## Tuesday, March 22, 2011

### ANSWERS TO NORMALITY, MOLARITY AND PERCENT SOLUTION QUESTIONS

2. What is the Molarity of a 0.5 N H2SO4 solution? (5 pts.)
3. What is the dilution if you add 0.75 ml of serum to 3.0 ml of diluent? ( 5 pts.)
4. How would you prepare 1:20 serum dilution? (5 pts.)
5. How would you prepare a 0.5 % NaCl solution? (5 pts.)
6. You are asked to prepare 200 ml of the following standard concentrations from a 20 mg/dL standard stock solution: Tabulate volume of solute and solvent and also dilution. ( 5 pts. each)

A. 2 mg/dL C. 8 mg/dL
B. 4 mg/dL D. 10 mg/dL
E. 15 mg/dL

What is the Molarity of a 0.5 N H2SO4 solution?

Since the Normality is known = 0.5 N

All you have to do is to make use of the shorter formula which is

M = Normality divided by the valence or N/v (factor)

M = 0.5 / 2

M = 0.25 M of H2SO4 (ANSWER)

What is the dilution if you add 0.75 ml of serum to 3.0 ml of diluent?

Consider the volume of serum as 1 part.

The dilution is the number of parts of the solute in proportion to the diluents plus 1.

So if 1 part = 0.75 mL

Then 3 ml is = 4 parts ( 3 ml divided by 0.75 ml)

So 1 part serum = 0.75 ml

+ 4 parts diluents = 3.0 ml

Will give you 5 parts ( 1 part serum + 4 parts diluent = 5 parts)

Dilution then is

QUESTION NO. 4

How would you prepare 1:20 serum dilution?

You can assume several volumes in this question. You can assume 1 ml as the volume of the solute as it is the easiest.

1. So 1 ml of serum + 19 ml of diluent = 1:20 serum dilution.

2. You can also assume a smaller volume for serum, especially if you were not able to extract more blood. Let’s say you have 0.5 ml of serum and you have to prepare 1:20 dilution. All you have to do is to assume that 0.5 ml is one part.

3. If 0.5 ml is one part, and you need 19 parts of the diluents to prepare a 1;20 dilution; all you have to do is to multiply 19 parts with 0.5 ml to get the volume of the 19 parts.

4. Your answer would then be 9.5 ml. ( 19 X 0.5 = 9.5)

5. So 0.5 ml of serum + 9.5 ml of diluent = 1:20 serum dilution (ANSWER)

QUESTION NO. 5

How would you prepare a 0.5 % NaCl solution?

The formula for % (W/V) is

% = W divided by the total volume multiplied by 100.

Therefore:

0.5% = W/V X 100

Assume that the total volume is 100 ml if no volume is given, so by transposing we come up with this formula:

W = 0.5% X 100 (total volume) / 100 %

W = 0.5 grams per 100 ml of diluent (ANSWER)

Note:

Convert volumes to ml and weights to grams to facilitate computation.

For QUESTION NUMBER 6, the ANSWERS WILL BE GIVEN NEXT POST.