Question #87882

1 Answer
Apr 1, 2017

Answer:

The normality is the number of gram equivalents in 1 L of solution.

Explanation:

Equivalent mass

A workable definition of equivalent mass (or equivalent weight) is:

the mass of one reactant in a balanced equation divided by the number of moles of another (this isn't the official definition).

Thus, equivalent mass depends on the reaction involved.

Gram equivalents

For example, in the reaction

#"H"_2"SO"_4 + "2NaOH" → "Na"_2"SO"_4 + "2H"_2"O"#

The equivalent mass of #"H"_2"SO"_4# is its molar mass divided by 2 (the coefficient of #"NaOH"#).

In the reaction

#"H"_2"SO"_4 + "Ba(OH)"_2 → "BaSO"_4 + "2H"_2"O"#

The equivalent mass of #"H"_2"SO"_4# is its molar mass divided by 1 (the coefficient of #"Ba(OH)"_2#).

An equivalent mass of a compound is often called an equivalent (eq) or a gram equivalent (geq).

If we call the number of moles of the other compound the n-factor, we can write

#color(blue)(bar(ul(|color(white)(a/a) "geq" = "molar mass"/"n-factor"color(white)(a/a)|)))" "#

Thus, for titration with #"NaOH"#,

#"1 geq of H"_2"SO"_4 = ("98.08 g H"_2"SO"_4)/2 = "49.04 g H"_2"SO"_4#.

For precipitation #"BaSO"4#,

#"1 geq of H"_2"SO"_4 = ("98.08 g H"_2"SO"_4)/1 = "98.08 g H"_2"SO"_4#.

Normality

Normality is defined as the number of gram equivalents of a compound in 1 L of solution.

#color(blue)(bar(ul(|color(white)(a/a)N = "geq"/"litres"color(white)(a/a)|)))" "#

Thus, a #1 N# solution of sulfuric acid for titration with #"NaOH"# will contain 49.04 g of the acid.

A #1 N# solution of sulfuric acid for precipitation of #"BaSO"_4# will contain 98.08 g of the acid.