Answers to Sample Normality and Molarity Problems

Before you can solve Normality and Molarity problems, you have to understand the definitions of these terms. Molarity is the gram molecular weight (GMW) per liter (L) of solution, while Normality is the gram equivalent weight per liter of solution.  The difference between the two is that valence is involved in Normality but not in Molarity.

You have also to remember these principles:

·         When the valence is one, Molarity is equal to Normality.

·         Molarity may be equal but is always lesser than Normality.

·         Normality may be equal but is always greater than Molarity.

·         Convert your volume to liters before using in the formula.

Here are ANSWERS to the sample problems:

1.       If you weigh 60 grams of NaCl (sodium chloride) and dissolved it in 1 liter of solution:

a.       What is the Molarity of the solution?

M= GMW/L ; since GMW = W/MW,

W = 60 grams and MW = 23 + 35.5 = 58.5,

Substitute now the values:

M= 60/58.5/1

60 = is your weight in grams

58.5 = is your Molecular Weight (MW)

1 = is your volume in liters

M = 1.026

b.      What is the Normality of the solution?

Since the valence is one the Normality is equal to the Molarity.

Hence, Normality = 1.026

c.       What is the percent solution?

The formula for percent is:

% = [W (in grams of solute)/total volume of solution (milliliters)] X 100,

Substituting:

% = (60/1,000) X 100

% = 6 %

2.       Compute for the Normality of a 2M H2SO4 solution.

Use the short cut formula N = M X Valence

N = 2 (Molar) X 2 (Valence)

N = 2 X 2

N = 4

3.       What is the Molarity of a 10% CaCl2 solution?

Use the formula:

M = % X 10/GMW

Substituting:

M = 10 X 10/111

M = 0.90

4.       Compute for the Molarity of a 0.5N NaCl solution.

Since the Normality is given, use the short cut formula, which is:

M = N/Valence

Substituting:

M = 0.5/1

M = 0.5

You could also use the principle that if the valence is 1, the Molarity is equivalent to Normality, hence, since the Normality is = 0.5, the Molarity is also 0.5 because the valence is 1.

5.       What is the Normality of a 1.5 M HCl solution?

You can use the same formula and principle above.

Hence, N = 1.5 also because the valence is 1.

Sample Normality and Molarity Problems

Here are sample problems:

1.       If you weigh 60 grams of NaCl (sodium chloride) and dissolved it in 1 liter of solution:

a.       What is the Molarity?

b.      What is the Normality?

c.       What is the percent solution?

2.       Compute for the Normality of a 2M H2SO4 solution.

3.       What is the Molarity of a 10% CaCl2 solution?

4.       Compute for the Molarity of a 0.5N NaCl solution.

5.       What is the Normality of a 1.5 M HCl solution?

Given:

Atomic weights:

Na = 23

Cl = 35.5

H = 1

O = 16

S = 30

Ca = 40

Valences:

H2SO4 = 2

NaCl = 1

CaCl2 = 2

HCl = 1

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Answers to Review Questions on Electrolytes

1. A - potassium
2. C - chloride
3. F – inorganic phosphorus
4. B - sodium
5. G-calcium
6. A - potassium
7. B- sodium
8. F – inorganic phosphate
9. A - potassium
10. C- chloride
11. E - bicarbonate
12. H- lithium
13. F – inorganic phosphorus

Answers to Review Questions on Qualtiy Control and Quality Assurance

Choose the BEST answer:

1.        Quality Control Charts (QCC) are useful in demonstrating:

a. average                                                                    d. analytical trends

b. median                                                                    e. all of the above

c.    accuracy

2.        The percentage of values of the normal population INCLUDED within the acceptable range is:

a. 85.6 %                                                                     d. 65.5 %

b. 95 %                                                                        e. NIL

c. 79.9 %

3.        The following may be used to analyze quality control data, EXCEPT:

a. Levey-Jennings plot                                                d. Westgard Rules

b. Shewhart Plot                                                         e.  NIL

c. trends and shifts

4.        The extent to which measurements agree to the true value of the quantity being measured is known as:

a. precision                                                                  d. reliability

b. accuracy                                                                  e. NIL

c. acceptable limits                                                                                                     

5.        The repeatability of test measurements is referred to as:

a. predictability                                                           c. precision      e. NIL

b. accuracy                                                                  d. reliability

6.        The middle value of a set of numbers that are arranged according to their value is known as:

a. median                                                                     c. arithmetic mean       e. NIL

b. coefficient of variation                                           d. mode

7.        The +- 2 SD range excludes the following percentage values, in a Gaussian distribution:

a. 5.5 %                                                                       c. 12.7 %           e. NIL

b. 31.3 %                                                                     d. 12.7%

8.  Compute for the coefficient of variation when +- 1SD = +-9 mg/dL and the mean is 90 mg/dL:

            a. 10.2 %                                                                     c. 13.5 %         e. NIL

            b. 5.8 %                                                                       d. 14.1 %

9.      When establishing a reference range, it is most desirable to obtain  specimens from at least the following number of individuals:

a. 125                                                                          c. 100              e. NIL

b. 250                                                                          d. 10

10.  The following should be taken into consideration when establishing a reference range, EXCEPT:

a. age                                                                           d. medical history

b. sex                                                                           e. NIL

c.    Sampling time

                                   

11.  When data fluctuation are due to chance and results are seen to vary in either direction, the problem is referred to as:

a.       systematic error                                         e. NIL

b.      random error

c.       traditional error

d.      all of the above                                                                

12.  This process encompasses all aspects of laboratory operation including patient ID, specimen collection, assaying and recording:

a. quality control                                             c. quality assurance     e. NIL

b. external control                                           d. internal control

13.  The following  Westgard Rules indicate a random error:

a.    1 (2S), 1 (3S), R (4S)

b.    10 X , 2 (2S), 1(3S)

c.    2 (2S), 1 (2S), 1 (3S)

d.    R (4S), 2 (2S), 2 (1S)

e.    NIL

14.  What is the importance of an external quality assurance program to the laboratory?

a.       Provides a means to compare tests performed by different sections within the same laboratory.

b.      Assessment of its performance in comparison with other laboratories using the same methods

c.       Provides data confirmation with previous tests on the same patient

d.      Provides reference intervals as basis of tests

e.       NIL

15.  An abrupt shift in the daily values of a Q.C chart is likely to be the result  of:

a.       Error in the quality control chart

b.      Shifting of operating technologist

c.       Calibrating the sample aspiration probe of the machine

d.      Varying the wavelength during a sample run

e.       Using new standards simultaneously with the current standard  kit

f.       NIL

16.  Which of these are classified as random errors?

1.      Mispipetting

2.      Mislabeling of sample

3.      Improper mixture of sample and reagent

4.      Sample instability

5.      Deterioration of reagent

A.    1 and 2           B. 3 and 4        C. 1,2 and 3    D. all  of the above     E. NIL

17.  Which of these is a good practice in the use of laboratory coats?

a.       Never  leave laboratory coat in the workplace

b.      Use secondary laboratory coat when performing phlebotomy outside the laboratory

c.       Use laboratory coat only when inside the laboratory

d.      Laboratory coat must be cleaned at home before coming to the workplace

e.       NIL

18. The following are included in patient identification, EXCEPT:

    a.  Introduce yourself before anything else.

    b.  Confirm identity of patient by stating his/her name.

    c.   Check for the age, sex and requested tests.

    d.   Explain the procedure briefly

    e.   NIL

19. These are considered as random errors, EXCEPT:

    a.  mispipetting

    b.  mislabeling

    c.  improper mixing

    d.  prolonged incubation

    e.  NIL

20. The following are considered as systematic errors, EXCEPT:

    a. expired reagents

    b. uncalibrated apparatus

    c. fluctuating voltage

    d. inappropriate temperature

    e. NIL

CHOICES FOR NUMBERS 21 to 24

ARRANGE CHRONOLOGICALLY THE FOLLOWING STEPS IN QUALITY CONTROL CHART PREPARATION:

A.    Solve for SD - #22

B.     Solve for mean - #21

C.     Plot SDs - #24

D.    Determine +- 1, 2 and 3 SDs - #23

25. For you to be able to interpret a quality control chart, you must have this number of data:

    A. 20 control values                                                C. 20 standard values

    B. 10 control values                                                D.10 standard values

                                                                                     E. NIL