Question

B. Solubility Equilibrium; Finding a Value for Ksp
2. Explain why PbCl 2 did not precipitate immediately on addition of HCl. What conditions must be met by [Pb2 + ] and [Cl- ] if PbCl 2 is to form? 



3. Explain your observations in Steps 3 (The amount of precipitate begins to decrease as it dissolves in the hot water.) and 4 (The precipitate reappears, forming after the test tube was put in ice water.) of the procedure. In which direction did Reaction 5 shift when heated? What must have happened to the value of Ksp in the hot solution? What does this tell you about the sign of ΔH in Reaction 5?



4.Explain why the PbCl 2 dissolved when water was added in Step 5 of the procedure. What was the effect of the added water on [Pb2 + ] and [Cl- ]? In what direction would such a change drive Reaction 5 — PbCl2 (s) <——> Pb2+ (aq) + 2Cl- (aq)?

Answer 1

t6 DATE: 120 PAGE No 1 Pbcl, Pb2+ + ace- K is equil boium constant k = [Pb 2+ ] [ce] 2 [Pbce, k[Pbu = kop = [Pb2+ ] [ce-] ² kup is solubility product At 20°c ksh for Polg ý 1.78105 Polly j as imic product. Solubility of | Phce in water i low er - po ceg(s) = Pb Prop) + 261 62) - when He Ÿ added, [ce ] increase slightly and [Pb2+ 1 decrease and thus solubility of pbleg Ý reduced by the presence of dilute н . But if [ce- ý much higher there å formation of two soluble Complex reactions Pb lg (S) + ce - [Pbce, 1- Pblu, (s) + 2 0 - [Pbc2- This two complex use the solubility of Phelg in he soluble Precipitate of Phlg are not dissolve in cold water but they are dissolue / solu in hot water and give Colour les solut But if cold water is added to brecipitas and test tube Ý Centrifuged and subeuns rolation be decanted into another test ture. If any pb in present and odbero lue / soluble Subernaton nd addito

DATE: / PAGE NO 20 og of cold he solution to the liquid will Cause white precipitate of Pb ilg. - pbcl, phat + acé į an endo- thermic process. AH ý positive and equilbrium shift to right hand side according to be-chatleir principle value of ksp hold constant at specific temp. but we cannot strictly say ksp always increase with increase in tempenature as solubility of in increase 4. If we add water to the Reaction chamber there ý no shift in equilbrium because Change in amount of H₂0 does not change the value of equilbrium constant due to Convention of activity of water is one.