A \"titration\" problem. Calculate the pH of a solution that results from mixing

Question

A "titration" problem. Calculate the pH of a solution that results from mixing 10.0 mL of 0.200 M HOAc (pK_a = 4.74) with 12.0 mL of 0.100 M NaOH. Fill in the following ICE table describing the complete reaction of the strong base with the weak acid. The reaction is HOAc + OH^- rightarrow H_2 O + OAc^- Now calculate the concentrations of the species that remain (based on the results of your ICE able above and the total volume of the mixed solutions): V_tot = _____ mL [HOAc] = M [OH^-] = _______ M [OAc^-] = _________ M Calculate the pH of the resulting solution. A Solubility Products problem. Calculate the molar solubility of PbBr_2 (K_sp = 6.60 times 10^-6 M^3) Write the reaction for which the value of K_sp is defined: Fill in the ICE table for the process Calculate the molar solubility of PbBr_2.

Explanation / Answer

(I)

Moles of acid taken = 0.01*0.2 = 0.002 moles

Moles of base added = 0.012*0.1 = 0.0012 moles

Moles of salt formed = Moles of base added = 0.0012

Moles of acid left after reaction with base = 0.0020-0.0012 = 0.0008 moles

Using equation:

pH = pKa + log(moles of salt/moles of acid) = 4.74 + log(0.0012/0.0008) = 4.916

(II)

Reaction for dissolution is:
PbBr2 (s) ----> Pb2+ + 2Br-

Ksp = [Pb2+]*[Br-]2.

Assuming 'x' moles of solute dissolve per liter

So, [Pb2+] = x and [Br-] = 2x

Thus, Ksp= 4x3 = 6.60*10-6

So, x = 1.875*10-2 moles/liter

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