# Unit One Review Accuracy and Precision The important things to remember about accuracy and precision: You want measurements that are both accurate and.

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Unit One Review

Accuracy and Precision The important things to remember about accuracy and precision: You want measurements that are both accurate and precise! Accurate : You hit the bulls-eye! (to also be precise you must hit it every time) Precise: you hit the same spot every time (you get the same measurement every time) You can be precise without being accurate

Accuracy vs. 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

If you are measuring the temperature of boiling water: 1 st measurement: 98 0 C; 2 nd measurement: 98 0 C; 3 rd measurement: 97 0 C 1 st measurement: 101 0 C; 2 nd 102 0 C; 3 rd 97 0 C 1 st measurement: 100 0 C; 2 nd 100 0 C; 3 rd 100 0 C

Measurements When we measure something, we can (and do) always estimate between the smallest marks. 21345

Measurements The better marks the better we can estimate. Scientist always understand that the last number measured is actually an estimate. 21345

Significant Figures Indicate precision of a measurement. Recording significant figures Significant figures in a measurement include the known digits plus a final estimated digit 2.35 cm

Significant Figures Counting Sig Figs Count all numbers EXCEPT: Leading zeros -- 0.0025 Trailing zeros without a decimal point -- 2,500

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

Significant Figures How many sig figs in the following measurements? 458 g 4085 g 4850 g 0.0485 g 0.004085 g 40.004085 g

Significant Figures Calculating Multiply/Divide - The # with the fewest sig figs determines the # of sig figs in the answer. (13.91g/cm 3 )(23.3cm 3 ) = 324.103g 324 g 4 SF3 SF

Significant Figures Calculating 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 224 g + 130 g 354 g  7.9 mL  350 g 3.75 mL + 4.1 mL 7.85 mL 224 g + 130 g 354 g

Scientific Notation 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. 65,000 kg  6.5 × 10 4 kg

Graphs Circle graphs – compare parts in a whole Bar graphs – compare quantities Line graphs – compare sets of data, show change and patterns over time.

Base Units Length - meter - m Mass - grams or kilogram - g Time - second - s Temperature – Kelvin - K Energy - Joules- J Volume - Liter - L Amount of substance - mole - mol

Prefixes kilo k 1000 times deci d 1/10 Centi c 1/100 milli m 1/1000 kilometer - about 0.6 miles centimeter - less than half an inch millimeter - the width of a paper clip wire

Conversion Practice Kilo- 1000 units Hecto- 100 units Deka- 10 units Base Unit Deci- 0.1 units Centi- 0.01 units Milli- 0.001 units To convert to a smaller unit, move the decimal point to the right or multiply. To convert to a larger unit, move the decimal point to the left or divide.

Converting khDdcm how far you have to move on this chart, tells you how far, and which direction to move the decimal place. The box is the base unit, meters, Liters, grams, etc.

Conversions Change 5.6 m to millimeters khDdcm l starts at the base unit and move three to the right. l move the decimal point three to the right 5600

Density How heavy something is for its size. The ratio of mass to volume for a substance. D = M / V Independent of how much of it you have gold - high density air low density.

Volume and Density Relationship Between Volume and Density for Identical Masses of Common Substances Cube of substance Mass Volume Density Substance (face shown actual size) (g) (cm 3 ) (g.cm 3 ) Lithium Water Aluminum Lead 10 19 0.53 10 10 1.0 10 3.7 2.7 10 0.58 11.4

Celsius & Kelvin Temperature Scales

Temperature Scales Zumdahl, Zumdahl, DeCoste, World of Chemistry  2002, page 136

Measuring Temperature Kelvin starts at absolute zero (-273 º C) degrees are the same size C = K -273 K = C + 273 Kelvin is always bigger. Kelvin can never be negative. 273 K

Specific Heat

States of Matter 3 states Gas No definite volume or shape Liquid Definite volume, but not shape Solid Definite shape and volume

Controlled Experiments 1. Manipulated Variable: is one thing (factor) you change or allow to be different in an experiment. 2. Responding Variable: is one thing (factor) that you are measuring or observing (the outcome of the experiment). 3. Controlled Variables: are factors or things that are kept the same at the beginning of the experiment.

Tulip Experiment Materials: Tulip plant Water Sun Minerals Fertilizer

CONTROL (Pot 2) Tulip plant Water Sun Fertilizer EXPERIMENTAL (Pot 1) Tulip plant Water Sun Minerals Fertilizer What are the variables in this experiment? CV: Tulip plant, Water, Sun, Fertilizer MV: Minerals RV: Color of the tulip flowers (ECC: no minerals)

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