Significant Figures

Reminders Lab reports were due at midnight in your PAP CHEM GOOGLE FOLDER You turn assignments into your PAP CHEM google folder. I grade them and put them back into the folder. You then upload the graded assignment to your google site Once it is in your google site you delete it from your google folder. That way we keep the folder clear but you still have your graded assignments on your site. If you are emailing assignments to me (only those without ipads that cannot turn assignment into google folder) then I will email your grade back to you and you will then upload i`t to your website

What is a significant figure? There are 2 kinds of numbers: Exact: the amount of money in your account. Known with certainty.

What is a significant figure? Approximate: weight, height—anything MEASURED. No measurement is perfect.

Accuracy- how close something is to the true value. How correct it is. Precision: how close 2 or more measurements are to each other. (Might not be accurate)

When to use Significant figures When a measurement is recorded only those digits that are dependable are written down.

When to use Significant figures If you measured the width of a paper with your ruler you might record 21.7cm. To a mathematician 21.70, or 21.700 is the same.

But, to a scientist 21.7cm and 21.70cm is NOT the same 21.700cm to a scientist means the measurement is accurate to within one thousandth of a cm.

RULE 1 Rule: All digits are significant starting with the first non-zero digit on the left.

RULE 2 In whole numbers that end in zero, the zeros at the end are not significant.

How many sig figs? 7 40 0.5 0.00003 7 x 105 7,000,000 1

RULE 3 If zeros are sandwiched between non-zero digits, the zeros become significant.

RULE 4 3rd Exception to rule: If zeros are at the end of a number that has a decimal, the zeros are significant.

How many sig figs here? 1.2 2100 56.76 4.00 0.0792 7,083,000,000 2 4 3

How many sig figs here? 3401 2100 2100.0 5.00 0.00412 8,000,050,000 4 2 5 3 6

What about calculations with sig figs? Rule: When adding or subtracting measured numbers, the answer can have no more places after the decimal than the LEAST of the measured numbers.

Add/Subtract examples 2.45cm + 1.2cm = 3.65cm, Round off to = 3.7cm 7.432cm + 2cm = 9.432 round to  9cm

Multiplication and Division Rule: When multiplying or dividing, the result can have no more significant figures than the least reliable measurement.

A couple of examples 75.8cm x 9.6cm = ? 56.78 cm x 2.45cm = 139.111 cm2 Round to  139cm2 75.8cm x 9.6cm = ?

Have Fun Measuring and Happy Calculating! The End Have Fun Measuring and Happy Calculating!