CH. 1 - MEASUREMENT I. Units of Measurement

m V D = A. Derived Units 1 cm3 = 1 mL 1 dm3 = 1 L Combination of base units. Volume (mL or cm3) length  width  height 1 cm3 = 1 mL 1 dm3 = 1 L D = m V Density (g/mL or g/cm3) mass per volume

B. Density Liquids Material Density (gm cm-3) Water at 4 C 1.0000 Water at 20 C 0.998 Gasoline 0.70 Mercury 13.6 Milk 1.03 Solids Magnesium 1.7 Aluminum 2.7 Copper 8.3-9.0 Gold 19.3 Iron 7.8 Lead 11.3 Platinum 21.4 Uranium 18.7 Osmium 22.5 Ice at 0 C 0.92 Density of a substance determines whether that substance will float or sink in a liquid Density of a substance does not change

B. Density Mass (g) Volume (cm3)

B. Density Direct Proportion y x Inverse Proportion y x

C. Measurement Measurement is uncertain because 1. Instruments may have errors 2. Involves estimation Measurement = all certain digits + 1 uncertain digit (estimate)

Accuracy vs. Precision ACCURATE = CORRECT PRECISE = CONSISTENT Accuracy - how close a measurement is to the accepted value Precision - how close a series of measurements are to each other ACCURATE = CORRECT PRECISE = CONSISTENT

D. Percent Error Indicates accuracy of a measurement – you will be using this calculation in the lab your value (observed value) accepted value

D. Percent Error % error = 2.94 % A student determines the density of a substance to be 1.40 g/mL. Find the % error if the accepted value of the density is 1.36 g/mL. % error = 2.94 % Always report %’s to the hundredths place!

E. Significant Figures Indicate precision of a measurement. Recording Sig Figs Sig figs in a measurement include the known digits plus a final estimated digit that falls between the tick marks on a measuring device 2.32 cm

E. Significant Figures Counting Sig Figs Count all numbers EXCEPT: Leading zeros -- 0.0025 what about: 60.0025 Trailing zeros without a decimal point -- 2,500 what about: 2500.5

Counting Sig Fig Examples E. Significant Figures Counting Sig Fig Examples 1. 23.50 1. 23.50 4 sig figs 2. 402 2. 402 3 sig figs 3. 5,280 3. 5,280 3 sig figs 4. 0.080 4. 0.080 2 sig figs

E. Significant Figures (13.91g/cm3)(23.3cm3) = 324.103g 324 g Calculating with Sig Figs Multiply/Divide - The # with the fewest sig figs determines the # of sig figs in the answer. (13.91g/cm3)(23.3cm3) = 324.103g 4 SF 3 SF 3 SF 324 g

E. Significant Figures + 4.25 24.3185 ?? 3.75 mL + 4.1 mL 7.85 mL Calculating with Sig Figs (con’t) Add/Subtract - The # with the lowest decimal value determines the place of the last sig fig in the answer. 3.75 mL + 4.1 mL 7.85 mL 3.75 mL + 4.1 mL 7.85 mL 20.0685 + 4.25 24.3185 ??  7.9 mL

F. Scientific Notation 65,000 kg  6.5 × 104 kg Converting into Sci. Notation: Move decimal until there’s 1 digit to its left. Places moved = exponent. Large # (>1)  positive exponent Small # (<1)  negative exponent Only include sig figs.

F. Scientific Notation Practice Problems 1. 2,400,000 g 2. 0.00256 kg 3. 7  10-5 km 4. 6.2  104 mm 2.4  106 g 2.56  10-3 kg 0.00007 km 62,000 mm

F. Scientific Notation Calculating with Sci. Notation (5.44 × 107 g) ÷ (8.1 × 104 mol) = Type on your calculator: ENTER = 5.44 7 8.1 EE ÷ 4 EE = 671.6049383 = 670 g/mol = 6.7 × 102 g/mol H.O.