Download Dimensional analysis

Why units matter.
How tall am I?
 58
 How meaningful is this information?
 How do we make it more meaningful?
 A number is useless unless a unit is attached.
 The unit provides the scale you are working in.
To swim for you life or not
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 What would help you get an idea of whether or not you
should stay out of this sharks way?
Having a scale reference gives
more info
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Changing between units
 58 inches.
 What other numbers does this value represent?
Why does this matter in chemistry?
• Can you count the number of atoms you are mixing?
• How do you measure chemicals?
• If you are making 4 bicycles how many wheels do you
need?
• We do the same kind of converting with chemical
equations.
• If I know how much salt I need then I can use
conversion (dimensional analysis) to determine the
amount of acid & base I need to mix together.
Practical applications
 How are cereals & chips packaged?
 The manufactures determine the number of packages
they need to produce then back track to determine the
amount of ingredients needed.
 Buying hardware in bulk.
 Money transactions.
 Other examples?
My way or the highway
• You will show your work when you do calculations.
• You will perform dimensional analysis using the
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strategy I outline.
I will not give credit for any other strategy.
I mean it.
This is the one exception to the my general philosophy
of wanting you to use whatever works for you to arrive
at the correct answer.
& I have a good reason for it.
Let’s practice calculating my way.
Other resources
 Conversion factors ppt by Normal Community High
School Chemistry department in Normal, IL.