Scientific Measurement Ch. 3 Why are precise measurements and calculations essential to the study of chemistry?

(3.1) Measurements Quantity that has a number and unit

Accuracy and Precision How close a measurement comes to the actual value of what is being measured How close a series of measurements are to one another

KNOW the rules for determining sig figs Pgs. 66-67 Significant Figures KNOW the rules for determining sig figs Pgs. 66-67

Measured values having digits that are known with certainty and a final digit that is estimated

1) ALL non-zero numbers are ALWAYS significant. 2) ALL zeroes between non-zero numbers are ALWAYS significant. 3) ALL zeroes which are to the right of the decimal point AND at the end of the number are ALWAYS significant. 4) ALL zeroes to the left of a decimal point and in front of nonzero digits are not significant. 5)Numbers in scientific notation…count those in the coefficient only.

48,923 5 3.967 4 500.06 5 0.0004 1 8.1000 5 501.040 6 3,000,000 1 10.0 3

Sig Figs in Calculations Many-Places Rule Mult./Div. – how many sig figs in least Plus/Minus – no. of places in least

305.1 x 35 5400 ÷ 9.89 305.7 + 35.035 5403 - 139.89

Percent Error Error = Experimental value - Theoretical Percent error =

Scientific Notation 6.02 x 1023 (see pg. R56 of text for more practice)