Measurement/Calculation Units of Measure
Metric System based on powers of ten, so it’s easy to convert between units. Remember: –KING HENRY DANCED BEFORE DAWN COUNTING MONEY –Or –KING HENRY DIED BY DRINKING CHOCOLATE MILK
Units MegakilohectodekaBASEdecicentimillimicro Mkhda(none)dcm or
SI base units QuantityBase UnitSymbol Timeseconds Lengthmeterm Massgramg TemperatureKelvinK Amount of a substancemolemol
SI derived units QuantityDerived UnitSymbol Volume: various formulas, such as LxWxH cubic centimeters or milliliters liters cm 3 or mL L Density: mass divided by volume grams per milliliter or grams per cubic centimeter g/mL or g/cm 3 (derived units are calculated from base units)
How to use Kilo Hecto Deka BASE Deci Centi Milli Left Right
NOTE: 1 cm 3 IS EQUAL TO 1 mL!!! And a cc is the same as a cm 3
Measurement/Calculation Scientific Notation/Accuracy &Precision
Rules to putting into Sci Not Must have a whole number between 1- 9 If you move: –Decimal to Left…exponent is Positive –Decimal to Right...exponent is Negative
Examples X X 10 -3
Examples 5.00 X X
Addition/Subtraction Make exponents the same by moving decimal place and changing exponent Then add/subtract and put in correct Sci Not OR Type into your calculator Change mode to Sci
Example 5.00 X X 10 4 OR Type into your calculator 5.00 X X X EXP EE EXP EE 3 Enter
Multiplication/Division Multiplication –Multiply numbers –Add exponents Division –Divide numbers –Subtract exponents Then put back in correct scientific notation!
Example (5.44 × 10 7 g) ÷ (8.1 × 10 4 mol) = 5.44 EXP EE ÷ ÷ EXP EE ENTER EXE = = 670 g/mol= 6.7 × 10 2 g/mol Type on your calculator: = 0.67 X 10 3 g/mol = 6.7 × 10 2 g/mol
Accuracy and Precision Accuracy: how close a measurement is to the true value (the “correct answer”) Precision: how close a value is to other values in that series
Are the following groups of measurements accurate, precise, both, or neither? 1) Given: true mass of sample of zinc is 14.5 g Measurements made: 13.2 g, 15.6 g, 17.9 g, 12.0 g 2)Given: true volume of sample of water is 33.3mL Measurements made: 22.4 mL, 22.2 mL, 22.4 mL, 22.3 mL 3) Given: true length of copper wire is 58.5 cm Measurements made: 58.4 cm, 58.5 cm, 58.5 cm, 58.4 cm
Qualitative: a descriptive measurement (quality); does not involve numbers Quantitative: a numerical measurement (quantity)
Appropriate Units for Measurement
Measurement/Calculation Significant Figures
Alternative Way Pacific (Present) Atlantic (Absent)
If the decimal is present, start on the Pacific side at the first nonzero digit and count it and all the digits to the right of it. If the decimal is absent, start on the Atlantic side at the first nonzero digit and count it and all the digits to the left of it. Pacific (Present) Atlantic (Absent)
Example: How many significant figures?
Adding/Subtracting Add/Subtract First The answer has only as many decimal places as the measurement having the least number of decimal places. Example g g g g Answer should have 1 decimal place g
Multiplication/Division The answer has only as many significant figures as the measurement with the least number of significant figures. Example g 11.3 mL 4 3 = g/mL Answer should have 3 significant figures 1.22 g\ml Mult/Divide First
Example –15000 – – 252252
Measurement/Calculation Density
Derived unit –g/mL or g/cm 3 Mass/Volume
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 = g=11 200g
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 = 28.74mL = 29 mL
D. Density 1.A marble has a mass of 5.6 g. It is placed in a graduated cylinder with 50.0 mL of water. The water level rises to 53.4 mL. What is the density of the marble? GIVEN: D = ? V = = 3.4 mL m = 5.6 g WORK : D = m V D = 5.6 g 3.4 mL D=1.647 g/mL = 1.6 g/mL 3.4 mL
Graphing Graphing is an important tool for expressing data so that it is easier to read and interpret Rules for graphing: --place the manipulated/independent variable (the one that was changed) on the x axis. --place the dependent/responding variable (the results of that change) on the y axis. (dry mix) DRY MIX y scale = largest y value – smallest y valuex scale = largest x value – smallest x value # of lines on the y axis# of lines on the x axis The graph should cover at least ¾ of the grid