Zeus - 28-3-2011 at 15:57
Hi
I hope this isn't to basic to ask, but I've had no luck finding this.
I'm attending a lab skills course currently and there's someone who doesn't yet understand molar solutions.
I'm trying to help a person in this course understand molar solutions, I understand them perfectly but I'm a hopeless teacher.
Generally working out molar solutions is a given for basic chem, so I've not found anything sufficently simple.
Could I be pointed to a resource, or told a different method? It's just the basic concept that's causing problems.
I hope this wasn't too disjointed, if you can imagine me teaching someone in the same manner, you could see why there's problems.
Bot0nist - 28-3-2011 at 17:44
Here's three good web-pages, a power point, and a pdf. They all seem to cover it pretty well.
<a href="http://www.wellesley.edu/Biology/Concepts/Html/molarsolutions.html">Web page 1</a>
<a href="http://en.wikipedia.org/wiki/Molar_concentration">Web page 2</a>
<a href="http://www.ehow.com/how_4514440_make-molar-solutions.html">Web page 3</a>
<a
href="http://www.google.com/url?sa=t&source=web&cd=8&ved=0CE0QFjAH&url=http%3A%2F%2Fwww.chalkbored.com%2Flessons%2Fchemistry-11%2Fmola
r-solutions-solids.ppt&rct=j&q=molar%20solutions&ei=GziRTd7aGYfZgAfix_gY&usg=AFQjCNEJE0WtRgGFWyoDqnFloR1TgKTuLw&sig2=8NQrUUvt_7JXs
VAi1bRdGg&cad=rja">Power point</a>
<a href="http://www.scn.org/~bh162/making_molar_&_normal_solutions.pdf">PDF file</a>
smaerd - 28-3-2011 at 18:39
Maybe try breaking everything down for them. Usually if someone isn't understanding a concept like this they aren't understanding one of the precepts
involved in it.
Something like:
Molar masses are the combined atomic masses of all of the elements in a compound. Ex: NH3 is comprised of 3 Hydrogens and 1 Nitrogen. Nitrogen weighs
~14 g/mol and Hydrogen ~1.01. thus:
3 * Hydrogen + 1 * Nitrogen = 3 * 1.01g/mol + 1 * 14g/mol = 17.03g/mol NH3.
Then maybe ask them to solve a couple of these simple molecular weight solution problems.
Now Molar concentration(M) is defined as Number of Moles/Liters of solution. So if we have 10 grams of NH3 in 1 Liter of water(solution).
10gNH3 * (1mol/17.03g) * 1mol/1liter = 0.587M NH3
Explain to them how units cancel each other out in the above example grams cancel grams, etc.
Then test them how to do the opposite. Say we wanted to make a 0.75M solution of NH3, how many grams do we need?
0.75 Mols of NH3/1 Liter of solution * 17.03grams NH3/1Mole = 12.7725g of NH3/Liter
Then perhaps work their way up to a slightly more difficult problem such as, say we wanted to make a 0.25M solution of NH3 in 500mL of water, how many
grams of NH3 would we need?
0.25Mols NH3/1 Liter of solution * 17.03g NH3/1Mole NH3 * 1 Liter H2O / 1000mililiters * 500mL H2O = 2.128g NH3
I don't know of any alternative resources, just practice, and understanding the concepts can really help. Make sure they get this down though if they
plan on doing things like equilibrium and titrations it's very important!
Zeus - 28-3-2011 at 21:13
Thanks for the advice, I've never been in the position to teach someone from a base level, I guess it's just a matter of patience.
I'll forward those links too, thanks for taking the time to find them.