Presentation is loading. Please wait.

Presentation is loading. Please wait.

Significant Figures Chemistry.

Similar presentations


Presentation on theme: "Significant Figures Chemistry."— Presentation transcript:

1 Significant Figures Chemistry

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

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

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

5 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 is the same.

6 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.

7 But, to a scientist 21.7cm and 21.70cm is NOT the same
If you used an ordinary ruler, the smallest marking is the mm, so your measurement has to be recorded as 21.7cm.

8 How do I know how many Sig Figs?
Rule: All digits are significant starting with the first non-zero digit on the left.

9 How do I know how many Sig Figs?
Exception to rule: In whole numbers that end in zero, the zeros at the end are not significant.

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

11 How do I know how many Sig Figs?
2nd Exception to rule: If zeros are sandwiched between non-zero digits, the zeros become significant.

12 How do I know how many Sig Figs?
3rd Exception to rule: If zeros are at the end of a number that has a decimal, the zeros are significant.

13 How do I know how many Sig Figs?
3rd Exception to rule: These zeros are showing how accurate the measurement or calculation are.

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

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

16 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.

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

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

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

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


Download ppt "Significant Figures Chemistry."

Similar presentations


Ads by Google