You are a CEM 262 TA and are preparing a 0.36 M ZnCl2 solution as an unknown for the EDTA titration experiment. The pH must be below what value to avoid precipitation of zinc hydroxide in the solution? The solubility product of Zn(OH)2 is 3×10-16. For this calculation, assume that the solution is ideal.

12

A student was asked to identify a compound. In an effort to do so, he first dissolved the compound in water. He found that no precipitate formed when hydrochloric acid was added, but when H2S was bubbled into this acidic solution, a precipitate formed. Which one of the following could be the precipitate? NiS AgCl HgS BaS

[References] a. Calculate the pH of a buffer that is 0.4 M in acetic acid (CH3 COOH) and 0.4 M in potassium acetate (CH3 COOK). The pK, for acetic acid is 4.74. pH = b. What is the pH of a buffer that is 3 M in acetic acid and 3 M in potassium acetate? pH = c. What is the difference between the buffers described in parts a and b? The solution in part b has buffer capacity than the solution in part a. Submit Answer Try Another Version 5 item attempts remaining

k Please don't provide handwriten solution

For each of the following compounds, decide whether the compound's solubility in aqueous solution changes with pH. If the solubility does change, pick the pH at which you'd expect the highest solubility. You'll find K data in the ALEKS Data tab. sp compound Does solubility change with pH? highest solubility pH = 4 pH = 5 pH = 7 O yes PbF, 0 O no O yes AgCN Ο O PbCl₂ О по Oyes O no 0

Complete the solubility table. Na+ Ag* Ca?+ Fe2+ OH- CIo, PO- Answer Bank insoluble soluble étv Aa

A student does not filter his/her saturated solution before titrating. Will the calculated Ksp probably be too high, too low, or unaffected? Why? Solid substances are not part of equilibrium equations, so their presence would leave the value of Ksp unaffected. The remaining solids would absorb excess H30+ ions during the titration, making the calculated value of [OH ], and thus Ksp, too low. O The remaining solids would dissolve during the titration to give more OH¯. The calculated Ksp would therefore be too high.