Scientific Measurement Part 2: Scientific Measurement

Importance of Measurement Not all measurements give the same amount of information. Qualitative Measurement Quantitative Measurement Descriptive Cannot be measured (color, feel) Nonnumerical Numerical Definite value (numbers & units)

Scientific Notation In chemistry, you will often encounter very small and very large numbers. Scientific Notation Makes numbers easier to work with and to write Makes long numbers shorter

Scientific Notation What happened? 36,000 becomes 3.6 X 104 What happened? The decimal point was moved either right or left to get only 1 number in front of decimal. (Hint: If no decimal showing, it is after the last number!)

Scientific Notation If move RIGHT…. 0.00789 = 7.89 X 10-3 Number of places decimal point moves is the power of 10 and it is NEGATIVE 0.00789 = 7.89 X 10-3

Scientific Notation If move LEFT…. 366,000,000 = 3.66 X 108 Number of places decimal point moves is the power of 10 and it is POSITIVE 366,000,000 = 3.66 X 108

Try it! Can you express the mass of a single atom of gold, which is 0.000 000 000 000 000 000 000 327 gram, in scientific notation?

3.27 X 10-22 gram It should be Try it! Answer

Try It! Can you express the distance to Mars, which is roughly 34,800,000 miles, in scientific notation? Hint: If no decimal point is showing, it is assumed to be behind the last number.

Try it! Answer 34,800,000 miles It should be 3.48 X 107 miles!

Your Turn! Complete the Scientific Notation Worksheet. Due next class period. Be prepared for Scientific Notation Quiz next class period.

Uncertainty in Measurements Accuracy Precision How “close” a measurement comes to the actual or true value How close repeated measurements are to one another

Precision Increased Precision = More Decimals Most Precise 35111.001 When you report a measurement, you should only include digits if you’re really confident about their values. The more significant figures in a measurement, the more precise that measurement must be! For Example: Increased Precision = More Decimals Most Precise 35111.001 35111.01 35111.1 35111 Least Precise 35110

Significant Figures (aka) Sig Figs Significant figures tell us: something about the data are important for measurements are all the possible digits plus one guess on a measurement We know 1 mm and 0.2 mm and then we guess at last digit  So, we record 1.25 mm

Sig Figs Tell people how good our measuring tool was PURPOSE: Tell people how good our measuring tool was Also shows how precise the measuring tool used was

Rules for Sig Figs Rule #1: Any non-zero digits are significant. 6.42 seconds contains 3 sig figs

Rules for Sig Figs Rule #2: All zeros between significant figures are significant. 307 mm = 3 sig figs

Rules for Sig Figs Rule #3: Leading zeros are not significant. 0.0642 mL and 0.00308 mg = 3 sig figs each

Rules for Sig Figs Rule #4: Trailing zeros are significant ONLY if after a decimal and after a significant figure. 0.0097500 L = 5 sig figs

Try it! 4 sig figs 2 sig figs 3 sig figs 2 sig figs 3 sig figs Determine the number of significant figures in each of the following: 6.751 g 0.070 kg 28.0 mL 2500 m 400. L 30.07 g 4 sig figs 2 sig figs 3 sig figs 2 sig figs 3 sig figs 4 sig figs

+ 67.68 mL 90.78 mL Should record 90.8 mL Try It! For the results of an experiment you need to add 23.1 mL of HCl acid and 67.68 mL of HCl acid. What results should you record? 23.1 mL + 67.68 mL 90.78 mL Should record 90.8 mL

Try It! 14.5 cm3 5.091034483 You should record 5.09 g/cm3 For the results of an experiment, you need to divide the mass of 73.82 g by 14.5 cm3 to find the density of a material. What is the density you should record for the results? 73.82 g = 14.5 cm3 5.091034483 You should record 5.09 g/cm3

Your Turn! Complete the Sig Fig Worksheet with partner. Be prepared for Sig Fig Quiz next class period. When done with Sig Fig WS, turn in and work on Sig Fig Lab/Hwk with partner Due next class period at start of class.

The SI System Chemists measure physical properties all the time, such as mass, volume, length, or temperature. They need a way to communicate their measurements to other chemists that is exact and agreed upon to use for a comparison. SI System is based on metric system (base 10-units)

The SI System Units of Measurement Quantity SI Base Unit Symbol Non-SI Unit Length meter m Volume cubic meter m3 Liter L Mass kilogram kg Density grams/cubic centimeter g/cm3 grams/milliliter g/mL Temperature kelvin K celsius 0C Time second s Pressure pascal Pa atmosphere atm Energy joule J calorie cal Amt of substance mole mol

The SI System

How do I convert units? Sometimes you start with one set of units and need to convert to another unit. How do we do this? Use Conversion Factors (Dimensional Analysis) Watch this helpful YouTube video! www.youtube.com/watch?v=DsTg1CeWchc

The SI System Common Conversions Others 1 kg = 1000 g 1 m = 10 dm 1 m = 100 cm 1 m = 1000 mm Others 1 mile = 5280 ft 1 inch = 2.54 cm 1 lb = 454 g

Now you Try It! x = 1000m 1 km 8.5 km 8500 km How many meters are in 8.5 kilometers? x = 1000m 1 km 8.5 km 8500 km

Try It! Express a mass of 5.712 grams in kilograms. x = 1 kg 1000 g 5.712 g 0.005712 kg

Try One More! x x x = 24 m/s 86km hr 1000m 1 km 1 hour 60 min 1 min Convert 86km/hr to m/s. x x x = 86km hr 1000m 1 km 1 hour 60 min 1 min 60 sec 24 m/s

Your Turn! Be prepared for SI System Quiz next class period. Now complete the SI System Worksheet #1 with a partner. When finished, have Mrs. Breeding check it. Then complete the SI System Worksheet #2 as homework. (Get it from Mrs. Breeding when you are done with Wksh #1) Be prepared for SI System Quiz next class period.

AND apply it to the Effervescent Launcher Lab! Your Turn! Now you need to take all the information you learned about: Scientific Method Scientific Measurement (SI System) Scientific Notation Sig Figs AND apply it to the Effervescent Launcher Lab!

Your Turn! Complete SI System Homework Sheet Due at start of next class

Derived SI Units Some units in the SI System are derived from multiplying or dividing standard units. One such unit is DENSITY

Density Density = mass = m volume V Density is the ratio of the mass of an object to its volume i.e. how much “stuff” there is in some amount of space Density = mass = m volume V

Density A 10.0 cm3 piece of lead has a mass of 114 g. What is the density of lead? D = m = = V 114 g 10.0 cm3 11.4 g/cm3

Densities of Some Common Materials Solids & Liquids Density at 200C (g/cm3) Gases (g/L) Gold 19.3 Chlorine 2.95 Mercury 13.6 Carbon dioxide 1.83 Lead 11.4 Oxygen 1.33 Aluminum 2.70 Air 1.20 Table sugar 1.59 Nitrogen 1.17 Water (40C) 1.000 Neon 0.84 Corn oil 0.922 Ammonia 0.718 Ice (00C) 0.917 Methane 0.665 Ethanol 0.789 Helium 0.166 Gasoline 0.66-0.69 Hydrogen 0.084 Cork 0.24

You Try It! D = m = = 612 g 245 cm3 2.50 g/cm3 A student finds a shiny piece of metal that she thinks is aluminum. In the lab, she determines that the metal has a volume of 245 cm3 and a mass of 612 g. Calculate the density. Is the metal aluminum? D = m = = V 612 g 245 cm3 2.50 g/cm3 So, her shiny metal is NOT aluminum.

You Try It! The density of silver at 200C is 10.5 g/cm3. What is the volume of a 68 g bar of silver? D =m so m = D * V then V = m V D V = 68 g = 6.5 cm3 10.5 g/cm3

Your Turn! Complete the Density Worksheet which is due next class period. Complete the “How Sweet It Is!” Lab.