Measurements in Chemistry Review Study the following Power Point as a review to this past week’s presentations. Come to class on Monday with any questions you have about Measurements, Significant Figures, and Scientific Notation. I will see you on Monday.

Measurements in Chemistry Physical quantities consist of both a number and a unit.

Common Units Quantity SI Unit Metric Unit Equivalent Mass Kilogram(kg) Gram (g) 454 g = 1 lb Length Meter (m) 1 m = 3.3 ft 2.54 cm = 1 in Volume Cubic Meter Liter (l) 1 l = 1.057 qt Temperature Kelvin (K) Celsius (oC) 1 oC = 1.8 oF Time Second (s)

Conversion factors you must know: Prefix Symbol Conversion (for grams) mega- M 106 g = 1 Mg kilo- k 103 g = 1 kg deci- d 1 g = 10 dg centi- c 1 g = 102 cg milli- m 1 g = 103 mg micro-  1 g = 106 g nano- n 1 g = 109 ng

The metric system is based on factors of 10 and is much easier to use than common U.S. units. Does anyone know how many teaspoons are in a gallon?

There may be many different units for measuring the same thing. How many different units for measuring length can you think of? In the metric system prefixes are applied to units to make saying and writing measurements much easier. The prefix pico (p) means “a trillionth of.” The radius of a lithium atom is 0.000000000152 meter (m). Try to say it. The radius of a lithium atom is 152 picometers (pm). Try to say it.

Significant Figures Some numbers are exact: There are, -60 seconds in 1 minute -25 cents in 1 quarter -12 eggs in one dozen *There is no uncertainty in any of these numbers. In other words there are 12.0000000000000000000000000000000000 eggs in 1 dozen (add as many zeros as you like)

Measurement and Significant Figures Every experimental measurement has a degree of uncertainty. The volume, V, at right is certain in the 10’s place, 10mL<V<20mL The 1’s digit is also certain, 17mL<V<18mL A best guess is needed for the tenths place.

To indicate the precision of a measurement, the value recorded should use all the digits known with certainty, plus one additional estimated digit that usually is considered uncertain by plus or minus 1. No further insignificant digits should be recorded. The total number of digits used to express such a measurement is called the number of significant figures. All but one of the significant figures are known with certainty. The last significant figure is only the best possible estimate.

Below are two measurements of the mass of the same object Below are two measurements of the mass of the same object. The same quantity is being described at two different levels of precision or certainty.

Rules for dealing with zeros in significant figures: Zeros in the middle of a number are always significant as in 2.08 (3 Sig. Figs) Zeros at the beginning of a number are not significant. Their purpose is to locate the decimal point as in .027 (2 Sig. Figs.) Zeros at the end of a number and after a decimal point are significant as in 2.530 (4 Sig. Figs.) Zeros at the end of a number and before an implied decimal point may or may not be significant, as in 25000. These should be written in scientific notation to indicate significant figures 2.50 x 104 How many significant figures are there in each of the following numbers? Number Number of Significant Figures 12.78 g 4 Significant Figures 0.000006 1 Significant Figures 3.905 mg 2.50 ml 3 Significant Figures 25000 kg 2, 3, 4, or 5 Significant Figures 2.50 x 104 kg

How many significant figures are there in 20.40?

How many significant figures are there in 40.0?

How many significant figures are there in 0.040?

Scientific Notation Scientific notation is a convenient way to write a very small or a very large number. Numbers are written as a product of a number between 1 and 10, times the number 10 raised to power. 215 is written in scientific notation as: 215 = 2.15 x 100 = 2.15 x (10 x 10) = 2.15 x 102

Two examples of converting standard notation to scientific notation are shown below.

Scientific notation is helpful for indicating how many significant figures are present in a number that has zeros at the end but to the left of a decimal point. The distance from the Earth to the Sun is 150,000,000 km. Written in standard notation this number could have anywhere from 2 to 9 significant figures. Scientific notation can indicate how many digits are significant. Writing 150,000,000 as 1.5 x 108 indicates 2 and writing it as 1.500 x 108 indicates 4. Scientific notation can make doing arithmetic easier. Rules for doing arithmetic with numbers written in scientific notation are reviewed in Appendix A.

Write each of the following in standard scientific notation. Number 4063 0.040 27.8 x 103 d) (4 x 10-2) (2 x 105) e) (6.8 x 103) (4.3 x 104) ** f) (9 x 108) ÷ (3 x 105) ** Remember that final answer in Scientific Notation must be a number >1 and <10 multiplied by a power of 10.

Write each of the following in standard scientific notation. Number 4063 4.063 x 103 0.040 4.0 x 10-2 27.8 x 103 2.78 x 104 d) (4 x 10-2) (2 x 105) 8 x 103 e) (6.8 x 103) (4.3 x 104) 29.24 x 107 = 2.924 x 108 ** f) (9 x 108) ÷ (3 x 105) 3 x 103 ** Remember that final answer in Scientific Notation must be a number >1 and <10 multiplied by a power of 10.

How many millimeters are there in 4.5 cm? .045 mm 0.45 mm 45.0 mm 450 mm

A person’s blood contains 185 mg of cholesterol per deciliter of blood A person’s blood contains 185 mg of cholesterol per deciliter of blood. How many grams of cholesterol are there in 1 liter of this blood? .0185 g 0.185 g 1.85 g 18.5 g 1850 g