Titration MCQ

When doing an acid-base titration, it is necessary to perform a neutralisation reaction. Here, the concentration of a given base or acid is determined through neutralisation, with an acid or base of known concentration being employed to do so. In this sort of titration, a drop of an indicator is employed at the beginning of the process, and the colour of the indicator changes to indicate the endpoint. The colour of the indicator changes in response to variations in the pH of the solution. To find the equivalence point and limit indicator error, it is necessary to apply a suitable indicator. There are a wide variety of titrations available, which are classified according to the nature of the chemical reaction that occurs between the sample and the titrant. These include: acid-base tests; precipitation tests; complex formation tests; oxidation-reduction tests (Redox tests); and chloride titrations.

Q1. Which of the following is used as an indicator in the titration of a strong acid and a weak base?

a) Methyl orange

b) Phenolphthalein

c) Thymol blue

d) Fluorescein

Answer : a) Methyl orange

Specifically, Methyl Orange is the correct signal to utilise in this situation. Choosing the appropriate indicator for titration in analytical chemistry is dependent on the pH range in which the indicator’s effective activity is found. While in basic solution, the acidic proton present in phenolphthalein will be grabbed by the hydroxide ions and will result in the formation of a quinoid structure that is pink in colour. As a result, the presence of the pink colour will aid in the identification of the titration’s end point.

Q2.  The ideal indicator for the titration of strong acid and weak base should have a pH range between ______.

a) 3-5

b) 4-6

c) 6-8

d) 7-9

Answer : b) 4-6

It is best to use an indicator in the pH range of 4-6 when measuring the strength of an acid and a weak base in titration. It is necessary to do a strong acid-strong base titration with the use of a phenolphthalein indicator. This particular pigment was chosen because it changes colour when the pH ranges between 8.3 and 10. The acid and base will react in a strong acid-strong base titration, resulting in the formation of a neutral solution. When the reaction reaches its equivalence point, the hydronium (H+) and hydroxide (OH-) ions will react to generate water, which will result in a pH of 7. This is true for every titration involving a strong acid and a strong base.

Q3. Find the concentration of HCl, if 10 ml of 0.5 M Ca(OH)2 is required to titrate 50 ml of HCl.

a) 1/10 M

b) 1/5 M

c) 5 M

d) 10 M

Answer : b) 1/5 M

The concentration (molarity) of the H+ ions in solution can be determined by calculating the pH of HCl in solution, which is by definition equal to 0.100 M. Because HCl is a strong acid, it completely ionises, and the pH of HCl in solution can be determined by computing the concentration (molarity) of the H+ ions in solution. (The chloride ion Cl–, which is the conjugate basic of the acid, would have a concentration of 0.100 M as well.) As a result, the pH is –log(0.100) = 1.000. Hydrochloric acid (HCl) is available for purchase in commercial quantities at concentrations mostly in the range of 28–36 percent weighted average.

Q4.  What is the concentration of the sulphuric acid solution, if 100 ml of the solution is neutralised by 50 ml of 0.5 M Ba(OH)2 solution?

a) 0.25 M

b) 0.5 M

c) 25 M

d) 50 m

Answer : a) 0.25 M

Q5. If 30 ml of acid is neutralised by 15 ml of 0.2 N alkali, then the concentration of acid is ______.

a) 0.1 N

b) 0.2 N

c) 0.3 N

d) 0.4 N

Answer : a) 0.1 N

Q6. Which of the following is a buffer solution?

a) CH3COOH + CH3COONH4

b) H2SO4 + CuSO4

c) CH3COONa + CH3COOH

d) NaCl + NaOH

Answer : c) CH3COONa + CH3COOH

Q7. Which of the following is used as an indicator in the titration of a weak acid and a strong base?

a) Methyl orange (3 to 4.6)

b) Bromothymol blue (6 to 7.5)

c) Phenolphthalein (8 to 9.6)

d) Methyl red (5 to 6.9)

Answer : c) Phenolphthalein (8 to 9.6)

The pH at the equivalence point is larger than 7.0 when titrating a weak acid, however, therefore an indicator with a pKin greater than 7.0, such as phenolphthalein or thymol blue, should be used in this case instead. A colourless, weak acid, phenolphthalein is often employed as an indicator in titration tests to signify the point at which the titration has reached its maximum concentration. Due to the fact that this molecule dissociates into pink anions when dissolved in water, the creation of a pink colour indicates the completion of the reaction.

Q8. What is the molarity of the solution of barium hydroxide, if 35 ml of 0.1 M HCl is used in the titration of 25 ml of the barium hydroxide solution?

a) 0.28

b) 0.21

c) 0.14

d) 0.07

Answer : d) 0.07

Q9. A difference between strong and weak acid is ________.

a) proton donation and electron acceptance

b) complete and partial ionisation

c) negative and positive pH

d) presence and absence of halogen ions

Answer : a) proton donation and electron acceptance.

A difference between strong and weak acid is proton donation and electron acceptance.

Q10. Which of the following titrations will have the equivalence point at a pH more than 8?

a) CH3COOH and NaOH

b) HCl and NaOH

c) CH3COOH and NH3

d) HCl and NH3

Answer : a) CH3COOH and NaOH

A weak acid is titrated with a strong base, and the conjugate base of the weak acid will raise the pH to a value larger than 7 at the equivalence point.