SI System
Standard International System of measurement – metrics
Has seven base units and many other units derived from these seven
Seven Base Units
Quantity Unit Abbreviation
length meter m mass gram g time second s temperature kelvin K amount mole mol current ampere amp intensity candela cd
Derived Units
Many other units are used in the metric system, but they are combinations of the base units
Volume
- volume = length x width x height
(m) x (m) x (m) = m3
- .001 m3 = 1 liter (L)
- 1 cm3 = 1ml
Prefixes
Metric system utilizes prefixes which indicate multiples of 10 of the unit
kilo- k 1000 hecto- h 100 deka- da 10 deci- d .1 centi- c .01 milli- m .001
Converting Between Metric Units
3.65 dam = __________cm
2587 mm = __________hm
.0087 hl = __________cl
Temperature
Metric unit – Kelvin – not used for measurement
Measured in C (celsius) K = C + 273.15
Old system is F (farenheit) C = 5/9 (F -32)
What is 69 F in C and K?
Temperature is an intensive property- does not depend on the amount
Extensive properties do depend on the amount
In the statement “a yellow sample is solid at 25 C. It weighs 6.0g and has a density of 2.3g/cm3” what are the intensive and extensive properties?
Uncertainty
We do not know infinite digits of a measurement Exact numbers are known for sure Inexact – have some question (estimates)
Precision and AccuracyAccuracy refers to the agreement of a
particular value with the true value.
Precision refers to the degree of agreement among several measurements made in the same manner.
Neither accurate nor
precise
Precise but not accurate
Precise AND accurate
Reporting Numbers
In recorded measurements, all the digits are considered exact up until the last digit which may be off by one
2.2405 ± .0001 All digits including the uncertain one are called
significant figures We are fairly confident of these digits Further uncertainty can be eliminated by
repeating the experiment
Which Digits Are Significant?
Any non-zero number is significant Any number to the left of a decimal is
significant Zeros to the right of a decimal and behind
other numbers are significant Zeros to the right of a decimal but in front
of other numbers are not significant
How many Significant Figures in each below?
1) 28.6 9) 3440.
2) 910 10) 0.04604
3) 0.0076000 11) 804.05
4) 0.0144030 12) 1002
5) 400 13) 400.
6) 700.0 14) 0.000625000
7) 0.4004 15) 6000
8) 1.30 16) 0.00067
Round each to 3 Significant Figures
1) 31.068 6) 149.51
2) 2.613 7) 6.561
3) 81.436 8) 13.1252
4) 0.001567 9) 143.81
5) 1.1353 10) 0.000355
Multiplying and Dividing
Multiply or divide the number out as normal but round the answer to the least number of significant figures in the problem
Solve each with correct Sig Figs
1) 2.4 x 15.82 =
2) 94.20 3.16722 =
3) (5.682 x 105) x (2.87 x 104) =
4) (2.145 x 10-5) (6.75 x 104) =
Addition and Subtraction
Add or subtract as normal but round the answer with the same number of decimal places as the quantity in the calculation having the least
Conversions
Often the units must be changed in order to do a problem
Conversion factor method Is utilized A26
Examples
How many inches in 3.5 km?
A chemical reaction produces 3.5 x 1025 atoms of product every hour. How many will be produced in 2.5 hours?
How many square cm in a square inch?