Ali Altharawi
altharawi@gmail.com
428-PHC Quiz#1 Answer Key
1- How many moles of Ca(NO3)2 are in 75 ml of 0.25 M solution?
(Atomic mass of Ca = 40.078, N = 14, O =16) (Show all calculation).
Mwt = 164 gm/mol
Molarity = # mole/ L of solution…………… or 0.25 M = # mol/ 0.075 L
Thus, # mole = 0.0188 mol
2- What is the molarity of a solution that contains 297 gm of Mg(NO3)2
per liter and a density of 1.114 gm/ml. (Atomic mass of Mg = 23.4, N
=14, O =16) (Show all calculation).
Mwt = 147.4 gm/mol………………..….. , and #mole = weight/Mwt
#mole = 297 / 147.4……………………………….#mole = 2.015 mol
Since 1 Liter is used to prepare the solution, the molarity is equal to
2.015 M (Molarity = # mole/ L of solution).
3- Calculate the volume of Con.HCl you will need to prepare 250 ml of
0.1 M HCl. (HCl has a density of 1.188 g/ml and is 37 wt%). (Atomic
mass of Cl =35.5, H =1.0) (Show all calculation)
First, calculate the molarity of Conc. HCl.
The amount of HCl per liter = 1.188 g x 1000 mL = 1188 g
However, Conc. HCl is 37 % by mass which means that only 37 g of
HCl is present in every 100 ml. Thus, 37 % of 1188 g is 439.56 gm.
# moles = 439.56/ 36 = 12.06 mole. Since calculation was done in a liter
solution, Molarity of the solution is molarity is 12.06 M.
Second, calculate the number of moles that you need to prepare.
The number of moles in 250mL of 0.1M HCL is 0.250 L x 0.1 M =0.0250
mol.
Finally, calculate the volume of 12.06 M HCl that contains 0.0250 mol
Volume (L) = 0.0250 mol/ 12.06 M ……………. Volume 0.002 L or 2.07
mL.
(If you have any questions, please do not hesitate to stop by and
ask).
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