CHEM 1151K Notes
December 2, 2004
Titration: Technique usually for finding the concentration of something in a sample.
Add a solution of known concentration of a chemical that will react with the chemical of
interest in the sample. The solution of known concentration is usually dispensed with a
buret.
 Buret (NaOH)
 acid sample
For example: You can determine the acid concentration in a sample by titrating it with a
NaOH sample of known concentration. Unfortunately, both these solutions are clear and
colorless and so it the resulting solution of products. An indicator (dye that changes color
with pH) is added to the acid so you can tell when just enough NaOH is added to react
with all of the acid.
The most commonly used indicator is phenolphthalein. It is colorless in acid and pink in
basic or neutral solutions. So, if you add it to the acid sample above, the solution in the
flask will initially be colorless. When just all of the acid is neutralized by adding NaOH,
the solution will turn pink. This is called the endpoint of the titration.
Litmus paper is something else use to test pH of solutions. There are two kinds of litmus
paper, red and blue. Each is impregnated with one dye that changes color with pH.
Red litmus paper turns blue in base.
Blue litmus paper turns red in acid.
pH paper has more general use than litmus paper. This kind of paper has several dyes in
it that change a range of colors over a wide range of pH. The manufacturer supplies a
color key so you know what the pH is.
Here is an example calculation with titrations.
Suppose a 10 mL sample of HCl requires 27.0 mL of 0.100 M NaOH to be neutralized.
What is the concentration of the HCl solution?
1. Find moles of NaOH used to complete the neutralization reaction.
Use the definition of molarity:
So
M = moles solute/ L solution = mol/L
mol = M x L = (0.100 M) x (0.0270 L) = 0.00270 moles NaOH
2. Find moles of HCl that reacted. You need the balanced chemical reaction for this. It
is just the middle step of the flowchart we used in chapter 3.
HCl (aq) + NaOH (aq)  NaCl (aq) + H2O (l)
Notice that HCl and NaOH react in a 1:1 ratio, so this time you should be able to find the
moles of HCl by inspection. It's the same as the number of moles of NaOH found in step
1.
Moles HCl in the sample = 0.00270 mol
3. Find the concentration of the original HCl sample. Just use the definition of molarity
again. Remember, the original acid sample volume was 10.0 mL.
M = moles solute/ L solution = 0.00270 mol HCl / 0.010 L = 0.270 M HCl
________________________________________________________________________
Chapter 12 - Nuclear Chemistry
There are 3 basic types of radiation:
1. Alpha particles () - consists of 2 protons and 2 neutrons (same as a helium nucleus)
charge is +2, mass is 4 amu, highly energetic
2. Beta particles () - very fast moving electrons, charge is -1, mass is about 1/2000 amu
(same as electron we covered early in the semester)
3. Gamma radiation () - Invisible light of very short wavelength (high energy), no mass,
no charge (shorter wavelength and higher energy than X-rays)
All kinds of radiation can ionize living tissue. That's what makes it dangerous.
Ionization involves chemical changes. These changes in living tissue can result in
disease, death or mutations that can be passed on in the next generation.
Ionizing power is proportional to the charge on the type of radiation.
 >

>

Penetration Power is a measure of how far radiation can go into a material. This is
important for living things. It is proportional to the "size" of the radiation. The smaller
and lighter, the easier it is for the radiation to pass through material. Gamma radiation
has no mass and is light, so it passes through things very easily. It takes a large thickness
of lead to stop gamma radiation. Alpha radiation is the heaviest and biggest and the
easiest to stop. It can be blocked by a piece of paper or even clothing.
Penetration Power

Thus ends CHEMISTRY 1151K
Happy holidays!
>

>
