Scientific Measurement

Ch. 3Why 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

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.

48,923 3.967 500.06 0.0004 8.1000 501.040 3,000,000 10.0

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 ErrorError = Experimental value - Theoretical

Percent error =

Scientific Notation • 6.02 x 1023

(see pg. R56 of text for more

practice)