It is a broad science that touches nearly every aspect of life. • Most things lead to chemistry (water ecology, farming, medicine, house wife/mother, masonry …..
Why study chemistry? • It plays a role in many areas of life (knowledge is power). • Many occupations require this knowledge. • It is fun to know how things work. • It helps develop the mind (reasoning power and observation skills). It is like weight training for the mind. • It can be very beautiful (like great music or art).
The Scientific Method • We make an observation. • We ask a question. • We formulate a tentative explanation (a hypothesis). • We design an experiment to test the hypothesis. • We analysis the result and conclude if we are right. • Report results and ask a new question.
How to design a good experiment • Experimental results are typically compared to the normal situation. • The control is that trial of the experiment in which everything is kept normal. (The control is the standard.) • The variable is that one aspect that is changed in each trial.
After many experiments and observations may develop: • A theory – It is a broad overview of understanding that explains things. (example: the molecular theory of matter) • A natural law – is an observation that nature always behaves the same way. (example: mass is conserved in chemical reactions)
The Math Tool Kit • International system of units (SI) • Length – meters (m) • Mass – gram (g) • Volume – liter (L) • See page 18
Units can be increased or decreased by using a prefix Prefix Abbreviation Meaning Nano n 10-9 Micro µ 10-6 Milli m 10-3 Centi c 10-2 Deci d 10-1 Kilo k 103 Mega M 106
Scientific Notation • Place the decimal point behind the first non-zero number and use a power of ten to indicate the magnitude of the number. Change 1,230,000,000 to scientific notation (1.23 x 109) Change 0.0000001401 to scientific notation (1.401 x 10-7) Multiply the above two numbers 172.323
Uncertainty in measurements and calculations • Exact numbers – definitions (example 12 inches = 1 foot) • Inexact numbers – measurements (example: 12.1 inches, 2.54 cm = 1 inch) • A measurement can be off by as much as ½ of the smallest increment (the last digit is an estimate) (example: 1.2 + or - .05g) The true mass could be closer to 1.15 or 1.25 than to 1.20g.
Percent Uncertainty in Inexact Numbers % uncertainty = uncertainty/value x 100 Example: mass of 1.2 g % uncertainty = 0.05g/1.2g (100) Uncertainty = 4.2% Exact numbers have 100% certainty
Calculate the % uncertainty in each of the following measurements. • 111.1 grams • .045% • 11 grams • 4.5% • .11 grams • 4.5% • Which value can you have the most confidence in?
Reliability in Measurement • Precision – the smallest increment of measurement, gives the same results again and again • Accuracy – how close the value is to the true value Target Analogy
Significant Digits • To reflect the degree of confidence that we can have in our number, we use rules in reporting the number. • These rules are the significant digit rules. • The greater number of significant digits, the lower the uncertainty and the more confidence we have in the number.
See the Significant Figures sheet • The more significant digits, the more confidence we can have in the number. • Complete the sig. digit worksheet.
Why use scientific notation? • It is good for very large or very small numbers. • It is also the best way to show the number of significant digits. • Complete practice worksheets. (Factor-label method)