As a novice (so need very plain answers but with enough detail), what is a measurement of normality in chemistry, why do we need it and how do I calculate it?

1 Answer
Nov 13, 2017

Answer:

#"Normality"# and #"molarity"# (but not #"morality"#!) are expressions of #"concentration"#....

Explanation:

And for a chemist, #"concentration"# determines the strength of a solution in terms of amount of stuff per unit volume of solution. And clearly, this extends beyond chemistry; if you put too much sugar in your tea or coffee it might be too sweet, too #"concentrated with respect to sugar"# to drink...

And so #"concentration"="amount of stuff"/"volume of solution"#. And note also that solutions could be in the solid phase, i.e. metal alloys, or in the gaseous phase; and in fact the air you are breathing now is such a gaseous solution, which is more concentrated with respect to dinitrogen than it is to dioxygen and carbon dioxide...

And now attend, because you will be using this definition thruout your career as a student, and later as a professional..

Most commonly, when we speak of #"concentration"#, we refer to #"molarity"#.

And #"molarity"# is defined as the quotient....

#"molarity"="moles of solute"/"volume of solution"#

The most common solvent is water, and most of the time when we add a solute to water, and it dissolves, the VOLUME of the solution changes negligibly with respect to the pure solvent. And so, were we to dissolve a #36.5*g# mass of #HCl(g)# in a #1*L# volume of water, we would have a concentration defined by....

#"Concentration"=((36.5*g)/(36.5*g*mol^-1))/(1*L)=(1.0*mol)/(1.0*L)=1*mol*L^-1#

i.e. #1.0*mol*L# #"with respect to HCl(aq)"#

Confused yet? Yet most concentrations refer to this quotient. Good luck. If you want clarification on some issue, or to check up on a problem, please reply on this thread....

#"Normality"# refers to concentrations of diacids, where a reagent such as sulfuric acid, that requires TWO equiv of base for neutralization is quoted in terms of #"normality"=2*"molarity"#. A half molar solution of #H_2SO_4# or #H_3PO_4# requires a DOUBLE volume of half molar solution of #NaOH# to reach equivalence, i.e. #"normality"# when #Na_2SO_4(aq)# or #Na_2HPO_4(aq)# are achieved by titration.