CHEM 111 Week 1 Learning Session

SI Units, Dimensional Analysis, and Significant Figures.

​Foundational skills you will continue to use this entire course!

​CHEM 111 - Week 1

Poll

What are you feeling most confident about?

• Significant Figures

• SI Units

• Dimensional Analysis

Poll

What do you need the most practice with?

• Significant Figures

• SI Units

• Dimensional Analysis

​SI Units:

​These prefixes can be used for any SI unit, like meters, or grams

mega- M - 10⁶

kilo- k​ - 10³

​centi- c - 10^-2

​milli- m - 10^-3

​micro- µ - 10^-6

​nano - n - 10^-9

​Practice moving the decimal place. 10² means move the decimal two places to the right to get to the base unit, 10^-2 means move the decimal 2 places to the left.

​

​centimeters are 10^-2 meters, so 25 centimeters equals 0.25 meters.

​

kilograms are 10³ grams, so 108 kilograms equals 108,000 grams.

Multiple Choice

How many grams are in 30 kilograms?

• 300

• 3

• 30,000

• 30,000,000

​Dimensional Analysis:

​Just the fancy word for Unit Conversion

​- Always start with the value you're given, and make sure that you end with the value you're asked for.

​

​- Whatever unit is on top first needs to go on the bottom next to cancel. Every unit EXCEPT your final unit should cancel

​

​

​Significant Figures: 2 Main Rules

​

​Addition/subtraction:

​Round your answer to the least number of decimal places.

​1.25 + 4.782 = 6.032

​

​Multiplication/Division:

​Round your answer to the least number of significant figures.

​4.8 * 14.2 = 68.16

​Which Figures are Significant?

​Non-zero digits are ALWAYS significant

​ - 5,498

​Zeros BETWEEN non-zero digits are ALWAYS significant

​ - 500498

​Zeros leading BEFORE the non-zero digits are NEVER significant

​ - 0.0005498

​Zeros trailing AFTER the non-zero digits are only significant IF there is a decimal place

​ - 5498000

​ - 5498000.0

Multiple Choice

How many significant figures are in 0.003500 ?

• 2

• 4

• 6

• 7

Multiple Choice

$$136.2+2.39275\ =\ ?$$  

• 139

• 138.6

• 138.59275

• 138.593

Multiple Choice

$$\left(125+2.48\right)\div\left(23.75-21.0\right)\ =\ ?$$  

• 50

• 46.36

• 46

• 46.4