Question

Buffers

Q1:

a.  Write the balanced chemical equation for the reaction of HCN with water. HCN + H₂ O----> CN^- + H₃O Do not answer this

b. What is the pH and concentration of CN^– in a 0.100M solution of HCN? [CN^-]=7.87 x 10^-6Do not answer this

c. What would happen if the equilibrium [CN^–] that you calculated in (b) was changed by adding 0.00500 moles of solid NaCN to 100.0 mL of the solution? (Which direction is the reaction going to “go” to minimize the disturbance?) pH: 5.10 Do not answer this

d. Determine the pH of the solution in (c) . Assume that the addition of solid NaCN does not change the volume of solution. pH:8.91 Do not answer this

e. What is the name of this type of solution?

f. Determine the pH of the solution from (c) AFTER 10.0 mL of 0.100M HNO₃ is added.

g. Determine the pH of the solution from (c) AFTER 10.0 mL of 0.100M KOH is added.

h. How many moles of strong acid could you reasonably expect to add to the solution in (c) before the pH would change drastically?

i. How many moles of strong base could you reasonably expect to add to the solution in (c) before the pH would change drastically?

Answer 1

Answers :

e. What is the name of this type of solution?

Answer : These type of solutions are called as Buffer solution. These solutions resist the change in pH on addition of a strong acid or base to some extent (called strength of buffer).

As it might be clear to you that we prepared this Buffer solution (now you come to know that it is called as buffer) by mixing solutions of weak acid and a salt of weak acid (conjugate base solution) of calculated molarities and with calculated volumes.

pH maintances is through these species.

If a strong base (providing HO- ions) added to buffer then A weak acid componant (HCN here) ionizes requisite number of H+ ions to nulify effect of HO- ions and pH is maintained (Le Chatelier's Principal).

If a strong acid (providing H+ ions) added to buffer then a conjugate base ion (CN- ion here) get protonate back to acid HCN and hence nulify added H⁺ ions therefor is the maintanance of pH.

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To Answer next questions, answers (calculations) to Q (a), (b), (c), (d) needed to be provided.

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