iii. Measurement I. Units of Measurement I.SI Base Units & Prefixes  Derived Units  Calculations  Significant Figures  Precision and Accuracy

B. SI Units QuantityBase UnitSymbol Length Mass Time Temp _______ kilogram _______ kelvin m ____ s Current_______A

Metric Conversions  6000 liters = ________ kl  0.23 g = _________mg  5 hm= ________ cm  9 g = ______ dg

Density  Density – an object’s mass per unit volume  A physical property  Formula:  D = M/V  M – mass (g)  V – volume (mL) or (cm 3 )

Triangle Method Put the formula in the triangle. Solve for the unknown. EXAMPLE: A 6 gram object has a volume of 3 ml. What is its density? Density = mass/volume so, D M VD 6 g 3 ml

C. Derived Units  Combination of base units.  Volume - length  _____  _______ 1 cm 3 = 1 ____  Density - mass per unit ______ (g/cm 3 ) D = D M V

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 = 11,220 g D M V

D. Density 1) 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 D M V WORK : V = M D V = 25 g 0.87 g/mL V = 28.7 mL

D. Density 2) You have a sample with a mass of 620 g & a volume of 753 cm 3. Find density. GIVEN: M = 620 g V = 753 cm 3 D = ? D M V WORK : D = M V D = 620 g 753 cm 3 D = 0.82 g/cm 3

Your turn to try!  The density of an object is 2.6 g/ml. It has a mass of 9 grams. Give its volume.  A cube is 3 cm long, 3 cm wide, and 3 cm tall. It has a mass of 7 grams. What is its density?  The density of an object is 0.98 g/ml. It has a volume of 19 cubic cm. What is its mass?

Significant Figures  Learn these rules: 1. All nonzero digits are significant Zeros to right of decimal and to right of non zero digit are significant Zeros between 2 nonzero digits are significant. 90,909 90, Zeros to the left of a decimal and left of a nonzero digit are not significant Zeros to the right of a decimal that serve as placeholders before nonzero digits are not significant Zeros to the left of an understood decimal and to the right of nonzero digits are not significant. 9,340,010,000

How many SF are in each? 1. 3, ,090, ,

Operations Using SFs  When adding or subtracting, the answer should contain the same number of decimal places as the number with the least number decimal places in the problem. Ex = = DP 2 DP 2DP 1DP Ex = = DP 1DP 3DP 1DP

Operations Using SFs  When multiplying or dividing, the answer should contain the same number of SF as the number with the least number SF in the problem. Ex. 500 x 11 = 5,500 = SF 2 SF 2SF 1SF Ex. 45/9.0 = 5 = 5.0 both have 2 SFs

Try these  Answer the following in proper number of SFs x 13 = 2. 9 x 2 = /9 = 4. 1/4 = 5. 32/4.0=

Precision vs. Accuracy  Precision is the ________ of a measurement to other measurements made in the same way.  Accuracy is the ________ of a measurement to the accepted value.

Accuracy and Precision Ex. You throw 3 darts. All three hit in the outer edge of the board within a few cm of each other. You are _______ with the throw but not ________. Ex. You throw 3 darts. All 3 hit in the center of the bulls eye. You throws were very _________ and they also were _________.

Another example  You use a balance to get the mass of an object. You do it three times. You get the answers 2 g, 9 g, and 10 grams. Your average is 7 grams. The book value is also 7 grams.  Were you precise?  Were you accurate?