Question

A solution contains 8.92×10-3 M chromium(III) nitrate and 6.95×10-3 M magnesium acetate. Solid potassium hydroxide is added slowly to this mixture.

A. What is the formula of the substance that precipitates first? formula = ______

B. What is the concentration of hydroxide ion when this precipitation first begins? [OH-] = _____M

Answer 1

chromium(horitate = C (NO3)3 magnarum acetate = ng CH2000), These both dessociate completely in aqueolu Boletion into their respective l'on Mg(CH2 600),(aq) After disociation Ca(NO3/3 lag) After dissociation Mg2+ (aq) + 2 CH3C00"(29) 6.95 X 10 -3M 2X 6. 95 X 10-3M (23+ (aq) + 3 NO3 lag 8.92810-3M 3x8.92x10-3 4 w Sold KOH give kt and OH-ion in aqueolus solution ) So intally we have [Mg2+ = 6.95 X 10-3M [Co 3+] = 8.92 X 10 -3 M Ksp values for Mg(OH)2 = 5:6X10-12 Cr COHlz= 1.6 X 16-30 let s is solubility of MgCotal (3) rg (0H12 Mg 2+ (aq) + 20H-lag) S 25 Ksp - [right] [OH-]2 5e6 X 10-12 - S (29)2 - SE 1.128 10-4 M = 453 let s' is solubility of CaCOHla cr cottolis (2 37 (ag) + 3 orrlag! SI 391 Ksp = [Co 3t ] [OH-] 1.68 10-30 a six (351)3 = 27514 31 = 1.56 810-8M

- As S(1:12 x 10-4) > S! (1:56 X108) It means Mg(OHh will precipitate out in laost o it is more soluble than croH13 - COHls ppt fint A) formula of the substance that precapitates first is croH3 | - B) CCOHla precipitate first - [(8 37) = 8.92 X 10 3 M Ksb = [C737] [OH-] 3 . 16 X10-30 = (8.92 X10-3) (OH-] 3 = [OH-] = 0.564 X10-9 M 1 [OH-] = 5.64 xlo tom Anwer Please Rate