a) What combination of a molecular base and a salt of the conjugate acid of the

Question

a) What combination of a molecular base and a salt of the conjugate acid of the chosen molecular base should you select to prepare a buffer solution that would maintain a pH of 10.00? (You will not be given credit if you use a salt of a weak acid and a weak acid for this problem) For full credit, explain your choice in a simple, straightforward manner, (keep answer under 40 words).

b) What ratio of concentrations of the molecular base you chose in part a and its conjugate acid would be necesarry to achieve a pH of exactly 10.00?

c) Describe, using one well-written sentence, a simple abd practical way to make 1.00L of the buffer solution you did calculations for in part b, assuming that a 1.0M solution of the molecular base is available and that the chloride salt of the conjugae acid is available as a solid. (Note: laboratory balances are calibrated to measure in grams and pipettes in mL, neither of these practicle instruments are calibrated in moles)

Explanation / Answer

a) pH = 10 hence pOH = 14-10 = 4

pOH = pkb + log [conjugate acid]/[[Base]

we need pkb value of base near 4 , lets take NH4 which has pkb = 4.75

b) hence pOh = 4 = 4.75 + log [NH4+]/[NH3]

[NH3]/[NH4+] = 5.62

c) we have 1M NH3

hence [NH4+] = 1/5.62 = 0.178 M

NH4+ moles = MV = 0.187 x 1 = 0.178 ,

NH4Cl mass required = moles x molar mass = 0.178 x 53.491 = 9.52 gm

hence 9.52 gm NH4Cl solid is disoolved in 1 liter solution of 1M NH3

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