Monday, April 29, 2013

Solutions, Suspensions, and Colloids... oh my!

Solutions are homogeneous well-mixed mixtures that cannot be separated easily (a change in phase) - like kool-aid or saltwater. Suspensions will settle and separate over time because of gravity or because of differences in density - like oil and water or orange juice with pulp. Suspensions are heterogeneous. Colloids are weird. Colloids should settle and separate over time but because the particles are super-tiny just running into each other (Brownian motion) keeps them in suspension. Colloids can also represent two different phases so if it seems weird like you cannot classify it as just one phase - like fog, jello, whipped cream - it's a colloid.

We also discussed colligative properties. Adding solutes to a solution changes basic properties like melting points and boiling points, no matter what solute is added. A perfect tie-in for today. Salt is put on our roadways to LOWER the freezing point of water to about -4*C. Because the freezing point is lowered, the ice appears to melt and stay liquid, thus making our roads less icy. They do not salt the roads in places where the normal daily temperature is below 0 because the salt would have little effect.

Because it doesn't matter what the solute is, sugar could be used for the same purpose - it is just a lot more expensive! To read more, click here

Electrolytes can conduct electricity because the solute breaks up into ions and the ions can carry the electric current. Pure water does not conduct electricity - but water with solutes in it can. We did an in-class demo similar to this one to test some solutions. Salt water does conduct electricity, but sugar water does not because of the carbon. Gatorade conducts electricity but barely because of the high sugar amount in the drink.

Molarity is moles/Liters and is a quantitative way to measure concentration. Molarity descirbes with numbers if a solution is dilute or concentrated. It is a pretty easy formula so students zoomed through it. Molarity changes with the amount of solute OR the amount of solvent (liquid) so we will be discussing dilutions tomorrow.

No comments: