Methods and Tools of
Chemistry
Chapter 2
Science Department
Corpus Christi School
Measurement
Certain digits
2.35cm
uncertain digit
Example 1
The volume of a sample of sodium
chloride solution is 19.80 mL.
Which is the uncertain digit in the
recorded volume of the sample?
Example 2
Which of the following
represents the mass of sodium
chloride with ' 5 ' as a uncertain
digit?
a. 5.246g
b. 2.546g
c. 5.245g
Example 3
The mass of a sample of salt is
found to be 6.3912 g, 6.4003 g,
and 6.3941 g in the first, second,
and third trail respectively. What is
the uncertain digit in each trial?
a. 1, 0, 4
c. 2, 3, 1
b. 3, 4, 3
d. 6, 6, 6
Significant Figures
RULE 1:
All nonzero digits are significant
Examples:
3.2cm – two sig. fig.
1.45m – three sig. fig
2.216g – four sig fig.
Significant Figures
RULE 2:
Zeros in between nonzero digits are
significant
Examples:
3.o2cm – three sig. fig.
1.405m – four sig. fig
2.2016g – five sig fig.
Significant Figures
RULE 3:
Zeros at the right of the decimal
point and at the right of the nonzero digits
are significant
Examples:
3.20 cm – three sig. fig.
1.450 m – four sig. fig
2.0 g – two sig fig.
Significant Figures
RULE 4:
Zeros at the right of the decimal point
but at the left of nonzeros that are written
only to indicate the decimal place are not
significant
Examples:
0.32 cm – two sig. fig.
0.0145m – three sig. fig
0.002216g – four sig fig.
Significant Figures
RULE 5:
For whole numbers, zeros after nonzero
digits are not significant unless a decimal point
or a bar on top of zero is placed to indicate the
zero, or all zeros including such zero with a
barline are significant
Examples:
10 cm – one sig. fig.
100.0 m – four sig. fig
1000 g – four sig fig.
Exercises
1. 0.0803 mg
2. 678.3 kg
3. 3 450. 000 L
4. 6500.7 ft
5. 0.00545 lb
6. 22 450 000 oz
7. 70.5230 in
Exercises
1. 21.0803 mg
2. 608.30 kg
3. 350 00.0 L
4. 6500.70 ft
5. 5 000 lb