Measurement Notes

Chemistry – Qualitative Measurement – Quantitative Measurement – the science that deals with the materials of the universe and the changes these materials undergo Qualities or observations that can be made about a substance ex: the substance is a yellow solid a measurement that consists of a number and a unit ex: the substance weighs 3.45 grams

Units tells what scale or standard is being used to represent the measurement International System (SI) SI Base Units: –Length: measures distance –Mass: quantity of matter present in an sample –Volume: 1 mL = 1 cm 3 three-dimensional space occupied by a sample –Temperature: T K = T °C –Time: –Pressure: –Energy/Heat: –Counting Atoms: meter grams Liter, centimeter cubed Kelvin, Celsius second Pascals Joules moles

Common prefixes (MEMORIZE) Giga 1 x 10 9 _ = 1 G_ Mega 1 x 10 6 _ = 1 M_ Kilo _ = 1 k_ Hecto _ = 1 H_ Deka - 10 _ = 1 D_ (base) – meter, liter, gram… deci- 1 _ = 10 d_ centi-1 _ = 100 c_ milli-1 _ = 1000 m_ micro-1 _ = 1 x 10 6  _(  = lowercase Greek Mu) nano-1 _ = 1 x 10 9 n_ pico-1 _ = 1 x p_ * * * * * *

Scientific Notation Expresses a number as a product of a number between 1 and 10 and the appropriate power of 10 If you move the decimal point: left  use positive exponent right  use negative exponent Ex:200g mL 12 2 x 10 2 g3.14 x mL 123

Converting from Scientific Notation to Ordinary Numbers move the decimal point: positive exponent => move right  negative exponent => move left  Ex: 6.32 x 10 1 cm3.92 x m cm m

Element Buddies Think-Pair-Share m g x 10 2 cL x L 6.57 x m 2.35 x g 934 cL L

Accuracy: - How _________ a measurement is to the actual or _________value. To evaluate accuracy you must __________ the true value. For example, knowing a watch is 5 min fast…The time on the watch is ________ accurate and you know it is not accurate b/c you know the real time and can make an ________. Shooting Free Throws - Accuracy can be measured by how many are __________. Uncertainty in Measurement close accepted know not adjustment baskets

Precision: 1st Meaning of Precision How close a ____________ of measurements are to the _________________. To evaluate precision you must compare the values of 2 or more _______________ measurements. Ex. Measure the temperature of water three times. Which set of measurements are more precise? Thermometer 1: 22.3 o C, 22.3 o C, 22.4 o C Thermometer 2: 24.5 o C, 20.1 o C, 18.7 o C Shooting Free Throws - Precision can be measured by how many _______ in the same _________. Ex. Consistently hitting the ___________ of the rim and missing. Not accurate b/c not making the shots, but precise b/c results are repeated. Science – should be both accurate (___________) and precise (can ____________ it consistently) set each other similar shotsspot side right repeat

2nd Meaning of Precision Precision can also refer to how __________ a measurement is (more decimal __________ = more precise) Consider mass of sugar in bubble gum –5 g - wide range of values that it could be! - Could be between 4.5 g and 5.4 g and rounded to 5 g. –5.0 g gives you more information – Could be between 4.95 g and 5.04 g. –5.00 g gives you even more information – Could be between g and g More numbers to ______________ of decimal, more precise the measurement is! precise places right

Element Buddies Oh buddy...summarize

Limits to Measurements When measuring you should always ______________ the _______ digit of your measurement You know what it is definitely _________ than, and you know what it is definitely _______ than. Divide those two points into imaginary ___________and estimate how far in between the measurement is. Your measurement should be recorded to ONE DECIMAL BEYOND the ______________marking Your Estimate (or _____________ number) should be the final one on the right. If the tool is digital, _________ the given number Measurements always have some degree of uncertainty (estimation) estimatelast less more line calibration uncertain record

Ex 1: Measure the volume of liquid in the graduated cylinder. Remember: The volume is read at the bottom of the liquid curve (called the meniscus) mL 7.5 cm 7.56 cm Ex 2: Measure the line using both rulers.

Element Buddies What does one digit beyond the calibration mean?

Significant Figures All certain numbers plus first uncertain digit Rules for counting Sig. Figs. 3. Exact numbers – have infinite number of sig. figs., they arise from definitions c. Trailing Zeros – come at the end of a number and count IF there is a DECIMAL POINT b. Captive (Trapped) Zeros – fall between two nonzero digits, they ALWAYS COUNT 2. Zeros a. Leading Zeros – precede all nonzero digits, they NEVER COUNT 1. All nonzero numbers are significant = 4 SF 236 = 3 SF.0025 = 2 SF.0009 = 1 SF 6008 = 4 SF = 5 SF = 3 SF 3000 = 1 SF = 4 SF = 5 SF = 7 SF 1 inch = 2.54 cm, 1 g = 1000 mg

Rounding If the digit to be removed is – a.less than 5, the preceding digit stays the same b.equal or greater than 5, increase the preceding digit by 1 When rounding off, use ONLY the first number to the right of the last significant figure Ex: Round to 3 SF $ 10, g cm mL = $10,100 = g = cm = 1.00 x 10 3 mL