Lab 11B Pre-Lab Questions Calculate the percent concentration by mass of a solut
ID: 1038894 • Letter: L
Question
Lab 11B Pre-Lab Questions Calculate the percent concentration by mass of a solution made from 15.0 g of Ca(OH)2 dissolved in 250.0 mL of water. (Show your work, all steps in the calculation.) 1. 2. Calculate the molarity of the solution described in Question #1. (Again, show your work!) 3. Describe a time in which you would make a dilution in your everyday life CALCULATIONS FROM PROCEDURE (Show your work!) Given the molecular formula for sucrose (C12H22011), determine the molar mass (molecular weight) in grams/mole 1. 2. Calculate the number of moles of sucrose needed to make 100.0 mL of a 0.100 M solution. Assuming that the Kool-Aid powder is almost all sugar (so mass of powder + mass of sucrose), calculate the mass of powder needed to make the solution in #2 3.Explanation / Answer
1.
Mass of Ca(OH)2 = 15.0 g
Mass of water = volume * density = 250.0 mL * 1.0 g/ ml= 250 g
Total mass of solution = Mass of Ca(OH)2 + Mass of water = 15.0 g + 250.0 g = 265.0 g
Mass percentage of Ca(OH)2 in solution = (mass of Ca(OH)2 / mass of solution) * 100% = (15.0/265.0) * 100% = 5.66%
2.
Volume of solvent = 250 ml = 0.25 L
Mass of Ca(OH)2 = 15.0 g
Molar mass of Ca(OH)2 = 74.093 g/ mole
Number of moles of Ca(OH)2 = (mass/ molar mass) = (15.0 g)/ (74.093 g/ mole) = 0.202 mole
Molarity of the solution = (moles of Ca(OH)2)/ (Volume of solution in Liters) = (0.202 mole/ 0.25 Liters) = 0.81 M
3.
A dilution in everyday's life: when you drink water.
1.
Molecular formula of sucrose is C12H22O11
Atomic mass of C is 12.0107 g/ mole, atomic mass of O is 15.999 g/ mole and atomic mass of H is 1.00794 g/ mole
Molar mass of sucrose = (12* 12.0107) + ( 22*1.00794 ) + (11*15.999) g/ mole = 342.292 g/ mole
2.
Volume = 100 mL = 0.1 L
Number of moles = volume in Liters * Molarity = (0.1 L) * (0.1 M) = 0.01 mole
3.
Mass required = moles * molar mass of sucrose = 0.01 mole * 342.292 g/ mole = 3.42 g
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