# Normality by ert554898

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```									Normality
Concentrations of Solutions

A brief review of molarity & molality

Number of moles of solute
Molarity =
Liter of solution

Number of moles of solute
Molality =        Kg of solvent
Preparing a Solution of Known Molarity
Would you use a volumetric flask to
prepare a solution of known molality?

How would you prepare a
solution of known molality?
Another way to express
solution concentration
• Now that you understand molarity…

Number of moles of solute
Molarity =
Liter of solution

…let’s consider normality!

Number of equivalents of solute
Normality =
Liter of solution
What’s an equivalent ?

• An equivalent of a substance is the
mass (grams) of that substance that
will combine with one mole of another
reactant.
• In an acid-base reaction, an equivalent
is that amount of a substance that
reacts with or liberates 1.0 mole of H+.
What’s an equivalent ?

• An equivalent of a substance is the
mass (grams) of that substance that
will combine with one mole of another
reactant.
• In a redox reaction, an equivalent is
that amount of a substance that gains
or loses 1.0 mole of e–s.
Making a 1.00N Solution
• Calculate the mass of one equivalent
of the substance, then measure that
number of grams of the substance.
• Put that substance in…. ??
Preparing a Solution of Known Normality
AbNormality?

• Why don’t many modern chemistry
textbooks cover normality?
• If we take a dimensional analysis
approach to problems solving,
normality is a superfluous concept.

• Consider the following problem:
What volume of a 0.500 M KOH
solution is required to titrate 10.0
mL of a 0.20 M H2SO4 solution?

H2SO4 + KOH          H2O + K2SO4

Could we just use this equation?

MaVa = MbVb
Here’s what we’d get if we used

MaVa = MbVb
0.20 M H2SO4 X 10.0 mL = 0.500 M KOH X ? mL

Solving this, we get 4.0 mL of 0.500 M KOH.
But is this correct? No, it’s wrong! Why?

So let’s see how we solve this correctly.
What volume of a 0.500 M KOH
solution is required to titrate 10.0
mL of a 0.20 M H2SO4 solution?

BALANCE THE CHEMICAL EQUATION!
H2SO4 + KOH                     H2O + K2SO4

M                   rx                   M
volume acid          moles acid           moles base          volume base
acid                coef.                base
What volume of a 0.500 M KOH
solution is required to titrate 10.0
mL of a 0.20 M H2SO4 solution?

H2SO4 + 2KOH                        2H2O + K2SO4

M                   rx                   M
volume acid            moles acid           moles base          volume base
acid                coef.                base

___ mol H2SO4       __ mol KOH          ____ ml soln
10.0 mL x                   x                   x                  = ___ mL
____ mL soln        __ mol H2SO4        ____ mol KOH
What volume of a 0.500 M KOH
solution is required to titrate 10.00
mL of a 0.20 M H2SO4 solution?

H2SO4 + 2KOH                       2H2O + K2SO4

M                   rx                    M
volume acid            moles acid           moles base           volume base
acid                coef.                 base

0.20 mol H2SO4       2 mol KOH           1000 ml soln
10.0 mL x                    x                  x                   = 8.0 mL
1000 mL soln        1 mol H2SO4        0.500 mol KOH
Notice this!

M                   rx                    M
volume acid            moles acid           moles base           volume base
acid                coef.                 base

0.20 mol H2SO4       2 mol KOH           1000 ml soln
10.0 mL x                    x                  x                   = 8.0 mL
1000 mL soln        1 mol H2SO4        0.500 mol KOH

Notice this!
This is what makes normality superfluous!
Is the following statement
true or false?
• Any volume of a base will completely
react with (neutralize) that same
volume of acid if the two solutions
have the same normality (vice versa too).
• In other words, is this true:

NaVa = NbVb
Is the following statement
true or false?
• Any volume of a reducing agent will
completely react with that same
volume of an oxidizing agent if the
two solutions have the same normality.
• In other words, is this true:

NoxVox = NredVred
Let’s solve a few problems
using normality

• Look at the handout that has sample
problems and work the first one.
And another thing…

• We also use equivalents and
milliequivalents as an amount
of a substance
• The same way that we use
moles (mol) and millimoles
(mmol) as an amount of a
substance
If you need more help:
Come by my office and I can give you
a few pages of worked examples from
a Schaum’s Solved Problems Series.