A sample of a mixture containing CaCl 2 and MgCl 2 weighed 2.000 g.The sample wa
ID: 817027 • Letter: A
Question
A sample of a mixture containing CaCl2 and MgCl2 weighed 2.000 g.The sample was dissolved in water, and H2SO4 was added until the precipitation of CaSO4was complete.
CaCl2(aq) + H2SO4(aq) ? CaSO4(s) + 2HCl(aq)
The CaSO4 was filtered, dried completely, and weighed. A total of 0.545 g of CaSO4 was obtained.
How many moles of Ca2+ were in the CaSO4?
How many moles of Ca2+ were in the original 2.000-g sample?
How many moles of CaCl2 were in the 2.000-g sample?
How many grams of CaCl2 were in the 2.000-g sample?
What was the percentage by mass of CaCl2 in the original mixture?
What was the percentage by mass of MgCl2 in the original mixture?
Explanation / Answer
a) find moles CaSO4 by 0.736g/molar mass of CaSO4. This will be the same as moles of Ca2+
b) This will also be moles of Ca2+ in original
c) as formula = CaCl2, moles CaCl2 = moles of Ca2+
d) mass of CaCl2 = moles CaCl2 x molar mass of CaCl2
e) whatever the mass of CaCl2 in the sample, the percentage by mass = (mass of CaCl2/2.000g) x 100