January 03, 2025, 03:51:35 AM
Forum Rules: Read This Before Posting


Topic: Calculating weight of Fe(OH)2 and molar concentration of Fe2+  (Read 8999 times)

0 Members and 1 Guest are viewing this topic.

Offline NewtoAtoms

  • Full Member
  • ****
  • Posts: 127
  • Mole Snacks: +8/-2
  • Gender: Female
Calculating weight of Fe(OH)2 and molar concentration of Fe2+
« on: February 04, 2009, 05:44:59 PM »
Would someone please tell me if my leg work and logic behind this question is correct?

Q: 2.20g of solid NaOH are added to 250 mL of 0.10 M FeCl2 solution.  Given the Ksp for Fe(OH)2 is 1.6 x 10-14 calculate:

a.  the weight of Fe(OH)2 formed
b.  the molar concentration of Fe2+ in the final solution.


I have done all the leg work, which makes perfect sense to me, unfortunately I am extremely worried that I am wrong.
Would you chemists please review my work and tell me if I am on the correct path?

a. weight of Fe(OH)2 formed

g FeCl2 ----> mol FeCl2 ----> mol fe(OH)2 ----> g Fe(OH)2

2.20g NaOH x 1mol/41.01 gNaOH x 1 mol Fe(OH)2/1 mol NaOH x 73.87 g/1 mol Fe(OH)2

= 3.99 g FeOH2- is what I would propose is the weight of Fe(OH)2 formed.  I calculated this using the stoichiometric ratios.

b. the molar concentraiton of Fe2+ in the final solution

            Fe(OH)2  <----------> Fe2+        2(OH-)
INITIAL                                   O               O
CHANGE                                  +s             +2s
EQUIL                                       S              2S

Ksp = [Fe][OH]2
Ksp = [ S][2S]2
Ksp = [ S] [4S2]
1.6 x 10-14 = 4s3  (divide both sides by four, then cube root right side)
1.59 x 10-5 = s

Therefore the molar concentration of Fe2+ in the final solution would be 1.59 x 10-5

Any help, direction and time would be deeply appreciated!!
« Last Edit: February 04, 2009, 06:21:05 PM by Borek »

Offline NewtoAtoms

  • Full Member
  • ****
  • Posts: 127
  • Mole Snacks: +8/-2
  • Gender: Female
Re: Calculating weight of Fe(OH)2 and molar concentration of Fe2+
« Reply #1 on: February 04, 2009, 05:45:25 PM »
I am sorry I am not sure why the end 1/2 of the question has a line through it...

Offline AWK

  • Retired Staff
  • Sr. Member
  • *
  • Posts: 7976
  • Mole Snacks: +555/-93
  • Gender: Male
Re: Calculating weight of Fe(OH)2 and molar concentration of Fe2+
« Reply #2 on: February 05, 2009, 01:42:28 AM »
Check this number
Quote
41.01
AWK

Sponsored Links