ANSWERS TO PRACTICE
PROBLEMS:
1.
IF YOU HAVE WEIGHED 90 GRAMS OF NAOH AND
DISSOLVED IT 1,500 ML OF WATER, WHAT IS THE;
A.
PERCENTAGE
% = Weight in grams X 100
Total Volume in mL
% = 90 x 100
1,500
% = 6 % of NaOH solution
B.
MOLARITY
M= W in grams
MW
Liter of solution
M = 90
40
1.5
M = 1.5 M NaOH
C.
NORMALITY
N= Mv
N = 1.5 X 1
N = 1.5 N NaOH
2.
HOW MANY GRAMS DO YOU NEED TO PREPARE 2M OF
NACL?
W = DM X DV X MW
W = 2 X 1 X 58.5
W =
117 grams of NaCl
How: weigh 117 grams of NaCl and dilute it
with DH20 up to the 1 Liter mark in a volumetric flask or measure 500 mL of
DH2O into a volumetric flask, weigh 117 grams of NaCl and dissolve. Add DH20 up
to 1 liter mark.
3.
HOW WOULD YOU PREPARE 1N OF HCL?
C1V1 = C2V2
C1= 12 N (Concentrated HCl)
C2 = 1N
V2 = 100 mL (assumption when no volume is
given)
V1 = unknown
V1 = C2V2
C1
V1 =
8.33 mL
How:
Add 8.33 mL of concentrated HCl to 91.67 mL of DH2O.
4.
HOW WOULD YOU PREPARE 0.85% NACL SOLUTION?
W = % X TV (total volume)
100
W = 0.85 X 100 (if no volumes are
given assume that TV is 100)
100
W =
0.85 g (grams) of NaCl
How: Measure 50 mL of DH2O into a
volumetric flask. Weigh 0.85 grams of NaCl and dissolve completely. Add DH2O up
to the 100 mL mark.
5.
WHAT IS THE NORMALITY OF A 0.5 M CACL2 SOLUTION?
N = M X v (factor)
N = 0.5 X 2
N =
1 N CaCl2
6.
HOW DO YOU PREPARE A 1:10 SERUM DILUTION?
When no volume is given assume that 1 mL is
one part; hence,
1 mL = 1 part of solute
9 mL = 9 parts of diluent
10 parts (total)
Hence:
dilution is 1:10
How: Add 1 mL of serum to 9 mL of NSS to
come up with a 1:10 serum dilution.
7.
MAKE UP 500 ML OF 5M SOLUTION OF HCL
C1V1 = C2V2
V1 = C2V2
C1
Before you substitute be sure that all your
units are the same. It does not matter what units you used as long as they are
similar units. i.e. if you use liters for volume all volumes should be
expressed in liters.
V1 = 5 M X 500 mL
12 (12 is standard Normal concentration of concentrated HCl, since
valence is 1, N=M.)
V1 =
208.33 mL
How: Add 208.33 mL to 291.67 of DH2O to produce 500 mL of 5M HCl solution.
8.
PREPARE THE FOLLOWING WORKING STANDARD SOLUTIONS FROM A STOCK SOLUTION OF 20 MG/DL:
STATE VOLUME OF DILUENT AND DILUTION.
A.
15 MG/DL
C1V1 = C2V2
V1 = C2V2
C1
V1 = 15
mg/Dl X 100 mL
20 mg/dL
V1 = 75 mL
75 mL of 20 mg/dL stock solution added to 25 mL of DH2O
75 mL of 20 mg/dL stock solution added to 25 mL of DH2O
B.
10 MG/DL
C1V1 = C2V2
V1 = C2V2
C1
V1 = 10
mg/Dl X 100 mL
20 mg/dL
V1 = 50 mL of 20 mg/dL stock solution added
to 50 mL of DH2O
C.
5 MG/DL
C1V1 = C2V2
V1 = C2V2
C1
V1 = 5
mg/Dl X 100 mL
20 mg/dL
V1 = 25 mL of 20 mg/dL stock solution added
to 75 mL of DH2O
D.
2 MG/DL
C1V1 = C2V2
V1 = C2V2
C1
V1 = 2 mg/Dl X 100 mL
20 mg/dL
V1 = 10 mL of 20 mg/dL stock solution added to 90 mL of DH2O
Volume of stock solution, diluent and dilution are the following:
Volume of stock solution
|
Volume of Diluent (DH2O)
|
Dilution
|
75 mL
|
25 mL
|
1:4 (diluent to solute)
|
50 mL
|
50 mL
|
1:2
|
25 mL
|
75 mL
|
1:4
|
10 mL
|
90 mL
|
1:9
|
1. 75 divided by 25 = 3 + 1= 4, hence dilution
is 1:4 (diluent to solute)
2. 50 divided by 50 = 1 + 1= 2, hence dilution
is 1:2
3. 75 divided by 25 = 3 + 1= 4 hence dilution
is 1:4
4. 90 divided by 10 = 8 + 1 = 9, hence
dilution is 1:9
