Please help me! super confused and is it possible to calculate the origianl conc

Question

Please help me! super confused and is it possible to calculate the origianl concetrations or do i need more information

A student has 20.0 mL of a solution that is 5.00 x 103 M in Fe3 M and Cr and has a pH of 1.00. To this solution the student adds 10.0 mL of 20% (by mass) NH4C1 and 5.00 mL of 15 M NH (a) What is the final pH and [OH-1 of the buffered solution? (assume that precipitation of metal hydroxides won't significantly effect loH-1 and pH) (b) which of the three metal cations will precipitate as hydroxide salts? (c) Can one of the metals be separated from the other two? If so, which one and what form is it in? dd) what are the concentrations of Fe Mg and Cr in the final solution once it has reached equilibrium?

Explanation / Answer

Solution:

(a) NH4Cl dissociates to give NH4+ ion and at equilibrium gives ammonium as NH4Cl=H+ + NH3,

Ka of NH4+ = 5.6*10-10 and the calculation are performed as below,

Ka= 5.6*10-10 = x(0.005+x) / 15-x

solving for x we get,

x = [H+]=1.599*10-6,

pH = -log(1.599*10-6) = 5.796

pOH = 14 - pH = 14 - 5.796 = 8.204

[OH-] = 6*10-9 M

(b) The Magnesium ion (Mg2+) will be precipitated as Mg(OH)2

(c) The Chromium metal can be separated fro the other two in the form of Cr(III)

(d) Need lab experiment values if any

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