2. THE LANGUAGE OF SCIENCE IS
NUMBERS AND UNITS
Both the number and the unit are important.
A number without a unit is meaningless
3. LET’S TALK ABOUT THE NUMBER PART FIRST…
What is the volume of the following graduated cylinder?
4. The total number of digits used to
express such a measurement
is called the number of
significant figures.
To indicate the precision of a measurement, the
value recorded should use all the digits known
with certainty, plus one additional estimated digit
that usually considered uncertain by plus or minus
1.
No further, insignificant, digits should be recorded.
All but one of the significant figures are known
with certainty. The last significant figure is only the
best possible estimate.
5. SOUNDS EASY BUT HERE’S THE
PROBLEM…..
What if the measurement is 100g…….
Do I mean somewhere between 0 & 200g (1 sig fig)?
Do I mean somewhere between 90 & 110g (2 sig figs)?
Do I mean somewhere between 99 & 101g (1 sig fig) ?
What is the real degree of precision of
the measurement?
6. RULES FOR DETERMINING THE NUMBER OF
SIGNIFICANT FIGURES
RULE 1 When reading a measured value, all
nonzero digits should be counted as significant
Example - 136 has 3 sig figs
.47 has 2 sig figs
RULE 2 Zeros between two nonzero digits
are always significant regardless of the
location of the decimal place
Example - 94.072 g has 5 sig figs
7. RULE 3 Zeros to the right of the decimal and the left of
a nonzero digit are not significant. They are place
holders and act to locate the decimal point.
Example - 0.0834 cm has 3 sig figs
0.02907 mL has 4 sig figs
RULE 4 Zeros at the end of a number and after the
decimal point are significant. It is assumed that these
zeros would not be shown unless they were significant
Example - 138.200 m has 6 sig figs.
If the value were known to 4 significant
figures, we would write 138.2 m.
8. RULE 5 Zeros at the end of a number and before an
implied decimal point may or may not be significant.
We cannot tell whether they are part of the
measurement or whether they act only as place
holders
Example – Back the number 100g, does it have 1, 2,
or 3 sig figs?
9. HOW MANY SIG FIGS ARE IN THE FOLLOWING NUMBERS ?
305
0.0056
305.0
0.00405
305.050
0.003020
250
2.0
250.0
2000003
250.07 0.0000023
