Ex 4

‫بسم ال الرحمن الرحيم‬ Name: ayedzahran Group: Day:

Experiment 4 "Water of hydration" _________________________________________________________________ I. Observations and results: Unknown number Molar mass of anhydrous salt Mass of crucible Mass of crucible and hydrate Mass of crucible and residue after heating Mass of hydrate Mass of anhydrous salt Mass of water of anhydrous salt Moles of anhydrous salt Moles of water Moles of water per 1 mol hydrate % water in the hydrate Molar mass of hydrate

Na2CO3010H2O 106 g/mol 123.52 g 124.97 g 123.80 1.43 g (1) 0.28 g 1.17 g (3) 0.00175 mol (4) 0.065 mol (5) 3.887 mol 81% (6) 176 g/mol (7)

II. Calculation: (1) Mass of hydrate = 124.95-123.52=1.43 g (2) Mass of anhydrous salt =123.80-123.52 =0.28 g (3) Mass of water of anhydrous salt =124.97 g -123.80=1.17 g (4) n =m/M=0.28 /106= 0.00175 mol (5) n= m/M=1.17 /18=0.065 mol (6) %water= (mwater/msample)*100%= (1.17 /1.43)*100%=81% (7) In hydrate (anhydrous salt : water) ,that’s mean the ratio between

anhydrous salt and water in hydrate as (0.00175: 0.065) or (1:38.23) ,from the ratio the hydrate is Na2CO304H2O ,and molar mass is 176 g/mol

III. Answer the following questions: 1. What percent by weight of water is in alum KAI(SO4)2.12H2O Take sample of hydrate ,nhydrate =m/M =100\474=0.211 mol 1 mole hydrate === 12 mole water 0.211 mol === ?? Moles of water =2.532 mol Mass of water =n*M =2.532*18 =45.576 g %water = (mwater/msample)*100% = (45.576/100)*100%=45.576% 2. A solid hydrate weighting 2.691 g was heated to drive off the water .A solid anhydrate residue remained which weighed 2.259 g /Calculate the percent by mass of water in the hydrate .If the anhydrous residue has a molar mass of 282 g/mol how many moles of water contained in one mole of hydrous salt? ,mwater = mhydrate-manhydrate=2.692-2.259=0.432 g %water =(mwater/msample)*100% =(0.432/2.691)*100% =16% ,nanhydrate = m/M=2.259/282 =0.008 mol , nwater = 0.432/18=0.024 mol 0.008 mol ===== 0.024 mol 1 mol ===== ?? , nwater =3 mol in one mole of hydrous Not: For experiment number , For calculation number , For the solution of answers .