A sample of calcium hydroxide, Ca(OH)_2, was weighed and found lo have a mass of
ID: 895492 • Letter: A
Question
A sample of calcium hydroxide, Ca(OH)_2, was weighed and found lo have a mass of 0.5000 g. In an effort lo discover the formula of calcium oxide, this simple was convened to calcium oxide by healing. The simple of calcium hydroxide obtained had a mass of 0. 3772 g. Follow the steps below to determine the formula of calcium oxide. Find the number of moles of calcium hydroxide in the initial sample. How many moles of calcium ions were in this initial sample? How many millimoles? How many grams of calcium ions w ere in the initial sample? How many mmoles of calcium ions were in the final sample? How many grams of calcium ions were in the final sample? How many grams of oxygen were in the final sample? What is the exact ratio of calcium to mmoles of oxygen in the final sample? To the nearest whole numbers, what is the ratio?Explanation / Answer
mass of Ca(OH)2 =0.5 gms
Molecular weight of Ca(OH)2= 40 +2*17= 74
moles of Ca(OH)2= 0.5/74=0.006757 moles
Ca(OH)2 ---- Ca+2 + 2 (OH)-
74 gms of Ca(OH)2 contains 40 gms of Calcium ion
0.5 gms contains 0.5*74/40 =0.925
56 gms contain 40 gms of Calcium ion
0.3772 gms contains 0.3773* 40/56= 0.2694 gms of Calcium ion
56 gms contain 16 gms of oxygen
0.3772 gms contains 0.3772* 16/56= 0.10771gms
moels of oxygen =0.10771/16= 0.006736 moles
CaO---- > Ca+ 1/2 O2
1 mole gives rise to 0.5 moles of oxygen
0.3772/56 gives rise 0.3772/56*0.5
molar ratio of Ca to Oxygen in the final sample =1/0.5 =2 :1
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