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Byju's Answer

Standard XII

Chemistry

Synthetic Dyes

In the titrat...

Question

In the titration of ${N H}_{4} O H$ with $H C l$ , the indicator which cannot be used is:

Phenolphthalein

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Methyl orange

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Methyl red

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Both orange and methyl red

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Solution

The correct option is A Phenolphthalein
In case of strong acid( $H C l$ ) and weak base( $N H_{4} O H$ ) phenolphthalein cannot be used as an indicator because it can detect $p H$ only in range of 8-10.

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Similar questions

Indicator	pH range
Methyl violet	0.3-1.8
Methyl orange	2.8-3.8
Congo red	2.8-4.8
Methyl red	3.8-6.1
Bromothylmol blue	6.0-7.9
Phenol Red	6.8-8.6

The table above shows the pH ranges of some common indicators. Given that

K_{a}

7.3 \times 10^{- 10}

for boric acid

(H_{3} B O_{3})

, Choose an indicator that can be used for the titration of

0.10 M K H_{2} B O_{3}

with 0.10 M HCl.

40 m L

0.05 M N a_{2} C O_{3} \cdot N a H C O_{3} \cdot 2 H_{2} O

(sesquicarbonate) is titrated against

0.05 M H C l . x m L

H C l

is used when phenolphthalein is the indicator and

y m L H C l

is used when methyl orange is the indicator in two separate titrations, hence

(y - x)

is________.

40

ml of

0.05 M

solution of sesqui-carbonate

(N a_{2} C O_{3} . N a H C O_{3} .2 H_{2} O)

is titrated against

0.05 M

H C l

x

mL of

H C l

is used when phenolphthalein is the indicator and

y

mL of

H C l

is used when methyl orange is the indicator in two separate titrations. Hence,

(y - x)

is :

Q. In the mixture of

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

, volume of

H C l

required is

x

mL with phenolphthalein indicator and then

y

mL with methyl orange indicator in same titration. Hence, volume of

H C l

for complete reaction of

N a_{2} C O_{3}

is :

Q. Assertion :In the acid-base titration involving a strong base and a weak acid, methyl orange can be used as an indicator. Reason: Methyl orange changes its colour in pH range

3

5

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In the titration of NH4OH with HCl, the indicator which cannot be used is:

The correct option is A PhenolphthaleinIn case of strong acid(HCl) and weak base(NH4OH) phenolphthalein cannot be used as an indicator because it can detect pH only in range of 8-10.

In the titration of ${N H}_{4} O H$ with $H C l$ , the indicator which cannot be used is:

The correct option is A Phenolphthalein
In case of strong acid( $H C l$ ) and weak base( $N H_{4} O H$ ) phenolphthalein cannot be used as an indicator because it can detect $p H$ only in range of 8-10.