December 4, 2009 (molecular formulas)

Finding Molecular Formulas
It is easy to do if you know the empirical formula and the Molar Mass.

If the empirical formula for a compound is CH2O and the molar mass is 90.0g/mol. Find the molecular formula.
Stock Solutions

• Are concentrated solutions from suppliers

12 M HCl
15 M HNO3
18M H2SO4

Makiki wants to make 200mL of 0.40M HCl. What volume of 10.0M HCl should she use?
V1= ? V2= 0.200L C2V2 = C1V1
C1= 10.0M C2= 0.40M (0.40M)(0.200L) = (10.0M) V1
V1 = 0.008L/ 8mL

Giving Directions - Dec2 Class

In today's class, we learned about which procedures we should use when it comes to concentrations. We also did a pre-lab about how much water we would need to dissolve Copper Chloride completely. We will be doing the lab this friday, Dec4.

Outline for experimental procedures:
- Find the mass you need

Johnny is asked to make 0.95M solution of K2S04. If he needs 300mL, what procedure should he use?
Con'c -> moles -> mass

Give directions to make 3.5 L of 4.5M NaOH

DILUTIONS OF SOLUTIONS
- When you add water, con'c decreases. If the volume is doubled, con'c is halved.

N1 = N2
C1V1=C2V2
Lauren adds 215.0 mL of water to 25.0 mL of 0.8M HCl. Find [HCl]
Janice adds water to 75.0 mL of 0.15M HF to a final volume of 310mL. Find the [HF]
Nicola dilutes 75.0 mL of 0.30M HNO3 to 0.10M. What is the final volume?

How much water did she add?
225mL-75mL = 150mL