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Indicators and acid-base titration - class-XII

indicators and acid-base titration

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Questions

Question 1 Multiple Choice (Single Answer)

1 kg of NaOH is added to 10 ml of 0.1N HCl, the resulting solution will:

  1. turn blue litmus red
  2. turn phenolphthalein solution pink
  3. turn methyl orange red
  4. will have no effect on red or blue litmus paper
Question 2 Multiple Choice (Single Answer)

From the following in which titration methyl orange is a best indicator?

  1. $CH _{3}COOH+NaOH$
  2. $H _{2}C _{2}O _{4}+NaOH$
  3. $HCl+NaOH$
  4. $CH _{3}COOH+NH _{4}OH$
Question 3 Multiple Choice (Single Answer)

Dissociation of ${ CH } _{ 3 }COOH$ is suppressed by adding

  1. HCL
  2. ${ H } _{ 2 }{ SO } _{ 4 }$
  3. $CH _{ 3 }COONa\quad$
  4. Any of the above
Question 4 Multiple Choice (Single Answer)

Which one of the following indicatprs works in the pH range $8-9.8$?

  1. Litmus
  2. Phenolphthalein
  3. Methyl red
  4. Methyl orange
Question 5 Multiple Choice (Single Answer)

For the titration between oxalic acid and sodium hydroxide, the indicator used is

  1. Potassium permanganate
  2. Phenolphthalein
  3. Litmus
  4. Methyl orange
Question 6 Multiple Choice (Single Answer)

Select the best indicator from the given table for titration of $20\space mL$ of $0.02\space M\space CH _3COOH$ with $0.02\space M\space NaOH$. Given $pK _a\ \text{of}\ CH _3COOH= 4.74)$

Indicator $pH$ range
(I) Bromothymol blue $6.0 - 7.6$
(II) Thymolphathalein $9.3 - 10.5$
(III) Malachite green $11.4 - 13$
(IV) M-Cresol purple $7.4 - 9.0$
  1. $(I)$
  2. $(II)$
  3. $(III)$
  4. $(IV)$
Question 7 Multiple Choice (Single Answer)

Assertion: In general, phenolphthalein is used as an indicator for the titration of weak acid (HA) against strong base (NaOH).
Reason: At equivalent point, solution is basic.

  1. Both Assertion and Reason are correct and Reason is the correct explanation of Assertion
  2. Both Assertion and Reason are correct but Reason is not the correct explanation of Assertion
  3. Assertion is correct but Reason is not correct

  4. Assertion is not correct but Reason is correct
  5. Both Assertion and Reason are not correct
Question 8 Multiple Choice (Single Answer)

A certain indicator (an organic dye) has $p{K} _{a} = 5$. For which of the following titrations it may be suitable?

  1. Acetic acid against $NaOH$
  2. Aniline hydrochloride against $NaOH$
  3. Sodium carbonate against $HCl$
  4. Barium hydroxide against oxalic acid
Question 9 Multiple Choice (Single Answer)

The amount of sodium hydrogen carbonate, $NaH{ CO } _{ 3 }$, in an antacid tablet is to be determined by dissolving the tablet in water and titrating the resulting solution with hydrochloric acid. Which indicator is the most appropriate for this titration?
Acid                  ${K} _{a}$
${ H } _{ 2 }{ CO } _{ 3 }$          $2.5\times { 10 }^{ -4 }$
${H{ CO } _{ 3} }^{ - }$           $2.4\times { 10 }^{ -8 }$

  1. Methyl orange, $p{ K } _{ In }=3.7$
  2. Bromothylmol blue, $p{ K } _{ In }==7.0$
  3. Phenolphtalein, $p{ K } _{ In }=9.3$
  4. Alizarin yellow, $p{ K } _{ In }=12.5$
Question 10 Multiple Choice (Single Answer)

A solution containing $Na _{2}CO _{3}$ and $NaOH$ requires $300\ mL$ of $0.1\ N\ HCl$ using phenolphthalein as an indicator. Methyl orange is then added to the above-titrated solution when a further $25\ mL$ of $0.2\ N\ HCl$ is required. The amount of $NaOH$ present in the original solution is:

  1. $0.5\ g$
  2. $1\ g$
  3. $2\ g$
  4. $4\ g$
Question 11 Multiple Choice (Single Answer)

In the titration of ${ NH } _{ 4 }OH$ with $HCl$, the indicator which cannot be used is:

  1. Phenolphthalein
  2. Methyl orange
  3. Methyl red
  4. Both orange and methyl red
Question 12 Multiple Choice (Single Answer)

In the titration of nitric acid against potassium carbonate, the indicator used is:

  1. Methyl orange
  2. Self indicator
  3. Phenolphthalein
  4. Diphenylamine
Question 13 Multiple Choice (Single Answer)

A solution containing $Fe^{2+}$ ions is titrated with $KMnO _{4}$ solution. Indicator used will be:

  1. phenolphthalein
  2. methyl orange
  3. litmus
  4. none of the above
Question 14 Multiple Choice (Single Answer)

In the mixture of $NaHCO _{4}$ and $Na _{2}CO _{3}$, volume of a given $HCl$ required is $x\ mL$ with phenolphthalein indicator and $y\ mL$ with methyl orange indicator in same titration. Hence, volume of $HCl$ for complete reaction of $Na _{2}CO _{3}$ present in the original mixture is

  1. $2x$
  2. $y$
  3. $x/2$
  4. $(y - x)$
Question 15 Multiple Choice (Single Answer)

$0.1\ N$ solution of $Na _{2}CO _{3}$ is being titrated with $0.1\ N\ HCl$, the best indicator to be used is:

  1. potassium ferricyanide
  2. phenolphthalein
  3. methyl orange
  4. litmus
Question 16 Multiple Choice (Multiple Answers)

Select incorrect statement(s) among the following.

  1. Phenolphthalein is suitable indicator for the titration of HCl (aq) with $NH _4OH(aq)$
  2. An acid-base indicator in a buffer solution of $pH=pK _{ln}+1$ is ionized to the extent of $\frac {1000}{11}$%
  3. In the titration of a monoacidic weak base with a strong acid, the pH at the equivalent point is always calculated by $pH=\frac {1}{2}[pK _w-pH _b-logC]$
  4. When $Na _3PO _4(aq)$ is titrated with HCl(aq), the pH of solution at second equivalent point is calculated by $\frac {1}{2}[pK _{a _1}+pK _{a _2}]$
Question 17 Multiple Choice (Single Answer)

A solution contains $Na _{2}CO _{3}$ and $NaHCO _{3}, 10\ mL$ of this solution required $2.5\ mL$ of $0.1\ M\ H _{2}SO _{4}$ for neutralisation using phenolphthalein indicator. Methyl orange is added after first end point, further titration required $2.5\ mL$ of $0.2\ M\ H _{2}SO _{4}$. The amount of $Na _{2}CO _{3}$ and $NaHCO _{3}$ in $1$ litre of the solution is:

  1. $5.3\ g$ and $4.2\ g$
  2. $3.3\ g$ and $6.2\ g$
  3. $4.2\ g$ and $5.3\ g$
  4. $6.2\ g$ and $3.3\ g$
Question 18 Multiple Choice (Single Answer)
Find the $pH$ of the resulting solution and then mark the option in which $pH$ exists between color transition range of an indicator.

$50$ ml of $0.1$ M $HCO _3^- \ +$ $50$ ml of $0.8$ M $CO _3^{2-}$.

[For $H _2CO _3$ : $K _{a _1}=4\times 10^{-7}$ and $K _{a _2}=2\times 10^{-11}$]
  1. Phenol red (6.8 to 8.4)
  2. Propyl red 4(4.6 to 6.4)
  3. Phenolphthalein (8.3 to 10.1)
  4. Malachite green (11.4 to 13)
Question 19 Multiple Choice (Single Answer)

When $20\ mL$ of $\dfrac {M}{10}NaOH$ are added to $10\ mL$ of $\dfrac {M}{10}HCl$, the resulting solution will:

  1. turn blue litmus red
  2. turn phenolphthalein solution pink
  3. turn methyl orange red
  4. have no effect on either red or blue litmus
Question 20 Multiple Choice (Single Answer)

An indicator $HIn$ has a standard ionization constant of $9.0\times {10}^{-9}$. The acid colour of the indicator is yellow and the alkaline colour is red. The yellow colour is visible when the ratio of yellow form to red form is $30$ to $1$ and the red colour is predominant when the ratio of red form to yellow form is $2$ to $1$. What is the $pH$ range of the indicator?

  1. < $6.568$
  2. $6.568$ to $8.346$
  3. > $8.346$
  4. None of these
Question 21 Multiple Choice (Single Answer)
Find the $pH$ of the resulting solution and then mark the option in which $pH$ exists between color transition range of an indicator.

50 ml of 0.2M HA solution $(K _a=10^{-5})$ + 50ml of 0.1M HCl solution + 100 ml of 0.13 M NaOH solution.
  1. Phenol red (6.8 to 8.4)
  2. Propyl red (4.6 to 6.4)
  3. Phenolphthalein (8.3 to 10.1)
  4. Malachite green (11.4 to 13)
Question 22 Multiple Choice (Single Answer)

In the titration of $CH _{3}COOH$ against $NaOH$, we cannot use the

  1. Methyl orange
  2. Methyl red
  3. Phenolphthalein
  4. Bromothymol blue
Question 23 Multiple Choice (Multiple Answers)

During the titration of mixture of $NaOH,{ Na } _{ 2 }{ CO } _{ 3 }$ and an inert substance against hydrochloric acid:

  1. Phenolphthalein is used to detect the end point when $NaOH$ is completely neutralized and half of ${ Na } _{ 2 }{ CO } _{ 3 }$ is neutralized
  2. Methyl orange is used to detect the final end point
  3. Methyl orange is used to detect the first end point
  4. Phenolphthalein is used to detect the final end point
Question 24 Multiple Choice (Single Answer)

(A) In general phenolphthalein is used as an indicator for the titration of weak acid $(CH _3COOH)$ and strong base (NaOH).
(R) At equivalence point solution is basic.

  1. Both (R) and (A) are true and reason is the. correct explanation of assertion
  2. Both (R) and (A) are true but reason is not correct explanation of assertion
  3. Assertion (A) is true but reason (R) is false
  4. Assertion (A) and reason (R) both are false
  5. Assertion (A) is false but reason (R) is true
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