An acid-base indicator has K a = 3 . 0 × 10 - 5 . The acid form of the indicator is red and the basic form is blue. Then:

pH is 5.00 when indicator is 75% blue.

pH is 5.00 when indicator is 75% red.

pH is 4.05 when indicator is 75% blue.

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Methyl orange gives red colour in

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Important Questions on Equilibria

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Chemistry>Physical Chemistry>Equilibria>Indicators and Acid-base Titrations

In base vs. Acid titration, at the end point methyl orange is present as

HARD

Chemistry>Physical Chemistry>Equilibria>Indicators and Acid-base Titrations

The Plot of

pH

-metric titration of weak base

{NH}_{4} OH

vs strong acid

HCl

looks like

EASY

Chemistry>Physical Chemistry>Equilibria>Indicators and Acid-base Titrations

100 mL

0.1 M HCl

is taken in a beaker and to it

100 mL

0.1 M NaOH

of is added in steps of

2 mL

and the

pH

is continuously measured. Which of the following graphs correctly depicts the change in

pH

HARD

Chemistry>Physical Chemistry>Equilibria>Indicators and Acid-base Titrations

A compound '

X

' is a weak acid and it exhibits colour change at

pH

close to the equivalence point during neutralization of

NaOH

with

{CH}_{3} COOH

. Compound '

X

' exists in ionized form in basic medium. The compound '

X

' is

HARD

Chemistry>Physical Chemistry>Equilibria>Indicators and Acid-base Titrations

In an acid-base titration,

0.1 M H C l

solution was added to the

N a O H

solution of unknown strength. Which of the following correctly shown the change of

p H

of the titration mixture in this experiment?
Question Image

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Chemistry>Physical Chemistry>Equilibria>Indicators and Acid-base Titrations

Phenolphthalein is not a good indicator for titrating

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Chemistry>Physical Chemistry>Equilibria>Indicators and Acid-base Titrations

The following graph represents the titration of

pH Vs volume of NaOH for

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Chemistry>Physical Chemistry>Equilibria>Indicators and Acid-base Titrations

The percentage protonation of an organic base in its 0.001 M aqueous solution is

5.2 \times 1 0^{- 3}

. Determine the K_b of base.

HARD

Chemistry>Physical Chemistry>Equilibria>Indicators and Acid-base Titrations

An indicator, HIn has a standard ionization constant of

9 \cdot 0 \times 1 0^{- 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 : 1

and the red colour is predominant when the ratio of red form to yellow form

2 : 1

. What is the

pH

range of the indicator? Hence, report

∆ pH

the difference in term

pH

values of the range.

HARD

Chemistry>Physical Chemistry>Equilibria>Indicators and Acid-base Titrations

0.001

mole of

[C o {(N H_{3})}_{5} (N O_{3}) (S O_{4})]

was passed through a cation exchanger and the acid coming out of it required 20 mL of 0.1M

N a O H

for neutralization. Thus, the complex is

HARD

Chemistry>Physical Chemistry>Equilibria>Indicators and Acid-base Titrations

In neutralization titration of

{Na}_{3} {PO}_{4}

, if phenolphthalein is used as indicator, the end point is indicated only when

{Na}_{3} {PO}_{4}

is converted into

{Na}_{2} {HPO}_{4}

, while if thymol blue is used as indicator, end point appears only when

{Na}_{3} {PO}_{4}

is converted into

H_{3} {PO}_{4}

. In an experiment, a

4.0 g

mixture containing

{Na}_{3} {PO}_{4}, {Na}_{2} {HPO}_{4} and {NaH}_{2} {PO}_{4}

is dissolved in

50 mL

water and its

10 mL

portion required

24.4 mL 0.1 M HCl

solution to reach the end point using phenolphthalein indicator. In a separate analysis,

10 mL

portion of the same stock solution required

23.60 mL 0.5 M HCl

solution to reach the end point using thymolblue as indicator. Determine mass percentage of all components in mixture.

HARD

Chemistry>Physical Chemistry>Equilibria>Indicators and Acid-base Titrations

The curve in the figure shows the variation of the

pH

during the course of the titration of a weak acid

HA

, with a strong base (

NaOH

). At which point in the titration curve is the concentration of the acid equal to that of its conjugate base?

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Chemistry>Physical Chemistry>Equilibria>Indicators and Acid-base Titrations

When

K M n O_{4}

solution is titrated with a solution containing

F e^{2 +}

ion, the indicator used in this titration is

EASY

Chemistry>Physical Chemistry>Equilibria>Indicators and Acid-base Titrations

The titration curve for titration of a $50 mL$ solution of a diprotic acid with $0.1 M NaOH$ is shown below.

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$K_{a 1}$ and $K_{a 2}$ are approximately

HARD

Chemistry>Physical Chemistry>Equilibria>Indicators and Acid-base Titrations

An acid-base indicator has

K_{a} = 3.0 \times 10^{- 5}

. The acid form of the indicator is red and the basic form is blue. Then:

HARD

Chemistry>Physical Chemistry>Equilibria>Indicators and Acid-base Titrations

18.3 g of a pure monobasic organic acid containing two 'O' atoms per molecule is burnt completely in excess of oxygen and CO₂ evolved is absorbed completely in one litre of an aqueous solution of NaOH. A 10 mL portion of this solution required 14.5 mL of a normal HCl solution to reach the phenolphthalein end point. An another 10 mL portion of the same solution required 25 mL of the same HCl solution to reach the methyl orange end point. If the organic acid contains 26.23% oxygen by weight, deduce the strength of original NaOH solution.

HARD

Chemistry>Physical Chemistry>Equilibria>Indicators and Acid-base Titrations

What is pH of 1 M acetic acid solution? If volume one litre solution be diluted to

X \times 10^{4}

L so that pH of resulting solution is twice the original value (K_a = 1.8 x 10^{- 5} ). Find the value of X.

HARD

Chemistry>Physical Chemistry>Equilibria>Indicators and Acid-base Titrations

An indicator has a pK_a of 7.5. What is the ratio of the concentration of the base form to the concentration of the acid form ([A^- ]/ [HA], in a buffer solution in which the pH is 6.5 ?

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Chemistry>Physical Chemistry>Equilibria>Indicators and Acid-base Titrations

0 .1 N

solution of

{Na}_{2} {CO}_{3}

is titrated with

0 .1 N

HCl

solution. The best indicator to be used is

EASY

Chemistry>Physical Chemistry>Equilibria>Indicators and Acid-base Titrations

If we use phenolphthalein as an indicator in a titration of

N a_{2} C O_{3}

with

H C l,

the usual result is

Methyl orange gives red colour in

Important Questions on Equilibria

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