Ch 2 Notes Chemistry Data Analysis

Let’s Review what you should already know:

SI Units of Measure:

Quantity	SI Unit
Mass	Kilograms (kg)
Length	Meters (m)
Time	Seconds (s)
Temperature	Kelvin (K)
Amount of Matter	Moles (mol)

OK- maybe you don’t know about the mole. So, I’ll explain it here.

Prefixes and their meanings:

SI Unit Prefixes
Prefix	Symbol	Meaning	Base Unit Multiplied by	Factor
giga-	G	billion	1,000,000,000	10⁹
mega-	M	million	1,000,000	10⁶
kilo-	k	thousand	1,000	10³
hecto-	h	hundred	100	10²
deca-	da	ten	10	10¹
Base units, no prefix - Ex.- meter, liter, gram				10⁰
deci-	d	tenth	0.1	10^-1
centi-	c	hundredth	0.01	10^-2
milli-	m	thousandth	0.001	10^-3
micro-	u or μ	millionth	0.000001	10^-6
nano-	n	billionth	0.000000001	10^-9
pico-	p	trillionth	0.000000000001	10^-12

It is important to remember that unit symbols and prefix abbreviations are case sensitive, so uppercase and lowercase letters have different meanings — for example, mm is the millimeter (one-thousandth of a meter), but Mm is the megameter (one million meters); See examples of correct and incorrect usage here.

Temperature (p. 30 of your textbook)

We will always measure temperature in ºC; examples: room temperature is 22 ºC; body temperature is 37 ºC; Water boils at 100 ºC;

At times we will need to convert to Kelvin by adding 273

Example: Water boils at 100 ºC + 273=373K (notice that we do not use the degree symbol º when expressing temperature in K)

If you need to convert from K to ºC, just subtract 273.

Example: 295K – 273=22 ºC

Compare the two scales below:

Derived Units (p. 27-29 of your textbook)

Definition- A unit that is defined by a combination of base units is called a derived unit. (we get derived units by multiplying or dividing base units)

Examples:

· Speed meters per second (m/s) (we won’t need this one for chemistry)

· Volume centimeters cubed (cm³) (solid) or mL (liquid)

1cm³ = 1mL

· Density

Definition: Mass per unit volume (ratio of mass to volume)

Unit: solid g/cm³

Liquid g/mL

Here is a PPT on Density with Practice Problems

Lab: Find the density of a regularly shaped solid, an irregular solid, and a liquid.

· Create 3 flow maps that show how to find the density of these 3 substances.

Practice/Homework Problems

New Info:

· Measure with accuracy & precision

· Calculate Percent Error

Accuracy vs. Precision (p. 36)

Define accuracy-refers to how close a measured value is to an accepted value

Define precision-how close a series of measurements are to one another

Measuring Rule of thumb-when measuring with a scientific instrument, estimate 1 digit beyond the graduations of the instrument. Example: You measure an object with a metric ruler that is marked in increments of 1 mm, or .1 cm. The object measures between the 84 mm and 85 mm lines. You may express your measurement as 8.45 cm. If the object had measured exactly to the 84 mm line, then you should express your answer as 8.40 cm. See how we estimated the last digit? Zero if it is exactly on the line, 5 if it is between lines.

Be Careful! Always try to read instruments even with eye level to prevent parallax errors!

Percent Error (p. 37-38 text)

The formula for calculating percentage error(deviation) is

error

Percentage Error = accepted value X 100%

Percent Error Practice Worksheet

Practice/Homework Assignment

Ø Time for a QUIZ over units, prefixes, & density

More new stuff:

· Express quantities in scientific notation

· Manipulate chemical quantities using dimensional analysis

· Express calculations using correct number of significant figures

Scientific Notation (p.31-33 text)

Scientific Notation Notes

· Scientific notation is a short way to write very large or very small numbers.

· It is written as the product of a number between 1 and 10 and a power of 10.

TO CONVERT A NUMBER INTO SCIENTIFIC NOTATION:

· Create a number between 1 and 10 by moving the decimal.

· Count the number of spaces the decimal moved to determine the exponent of 10

EXAMPLE: 3,346,000,000. = 3.346 x 10⁹

power of ten

The decimal moved 9 places # between 1 & 10

Add zeros as needed for place holders.

TO CONVERT A NUMBER INTO STANDARD FORM:

Move the decimal to the right the number of spaces indicated by the exponent.

EXAMPLE: : 1.312 x 106 = 1,312,000

The decimal moved 6 places to the RIGHT. Add zeros as needed for place holders.

Scientific Notation Practice

Write each number in scientific notation.

1. 890,000,090 ____________________

2. 605,000 ____________________

3. 706,079 ____________________

Write in standard form.

4. 8.3 X 105 ____________________

5. 9.43 X 103 ____________________

6. 7.002 X 101 ____________________

7. What is 4,100,000 in scientific notation? ________________

8. What is 23,070,000 in scientific notation? _______________

Tutorial with Videos –How to write a number in scientific notation

You must know how to use your calculator to add/subtract/multiply/divide numbers in scientific notation. You must bring a calculator everyday.

How to use your calculator to add/subtract/multiply/divide numbers in scientific notation-Click on Math Skills

Practice/Homework Assignment

Significant Figures & Rounding (p.38-40 text)

Scientists indicate the precision of measurements by the number of digits that they report.

Significant figures include all known figures plus one estimated digit.

Let's summarize the rules for significant figures:

1) ALL non-zero numbers (1,2,3,4,5,6,7,8,9) are ALWAYS significant.

2) ALL zeros between non-zero numbers are ALWAYS significant.

3) ALL final zeros to the right of the decimal point are ALWAYS significant.

4) Zeroes that act as placeholders are not significant. Convert quantities to scientific notation to eliminate place holder zeros.

5) Counting numbers and defined constants have an infinite number of significant figures. For example: 60 s has 2 significant figures.

Ø A helpful way to check rules 3 and 4 is to write the number in scientific notation. If you can/must get rid of the zeroes, then they are NOT significant.

Check here for a table of examples

To find out how to use this information when performing mathematical operations (addition, subtraction, multiplication, division), see "Significant Figures: Mathematical Operations."

Here’s a great Interactive Quiz of measuring and using significant digits

Practice/Homework Assignment

Time for a Quiz over Scientific notation, significant figures, & % error

Dimensional Analysis (p. 34-35 text)

What? A method of converting one value to an equal value with a different unit.

HOW? Multiply the known value by a conversion factor.

· A conversion factor is a ratio of equivalent values used to express the same quantity in different units.

· A conversion factor is always equal to 1.

· Because a quantity does not change when multiplied or divided by 1, conversion factors change the units without changing the value.

Converting Units

4 Step plan for converting units

1. Identify (write down) the unknown, including units

2. list the connecting conversion factor(s) with units (make sure the unit that you want to eliminate is in the denominator)

3. multiply starting measurement by conversion factor(s) & cancel out any units that you can

4. check the result: does the answer make sense? (Do not leave your answer in fraction form, multiply/divide it out.)

The biggest problem students seem to have is converting derived units, such as this:

Example 3: kilometers/hour to meters per second

Practice/Homework Assignment

Get Ready for a Ch 2 TEST!