1. Problem solving
And
Unit Conversions

2. Problem Solving
One of the most important things we do in life is solve problems.
The more creative we are at solving problems, the more successful we will be.
It is helpful to use the following steps when solving a problem.

3. Where Do We Want To Go?
To solve a problem, we need to be able to state the problem clearly.
What Do We Know?
This represents the starting point.
How Do We Get There?
How do we use the facts we know and the understanding we have of the relevant concepts to proceed from the starting point to the eventual goal – the solution to the problem.

4. Does It Make Sense?
After we have reached the solution, we need to evaluate it. Is the answer we have obtained reasonable?
Converting Units of Measurement
This is something you encounter all the time: converting from one unit of measurement to another.
Where Do We Want To Go?
2 dozen doughnuts = $?

5. What Do We Know?
1 dozen = 12
1 doughnut =$0.50
How Do We Get There?
Convert dozens of doughnuts to numbers of doughnuts then to cost of doughnuts:
2 dozen doughnuts → numbers of doughnuts →cost of doughnuts

6. We can make each of these conversions as follows:
The doughnuts will cost $12.
Does It Make Sense?
The answer $12 seems reasonable. First, the units are correct and each doughnut costs less than $1 so we should have an answer less than $24.

7. Conversion Factors = or Ratio derived from the equality between two
different units that can be used to convert from
one unit to another.
Example: 4 quarts in 1 gallon = or

8. or Which conversion factor should be used to
convert from gallons to quarts? or
Let’s convert 0.75 gallons to quarts. 4
quarts
3.0
quarts
0.75 gallons x = 1
gallon

9. Dimensional
Analysis
Changing from one unit to another via conversion factors (based on the equivalence statements between the units) is often called dimensional analysis.
We will use this method throughout our study of chemistry.

10. Temperature Conversions
Three scales: Fahrenheit scale, Celsius scale, and Kelvin scale.
Fahrenheit scale: water boils at 212oF and freezes at 32oF and normal body temperature is 98.6oF. Used widely in the US and Great Britain.
Named after Daniel Gabriel Fahrenheit.

11. OF and oC Celsius scale: water boils at 100oC and freezes at 0oC.
On both the Celsius and Fahrenheit scales, the unit of temperature is called a degree, and the symbol for it is followed by the capital letter representing the scale.
Named after
Anders Celsius.
OF and oC

12. William Thomson, who received the title, Lord Kelvin.
Kelvin scale: water freezes at 273 K and boils at 373 K. The unit of temperature is called a kelvin and is symbolized by K.
Named after
William Thomson, who received the title, Lord Kelvin.
The size of each temperature unit (each degree) is the same for the Celsius and Kelvin scales.
The Fahrenheit degree is smaller than the Celsius degree and the Fahrenheit unit.
The zero points are different on all three scales.

13. Converting Between the Kelvin and Celsius Scales
TCelsius = TKelvin
Converting Between the
Fahrenheit and Celsius
Scales

14. Density is a characteristic physical property of
a substance and can be used for identification.
Density is the ratio of mass to volume, or mass
divided by volume (D = m/v).
The SI unit for density is kg/m3. In the lab you
will usually see density expressed as g/mL or
g/cm3.