Question

1-Synthesis of an Alum: a) define the term alum. b) Are the tewelve waters of hydration used to caculate the theoretical yield of alum?Explain.

2-Draw absorbance (A) vs Conc .Graph from the known data as given below and determine the concentration of a solution, if the absorbance is 0.64:

Absorbance(A) ___________________Concentration (in molarity)

0.22____________________________ 0.0050

0.45____________________________ 0.0120

0.58____________________________ 0.0160

0.78 ____________________________0.0225

1.10 ____________________________0.0325

Answer 1

1) a) ALUM = It is a colourless compound which is a hydrated double sulphate of aluminium and potassium.

    Alum is a "double salt" consisting of a monovalent cation , a trivalent cation, and two sulfate ions with twelve waters of hydration.

     Chemical Formula of Alum = KAl(SO₄)₂.12 H₂O

b) Yes.

Since 12 H₂O is integral part of Alum formula , the tewelve waters of hydration used to caculate the theoretical yield of alum. Otherwise it would be just K-Al double sulfate.