1. Solutions & Concentration

2. Mixtures that are NOT Solutions:
Suspensions: mixtures that slowly settle upon standing. Example: sand in water
Can be separated by filtering
Suspensions exhibit the Tyndall effect - the scattering of visible light in all directions.
Colloids: heterogeneous mixtures with particles between the size of suspensions and true solutions

3. Many colloids are cloudy or milky in appearance when concentrated, but almost clear when dilute
They do not settle out
They cannot be filtered out
Colloids also show the Tyndall effect

4. Should you drive in fog with your high beams on? Why?
The Tyndall Effect
You can see the light beam because the large particles reflect the light
Here you cannot see the light beam; particles are too small to reflect light
Colloids and suspensions scatter light, making a beam visible, due to their large particle size.
Solutions do not scatter light, because of their small particle size.
colloid
solution
Should you drive in fog with your high beams on? Why?

5. Note that you can easily see the “sunbeams”, probably due to the presence of fog (a colloid) in the forest reflecting light

6. Solvation… Solution - homogeneous mixture
Solute - substance being dissolved
Solvent - present in greater amount

7. NaCl(s)  Na+(aq) + Cl–(aq)
Solvation (cont’d)…
Dissociation
separation of an ionic solid (has charged particles) into aqueous ions
NaCl(s)  Na+(aq) + Cl–(aq)

8. HNO3(aq) + H2O(l)  H3O+(aq) + NO3–(aq)
Ionization
breaking apart of some polar molecules into aqueous ions
HNO3(aq) + H2O(l)  H3O+(aq) + NO3–(aq)

9. Molecular Solvation
molecules stay intact
C6H12O6(s)  C6H12O6(aq)

10. Concentration of Solutions
The amount of solute in a solution.
Describing Concentration
% by mass - medicated creams
% by volume - rubbing alcohol
ppm, ppb - water contaminants
molarity - used by chemists (moles of solute per liter of solvent)
molality - used by chemists (moles of solute per kg of solvent)

11. A concentrated solution has a large amount of solute.
A dilute solution has a small amount of solute.

12. Concentrated vs. Dilute
Lots of solute, but little solvent
Lots of solvent, but little solute

13. Concentration is usually a qualitative description…if numbers are used, it then becomes a quantitative description.
Molarity (M) is a unit of concentration that we will eventually learn more about (it is the most widely used unit of concentration in chemistry)!

14. LecturePLUS Timberlake
Molarity (M)
A concentration that expresses the
moles of solute in 1 L of solution
Molarity (M) = moles of solute
1 liter solution
LecturePLUS Timberlake