25 ml of a solution containing NaOH and Na2CO3 required (i) 50 ml of 0...
Solution:
Given,
Volume of solution = 25 ml
Volume of 0.2 N HCl required with phenolphthalein as an indicator = 50 ml
Volume of 0.2 N HCl required with methyl blue as an indicator = 72 ml
Let us take the weight of NaOH and Na2CO3 as x and y respectively.
Then,
1) N1V1 = N2V2
Where,
N1 = Normality of HCl = 0.2 N
V1 = Volume of HCl = 50 ml
N2 = Normality of the given solution
V2 = Volume of the given solution
We can calculate the normality of the given solution as follows:
25 ml of the given solution contains NaOH and Na2CO3.
Let the concentration of NaOH and Na2CO3 be x and y respectively.
Molecular weight of NaOH = 40
Molecular weight of Na2CO3 = (2 x 23) + 12 + (3 x 16) = 106
So,
x + y = concentration of the given solution
40x/106 + 2y/106 = N2
=> 20x/53 + y/53 = N2
=> 0.377 (x + y) = N2
Using the above value in equation (1),
0.2 x 50 = N2 x 25
N2 = 0.4 N
2) Using methyl blue indicator:
N1V1 = N2V2
Where,
N1 = Normality of HCl = 0.2 N
V1 = Volume of HCl = 72 ml
N2 = Normality of Na2CO3
V2 = Volume of the given solution
Here, NaOH does not react with methyl blue.
So,
N2 = N1 x (V1 - V2)/V2
=> N2 = 0.2 x (72 - 50)/50
=> N2 = 0.064 N
Now, we can write two equations using the weight of NaOH and Na2CO3 and solve them to get the ratio of their weights.
Let us consider the weight of NaOH and Na2CO3 to be x and y respectively.
Weight of NaOH = x g
Weight of Na2CO3 = y g
Molecular weight of NaOH = 40
Molecular weight of Na2CO3 = (2 x 23) + 12 + (3 x 16) = 106
1) Using phenolphthalein indicator:
0.4 x 50 x 1/40 x 1000 = x
=> x = 50 g
2) Using methyl blue indicator:
0.064 x (25/1000) x 106/1000 = y
=> y = 0.17 g
So, the ratio of weight of NaOH and Na2CO3 in the solution is:
x/y = 50/0.17 = 294.12
=> x:y = 294.12:1
=> y/x = 1/294.12
=> y/(x+y) = 1/(294.12+1)
=> y/(x+y) = 0.00338
So,
25 ml of a solution containing NaOH and Na2CO3 required (i) 50 ml of 0...
In case of phonophthalin na2co3 converted to nahco3 & for methyl orange it convert to h2co3
so Valency factor changes
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