Download Lab 1

Chemistry
Significant Figures
Rules For Significant Figures:
1.
Non zero integers:
2.
3.
Zeros:
Non zero integers always count as significant figures.
a.
Leading zeros are zeros that precede all of the non-zero digits.
They do not count as significant figures.
0.0025 = two significant figures.
b.
Captive zeros are zeros between non-zero digits. They always
count as significant.
1.008 = four significant figures.
c.
Trailing zeros are zeros at the right end of the number. They
are significant only if there is a decimal point.
100 = 1 significant figure.
100. = 3 significant figures.
Exact Numbers
These are defined or counting numbers such as 1 dozen = 12
(defined number) or 7 people (counting number). They have
an infinite number of significant figures.
Calculations Using Significant Figures.
1.
Multiplication and Division:
When multiplying and/or dividing, use the least number of
significant digits in your final answer.
2.
a.
If the figure following the last number to be retained is less
than 5, all the unwanted figures are discarded and the last
number is left unchanged.
3.6247 is 3.62 to three significant figures.
b.
If the figure following the last number to be retained is 5 or
greater, the last figure is increased by 1 and the unwanted
figures are discarded.
7.565 is 7.57 to three significant figures.
Addition and Subtraction:
The result of an addition or subtraction should be reported to
the same number of decimal places as that of the term with the
least number of decimal places.
161.032
5.6
32.4524
199.0844 = 199.1 since the number 5.6 only has one digit
following the decimal point.
3.
Combination:
When all four operations are involved, obtain the significant
figures from addition and subtraction first then from
multiplication and division.
(5.63 - 2.5) (3.667) = 1.710538
(2.11 + 4.6)
(5.63 - 2.5) = two significant figures
3.667 = four significant figures
(2.11 + 4.6) = two significant figures
Thus, the least number of significant figures is two and the
answer should be 1.7.
Exercise:
1.
State the number of significant figures in each of the following measured quantities.
a.
23.2 cm
__________
e.
2.440 g
__________
b.
40.1 kg
__________
f.
0.00035 g
__________
c.
0.00025 nm
_________
g.
20000 m
__________
2.
Round off each of the following numbers to give the number of significant figures indicated.
a.
35.7823
(3)
d.
0.578
(3)
b.
0.002624
(2)
e.
0.12256
(3)
c.
381.268
(1)
f.
87.025
(3)
3.
figures.
Perform the following operations and give the answers with the correct number of significant
a.
(56.8)(0.37)
f.
(5.653-3.2)
b.
71.4
11
g.
(3.36 + 2.1)(5.00)
c.
25.0
5.00
h.
(600. - 32)
15.45
d.
(2.075)(0.585)
(8.42)(0.0045)
i.
(3.58)
2.005
e.
(4.0)(8.00)
16
j.
(24.6 - 24.3)(5.00)
2.25