Sept. 16 – Density Problems

Learning Goals: Understand how to solve problems involving density.

Success Criteria: You can use the GRASS method to solve density problems.


Today I distributed text books!  Hold onto them tightly as you are responsible for returning that one at the end of the term.  Always have them handy for class.

We started by watching will it float!  http://www.youtube.com/watch?v=zm-AkvwPdZ4
As it turns out, a log of cheese sinks.  What does this tell you about the density of cheese?

I did some more examples of density problems such as this one:

A beaker when empty has a mass of 225 g.  When 350 mL of an unknown liquid are poured into the beaker the combined mass is 500 g.  What is the density of the liquid?

Given:
beaker mass = 225 g
liquid volume = 350 mL
combined mass = 500 g

Required:
Density of the liquid.

Analyze: We need to use our density formula, D = m ÷ V, but the 'm' needs be the mass of the liquid, not the beaker.  We must subtract to get the liquid's mass.

Solve:
 m = combined mass – beaker mass
 m = 500 g – 225 g
 m = 275 g

D = m ÷ V
D = 275 g ÷ 350 mL
D = 0.78571428571428571428 g/mL

Statement:
The density of the liquid is 0.786 g/mL.  (Notice how each number given has three significant figures, therefore, we round the answer to three significant figures as well. We will review more rounding rules as we go along.)

Homework: Study for the Quiz!