Normality Dr. Steve Badger. Concentrations of Solutions A brief review of molarity & molality Molarity = Number of moles of solute Liter of solution Molality.

NormalityDr. Steve Badger

Concentrations of Solutions

A brief review of molarity & molality

Molarity =

Number of moles of soluteLiter of solution

Molality =

Number of moles of soluteKg 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…

Normality =

Number of equivalents of soluteLiter of solution

…let’s consider normality!

Molarity =

Number of moles of soluteLiter 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…. ??• Add how much solvent?

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:

H2SO4 + KOH H2O + K2SO4

What volume of a 0.500 M KOH solution is required to titrate 10.0 mL of a 0.20 M H2SO4 solution?

MaVa = MbVb

Could we just use this equation?

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.

volume acid moles acid moles base volume base

H2SO4 + KOH H2O + K2SO4

M

acid

rx

coef.

M

base

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!

What volume of a 0.500 M KOH solution is required to titrate 10.0 mL of a 0.20 M H2SO4 solution?

volume acid moles acid moles base volume base

___ mol H2SO4

____ mL solnx

__ mol KOH

__ mol H2SO4

x____ ml soln

____ mol KOHx10.0 mL = ___ mL

M

acid

rx

coef.

M

base

H2SO4 + 2KOH 2H2O + K2SO4

What volume of a 0.500 M KOH solution is required to titrate 10.00 mL of a 0.20 M H2SO4 solution?

volume acid moles acid moles base volume base

H2SO4 + 2KOH 2H2O + K2SO4

0.20 mol H2SO4

1000 mL solnx

2 mol KOH

1 mol H2SO4

x1000 ml soln

0.500 mol KOHx10.0 mL = 8.0 mL

M

acid

rx

coef.

M

base

volume acid moles acid moles base volume base

0.20 mol H2SO4

1000 mL solnx

2 mol KOH

1 mol H2SO4

x1000 ml soln

0.500 mol KOHx10.0 mL = 8.0 mL

M

acid

rx

coef.

M

base

Notice this!

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.

You can download this PowerPoint file at my EU web site:

www.evangel.edu/Personal/badgers/Web/

The End

Now wasn’t that fascinating?