Chemistry a science that studies matter – its properties and changes. Matter is anything that has mass and takes up space. Matter is made up of atoms and molecules. Scientific Method
Observation of nature → Hypothesis (possible explanation) → Experiments to confirm or revise hypothesis Many observations lead to scientific law – a statement of the relationship between different parts of nature. Ex: law of conservation of mass- “ matter is neither created or destroyed” aka “the number and kind of atoms before a chemical reaction must be the same as after a reaction”. A theory describes a broader explanation of nature. Over time theories and laws are changed.
Chapter 2 Measurement and Problem Solving
Measurements have 1) numbers, 2) units, 3) uncertainty. The last digit is uncertain. Only one digit in a measurement is uncertain.
Decimal part x exponential part : X.YZ x 10abc
Only one digit left of the decimal point!
100 = 1Positive exponents are numbers bigger than one.
101 = 1010-1 = 1/10 = 0.1Negative exponents are numbers smaller than one. 102 = 10010-2 = 1/100 = 0.01
CALCULATOR KEYSTROKE SEQUENCE IS MISSION CRITICAL
Convert to scientific notation
5983 Express as number with only one digit left of decimal point 5.983 Count the number of decimal places moved: if move to left exponent is positive 5.983 x 103 0.005983 5.983 x 10-3 if move to right exponent is negative
Convert from scientific notation to decimal notation
Move the decimal to the left if the exponent is negative. 3.456 x 10-4 = 0.0003456 Move the decimal to the right if the exponent is positive. 3.456 x 104 = 34560
Significant Figures are rules to express measured quantities with the correct amount of precision and uncertainty. Thing that are counted (number of pennies or students) do not have sig figs or unlimited sig figs. Definitions of quantities have no sig figs. 1 mile = 5280 ft. Recording measurements with the correct number of sig figs.
Note the smallest increment the instrument will read.
A bathroom scale - 1 lb +/- 0.1 lb
A kitchen thermometer – 1 oF +/- 0.1 oF
Estimate the reading to the next smallest decimal.
If the instrument has a digital readout, assume that the last decimal is estimated for you. Counting Sig Figs
We need to know the number of sig figs in a measurement for doing calculations. 1. All nonzero digits are sig figs.
2. Zeroes between digits are sig figs.
3. Trailing zeroes to left of decimal are not sig figs. This is ambiguous – express in Scientific notation. 4. Trailing zeroes to the right of the decimal are sig figs. 5. Leading zeroes to the right of the decimal are not sig figs. Calculations with Sig Figs
Multiplication/Division: Result has the same # sig figs as the measurement with the fewest sig figs.
1.002g/0.99 mL = 1.0 g/mL
Addition/Subtraction: result has the same # number of decimal places as the measurement with the fewest decimal places.
mass of beaker + sample5.0251g
mass of beaker1.940 g
mass of sample3.085 g
Round to the correct # sig figs: 5 or more rounds up; 4 or less rounds down.
Round to 3 sig figs: 2.342.3
9.95 10 but to indicate 2 sig figs express in scientific notation 1.0 x 101
Calculations with +/- and multiply & divide
Follow order of operations, ( ) 1st, do not round, underline least significant digit. Finish calculation. Round last step.
3.489 x (5.67 – 2.3)
5.67 -2.3 = 3.37 2 sig figs
3.489 x 3.37 = 11.758round to 2 sig figs 12
Basic Units of Measurement
Metric System = International System
length = meter m
mass = kilogramkg (a measure of the quantity of matter – not weight!) time = seconds
temperature = KelvinK = oC + 273
volume = literL
SI Unit Prefixes
kilok1000 or 103
centic0.1 or 10-1
millim0.001 or 10-3