Following is the titration curve of CH 3 COOH against NaOH added with phenolphthalein as the indicator. K In value of phenolphthalein is 4.0 x 10 -10 . Thus, incorrect statement is

It begins to change colour from the pH 9.4

It begins to change colour from acid colourless at pH 8.4 to the base form (reddish pink) at pH 10.4

Phenolphthalein is suitable indicator for CH 3 COOH-NaOH titration

An acid-base indicator has a K a of 3 . 0 × 10 - 5 . If 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.

HARD

Earn 100

An acid-base indicator ( $pKa = 4.53$ ) has the acid form red and basic form blue. If we need $75$ $%$ red to be converted into $75 %$ blue form in solution, the change in $pH$ of solution should be:

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Important Questions on Equilibria

HARD

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

MEDIUM

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

You are given the dilute sulphuric acid. What is effect of it on the phenolphthalein?

HARD

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

Following is the titration curve of CH₃COOH against NaOH added with phenolphthalein as the indicator.

Question Image

K_In value of phenolphthalein is 4.0 x 10^-10. Thus, incorrect statement is

MEDIUM

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

Why does a pink colour appear upon gradually adding sodium hydroxide to a solution of acid having

2 - 3

drops of phenolphthalein?

HARD

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

An acid-base indicator has a

K_{a}

3.0 \times 10^{- 5} .

If the acid form of the indicator is red and the basic form is blue, then

EASY

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

What will you observe when a drop of phenolphthalein is added to the solution of lime water.

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.

MEDIUM

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

An acid-base indicator(pK_a = 4.5271)has the acid form red and basic form blue. If we need 75% red to be converted into 75% blue form in solution, the change in pH of solution should be :

HARD

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

What is the colour of this indicator in (a) Neutral (b) Acidic (c) Basic solution?
Phenolphthalein

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.

EASY

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

Write the quadrants in which the following points lie:

$(- 4, 7)$

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 ?

EASY

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

Name any two human-made indicators.

MEDIUM

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

When