HONORS CHEMISTRY August 3-4, 2011

Brain Teaser Quizlet Open Note Quizlet Place Notes (Ch 2.6-2.8) on your desk

Brain Teaser What do you think will happen if I light the bubbles on fire? Why? Demo Record Observations Was your prediction correct? Explain the science behind it

Agenda Brain Teaser Quizlet Measurement Terms Numbers Notes: Homework SI Units Intro to Significant Figures Measurement and Significant Figures Mini Lab Scientific Notation Homework Significant Figures Worksheet Qualitative and Qunatitative Worksheet Blubbenbacher’s Foods Lab Report  Due This Friday

Data Terms Quantitative Measurements Examples Give results in a definite form, usually values 24L, 10 cm, 14 ºC

Data Terms Qualitative Measurements Examples Give results in a descriptive, non-numeric form. The beaker was warm. The density was greater than that of water.

Data Terms Accuracy Examples How close a measurement comes to the actual value of whatever is being measured Water freezes at 0º C, and boils at 100º C. How close is the measurement to the values.

Data Terms Precision Examples Reproducibility of the measurement 9 out of 10 lab groups report the temperature of boiling water to be 95º C. A basketball player shoots 20 free throws, 18 of which bounce off the right side of the rim.

Accuracy vs. Precision Target Practice Accurate Precise Accurate & Precise

Percent error Theoretical – Experimental x 100 = % error Theoretical

Closure Give and example of a qualitative and quantitative measurement.

SI Units (Le Systéme Internationale) Units of measurement SI Units (Le Systéme Internationale) Scientists need to report data that can be reproduced by other scientists. They need standard units of measurement. Base Units A base unit is a defined unit in a system of measurement There are seven base units in SI. Refer to the handout on SI Units Le 12

Base Units Official definitions of the seven base units http://www.unc.edu/~rowlett/units/sifundam.html 13

Metric staircase 14

Significant Figures Significant Figures Digits in a measurement that have meaning relative to the equipment being used

Significant Figures Place What is the increment on the equipment? What you know for sure.

Significant Figures Digits with meaning Examples Digits that can be known precisely plus a last digit that must be estimated. Refer to Examples on the board: 1. 2. 3. 4

Scale Reading and Uncertainty Uncertainty: Limit of precision of the reading (based on ability to guess the final digit). Existed in measured quantities versus counted quantities Refer to Example (2 rulers) Addition and substraction(no. of sig. figs) Division and Multiplication (no. of sig. figs) 19

Significant Figures: Mini Lab Equipment to Evaluate To what place (tenths, hundredths, etc.) can these measurement instruments accurately measure? What place is the estimation? Triple beam balance Analytical balance Thermometer Graduated cylinders Beakers Ruler Burette

Significant Figures What do you notice? Depends on type of equipment being used. Depends on size of equipment used.

Significant Figures Raw Data Rules All digits 1-9 are significant. How do you know how many sig figs? All digits 1-9 are significant. Zeros between significant digits are always significant. Trailing 0’s are significant only if the number contains a decimal point Zeros in the beginning of a number with a decimal point are not significant. Zeros following a significant number with a decimal are significant.

Significant Figures Pacific to Atlantic Rule Examples Pacific = Decimal Present Start from the Pacific (left hand side), every digit beginning with the first 1-9 integer is significant 20.0 = 3 sig digits 0.00320400 = 6 sig digits 1000. = 4 sig digits

Significant Figures Atlantic Rule to Pacific Examples Atlantic = Decimal Absent Start from the Atlantic (right hand side), every digit beginning with the first 1-9 integer is significant 100020 = 5 sig digits 1000 = 1 sig digits

Practice How many significant figures are in 400.0 4000 4004 0.004

Rally Rows How many significant figures are in 0.02 0.020 501 501.0 5000 5000. 5050 01.0050 50300 5.0300

Summary Things to consider What do significant figures tell you about the measurement equipment? If you wanted to measure the mass of a whale, what scale would you want to use? Would it matter if you know its mass accurately to 1 gram? If you wanted to measure the mass a grain of sand , what scale would you want to use? Would it matter if you know its mass accurately to 1 gram?

Instrument Measure Need to make sure you are measuring and recording to the correct number of digits Measure what you know for sure and then guess one more digit Rulers Draw a line on your paper and measure it to the correct number of digits Beaker vs. graduated cylinder Electronic balance vs. triple beam balance

Scientific Notation

Scientific Notation Scientific Notation Example Shorthand way of expressing numbers that make them easier to work with 6.02 x 1023 2.34 x 105 3.78 x 10-3

Scientific Notation Any Patterns?

Scientific Notation Rules Base number 1-9 Exponent = the number of times the decimal must be moved to bring the base number to 1-9. Numbers greater than 1 have a positive exponent, numbers less than 1 a negative exponent

Scientific Notation Examples 0.0025 1,750,000 2.5 x 10-3 1.75 x 106

Scientific Notation Problems 0.0000678 Express in Scientific Notation 998953000000 0.5768

Scientific Notation Problems 1.567 x 10-3 Express in Standard Notation

Sig Figs in Scientific Notation The numbers expressed in the scientific notation are significant Examples: 5.02 x 104  5.02 x 104  3 S.F The number of significant figures in a set of numbers will be the # of sig figs in the scientific notation. 50.200  5 SF  5.0200 x 101

Survivor Science Convert the following to exponential notation or to ordinary notation Tell me how many Sig Figs. 76 896745 8.9 x 103 3.45 x 10-1 0.222

6. 5.38 x 10-3 5 million 8.00 x 104 0.00859 953.6

Significant Figures in Calculations What are Significant Digits? Examples Triple Beam Balance Graduated Cylinder All the certain digits plus the estimated digit in a measurement. How many decimal places can we count

Significant Figures in Calculations Exact Numbers Examples Infinite # of sig figs Do not affect the number of significant digits in the final answer. They are not measurements!! 1000m = 1 km 12 in = 1 foot

Significant Figures in Calculations Multiplication and Division Example The number with the smallest number of significant digits determines how many significant digits are allowed in the final answer. Volume of a box L x W x H (3.05m)(2.10m)(0.75m) 2 sig figs 4.8m3

Significant Figures in Calculations Example Density of a penny M = 2.53g V = 0.3mL D = M / V # significant figures allowed D = 8g/mL

Significant Figures in Calculations Addition and Subtraction Example The number of significant digits depends on the number with the largest uncertainty. (you may be using different scales) Shoes 951.0 g Clothes 1407 g Ring 23.911 g Glasses 158.18 g Total 2540. g

Significant Figures in Calculations Example What is the mass of a penny if, the weighing paper alone has a mass 0.67 g and weighing paper plus the penny has a mass of 3.2 g. 3.2 g -0.67 g 2.5 g

Significant Figures in Calculations Remember A calculated number can only be as precise as the least precise measurement in the calculation.

Practice Calculate each of the following to the correct number of significant figures. Include units on your answer. (25 g/mol)(4.0 mol) = (3.48 in)(1.28 in)(0.010 in) = 2.06 cm + 1.8 cm + 0.004 cm = If the mass of a lead cube is 176.91 g and it measures 2.51cm x 2.49 cm x 2.49 cm, what is the density of lead?

Practice Calculate each of the following to the correct number of significant figures. Include units on your answer. (25 g/mol)(4.0 mol) =1.0 x 102 (3.48 in)(1.28 in)(0.010 in) = .045 in3 2.06 cm + 1.8 cm + 0.004 cm = 3.9 cm If the mass of a lead cube is 176.91 g and it measures 2.51cm x 2.49 cm x 2.49 cm, what is the density of lead? 11.3 g/cm3

Rally rows Sig figs in Calculations 12 cm + 0.031cm + 7.969 cm = (41.025 g - 23.38g) ÷ 8.01 mL= 17.3 cm x 6.2 cm + 3.28 cm2 = 109.3758 m2  45.813 m = What is the mass of Salt (NaCl) if the sodium has a mass of 22.99 g and the Cl a mass of 35.5g?

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