Lesson 5: Measurement Part II Accuracy & Precision SI Units

Transcription

1 Lesson 5: Measurement Part II Accuracy & Precision SI Units

2 Do Now: 6 th grade Record information from CJ board into your CJ. KEEP CJ s OUT on your desk opened to today s date: Sept.22 Take out notes from last class: Measurement Precision SI Units and open to the practice problems you did for HW. Answer the following questions in the margins of your notes: 1. Why does a meniscus form when a liquid is held in a graduated cylinder/volumetric flask? 2. Write a set of measurements that are accurate but not precise if the correct measurement is 100 L cm = mm?

3 Important! Write into your notes

4 Which is the most accurate??

5 Measuring Tools Beaker = least accurate rough measurements of large volumes, mixing reagents, carrying out reactions Graduated Cylinder = pretty accurate Measuring out different volumes of liquid Volumetric Flask = MOST accurate Designed to measure one specific volume Tall narrow neck for precision For solution preparation

6 Lab Scales & Balances Used to measure mass very precisely Units: Grams Triple beam uses counterweights Analytical scale is digital

7 Also write in notes -

8 Lab Scales & Balances Must tare the balance - = Mass of fish + weigh boat Mass of weigh boat Mass of fish

9 Temperature In science, measured in Kelvin and Celsius F C T C = (T F - 32 F )*(5 C / 9 F ) C F T F = T C * (9 F / 5 F ) + 32 F C K T K = T C Understand the process of converting one temperature scale to another do not simply memorize the equation!

10 F C K Temperature Boiling point of water 212 F 100 C K Difference: 180 degrees F 100 degrees C 100 kelvins Freezing point of water 32 F 0 C K Just REALLY cold -40 F -40 C K

11 Measuring Length

12 Fractions & Decimals Review One centimeter = 100 millimeters One tenth of a centimeter = 1 millimeter 1/ one tenth = = 0.1 cm = 1 mm

13 Go Over HW: Measurement

14 Accuracy vs. Precision

15 Accuracy vs. Precision Accuracy The closeness of measurements to the correct or accepted value of the quantity measured. Precision The closeness of the set of measurements of the same quantity made in the same way.

16 Accuracy vs. Precision

17 Accurate or Precise? Accurate and Precise NOT Accurate, but Precise Accurate, but NOT Precise NOT Accurate, NOT Precise

18 Accurate / Precise / Neither? A measurement was taken three times. The correct measurement was 77.5 ml ml, 43.9 ml, 2 ml ml, 77.5 ml, 77.6 ml ml, 98.2 ml, 97.9 ml ml, 77.3 ml, 72.6 ml NOT precise, NOT accurate Precise and Accurate Precise BUT NOT Accurate Accurate BUT NOT Precise

19 Accuracy vs. Precision Why would we want to make sure that lab equipment is accurate AND precise?

20 Do Now: Take your CJ s out, keep them on desk opened to today s notes. Homework? Take out notes packet from Monday = Measurement, Accuracy vs. Precision, SI Units Answer the following questions: 1. Targets to the right: accurate? precise? 2. There are millimeters in 1 centimeter. 3. There are millimeters in 1 meter. 4. What piece(s) of lab equipment are used as a heating source? 5. Describe/define the control group within a fair experiment. A B

21 Le Système Internationale SI units are units of measurement standardized for international trade. As of 2006, 95% of the world s population lives in metricated countries. There are only 3 countries on Earth that do not use the metric system: USA, Liberia, and Myanmar (Burma)

22 SI Base Units Measurement Unit Name Abbreviation Length Meter m Mass Gram g Time Second s Temperature Kelvin K Amount of substance Mole mol

23 SI Prefixes Prefixes are used with a variety of units to denote larger or smaller measurements. Prefix Unit Abbv Exponent factor Mega- M 10 6 Kilo- k 10 3 Hecto- h 10 2 Deka- da Deci- d 10-1 Centi- c 10-2 Milli- m 10-3

24 Quick Tip! An easy way to remember the prefixes is: King (kilo) Henry (hecto) Died (deca) By (Base unit) Drinking (deci) Chocolate (centi) Milk (milli)

25 Measurement SI is NOT the metric system. The basic units used are: Length: Meter (m). 1m ~ 3.2 feet. Mass: Kilogram (kg) 1kg ~ 2.2 lbs. Time: Second (s)

26 Derived Units All other measurements are derived from (or a combination of) the seven SI units. They have special names. Examples Frequency = per second = Hertz (Hz) (s -1 ) DENSITY = mass volume 4.21 g 1 ml = 4.21g/mL Volume = multiplying lengths 3.2 m 1.0 m = 3.2 m 2

27 Important Note All of these units represent a measurement of volume cm 3 ml L m 3

28 Which units? What are the units appropriate to express the following? The mass of a gold bar Grams (g) The volume of a gas storage tank Liters (L) The length of a garden hose Meters (m) The area of a desktop Meters 2 (m 2 ) The time required to run 800 m Seconds (s)

29 What are we measuring? Indicate whether the following are measurements of length, area, volume, mass, density, time or temperature. a) 5 ns time e) 173 K b) 3.2 kg/l density f) 15 ml c) 0.88 pm distance g) 2 cm 3 d) 540 m 2 area temperature volume volume