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A Certain monoprotic acid (weak) serves...

A Certain monoprotic acid (weak) serves as indicator . Assuming that colour change is seen when `1//3^(rd)` of the indicator has been converted to ions and that at end point the pH of solution is 6 , what is the value of `pK_(In)` ?

Text Solution

AI Generated Solution

To solve the problem, we will use the Henderson-Hasselbalch equation, which is given by: \[ \text{pH} = \text{pK}_{\text{In}} + \log \left( \frac{[\text{In}^-]}{[\text{HIn}]} \right) \] Where: - \(\text{In}^-\) is the ionized form of the indicator (the conjugate base), ...
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(a) Define a universal indicator. Mention its one use. (b) Solution A gives pink colour when a drop of phenolphthalein indicator is added to it. Solution B gives red colour when a drop of methyl orange is added to it. What type of solutions are A and B which one of the solutions A and B will have a higher pH value ? (c) Name one salt whose solutions has pH more than 7 and one salt whose solution has pH less than 7.

Acid-base indicator such as methy 1 orange, phenolphthalein, and bromothymol blue ate substances which change colour accroding to the hydrogen ion concentration of the solution to which they are added. Most indicators are weak acids (or more rarely weak base) in which the undissociated and dissociated forms have different and distinct colours. If methy 1 orange is used as the examples and the un-dissociated forms is written as HMO , then dissociation occurs as shown below: Reaction: {:(HMOhArr,H^(o+)+,MO^(Theta),,),(Red,"Colourless","Yellow",,):} The indicator should have a sharp colour change with the equivalence point of the titration. Usually the colour change of the indicator occurs over a range of about two pH units. It should be noted that the eye cannot detect the exact end point of the tiytration. The pK_(a) of the indicator should be near the pH of the solution at the equivalance point. Which of the following sitution exists at the equivalence point of titration?

Knowledge Check

  • An indicator has pK_(In)=5.3 . In a certain titration, this indicator is found to be 80% ionized in its acid form. Thus, pH of the solution is

    A
    `4.7`
    B
    `5.3`
    C
    `5.9`
    D
    `6.2`

  • An indicator is a weak acid and pH range of its colour is 3 to 5 . If the neutral point of the indicator lies in the centre of the [H^(+)] corresponding to given pH range, then pH at the equivalence point is

    A
    `7.0`
    B
    `4.0`
    C
    `3.3`
    D
    `5.0`

  • A 0.015 M solution of a weak acid has a pH of 3.52 . What is the value of the K_a for this acid?

    A
    `2.0xx10^(-2)`
    B
    `6.2xx10^(-6)`
    C
    `9.1xx10^(-8)`
    D
    `1.4xx10^(-9)`

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    When phenolphthalein is used as the indicator in a titration of an HCl solution with a solution of NaOH , the indicator undergoes a colour change from colourless to poink at the end point of the tiration. This colour change occurs abruptly because

    Acid base indicators are either weak organic acids or weak organic bases. Indicator change colour in dilute solution when the hydronium ion concentration reaches a particular value. For example, phenopthalein is a colour less substance in any aqueous solution with a pH less than 8.3 in between the pH range 8.3 to 10 , transaction of colour (colourless to pink) takes place and if pH of solution is greater than 10 , then solution colour is dark pin. Considering an acid indicator HIn, base In^(-) can be represented as : HIn hArr H^(+) + In^(-) acidic form basic form pH of solution can be computed as : pH = pK_(In) + "log" ([In^(-)])/([HIn]) In general, transition of colour takes place in between the pH range pK_(In) +-1 An indicator is a weak acid and pH range is 4.0 to 6.0 . If indicator is 50% ionized in a given solution then what is ionization consatant of the acid?

    Acid base indicators are either weak organic acids or weak organic bases. Indicator change colour in dilute solution when the hydronium ion concentration reaches a particular value. For example, phenopthalein is a colour less substance in any aqueous solution with a pH less than 8.3 in between the pH range 8.3 to 10 , transaction of colour (colourless to pink) takes place and if pH of solution is greater than 10 , then solution colour is dark pin. Considering an acid indicator HIn, base In^(-) can be represented as : HIn hArr H^(+) + In^(-) acidic form basic form pH of solution can be computed as : pH = pK_(In) + "log" ([In^(-)])/([HIn]) In general, transition of colour takes place in between the pH range pK_(In) +-1 If an indicator is to be used in an acid base titration having an equivalence point in pH range 8 to 10 , the indicator must

    An indicator is a weak acid and pH range of its colour is 3.1 to 4.5 . If the neutral point of the indicator lies in the centre of the hydrogen ion concentrations correspondin to the given pH range, calculate the ionisation constain of the indicator.

    Acid-base indicator such as methy 1 orange, phenolphthalein, and bromothymol blue ate substances which change colour accroding to the hydrogen ion concentration of the solution to which they are added. Most indicators are weak acids (or more rarely weak base) in which the undissociated and dissociated forms have different and distinct colours. If methy 1 orange is used as the examples and the un-dissociated forms is written as HMO , then dissociation occurs as shown below: Reaction: {:(HMOhArr,H^(o+)+,MO^(Theta),,),(Red,"Colourless","Yellow",,):} The indicator should have a sharp colour change with the equivalence point of the titration. Usually the colour change of the indicator occurs over a range of about two pH units. It should be noted that the eye cannot detect the exact end point of the tiytration. The pK_(a) of the indicator should be near the pH of the solution at the equivalance point. Given that the K_(a) (methy 1 orange) = 4.0 xx 10^(-4) , a solution at pH = 2 containing the indicator would be

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