chemistry unit 1 part 2

1. Unit 1
SIGNIFICANT FIGURES

2. Accuracy in measurements

3. Chemistry: volume measurements

4. Significant digits
Every nonzero digit in a
reported measurement is
assumed to be significant.
Zeroes appearing between
nonzero digits are significant.

5. Zero . . .
Zeroes appearing in front of
nonzero digits are not
significant. They act as
placeholders.
0.0000205

6. Zero . . .
Zeroes appearing in front of
nonzero digits are not
significant. They act as
placeholders.
0.0000205
or 2.05 x 10-5

7. Zero . . .
Zeroes at the rightmost end of a
measurement that lie to the left of an
understood decimal point are not
significant if they serve as placeholders
to show the magnitude of the number.
20,500

8. Zero . . .
Zeroes at the rightmost end of a
measurement that lie to the left of an
understood decimal point are not
significant if they serve as placeholders to
show the magnitude of the number.
20,500
or 2.05 x 10
4

9. Zero . . .
Zeroes at the end of a number and
to the right of a decimal point are
always significant.
20.050
all digits are significant

10. Unlimited:
There are two situations in which numbers have
an unlimited number of significant figures:
First: A number that is counted is exact.
25 books
Second: exactly defined quantities such as
those found within a system of measurement.
453.5 grams = 1 pound

11. Rounding
◦If the digit immediately to the right of the
last significant digit is less than 5, it is
simply dropped and the value of the last
significant digit stays the same.
◦If the digit in question is 5 or greater, the
value of the digit in the last significant
place is increased by 1.

12. Addition and subtraction
The answer to an addition or
subtraction calculation should be
rounded to the same number of
decimal places (not digits) as the
measurement with the least number of
decimal places.

13. Addition and subtraction:
450.0 – 100.30 =

14. Addition and subtraction:
450.0 – 100.30 =
349.7

15. Addition and subtraction:
3.2936 + 2.178 +
0.01 + 1.09 =

16. Addition and subtraction:
3.2936 + 2.178 +
0.01 + 1.09 =
6.6

17. Multiplication and division:
In calculations involving
multiplication and division, you
need to round the answer to the
same number of significant figures
as the measurement with the
least number of significant figures.

18. Multiplication and division:
3.10 x 0.0020 =
1.002790

19. Multiplication and division:
3.10 x 0.0020 =
1.002790
0.0062

20. Can I get partial credit?
Significant digits matter . . .