Question

1. An aqueous solution contains 0.28 M hypochlorous acid.

One Liter of this solution could be converted into a buffer by the addition of:

(Assume that the volume remains constant as each substance is added.)0.14 mol HClO₄

0.142 mol NaOH

0.28 mol NaBr

0.29 mol NaClO

0.29 mol HClO₄

2.

A 1.00 liter solution contains 0.31 M ammonia and 0.40 M ammonium perchlorate.

If 0.200 moles of sodium hydroxide are added to this system, indicate whether the following statements are true or false.

(Assume that the volume does not change upon the addition of sodium hydroxide.)

_______TrueFalse A. The number of moles of NH₃ will remain the same.

_______TrueFalse B. The number of moles of NH₄⁺ will decrease.

_______TrueFalse C. The equilibrium concentration of H₃O⁺ will decrease.

_______TrueFalse D. The pH will increase.

_______TrueFalse E. The ratio of [NH₃] / [NH₄⁺] will decrease.

Answer 1

Answer 1.

according to Handerson equation

pH = pKa - log[acid]/[base] =pKa + log[base]/[acid]

here to make buffer of 0.28 M hypochlorous acid we need a base or conjugate base.

When we will add 1L of 0.29 mol NaClO to 0.28 M hypochlorous acid then it will be a buffer solution.

2.

answer. A--True (because we are not changing the concentration of NH3 so it will be constant throughout the addition of small amount of NaOH, because of buffer action)

answer. B---False (because of buffer action there will be no change in the number of moles of NH4+ because the volume of NaOH added is very small as the volume does not change upon the addition of sodium hydroxide and this much amount of NaOH will be taken care by the buffer action)

answer. C--False

answer . D--False

answer. E--False

Since we are adding a small amount of NaOH so that the volume is not changing and hence that is negligible which will be taken care by the mixture of  0.31 M ammonia and 0.40 M ammonium perchlorate, which is acting as a buffer solution and because of buffer action it will resist small change in pH by buffer action.