CHEMISTRY July 31, 2012

Brain Teaser (write the question & answer) Convert 100m to cm. Convert 158 kL to L. Convert 85 mg to kg. How many sig digits are in ? How many sig digits are in 12.40? How many sig digits are in ? How many sig digits are in x 10^2?

Introduction to Chemistry Chemistry: The Central Science Chemistry is the science that investigates and explains the structure and properties of matter. Seeks to explain the submicroscopic events that lead to macroscopic observations

Branches of Chemistry BranchArea of Emphasis Examples Organic chemistry most carbon-containing chemicalspharmaceuticals, plastics Inorganic chemistry in general, matter that does not contain carbon minerals, metals and nonmetals, semi- conductors Physical chemistry the behavior and changes of matter and the related energy changes reaction rates, reaction mechanisms Analytical chemistry components and composition of substances food nutrients, quality control Biochemistrymatter and processes of living organisms metabolism, fermentation

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. Units of measurement

Base Units

Why do we use the (SI) system? Advantages Simple to use Easy to convert from one unit to another Dimensional Analysis Universal – used worldwide By all scientists to communicate By all industrialized nations  Except United States  U.S. loses billions of dollars in trade

Practice Convert 10mL to KL Convert 5.3g to cg

Agenda Brain Teaser Notes: Significant Figures Calculations Accuracy and Precision Homework Accuracy and Precision Worksheet Remember: Lab questions due next Wed/Thurs (8/10-8/11) QUIZ!!! M 8/8

Accuracy and Precision

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

An archery target illustrates the difference between accuracy and precision.

Accuracy and Precision Measurements

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

Percent error Theoretical – Experimental x 100 = % error Theoretical

Repeat of Accuracy and Precision

Accuracy Versus Precision What is the difference between accuracy and precision?

Precision versus Accuracy Precision: is a measure of how closely an individual measurements agree with one another Can be precise but inaccurate Accuracy: refers to how closely individual measurements agree with the correct, or “true” value Examples using the dartboard

SIGNIFICANT FIGURES

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

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

Significant Figures Digits with meaning Digits that can be known precisely plus a last digit that must be estimated.

Triple Beam Balance (DO NOT USE) online.com/objects/index_tj.asp?objID=GCH online.com/objects/index_tj.asp?objID=GCH2 02 DO NOT USE What are the units?

Ruler What are the units?

Graduated Cylinder ape/labdocs/catofp/measurea/volume/gradcyl /gradcyl.htm ape/labdocs/catofp/measurea/volume/gradcyl /gradcyl.htm What are the units?

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

Significant Figures Raw Data Rules How do you know how many sig figs? 1. All digits 1-9 are significant. 2. Zeros between significant digits are always significant. 3. Trailing 0’s are significant only if the number contains a decimal point 4. Zeros in the beginning of a number with a decimal point are not significant. 5. 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 = 6 sig digits = 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 = 5 sig digits 1000 = 1 sig digits

Practice How many significant figures are in

Rally Rows How many significant figures are in

Review Questions Determine the number of significant figures in the following:

Review Questions Determine the number of significant figures in: 72.3 g 60.5 g 6.20 g g 4320 g g 4.05 x 10^5 g g

Quick Review 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 Hundreths Depends on the size

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 4.8m 3

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 g Clothes 1407 g Ring g Glasses g Total 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 g 2.5 g

Significant Figures in Calculations RememberA 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. 1. (25 g/mol)(4.0 mol) = 2. (3.48 in)(1.28 in)(0.010 in) = cm cm cm = 4. If the mass of a lead cube is 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. 1.0 x (25 g/mol)(4.0 mol) =1.0 x in 3 2. (3.48 in)(1.28 in)(0.010 in) =.045 in cm cm cm cm = 3.9 cm 11.3 g/cm 3 4. If the mass of a lead cube is g and it measures 2.51cm x 2.49 cm x 2.49 cm, what is the density of lead? 11.3 g/cm 3

Rally rows Sig figs in Calculations cm cm cm = 2. ( g g) ÷ 8.01 mL= cm x 6.2 cm cm 2 = m 2  m = 5. What is the mass of Salt (NaCl) if the sodium has a mass of g and the Cl a mass of 35.5g?