chemistry presentation2 by sir pj de castro

Types of Observations and Measurements:

Types of Observations and Measurements We make QUALITATIVE observations of reactions — changes in color and physical state. We also make QUANTITATIVE MEASUREMENTS, which involve numbers. Use SI units — based on the metric system

SI measurement:

SI measurement Le Système international d'unités The only countries that have not officially adopted SI are Liberia (in western Africa) and Myanmar (a.k.a. Burma, in SE Asia), but now these are reportedly using metric regularly Metrication is a process that does not happen all at once, but is rather a process that happens over time. Among countries with non-metric usage, the U.S. is the only country significantly holding out . The U.S. officially adopted SI in 1866. Information from U.S. Metric Association

Standards of Measurement:

Standards of Measurement When we measure, we use a measuring tool to compare some dimension of an object to a standard. For example, at one time the standard for length was the king’s foot. What are some problems with this standard?

What is Scientific Notation?:

What is Scientific Notation? Scientific notation is a way of expressing really big numbers or really small numbers. For very large and very small numbers, scientific notation is more concise.

Scientific notation consists of two parts::

Scientific notation consists of two parts: A number between 1 and 10 A power of 10 N x 10 x

To change standard form to scientific notation…:

To change standard form to scientific notation… Place the decimal point so that there is one non-zero digit to the left of the decimal point. Count the number of decimal places the decimal point has “moved” from the original number. This will be the exponent on the 10. If the original number was less than 1, then the exponent is negative. If the original number was greater than 1, then the exponent is positive.

Examples:

Examples Given: 289,800,000 Use: 2.898 (moved 8 places) Answer: 2.898 x 10 8 Given: 0.000567 Use: 5.67 (moved 4 places) Answer: 5.67 x 10 -4

To change scientific notation to standard form…:

To change scientific notation to standard form… Simply move the decimal point to the right for positive exponent 10. Move the decimal point to the left for negative exponent 10. (Use zeros to fill in places.)

Example:

Example Given: 5.093 x 10 6 Answer: 5,093,000 (moved 6 places to the right) Given: 1.976 x 10 -4 Answer: 0.0001976 (moved 4 places to the left)

Learning Check:

Learning Check Express these numbers in Scientific Notation: 405789 0.003872 3000000000 2 0.478260

UNITS OF MEASUREMENT:

UNITS OF MEASUREMENT Use SI units — based on the metric system Length Mass Volume Time Temperature Meter, m Kilogram, kg Seconds, s Celsius degrees, ˚C kelvins, K Liter, L

Mass vs. Weight:

Mass vs. Weight Mass: Amount of Matter (grams, measured with a BALANCE) Weight: Force exerted by the mass, only present with gravity (pounds, measured with a SCALE)

Some Tools for Measurement:

Some Tools for Measurement Which tool(s) would you use to measure: A. temperature B. volume C. time D. weight

Learning Check :

Learning Check Match L) length M) mass V) volume ____ A. A bag of tomatoes is 4.6 kg. ____ B. A person is 2.0 m tall. ____ C. A medication contains 0.50 g Aspirin. ____ D. A bottle contains 1.5 L of water. M L M V

Learning Check :

Learning Check What are some U.S. units that are used to measure each of the following? A. length B. volume C. weight D. temperature

Metric Prefixes:

Metric Prefixes Kilo- means 1000 of that unit 1 kilometer (km) = 1000 meters (m) Centi- means 1/100 of that unit 1 meter (m) = 100 centimeters (cm) 1 dollar = 100 cents Milli- means 1/1000 of that unit 1 Liter (L) = 1000 milliliters (mL)

Metric Prefixes:

Metric Prefixes

Units of Length:

Units of Length ? kilometer (km) = 500 meters (m) 2.5 meter (m) = ? centimeters (cm) 1 centimeter (cm) = ? millimeter (mm) 1 nanometer (nm) = 1.0 x 10 -9 meter O—H distance = 9.4 x 10 -11 m 9.4 x 10 -9 cm 0.094 nm

Learning Check :

Learning Check Select the unit you would use to measure 1. Your height a) millimeters b) meters c) kilometers 2. Your mass a) milligrams b) grams c) kilograms 3. The distance between two cities a) millimeters b) meters c) kilometers 4. The width of an artery a) millimeters b) meters c) kilometers

Conversion Factors:

Conversion Factors Fractions in which the numerator and denominator are EQUAL quantities expressed in different units Example: 1 in. = 2.54 cm Factors: 1 in. and 2.54 cm 2.54 cm 1 in.

Learning Check :

Learning Check Write conversion factors that relate each of the following pairs of units: 1. Liters and mL 2. Hours and minutes 3. Meters and kilometers

How many minutes are in 2.5 hours? :

How many minutes are in 2.5 hours ? Conversion factor 2.5 hr x 60 min = 150 min 1 hr cancel By using dimensional analysis / factor-label method, the UNITS ensure that you have the conversion right side up, and the UNITS are calculated as well as the numbers!

Steps to Problem Solving:

Steps to Problem Solving Write down the given amount. Don’t forget the units! Multiply by a fraction. Use the fraction as a conversion factor. Determine if the top or the bottom should be the same unit as the given so that it will cancel. Put a unit on the opposite side that will be the new unit. If you don’t know a conversion between those units directly, use one that you do know that is a step toward the one you want at the end. Insert the numbers on the conversion so that the top and the bottom amounts are EQUAL, but in different units. Multiply and divide the units (Cancel). If the units are not the ones you want for your answer, make more conversions until you reach that point. Multiply and divide the numbers. Don’t forget “Please Excuse My Dear Aunt Sally”! (order of operations)

Sample Problem:

Sample Problem You have P7.25 in your pocket in quarters. How many quarters do you have? 7.25 pesos X 4 quarters 1 dollar = 29 quarters

You Try This One!:

You Try This One! If Jacob stands on Spencer’s shoulders, they are two and a half yards high. How many feet is that?

Learning Check :

Learning Check A rattlesnake is 2.44 m long. How long is the snake in cm? a) 2440 cm b) 244 cm c) 24.4 cm

Solution :

Solution A rattlesnake is 2.44 m long. How long is the snake in cm? b) 244 cm 2.44 m x 100 cm = 244 cm 1 m

Learning Check :

Learning Check How many seconds are in 1.4 days? Unit plan: days hr min seconds 1.4 days x 24 hr x ?? 1 day

Wait a minute!:

Wait a minute! What is wrong with the following setup? 1.4 day x 1 day x 60 min x 60 sec 24 hr 1 hr 1 min

English and Metric Conversions:

English and Metric Conversions If you know ONE conversion for each type of measurement, you can convert anything! You must memorize and use these conversions: Mass: 454 grams = 1 pound Length: 2.54 cm = 1 inch Volume: 0.946 L = 1 quart

Learning Check :

Learning Check An adult human has 4.65 L of blood. How many gallons of blood is that? Unit plan: L qt gallon Equalities: 1 quart = 0.946 L 1 gallon = 4 quarts Your Setup:

Equalities :

Equalities State the same measurement in two different units length 10.0 in. 25.4 cm

Steps to Problem Solving:

Steps to Problem Solving Read problem Identify data Make a unit plan from the initial unit to the desired unit Select conversion factors Change initial unit to desired unit Cancel units and check Do math on calculator Give an answer using significant figures

Dealing with Two Units:

Dealing with Two Units If your pace on a treadmill is 65 meters per minute, how many seconds will it take for you to walk a distance of 8450 feet?

What about Square and Cubic units? :

What about Square and Cubic units? Use the conversion factors you already know, but when you square or cube the unit, don’t forget to cube the number also! Best way: Square or cube the ENITRE conversion factor Example: Convert 4.3 cm 3 to mm 3 4.3 cm 3 10 mm 3 1 cm ( ) = 4.3 cm 3 10 3 mm 3 1 3 cm 3 = 4300 mm 3

Learning Check:

Learning Check A Nalgene water bottle holds 1000 cm 3 of dihydrogen monoxide (DHMO). How many cubic decimeters is that?

Solution:

Solution 1000 cm 3 1 dm 3 10 cm ( ) = 1 dm 3 So, a dm 3 is the same as a Liter ! A cm 3 is the same as a milliliter.

Learning Check :

Learning Check A rattlesnake is 2.44 m long. How long is the snake in cm? a) 2440 cm b) 244 cm c) 24.4 cm

Solution :

Solution A rattlesnake is 2.44 m long. How long is the snake in cm? b) 244 cm 2.44 m x 100 cm = 244 cm 1 m

Temperature Scales:

Temperature Scales Fahrenheit Celsius Kelvin Anders Celsius 1701-1744 Lord Kelvin (William Thomson) 1824-1907

Temperature Scales:

Temperature Scales Notice that 1 kelvin = 1 degree Celsius Boiling point of water Freezing point of water Celsius 100 ˚C 0 ˚C 100˚C Kelvin 373 K 273 K 100 K Fahrenheit 32 ˚F 212 ˚F 180˚F

Calculations Using Temperature:

Calculations Using Temperature Generally require temp’s in kelvins T (K) = t (˚C) + 273.15 Body temp = 37 ˚C + 273 = 310 K Liquid nitrogen = -196 ˚C + 273 = 77 K

Fahrenheit Formula:

Fahrenheit Formula 180°F = 9°F = 1.8°F 100°C 5°C 1°C Zero point: 0°C = 32°F °F = 9/5 °C + 32

Celsius Formula – Honors Only:

Celsius Formula – Honors Only Rearrange to find T°C °F = 9/5 °C + 32 °F - 32 = 9/5 °C ( +32 - 32) °F - 32 = 9/5 °C 9/5 9/5 (°F - 32) * 5/9 = °C

Temperature Conversions – Honors Only:

Temperature Conversions – Honors Only A person with hypothermia has a body temperature of 29.1°C. What is the body temperature in °F? °F = 9/5 (29.1°C) + 32 = 52.4 + 32 = 84.4°F

Learning Check – Honors Only :

Learning Check – Honors Only The normal temperature of a chickadee is 105.8°F. What is that temperature in °C? 1) 73.8 °C 2) 58.8 °C 3) 41.0 °C

Learning Check – Honors Only :

Learning Check – Honors Only Pizza is baked at 455°F. What is that in °C? 1) 437 °C 2) 235°C 3) 221°C

Slide 48:

Three targets with three arrows each to shoot. Can you hit the bull's-eye? Both accurate and precise Precise but not accurate Neither accurate nor precise How do they compare? Can you define accuracy and precision?

ACCURACY vs. PRECISION:

ACCURACY vs. PRECISION Accurate & precise I naccurate but precise Inaccurate & imprecise

Significant Figures:

Significant Figures The numbers reported in a measurement are limited by the measuring tool Significant figures in a measurement include the known digits plus one estimated digit

MEASUREMENTS Significant Figures:

MEASUREMENTS S ignificant F igures All nonzero numbers are significant figures. 33387564 has 8 SF Zero’s follow the rules below: Zero’s between numbers are significant. 30.09 has 4 SF Zero’s that precede are NOT significant. 0.000034 has 2 SF Zero’s at the end of decimals are significant. 0.00900 has 3 SF Zero’s at the end without decimals are either. 4050 has either 4 SF or 3 SF

Counting Significant Figures :

Counting Significant Figures RULE 1. All non-zero digits in a measured number are significant. Only a zero could indicate that rounding occurred. Number of Significant Figures 38.15 cm 4 5.6 ft 2 65.6 lb ___ 122.55 m ___

Leading Zeros:

Leading Zeros RULE 2. Leading zeros in decimal numbers are NOT significant. Number of Significant Figures 0.008 mm 1 0.0156 oz 3 0.0042 lb ____ 0.000262 mL ____

Sandwiched Zeros:

Sandwiched Zeros RULE 3. Zeros between nonzero numbers are significant. (They can not be rounded unless they are on an end of a number.) Number of Significant Figures 50.8 mm 3 2001 min 4 0.702 lb ____ 0.00405 m ____

Trailing Zeros:

Trailing Zeros RULE 4. Trailing zeros in numbers without decimals are NOT significant. They are only serving as place holders. Number of Significant Figures 25,000 in. 2 200. yr 3 48,600 gal ____ 25,005,000 g ____

Learning Check :

Learning Check A. Which answers contain 3 significant figures? 1) 0.4760 2) 0.00476 3) 4760 B. All the zeros are significant in 1) 0.00307 2) 25.300 3) 2.050 x 10 3 C. 534,675 rounded to 3 significant figures is 1) 535 2) 535,000 3) 5.35 x 10 5

Learning Check:

Learning Check In which set(s) do both numbers contain the same number of significant figures? 1) 22.0 and 22.00 2) 400.0 and 40 3) 0.000015 and 150,000

Learning Check:

State the number of significant figures in each of the following: A. 0.030 m 1 2 3 B. 4.050 L 2 3 4 C. 0.0008 g 1 2 4 D. 3.00 m 1 2 3 E. 2,080,000 bees 3 5 7 Learning Check

Significant Numbers in Calculations:

Significant Numbers in Calculations A calculated answer cannot be more precise than the measuring tool. A calculated answer must match the least precise measurement. Significant figures are needed for final answers from 1) adding or subtracting 2) multiplying or dividing

Adding and Subtracting:

Adding and Subtracting The answer has the same number of decimal places as the measurement with the fewest decimal places. 25.2 one decimal place + 1.34 two decimal places 26.54 answer 26.5 one decimal place

Learning Check :

Learning Check In each calculation, round the answer to the correct number of significant figures. A. 235.05 + 19.6 + 2.1 = 1) 256.75 2) 256.8 3) 257 B. 58.925 - 18.2 = 1) 40.725 2) 40.73 3) 40.7

Multiplying and Dividing:

Multiplying and Dividing Round (or add zeros) to the calculated answer until you have the same number of significant figures as the measurement with the fewest significant figures.

Learning Check :

Learning Check A. 2.19 X 4.2 = 1) 9 2) 9.2 3) 9.198 B. 4.311 ÷ 0.07 = 1) 61.58 2) 62 3) 60 C. 2.54 X 0.0028 = 0.0105 X 0.060 1) 11.3 2) 11 3) 0.041

Reading a Meterstick:

Reading a Meterstick . l 2 . . . . I . . . . I 3 . . . .I . . . . I 4 . . cm First digit (known) = 2 2.?? cm Second digit (known) = 0.7 2.7? cm Third digit (estimated) between 0.05- 0.07 Length reported = 2.75 cm or 2.74 cm or 2.76 cm

Known + Estimated Digits:

Known + Estimated Digits In 2.76 cm… Known digits 2 and 7 are 100% certain The third digit 6 is estimated (uncertain) In the reported length, all three digits (2.76 cm) are significant including the estimated one

Learning Check:

Learning Check . l 8 . . . . I . . . . I 9 . . . .I . . . . I 10 . . cm What is the length of the line? 1) 9.6 cm 2) 9.62 cm 3) 9.63 cm How does your answer compare with your neighbor’s answer? Why or why not?

Zero as a Measured Number :

Zero as a Measured Number . l 3 . . . . I . . . . I 4 . . . . I . . . . I 5 . . cm What is the length of the line? First digit 5.?? cm Second digit 5.0? cm Last (estimated) digit is 5.00 cm

Slide 68:

Always estimate ONE place past the smallest mark!

MEASUREMENTS Scientific Notation:

MEASUREMENTS Scientific Notation Give the following in scientific notation (or write it out) with the appropriate significant figures. 1. 528900300000 = 2. 0.000000000003400 = 3. 0.23 = 4. 5.678 x 10 -7 = 5. 9.8 x 10 4 = 5.289003 x 10 11 3.400 x 10 -12 2.3 x 10 -1 0.0000005678 98000

MEASUREMENTS Scientific Notation:

MEASUREMENTS Scientific Notation Give the following in scientific notation (or write it out) with the appropriate significant figures. 1. 528900300000 = 2. 0.000000000003400 = 3. 0.23 = 4. 5.678 x 10 -7 = 5. 9.8 x 10 4 = 5.289003 x 10 11 3.400 x 10 -12 2.3 x 10 -1 0.0000005678 98000

PRACTICE PROBLEMS #1:

PRACTICE PROBLEMS #1 Show your work for the following questions on the back. Always give the correct significant figures. 1. Express each of the following numbers in scientific notation & 3 significant figures. A) 3445490087 _______ C) 0.008768 _______ B) 0.0000008243 _______ D) 23560 _______ 2. 0.003496 - 0.002998 = ________________ 3. (4.36-5.62) / (32.98 + 2.4) = ______________________ 4. 8.453 x 10 - 43 / 7.7 x 10 -33 = ________________ 5. [(56.7 x 10 -6 ) (32 x 10 11 )] 5 / (5.6 x 10 17 ) 1/2 = __________ 3.45 x 10 9 8.24 x 10 -7 8.77 x 10 -3 2.36 x 10 4 4.98 x 10 -4 - 3.56 x 10 -2 1.1 x 10 -10 2.6 x 10 32

Slide 72:

Show all work for the following questions on the back page. Always give the correct significant figures. 1. What is the scientific method? 2. Describe the difference between accuracy and precision. 3. Explain why tasting chemicals during an experiment is not a safe practice? 4. Express each of the following numbers in scientific notation. a) 0.0404 _______ b) 0.0081 _______ c) 40.0 _______ d) 2900000 _______ e) 0.0000055 _______ f) 40300 _______ 6. (452 x 6.2) / 14.30 = ______________________ 7. 98.78564 - 97.9299 = ________________ 8. 6.022 x 10 23 / 1.9 x 10 -19 = ________________ 9. ( 0.3 - 0.09) / (4.3 x 10 -3 + 7.232 x 10 -4 ) = ____________ 10. [(2.4 x 10 12 ) (5.78 x 10 -31 )] 3 / (2.965 x 10 14 ) 1/2 = __________