CH. 2 - MEASUREMENT

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

Qualitative and Quantitative Data Click below to watch the Visual Concept. Visual Concept

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.

Quantity = number + unit Number vs. Quantity Quantity = number + unit UNITS MATTER!!

SI Measurement Agreed upon single measurement system 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

SI Base Units

SI Prefix Conversions Prefix Symbol Factor mega- M 106 kilo- k 103 BASE UNIT --- 100 deci- d 10-1 move left move right centi- c 10-2 milli- m 10-3 micro-  10-6 nano- n 10-9 pico- p 10-12

M K H D B d c m u n p 0.2 32 45,000 0.0805 SI Prefix Conversions 1) 20 cm = ______________ m 2) 0.032 L = ______________ mL 3) 45 m = ______________ nm 4) 805 dm = ______________ km 0.2 32 45,000 0.0805 M K H D B d c m u n p

M V D = 1 cm3 = 1 mL 1 m3 = 1 L Derived Units Density (kg/m3 or g/cm3) Combination of units. Volume amount of space occupied by an object length  length  length (m3 or cm3) 1 cm3 = 1 mL 1 m3 = 1 L Density (kg/m3 or g/cm3) mass per volume D = M V

Derived SI Units

V = 825 cm3 M = DV D = 13.6 g/cm3 M = (13.6 g/cm3)(825cm3) M = ? Density An object has a volume of 825 cm3 and a density of 13.6 g/cm3. Find its mass. GIVEN: V = 825 cm3 D = 13.6 g/cm3 M = ? WORK: M = DV M = (13.6 g/cm3)(825cm3) M = 11,200 g C. Johannesson

D = 0.87 g/mL V = M V = ? M = 25 g V = 25 g 0.87 g/mL V = 29 mL 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 C. Johannesson V = 29 mL

https://www.youtube.com/watch?v=KqVQxPRobgw

The unit m3 is used to express ________ CH. 2 - MEASUREMENT Review ?????? The unit m3 is used to express ________ One cubic centimeter is equivalent to ___ The relationship between the mass m of a material and its its volume V is __________

ACCURATE = CORRECT PRECISE = CONSISTENT Accuracy & Precision 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

Accuracy and Precision Click below to watch the Visual Concept. Visual Concept

Indicate precision of a measurement. Significant Figures Indicate precision of a measurement. 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: Leading zeros -- 0.0025 Trailing zeros without a decimal point -- 2,500

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

Calculating with Significant Figures 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

Calculating with Significant Figures 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 224 g + 130 g 354 g 224 g + 130 g 354 g  7.9 mL  350 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) = 2.390625 g/mL  2.4 g/mL 4 SF 2 SF = 2.390625 g/mL  2.4 g/mL 2 SF 18.9 g - 0.84 g  18.1 g 18.06 g

Scientific Notation WHY???? Don’t copy 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 0.000000000000000000000000000911 g We need a shorter way of writing these numbers

65,000 kg  6.5 × 104 kg Scientific 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.

Scientific Notation Practice Problems 7. 2,400,000 g 8. 0.00256 kg 9. 7  10-5 km 10. 6.2  104 mm 2.4  106 g 2.56  10-3 kg 0.00007 km 62,000 mm

Scientific Notation Calculations (5.44 × 107 g) ÷ (8.1 × 104 mol) = Type on your calculator: EXP EE EXP EE ENTER EXE 5.44 7 8.1 ÷ 4 = 671.6049383 = 670 g/mol = 6.7 × 102 g/mol

Review ?????? Day 3 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?

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

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

Click below to watch the Visual Concept. https://www.youtube.com/watch?v=hQpQ0hxVNTg

Using Scientific Measurements Direct Proportions Two quantities are directly proportional to each other if dividing one by the other gives a constant value. variables do the same thing

Using Scientific Measurements Inverse Proportions Two quantities are inversely proportional to each other if their product is constant. variables do the opposite

Percent Error your value accepted value Indicates accuracy of a measurement your value accepted value

% error = 2.9 % 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. % error = 2.9 %