109 weiah 2 Name Ur 103 Locker Number REPORT SHEET: Hydrates and the Determinati

Question

109 weiah 2 Name Ur 103 Locker Number REPORT SHEET: Hydrates and the Determination of the Formula of a Hydrate A. Determining the Percent Water and the Formula of a Hydrate Unknown number: Trial 2 is to be carriad out if the results of trial 1 are unsatisfactory Trial 1 Trial 2 Mass of crucible +lid +unknown Mass of crucible +lid Mass of unknown hydrate Mass of crucible + lid + residue.. 39.058 I. 756, - after first heating after second heating after third heating Mass of anhydrous salt Mass of water lost Percent water in unknown hydrate 0.4 1.42 13 1756 Formula of unknown hydrate (from your instructor) Moles of water in the hydrate sample Moles of anhydrous salt in the hydrate sample Complete formula of the hydrate

Explanation / Answer

Let us suppose as you have written that the formula be CaSO4.xH2O

Mass of CaSO4 per 100g of Hydrous salt= 80.866 g
moles = 80.866 g / 136 g/mol = 0.594 moles

mass H2O = 19.134 g
moles H2O = 19.134 g / 18 g/mol = 1.063 mol

so ratio of CaSO4 : H2O
is 0.594 mol : 1.063 mol

divide each number in the ratio by the smallest number to get it to whole numbers

0.594 / 0.594 : 1.063 / 0.594
= 1 : 2 (Approximately)

so for each CaSO4 there are 2 H2O

So the answers would be

Moles of Anhydrous Salt= 1

Moles of water in salt= 2

Formula= CaSO4.2H2O

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