CHEM 1122011 NAME: ANSWER KEY Vining, Exm # SHORT ANSWER QUESTIONS ============= 4 points ech ============ All work must be shown. 1. Wht re [H O ] nd [OH ] for solution tht hs ph of 9.0? Choose one. () [H O ] = 9 M nd [OH ] = 5 M (b) [H O ] = 5 M nd [OH ] = 9 M (c) [H O ] = 1 x 10 9 M nd [OH ] = 1 x 10 5 M [H O ] = 10 ph ; [OH ] = 1 x 10 14 /[H O ] (d) [H O ] = 1 x 10 5 M nd [OH ] = 1 x 10 9 M (e) [H O ] = 1 x 10 9 M nd [OH ] = 1 x 10 5 M 2. Wht is the conjugte bse of HC 2 O 4? () H 2 C 2 O 4 (b) C 2 O 4 2 (c) 2 CO 2 (d) H C 2 O 4 The conjugte bse of n cid hs the sme formul, less n H... Will solution of NH 4 Br be cidic bsic neutrl NH 4 is n cid; Br is ph neutrl b. Will solution of NCN be cidic bsic neutrl N is ph neutrl; CN is bse c. Will solution of NNO be cidic bsic neutrl Both N nd NO re ph neutrl 4. Will Cu (PO 4 ) 2 be more soluble in pure wter, or in wter in which N PO 4 hs been dissolved? Cu (PO 4 ) 2 (s) Cu 2 (q) 2 PO 4 (q) circle nswer: pure wter or N PO 4 solution This is the commonion effect. 5. Consider the following two rection steps. Add the following lbels to the species they represent. Point to the species nd dd the lbel. You lbel four things in totl. If something is both Lewis nd Bronsted, lbel it Bronsted. BA = Bronsted Acid LA = Lewis Acid BB = Bronsted Bse LB = Lewis Bse
6. Exmine the Tble of Acids nd Bses on the lst pge.. Which cid is stronger: H 2 CO or NH 4 b. Which bse is stronger: HCO 2 or CN 7. Which cid bse pir would be best to use for creting buffer of ph =. Circle one.. HF/F b. CH CO 2 H/CH CO 2 c. NH 4 /NH d. HCO /CO 2 8. Consider the lph plot below, which is for n cidbse system HA/A.. which species is minly prevlent t ph = 8? HA or A b. Wht is pk of HA? 10 c. Wht is K of HA? 1 x 10 10 9. Compre the K sp vlues from the dt sheet. Which is more soluble (in mol/l): PbSO 4 or PbCrO 4 10. Which of the following mixtures will form buffer solution (in 1 L wter). Circle ll correct choices. 0.10 mol CH CO 2 H 0.070 mol NCH CO 2 0.10 mol HCl 0.0 mol NCH CO 2 0.10 mol NOH 0.10 mol NCH CO 2 0.10 mol NCl 0.10 mol CH CO 2 H
11. Write the K sp expression for the dissolution of AlPO 4. K sp = [Al ][PO 4 ] 12. Write the K expression for H PO 4. K = [HO ][H2PO 4 ] [H PO ] 4 Write the K b expression for CO 2. [OH ][HCO ] K = [CO ] b 2 1. Se nd Te hve very similr electronegtivity vlues. In generl, lrger toms form weker bonds. Which should be the stronger cid: H 2 Se or H 2 Te 14. A buffer is mde contining NH nd NH 4 Cl. Write netionic equtions for: The buffering rection tht occurs when HCl is dded to the buffer: NH H > NH 4 The buffering rection tht occurs when NOH is dded to the buffer: NH 4 OH > NH H 2 O 15. When choosing n cidbse titrtion indictor, you wnt: (circle one) ) the ph of the indictor to be close to the ph of the titrtion equivlence point b) the pk of the indictor to be close to the pk of the cid being titrted c) the pk of the indictor to be close to the ph of the titrtion equivlence point d) the pk b of the bse form of the indictor to be close to the K of the cid being titrted
LONG ANSWER QUESTIONS ============= 10 points ech ============ All work must be shown. 16.. Wht is the solubility of CF 2, in grms per liter? Molr mss = 78.08 g/mol. CF 2 (s) C 2 (q) 2 F (q) Equilibrium x 2x solubility is x mol/l K K sp = [C 2 ][F ] 2 = (x)(2x) 2 = 4x x = sp = 2.7 10 4 mol/l 4 Solubility = 78.08 g CF mol 4 2 2.7 10 mol/l = 0.018 g/l ============================================================================= b. Wht is the solubility of CF 2 in solution tht contins 0.50 M NF? In moles per liter. CF 2 (s) C 2 (q) 2 F (q) Equilibrium x 0.50 2x solubility is x mol/l K sp = [C 2 ][F ] 2 = (x)(0.50 2x) 2 x(0.50) 2 K 5. 10 (0.50) 0.25 11 sp 10 x = = = 2.12 10 mol/l 2 ======================================================================================= 17. Wht is the ph of 0.80 M solution of CH CO 2 H? K = 1.8 x 10 5 Show your work, the ICE method must be used nd presented correctly. Qudrtic eqution is not needed for this. CH CO 2 H H 2 O CH CO 2 H O I 0.80 0 0 C x x x E 0.80 x x x 2 [HO ][CHCO 2 ] ( x)( x) x K = = [CH CO H] (0.80 x) 0.80 2 5 0.80 1.8 10 0.80 0.0079 x= K = = ph = log[h O ] = log(0.0079) = 2.42
18. Consider the titrtion curve below involving wek cid (HA) nd wek bse (A ).. Which does this titrtion represent? Circle it. wek cid being titrted with NOH or wek bse being titrted with HCl b. Wht is the pproximte vlue of K for the cid form of the studied cidbse pir? pk is bout 4.8, so K = 1.6 x 10 5 nything round 10 5 is fine for this c. Wht cidbse species is/re minly in solution t point A? HA, wek cid d. Wht cidbse species is/re minly in solution t point B? HA nd A e. Wht cidbse species is/re minly in solution t point C? wek bse, A ============================================================================================= 19.. Wht is the ph of buffer solution mde by mixing 100 ml of 0.14 M H 2 PO 4 nd 100 ml of 0.55 M HPO 4 2? K (H 2 PO 4 ) = 6.2 x 10 8 K (HPO 4 2 ) =.6 x 10 1 This is buffer becuse it is mixture of wek cid nd its conjugte bse. Of these, H 2 PO 4, is the cid, so pk = log(6.2 x 10 8 ) = 7.21 This is buffer, so [bse] 0.55 M ph = pk log = 7.21 log = 7.80 [cid] 0.14 M b. If 50 ml of wter is dded to this buffer, the ph will:. increse b. decrese c. remin nerly constnt This is buffer nd ph does not chnge much with dilution.