CH. 2 - MEASUREMENT

Observing and Collecting Data Data may be Qualitative (descriptive) Flower is red Quantitative (numerical) 100 flowers

Click below to watch the Visual Concept. Visual Concept QUALITATIVE AND QUANTITATIVE DATA

Units of Measurement - Measurements represent quantities. - A quantity is something that has magnitude, size, or amount. - Measurement  quantity the teaspoon is a unit of measurement volume is a quantity The choice of unit depends on the quantity being measured.

NUMBER VS. QUANTITY Quantity = number + unit Quantity = number + unit UNITS MATTER!!

SI MEASUREMENT Agreed upon single measurement system Agreed upon single measurement system Standard of measurement, constant value, easy to preserve, reproduce, and practical in size Standard of measurement, constant value, easy to preserve, reproduce, and practical in size Prefixes added to base units to represent quantities that are larger or smaller than the base Prefixes added to base units to represent quantities that are larger or smaller than the base

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SI Base Units

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

SI PREFIX CONVERSIONS 1. Find the difference between the exponents of the two prefixes. 2.Move the decimal that many places. To the left or right?

SI PREFIX CONVERSIONS mega-M10 6 deci-d10 -1 centi-c10 -2 milli-m10 -3 PrefixSymbolFactor micro-  nano-n10 -9 pico- p kilo-k10 3 move left move right BASE UNIT

SI PREFIX CONVERSIONS 1) 20 cm = ______________ m 2) L = ______________ mL 3) 45  m = ______________ nm 4) 805 dm = ______________ km , K H D B d C M

DERIVED UNITS Combination of units. Combination of units. Volume amount of space occupied by an object Volume amount of space occupied by an object length  length  length length  length  length (m 3 or cm 3 ) (m 3 or cm 3 ) D = MVMV 1 cm 3 = 1 mL 1 m 3 = 1 L Density (kg/m 3 or g/cm 3 )  mass per volume

Derived SI Units

Click below to watch the Visual Concept. Visual Concept EQUATION FOR DENSITY

DENSITY An object has a volume of 825 cm 3 and a density of 13.6 g/cm 3. Find its mass. An object has a volume of 825 cm 3 and a density of 13.6 g/cm 3. Find its mass. C. Johannesson 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

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

CH. 2 - MEASUREMENT The unit m 3 is used to express ________ The unit m 3 is used to express ________ One cubic centimeter is equivalent to ___ One cubic centimeter is equivalent to ___ The relationship between the mass m of a material and its its volume V is __________ The relationship between the mass m of a material and its its volume V is __________ Review ??????

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

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Click below to watch the Visual Concept. Visual Concept MEASURING THE VOLUME OF LIQUIDS

SIGNIFICANT FIGURES Indicate precision of a measurement. Indicate precision of a measurement. Consists of all the digits known with certainty plus one final digit, which is somewhat uncertain or estimated Consists of all the digits known with certainty plus one final digit, which is somewhat uncertain or estimated 2.35 cm

SIGNIFICANT FIGURES RULES Counting Sig Figs Count all numbers EXCEPT: Counting Sig Figs Count all numbers EXCEPT: Leading zeros Leading zeros Trailing zeros without a decimal point -- 2,500 Trailing zeros without a decimal point -- 2,500

Significant Figures, continued Rounding

COUNTING SIG FIG EXAMPLES , , sig figs 3 sig figs 2 sig figs

CALCULATING WITH SIGNIFICANT FIGURES Multiply/Divide - The # with the fewest sig figs determines the # of sig figs in the answer. Multiply/Divide - The # with the fewest sig figs determines the # of sig figs in the answer. (13.91g/cm 3 )(23.3cm 3 ) = g 324 g 4 SF3 SF

CALCULATING WITH SIGNIFICANT FIGURES Add/Subtract - The # with the lowest decimal value determines the place of the last sig fig in the answer. Add/Subtract - The # with the lowest decimal value determines the place of the last sig fig in the answer mL mL 7.85 mL 224 g g 354 g  7.9 mL  350 g 3.75 mL mL 7.85 mL 224 g g 354 g

CALCULATING WITH SIGNIFICANT FIGURES  Exact Numbers do not limit the # of sig figs in the answer.  Counting numbers: 12 students  Exact conversions: 1 m = 100 cm  “1” in any conversion: 1 in = 2.54 cm

PRACTICE PROBLEMS (15.30 g) ÷ (6.4 mL) = g/mL  18.1 g 18.9g g g 4 SF2 SF  2.4 g/mL 2 SF

Conversion Factors A conversion factor is a ratio derived from the equality between two different units that can be used to convert from one unit to the other. example: How quarters and dollars are related

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Conversion Factors, continued Dimensional analysis is a mathematical technique that allows you to use units to solve problems involving measurements. quantity sought = quantity given × conversion factor example: the number of quarters in 12 dollars number of quarters = 12 dollars × conversion factor

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Click below to watch the Visual Concept. Visual Concept RULES FOR ROUNDING NUMBERS

REVIEW ?????? A chemical reaction was carried out three times. The mass of the product was 8.93 g for the first trial, 8.94 g for the second trial, and 8.92 g for the third trial. Under the conditions of the experiment, the reaction is known to yield 8.60 g of product. The three mass values measured are? A chemical reaction was carried out three times. The mass of the product was 8.93 g for the first trial, 8.94 g for the second trial, and 8.92 g for the third trial. Under the conditions of the experiment, the reaction is known to yield 8.60 g of product. The three mass values measured are? Day 3

SCIENTIFIC NOTATION  WHY????  Chemistry often deals with very large and very small numbers.  There are 602,000,000,000,000,000,000,000 molecules of water in 18 mL  one electron has a mass of g  We need a shorter way of writing these numbers

SCIENTIFIC NOTATION Move decimal until there’s 1 digit to its left. Places moved = exponent. Move decimal until there’s 1 digit to its left. Places moved = exponent. Large # (>1)  positive exponent Small # ( 1)  positive exponent Small # (<1)  negative exponent Only include sig figs. Only include sig figs. 65,000 kg  6.5 × 10 4 kg

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SCIENTIFIC NOTATION PRACTICE PROBLEMS SCIENTIFIC NOTATION PRACTICE PROBLEMS 7. 2,400,000  g kg 9.7  km  10 4 mm 2.4  10 6  g 2.56  kg km 62,000 mm

SCIENTIFIC NOTATION CALCULATIONS (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:

Direct Proportions Two quantities are directly proportional to each other if dividing one by the other gives a constant value. read as “y is proportional to x.” Using Scientific Measurements

Inverse Proportions Two quantities are inversely proportional to each other if their product is constant. read as “y is proportional to 1 divided by x.” Using Scientific Measurements

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PERCENT ERROR Indicates accuracy of a measurement Indicates accuracy of a measurement your value accepted value

PERCENT ERROR 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. 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 = 2.9 %