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Standard XII

Chemistry

Enthalpy of Neutralisation

58.One c.c of...

Question

58.One c.c of phosphoric acid was diluted to 250 cc; 25cc of this solution required 34. 8 CC of 0. 102N NaoH for neutralization, using phenolphthalein as indicator. What is the specific gravity of the acid?

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25 m L

of a mixture of

N a O H + N a_{2} C O_{3}

, when titrated with

\frac{N}{10} H C l

using phenolphthalein indicator required

25 m L H C l

to decolourise phenolphthalein. At this stage, methyl orange was added and the addition of acid was continued. The second endpoint was reached after further addition of

5 m L

of the acid. Calculate the amount of

N a_{2} C O_{3}

and

N a O H

in one litre of the solution.

Q. A solution contained

N a_{2} C O_{3}

and

N a H C O_{3}

15 m l

of the solution required

5 m l

\frac{N}{10} H C l

for neutralization using phenolphthalein as an indicator. Addition of methyl orange required a further

15 m l

of the acid for neutralization. The amount of

N a_{2} C O_{3}

present in the solution is:

25 m L

0.107 M H_{3} P O_{4}

was titrated with

0.115 M

solution of

N a O H

to the end point identified by indicator bromocresol green. This required

23.1 m L

The titration was repeated using phenolphthalein as indicator. This time

25 m L

0.107 M H_{3} P O_{4}

required

46.2 m L

of the

0.115 M N a O H

. What is the coefficient

^{'} n^{'}

in the following reaction?

H_{3} P O_{4} + n O H^{-} \to [H_{3 - n} P O_{4}]^{n -} + n H_{2} O

Question 10

On adding phenolphthalein indicator to a colourless solution, no change is observed. What is the nature of this solution?
(a) Basic
(b) Either acidic or basic
(c) Either acidic or neutral
(d) Either basic or neutral

Q. Find the percentage of nitrogen in an organic compound analysed by Kjeldahl method

1.61

g of the compound produced

N H_{3}

which was absorbed in

250

mL of

\frac{N}{2} H_{2} S O_{4}

solution. The remaining acid was then diluted to one litre,

25

mL of which required

25.5

mL of

N / 10

N a O H

for exact neutralization.

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