What is a significant figure? Significant figures in a measurement consist of all the digits known with certainty plus one final digit that is estimated. Your answer can only be as accurate as your least accurate measurement.

How do I determine the number of significant figures? All non-zero numbers are significant (Only determine if significant for 0’s). Zeros in FRONT of significant numbers are NOT significant. EX Zeros BEHIND significant numbers when a decimal is present ARE significant. Ex Zeros BEHIND significant numbers when a decimal is not present are NOT significant. Ex (This is an estimate, zeros are placeholders). Zeros in between significant numbers are significant.

SIG FIGS

X X 10 10

Rules for Multiplying and Dividing How many sig figs go in answer? The number of sig figs in product (or quotient) should equal the LEAST number of sig figs in problem. Ex. – (7.21)(1.245)= – (6.6)/(2.2) = – (3.4 X 10 9 )(2.3 X 10 2 )=

Adding and Subtracting with Sig Figs The number of sig figs in the answer will depend on the number of digits past the decimal. When the numbers are aligned with the decimal, the answer will be the same as the least number of decimal places. Ex.

Percent Error Percent error is used to compare the experimental data to its true value to determine accuracy. Formula: % error=experimental value – accepted value X 100 accepted value Experimental data– data obtained from experiment Accepted value—value believed to be true (CRC Handbook of Physics and Chemistry)

Example: What is the percentage error for a mass measurement of 17.7g, given the correct value of 21.2g? A volume is measured experimentally as 4.26 mL. What is the percentage error, given that the correct value is 4.15 mL?

Measurement Measurements represent quantities. A quantity has magnitude, size, or amount. Scientists use the SI system of measurement, called the Le Systeme International d’Unites. Aka metrics. This system was adopted in SI now has 7 base units, and most other units are derived from these 7.

Quantitysym bol unitUnit abbr ev. definitiontool lengthlmete r mThe length of the path traveled by light in a vacuum during a time interval of 1/ second. (Distance between 2 points) meterstick massmkilogr am kgThe amount of matter in an objectTriple beam balance timetsecon d sInterval between 2 eventsstopwatch Tempera- ture TkelvinKHow hot or cold an object is o C thermometer amountnmolemol6.02 X particlesUsually triple beam balance Volume- liquid literlThe amount of space occupied by an object Graduated cylinder Volume- solid Cubic centi- mete rs cm 3 or cc Length X width X heightmeterstick

Mass vs. Weight Mass is a measure of the quantity of matter. Weight is a measure of the gravitational pull on matter. Mass does not depend on gravity; weight does. Mass is measured with a balance, weight is measured with a spring scale. On Earth, weight increases as mass increases. The weight of an object on the moon is about 1/6 of its weight on Earth.

Derived Units Derived units are combinations of 2 or more base units. They are produced by multiplying or dividing standard units. Examples: area, volume, density, energy, pressure. Density is mass/volume, so divide an objects mass by its volume. The unit will be g/ml, a derived unit. Volume is l X w X h, so unit is cm 3 or cmX cmX cm.

Metric Conversions