Chapter 3 Section 2 precision- how close a series of measurements are to one another accuracy- the closeness of measurements to the true value of what is being observed *Can be precise, but not accurate or vice versa -page 54 figure 3.4 -to evaluate the accuracy you must compare with the actual value

accepted value- correct value based on reliable references ex- boiling point of water = 100°C or 212°F experimental value- the value measured in the lab ex- measured bp of water = 99.1°C error- │experimental value – accepted value│ ex- error = │ 99.1°C - 100°C │ = 0.90°C

percent error = error X 100 accepted value ex- 0.90°C X °C =0.90%

Significant Figures -all the digits that can be known precisely in a measurement plus a last estimated digit Rules for Counting Sig Figs 1)all non zero digits are significant 2)all zeroes between two #’s are significant 3)all zeroes to the right of a # without a decimal point are NOT significant 4)all zeroes to the right of a # with a decimal point are significant

5) all zeroes to the left of a number containing a decimal point are NOT significant 6)if counting, all numbers are significant Examples 1100m ML2003g (2) (3) (4) 3000 cars (4) (3) (4)

Atlantic Rule -if a decimal point is absent, start counting from the first non-zero digit from the Atlantic Ocean side inland (right → left) Pacific Rule -if a decimal point is present, start counting from the first non-zero digit from the Pacific Ocean side inland (left → right) **All #’s significant when counting 10400L308g m L 230L g 5600mg200 pens

Rounding Sig Figs Round each number to 2 sig figs:

Multiplying/Dividing Sig Figs -the answer must have the same number of sig figs as the factor with the fewest sig figs Ex- (40)(56)(340) (1 sig fig) Ex ÷ (3 sig figs)

Adding/Subtracting Sig Figs -the result must have the same number of decimal places as the quantity with the fewest decimal places Ex (2 decimal places) Ex- 5.9 – (1 decimal place)