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 0.0031324? How many sig digits are in 12.40? How many sig digits are in 386.042? How many sig digits are in 3100.0 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

Branch Area of Emphasis Examples

Organic chemistry

most carbon-containing chemicals pharmaceuticals, 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

Biochemistry matter 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

Accuracy and Precision

Data Terms

Quantitative Measurements

Examples

Give results in a definite form, usually values

24L, 10 cm, 14 ºC

Data TermsQualitative

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. PrecisionTarget 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 errorTheoretical – Experimental x 100 = % error

Theoretical

SIGNIFICANT FIGURES

Significant Figures

Significant Figures

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

Significant FiguresPlace What is the increment on the

equipment?

What you know for sure.

Significant FiguresDigits with

meaningDigits that can be known

precisely plus a last digit that must be estimated.

Triple Beam Balance (DO NOT USE)

http://www.wisc-online.com/objects/index_tj.asp?objID=GCH202

DO NOT USE What are the units?

Ruler

http://www.funbrain.com/measure/

What are the units?

Graduated Cylinder

http://www.uwplatt.edu/chemep/chem/chemscape/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

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

1. 400.0

2. 4000

3. 4004

4. 0.004

Rally Rows How many significant figures are in1. 0.022. 0.0203. 5014. 501.05. 50006. 5000.7. 50508. 01.00509. 5030010. 5.0300

Review Questions

Determine the number of significant figures in the following: 1005000 1.005 0.000125 1000. 0.02002 2002 200.200

Review QuestionsDetermine the number of significant figures in: 72.3 g 60.5 g 6.20 g 0.0253 g 4320 g 0.00040230 g 4.05 x 10^5 g 4500. 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 km12 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 gClothes 1407 gRing 23.911 gGlasses 158.18 gTotal 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.

PracticeCalculate 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) =

3. 2.06 cm + 1.8 cm + 0.004 cm =

4. 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?

PracticeCalculate each of the following to the correct

number of significant figures. Include units on your answer.

1. (25 g/mol)(4.0 mol) =1.0 x 101.0 x 1022

2. (3.48 in)(1.28 in)(0.010 in) = .045 in.045 in33

3. 2.06 cm + 1.8 cm + 0.004 cm = 3.9 cm3.9 cm

4. 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/cm11.3 g/cm33

Rally rowsSig figs in Calculations

1. 12 cm + 0.031cm + 7.969 cm =

2. (41.025 g - 23.38g) ÷ 8.01 mL=

3. 17.3 cm x 6.2 cm + 3.28 cm2 =

4. 109.3758 m2 45.813 m =

5. 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?