Sunday, June 25, 2017

Answers to Normality and Molarity Review Questions

Solving the Normality and Molarity of solutions is quite easy by remembering the relationship of Normality to Molarity.

1.    Normality may be equal but is always greater than the Molarity in the same solution.

2.    If the valence is 1, Normality is equal to Molarity.

Try solving these problems. Atomic weights: Na = 23; Cl = 35.5, H = 1, Ca = 40, Valences: Ca = 2, NaCl = 1, HCl = 1.

1.    If you have dissolved 20 grams of sodium chloride in 1.5 Liter of distilled water, what is the:
1.1.    Normality

You have to remember that Normality is the Gram Equivalent Weight of substances. Hence, valence is involved. The formula would be:

N = W/GEW/Liter of solution
GEW = W/MW/valence

So, you have to solve first the MW (sum of atomic weights);
MW = 23 (Na) + 35.5 (Cl) = 58.5

Thus, substituting the values: GEW = 20/58.5/1

GEW = 0.3418803

N = GEW/Liter of solution
N = 0.3418803/1.5
N = 0.2279202

N - Normality
W = weight of substance
GEW = Gram Equivalent Weight
MW = Molecular Weight
M = Molarity

1.2.    Molarity

Since you already know the Normality of the solution, you can make use of the short-cut formula, which is:

M = N/valence

Thus, substituting the values:

M = 0.2279202  x 1
M = 0.2279202

The answer is the same. This follows the rule: If the valence is 1, Normality is equivalent to Molarity.

1.3.    Percent solution

You don’t usually need the molecular weights when solving percent solutions. You could use the general formula:      

% = weight/total volume x 100


In solving for percent solutions, you have to convert the volume to milliliters. So,

1.5 Liters x 1000 mL/1 Liter = 1, 500 mL

% = 20/1,500 x 100
% = 1.33333%

2.    What is the Molarity of 1 N Hydrochloric acid?
Again in this problem, since you know the Normality, make use of the short-cut formula:

    M = N/valence
    M = 1/1
    M = 1

Again: If the valence is 1, Normality is equivalent to Molarity.       

3.    What is the Normality of 0.8 M calcium chloride?

Use the short-cut formula:
N = M x valence
N = 0.8 x 2
N = 1.6

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