Dr. Steward s CHM152 Exam #2 Review Spring 2014 (Ch ) KEY

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1 Dr. Stewrd s CHM152 Em #2 Review Spring 2014 (Ch ) KEY 1. Eplin the commonion effect. Wek cid or wek bse s % dissocition will decrese if they re plced in solutions with one of the products of dissocition. For emple, The % dissocition of HCN will be decrese if dditionl CN is dded to the solution (s NCN, for emple). HCN(q) + H 2 O(l) H O + (q) + CN (q) 2. Clculte the percent ioniztion of M solution of HF (pk =.17). HF + H 2 O H O + + F I M 0 0 C + + E + + ()() K %. Clculte the percent ioniztion if there is lso 0.50M concentrtion of NF in solution. HF + H 2 O H O + + F I M M C + + E ()(0.500) % 4. Clculte the percent ioniztion if the ph of the solution before the HF ws dded ws 0.0. HF + H 2 O H O + + F I M 0.500M 0 C + + E [HO ] M (0.500)() % 5. You re titrting 10.00mL of M of HCl with 2.00M NOH. Wht would be the ph fter 2.50 ml of NOH re dded? NOH + HCl H 2 O + NCl mol 2.00mol of NOH ( L) mol NOH 1L HCl + NOH H 2 O + NCl B mol mol Δ mol mol A mol 0 mol mol of HCl. ( L) molNOH 1L

2 ph log[h ] log mol HCl totl volume mol log log(0.40) L L Wht would be the ph fter 5.00ml totl of NOH re dded? mol 2.00mol of NOH ( L) mol NOH 1L H + + OH H 2 O B mol mol Δ mol mol A 0 0 There will only be neutrl slt t the equivlence point of Strong Acid/Strong Bde titrtion. ph = 7 Wht would be the ph fter dding totl of 5.75mL of NOH? Totl mol 2.00mol of NOH ( L) mol NOH 1L H + + OH H 2 O B mol mol Δ mol mol A mol After the equivlence point, you re just dding etr OH ions to the solution mol ph14 log L L 6. You re titrting 10.00mL of M of benzoic cid (K is ) with 2.00M NOH. Wht would be the ph fter 2.50 ml hs been dded? HA + OH H 2 O + A B mol mol 0 Δ mol mol mol A mol mol ph pk log ph 4.19 log mol mol 4.19

3 Wht would be the ph fter dding totl of 5.00 ml NOH? HA + OH H 2 O + A B mol mol 0 Δ mol mol mol A 0 0mol mol mol of A mol A [ A ] M totl volume L L A + H 2 O OH + HA I M 0 0 C + + E Kw Kb K ( ()() )(0.6667) ph = 14log[OH ] = 14log ( ) = Wht would be the ph fter dding totl of 5.75 ml NOH? HA + OH H 2 O + A B mol mol 0 Δ mol mol mol A mol mol Totl mol 2.00mol of NOH ( L) mol NOH 1L Although you hve two bses fter the equivlence point, ssume tht the concentrtion is going to hve much greter effect on ph thn the wek bse mol ph14 log L L pk logk b 7. Wht is the ph of 100.0mL solution contining 0.0 M NH nd 0.0 M NH 4 NO (K b of NH is )? 0.0M ph pk log log M b 5 log pk 14 pk Wht is the ph fter dding ml of 2.00M NOH Since this hs the components of buffer solution, we cn use HendersonHssleblch + NOH + NH 4 NH B mol 0.00mol 0.00mol 0.0mol molsof NH ndnh L 0.00molsof ech 1L 2.00mol molsof NOH dded L molsof NOH 1L

4 Δ mol mol mol A mol 0.02mol ph pk log log 0.02mol 0.028mol 9.1 Wht is the ph fter dding 2.00mL of M HCl? + HCl + NH NH 4 B mol 0.00mol 0.00mol Δ mol mol mol A mol 0.02mol molsof HCl mol dded L molsof HCl 1L ph pk log log 0.028mol 0.02mol You hve 60.00mL of buffer solution consisting of 0.900M CH COOH nd 1.10M NCH COO. K b = Determine the ph of the solution fter dding 10.11mL of 2.2M HBr mol CH COOH.06000L CH COOH 1L CH COOH mol CH COOH 2.2mol HBr L HBr mol HBr K L HBr mol CH COO L CH COO mol CH COO 1L CH COO HBr + CH COO CH COOH + Br B mol mol mol ph pk log 4.74 log Δ mol mol mol A mol mol How much totl HBr would you hve to dd until the buffer ws used up? 1.10mol CH COO 1mol HBr.06000L CH COO 1L CH COO 1mol CH COO 1L HBr 2.2 mol HBr L Wht would be the ph when t the point (tht you clculted bove?) HBr + CH COO CH COOH + Br B mol mol mol Δ mol mol mol A 0 0mol mol mol CH COOH 1.4M ( L L) CH COOH + H 2 O H O + + CH COO I 1.4M 0 0 ( )(1.4) 4.910

5 C + + E 1.4M ()() ph log(4.910 ) If you strt over with fresh buffer (sme conditions/volumes s originl), wht would be the ph of the solution fter dding 20.00mL of 2.2M KOH? 0.900mol CH COOH.06000L CH COOH 1L CH COOH 0 2.2mol NOH L NOH 1L NOG mol NOH mol CH COOH 1.10mol CH COO L CH COO mol CH COO 1L CH COO NOH + CH COOH CH COO + N + B mol mol mol ph pk Δ mol mol mol A mol mol log 4.74 log After dding 0.00mL of 2.2 KOH? 2.2mol NOH L NOH 1L NOG mol NOH NOH + CH COOH CH COO + N + B mol mol mol Δ mol mol mol A mol 0 mol mol mol NOH 0.01M NOH ( L L) poh log[oh ] log( 0.01) 2.0 ph If you wnted to mke buffer with ph of.90 using the sme buffer s before with totl concentrtion of 2.00M, wht would the concentrtion of ech prt of the buffer need to be? ph pk log log (2.0 ) (2.0 ) log (2.0 ) log (2.0) M 2.00M 0.25M 1.75M

6 11. *If moles of AgNO is dded to L of M NCl, will AgCl precipitte form? (K sp AgCl = ). Eplin. AgCl(s) Ag + (q) + Cl (q) K sp = [Ag][Cl] Q sp = ( )(0.0020) = since Q > K will shift to the left (solid AgCl), so it will precipitte! Wht would the minimum concentrtion of NCl need to be to form precipitte? K sp = [Ag][Cl] = ( )[Cl ] = [Cl ] = M 12. Ni(OH) 2 is n insoluble compound in wter. How would the molr solubility be ffected in ech if the following situtions? NOH is dded Decrese solubility (common ion) NCl is dded No effect on solubility. Does not rect with Ni 2+ or OH HCl is dded Increse solubility. H + rects with OH. 1. Assume you hve sturted solution of nickel (II) phosphte with some solid in the continer (K sp = ). Wht is it s molr solubility? Determine the concentrtion of the Ni 2+ nd PO 4 ions in the solution. Ni (PO 4 ) 2 Ni PO 4 K sp = [Ni 2+ ] [PO 4 ] = () (2) 2 =(27 )(4 2 ) I 0 0 C = = = molr solubility = E M [Ni 2+ ] = ()( ) = M [PO 4 ] = (2)( ) = M 14. Wht would be its molr solubility be of nickel (II) phosphte if 0.100moles of N 2 PO 4 ws dded to L of the solution bove? Wht would be the concentrtions of the Ni 2+ nd PO 4 ions? Ni (PO 4 ) 2 + H 2 O Ni PO 4 (27 )(0.0100) I K sp = [Ni 2+ ] [PO 4 ] = () (0.100) 2 =

7 C = = E = molr solubility = M [Ni 2+ ] = ()( ) = M [PO 4 ] = (2)( ) 0.100M 15. How much (in g) brium sulfte (BSO 4, MW=2.9) will dissolve in 500. ml of wter. For BSO 4 : K sp = B 2 SO 4 + H 2 O B SO 4 K sp = [B 2+ ][SO 2 4 ] = 2 I 0 0 C + = = molr solubility = M E molbso4 2.9g BSO L H2O gbso4 1L H O 1molBSO 2 4