I II III Units of Measurement MEASUREMENT

Chemistry In Action On 9/23/99, $125,000,000 Mars Climate Orbiter entered Mars’ atmosphere 100 km lower than planned and was destroyed by heat. 1 lb = 1 N 1 lb = 4.45 N “This is going to be the cautionary tale that will be embedded into introduction to the metric system in elementary school, high school, and college science courses till the end of time.”

A. Number vs. Quantity  Quantity - number + unit UNITS MATTER!!

Mass vs. Weight  Mass: Amount of Matter (grams, measured with a BALANCE)  Weight: Force exerted by the mass, only present with gravity (pounds, measured with a SCALE)

Why Metric? StandardMetric Length Mile, inch, foot, yard, League, fathom, hand Meter (m) Mass Pound, ounce, ton Stone, Gram (g) Volume Pint, cup, teaspoon, Tablespoon, quart, gallon, Bushel, gross, Fl. ounces Liter (L)

B. SI Units mega-M10 6 deci-d10 -1 centi-c10 -2 milli-m10 -3 PrefixSymbolFactor micro-  nano-n10 -9 pico-p kilo-k10 3 BASE UNIT

Metric Conversions

Examples 6.24 km= m ml = dal cm = km 1.23 x 10 -3

What is Scientific Notation?  Scientific notation is a way of expressing really big numbers or really small numbers.  For very large and very small numbers, scientific notation is more concise.

To change standard form to scientific notation…  Place the decimal point so that there is one non-zero digit to the left of the decimal point.  Count the number of decimal places the decimal point has “moved” from the original number. This will be the exponent on the 10.  If the original number was less than 1, then the exponent is negative. If the original number was greater than 1, then the exponent is positive.

Examples  Given: 289,800,000  Use: (moved 8 places)  Answer: x 10 8  Given:  Use: 5.67 (moved 4 places)  Answer: 5.67 x 10 -4

Notation on Calculator  Calculating with Sci. Notation (5.44 × 10 7 g) ÷ (8.1 × 10 4 mol) = Type on your calculator: 5.44 EXP EE 7 ÷ ÷ 8.1 EXP EE 4 ENTER EXE = = 670 g/mol= 6.7 × 10 2 g/mol

Dimensional Analysis  How many minutes are in 2.5 hours ? Conversion factor 2.5 hr x 60 min = 150 min 1 hr 1 hr cancel By using dimensional analysis / factor-label method, the UNITS ensure that you have the conversion right side up, and the UNITS are calculated as well as the numbers!

Steps to Convert 1. Write down the given amount. Don’t forget the units! 2. Multiply by a fraction. 3. Use the fraction as a conversion factor. Determine if the top or the bottom should be the same unit as the given so that it will cancel. 4. Put a unit on the opposite side that will be the new unit. If you don’t know a conversion between those units directly, use one that you do know that is a step toward the one you want at the end. 5. Insert the numbers on the conversion so that the top and the bottom amounts are EQUAL, but in different units. 6. Multiply and divide the units (Cancel). 7. If the units are not the ones you want for your answer, make more conversions until you reach that point. 8. Multiply and divide the numbers. Don’t forget “Please Excuse My Dear Aunt Sally”! (order of operations)

= 29 quarters  You have $7.25 in your pocket in quarters. How many quarters do you have? 7.25 Dollars 1 Dollar 4 quarters

How many Km in 15,000dm? 15,000 dm 1 m 10 dm 1 Km 1000 m = 1.5 km

C. Derived Units  Combination of base units.  Volume (m 3 or cm 3 )  length  length  length D = MVMV 1 cm 3 = 1 mL 1 dm 3 = 1 L  Density (kg/m 3 or g/cm 3 )  mass per volume

D. Density Mass (g) Volume (cm 3 )

Problem-Solving Steps 1. Analyze 2. Plan 3. Compute 4. Evaluate

D. Density  An object has a volume of 825 cm 3 and a density of 13.6 g/cm 3. Find its mass. GIVEN: V = 825 cm 3 D = 13.6 g/cm 3 M = ? WORK : M = DV M = (13.6 g/cm 3 )(825cm 3 ) M = 11,200 g

D. Density  A liquid has a density of 0.87 g/mL. What volume is occupied by 25 g of the liquid? GIVEN: D = 0.87 g/mL V = ? M = 25 g WORK : V = M D V = 25 g 0.87 g/mL V = 29 mL