Question

An anhydrous sample of calcium sulphate weighs 2.59 g. When mixed w/ water it hardens to form 3.54 g. of plaster of paris (CaSO4.xH20)

a. Define x
B. What is the formula for the hydrate?
c. Name the hydrate

Answer 1

\[
CaSO_4+xH_2O\longrightarrow CaSO_4\cdot xH_2O
1:x\qquad 1:x
\]
compare the number of moles

Answer 2

follow?
molar mass of CaSO4 \(= 40 + 32 + (16)(4) =136\)
similarly,
molar mass of H2O \(=2(1)+16=18\)
molar mass of plaster of paris = \(136+18x\)

in the problem,
number of moles of CaSO4 \(\displaystyle = {2.59\over136}=0.019\)
number of moles of plaster of paris = \(\displaystyle {3.54\over 136+18x}=0.019\)
now, solve for "x"

Answer 3

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Answer 4

Thanks!