## Saturday, January 8, 2011

### How Do Chemists PREPARE SOLUTIONS Without Blowing the Lab Up?!

Fact: Chemicals are shipped in their most CONCENTRATED form.

This is pretty much common sense, right? I mean, if they were shipped already diluted, it'll cost more.

Diluted Chemicals=More Chance of Spillage=More Shipping/Packages=More Money=More Greenhouse Gases (due to shipping)

So, chemists and chemistry students like yourself  need to learn how to dilute these concentrated substances.
But before you learn how to do that, burn this concept into your mind:

MOLES OF SOLUTE IS CONSTANT
ie. moles in the solute before=moles in the solute after dilution

Let's break down a question:
Concentrated HCl is 55.6mole/L. How can we make 250 mL of 0.500 mole/L HCl?
1. Write down the formula.
M1L1=M2L2
2. Plus in the numbers.
(55.6M)(L1)=(0.500M)(0.250L)
3. Solve for L1.
(55.6M)(L1)=(0.500M)(0.250L)
55.6L1=0.125
55.6       55.6
L1=0.002248L
4. Put answers to the appropriate number of sig. figs.
L1=2.25mL
5. Don't forget to include UNITS!!

More Practice Problems:
1. 150.0mL of 0.025M KOH solution is added to 150.0mL of water. Calculate the new molarity.

2. A 0.225M solution is concentrated by evaporation to reduce the final volume of 75.0mL and a molarity of 0.275M. Calculate the original volume.

VIDEO TIME! -insert applause-

Good luck in mastering this relatively new concept!

Written by Jialynn.