Monday, September 2, 2013

Problem Solving: Normality, Molarity, Percent Solution Problems


PROBLEM SOLVING : Normality, Molarity, Percentages

1.    WRITE DOWN FORMULA 1ST.
2.    SHOW COMPUTATIONS.
3.    ENCLOSE ANSWERS IN BOXES.

ATOMIC WEIGHTS:

Na = 23           H = 1               S = 32
Cl= 35.5          O = 16            

1.       If you weigh 10 g NaCl solution and dissolve it in 600 ml of diluent. ( 5 pts. each)

A.    What is the Molarity?

M= 10
       58.5
      0.6 L

ANSWER= M = 0.28 M NaCl


B.     What is the Normality?

N= M X v or factor

N= 0.28 X 1

ANSWER N = 0.28 N NaCl

C.     What is the percent solution?

% = Weight of solute X 100
        Total Volume of solution

% = 10 X 100
          600

ANSWER % = 1.67%


2.      What is the Molarity of a 2 N H2SO4 solution? ( 5 pts.)

M= N
       v (valence or factor)

M= 2
       2

ANSWER M = 1 M H2SO4

3.      What is the dilution if you add 0.25 ml of serum to 5.0 ml of diluent? ( 5 pts.)

0.25 mL =  1 part
5.0 mL =  20 parts
               1:21

ANSWER Dilution = 1:21

Or

Parts of diluent = 5/0/25

5  
0.25

= 20 parts of diluent

DILUTION FACTOR= parts of solute + parts of diluent

Dilution factor = 1 + 20 = 21

ANSWER Dilution = 1:21

4.    How would you prepare  1:6 serum dilution? ( 5 pts.)

THERE ARE VARIOUS WAYS TO PREPARE SERUM DILUTIONS:

THE SIMPLEST WAY IS TO CONSIDER 1 mL of SERUM AS 1 PART.
ANSWERS:

1mL of serum = 1 part
5 mL of NSS  =  5 parts
                           6 parts

Dilution = 1:6

0.25 mL of serum   = 1 part
0.25 X 5 = 2.25 mL= 5 parts
                                   6 parts

Dilution = 1:6


5.    How would you prepare a 0.85 % NaCl solution? (5 pts.)


W=(%) X Total volume of solution
                100


W= 0.85 X 100
           100

ANSWER W= 0.85 g NaCl diluted to 100 mL of water in a volumetric flask


6. What is the Normality of a 10% CaCl2 solution?

N= % X 10
         EW (MW/v)


N= 10 X 10
        111/2


ANSWER N = 1.80 N CaCl2

7. Convert 40 mEq/L of calcium to mg/dL

40 mEq  X   1L    X  20 mg (40 atomic weight / valence)
     L            10 dL      1 mEq


ANSWER= 80 mg/dL

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