = 289500 x 0.2 = 57,900C
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A solution of HCl is electrolysed. What current is neededto produce 4.8 l of H2 gas in 3 min 13 sec? 1 mole of gasoccupies 24 l .
a. 20 A
b. 50 A
c. 100 A
d. 200 A
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1st hintHow many moles of hydrogen does 4.8 l represent?
a hint!!!!
2nd hintHow many moles of electrons do you need to deposit 1 molof hydrogen gas?
Q = I x t
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A solution of HCl is electrolysed. What current is neededto produce 4.8 l of H2 gas in 3 min 13 sec? 1 mole of gasoccupies 24 l ?
Correct because……..
2H+ (aq) + 2e- H2 (g)
So to produce a mole of hydrogen gas, 2 mol of electrons are needed.4.8l = 4.8/24 mol = 0.2 mol of gas produced.1 mol of gas would need 96500 x 2 C0.2 mol would need (96500 x 2) x 0.2 C = 3860 CQuantity of charge = current x time
Q = I x t
So I = Q/t = 3860 / 193 = 20 A