Question

1. Aluminum potassium sulfate, or potash alum, KAI(SO_​4)_^​​2 ​. 12 H₂​O, is used as an antisepsis in various food preparation processes and as a flocculant for water purification. Potash alum has a molar mass of 474.39 g/mol, it disolves readily in aqueous solution to produce potassium, aluminum, and sulfate ions.

A. A solution was prepared by dissolving 1.27 g of potah alum in enough water to make a 225 mL solution (Solution I). Calculate the molarity of potash alum in Solution I.

B. A 500-mL sample of Solution I was transferred to a 250-mL volumetric flask and diluted to the mark with water (Solution II). What are the molarities of potash alum and of the sulfate ion in the Solution II.

Answer 1

[A]

moles of potas alum = 1.27/474.39 = .002677 mols in 250 mL water.

so in 1000 mL the amount of alum = .002677*1000/250 = 0.0107 moles.

So, molarity of potash alum in Solution I = 0.0107 M.

[B] 500 mL solution can not transferred to 250 mL flask. I think the value may be 50 insted of 500.

Now, V1S1 = V2S2;

50 mL x 0.0107 M = 250 mL x S2

or, S2 = .0107*50/250 = 0.00214 M.

so molarity of potash alum in solution II = 0.00214 M

AND, molarity of Sulphate ion = 0.00214 M x 2 = 0.00428 M.