Test: Measurement of pH


20 Questions MCQ Test Sensor & Industrial Instrumentation | Test: Measurement of pH


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QUESTION: 1

The hydrogen ion content in water goes from 0.203 g/L to 0.0032 g/L. How much does the pH change?

Solution: A change of 1 pH unit means that the concentration of hydrogen ions has increased (or decreased) by a factor of 10, and a change of 2 pH units means the concentration has changed by a factor of 100. The pH value is given by

pH = log10 [1/hydrogen ion concentration]

pH1 = log(1/0.203) = 0.69

pH2 = log (1/ 0.0032) = 2.495

Change in pH = 0.69 − 2.495 = −1.805

QUESTION: 2

Which of the following is the formula for pH calculation?

Solution: pH is defined as the negative logarithm of hydrogen ion concentration. Hence, its formula is -log10[H+].
QUESTION: 3

Pure water is known to be which of the following?

Solution: Pure water is a weak electrolyte. It dissociates to form hydrogen ions and hydroxyl ions.
QUESTION: 4

Which of the following is the value of hydrogen ion concentration of pure water?

Solution: The hydrogen ion concentration of pure water is 1×107 moles/litre. It can be represented as [H+]=1×107 moles/litre.
QUESTION: 5

Which of the following is the relation between hydrogen and hydroxyl ion concentration of pure water?

Solution: In water, the value of hydrogen and hydroxyl ion concentrations are the same. It can be represented as [H+]=[OH-].
QUESTION: 6

The Nernst equation is given by which of the following statements?

Solution: The Nernst equation is represented as, E=Eo + 2.303 RT/F log CH. it is used for measuring the potential of electrodes.
QUESTION: 7

Which of the following is the relation between the concentration of hydrogen and hydroxyl ions in an acidic solution?

Solution: In an acidic solution, the value of hydrogen ion concentration is greater than that of hydroxyl ion concentration. It can be represented as [H+]>[OH-].
QUESTION: 8

Which of the following is the relation between the concentration of hydrogen and hydroxyl ions in a basic solution?

Solution: In a basic solution, the value of hydroxyl ion concentration is greater than that of hydrogen ion concentration. It can be represented as [H+]<[OH-].
QUESTION: 9

The measurement of hydrogen ion concentration can be made by measuring the potential developed in an electrochemical cell.

Solution: The measurement of hydrogen ion concentration can be made by measuring the potential developed in an electrochemical cell.
QUESTION: 10

Slope factor is independent of temperature.

Solution: Slope factor is dependent on temperature. Slope factor is given by – 2.303 RT/F.
QUESTION: 11

Which of the following is the simplest of pH meters?

Solution: Null-detector type pH meter is the simplest of all pH meters. It is also known as the potentiometer type.
QUESTION: 12

In which of the following ways can zero drift be reduced in pH meters?

Solution: Zero drift be reduced in pH meters using balanced and differential amplifiers. Their response to external signals is additive and to internal noise is subtractive.
QUESTION: 13

Which of the following can be used to provide automatic temperature compensation?

Solution: To provide automatic temperature compensation, thermistors must be used. As the temperature of the solution changes, the circuit constants are altered accordingly.
QUESTION: 14

Which of the following is not the characteristic of null-detector type pH meter?

Solution: Null-detector type pH meter has greater accuracy than 0.01 pH. pH value is read from the calibrated precision voltage source dial.
QUESTION: 15

Which of the following is not the characteristic of direct-reading type pH meters?

Solution: Direct reading type pH meters do not require a balancing process. Its operation is simple and readings can be read directly.
QUESTION: 16

Which of the following is not the characteristic of the chopper amplifier pH meter?

Solution: The use of a chopper amplifier in the pH meter leads to zero instability. It leads to various other problems for high-input resistance.
QUESTION: 17

In which of the following ways can the disadvantages of chopper amplifier type pH meter be overcome?

Solution: The disadvantages of chopper amplifier type pH meter can be overcome using a vibrating condenser. It is used in the place of the mechanical chopper.
QUESTION: 18

The zero stability of vibrating condenser amplifier type pH meter is much better than a direct-coupled amplifier.

Solution: The zero stability of vibrating condenser amplifier type pH meter is much better than a direct-coupled amplifier. The capacity can be changed by vibrating one of its plates.
QUESTION: 19

In vibrating condenser amplifier type pH meter, to maintain good performance which of the following has to be done?

Solution: In a vibrating condenser amplifier type pH meter, to maintain good performance, both frequency and amplitude of the vibrator should be constant and stable.
QUESTION: 20

Given below is the block diagram of the digital pH meter. Identify the unmarked component.

Solution: The unmarked component is an A/D converter. Microprocessor operates only on digital data. Electrodes give analog signals. Hence, the A/D converter must be present.

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