Quiz 1

Announcements

I am hoping to find out when our recitation time and day is. I believe it will be 4-5PM on Mondays. Not sure what room. Stay tuned watch blog.

Do not fall behind. You should be reading Chapter 1 (and almost be at the end) and doing the assigned problems (see blog).

Be ready to be called on in class.

Please ask questions.

More Chemistry Lingo: Measured Quantities, Numbers and Units

1. Introduce the basic SI units of measurements for mass, volume, temperature, density, area.

2. Convert units using the factor-label method

3. Understand significant figures in performing calculations.

Science uses short-hand for writing very small and very large numbers. It’s called scientific notation.

0.000000000000000000000001673 g1.673 X 10-24 g

Mass H Atom: LonghandScientific notation

29900000000 cm/sec 2.99 X 1010 cm/sec

Speed of Light: LonghandScientific notation

The mechanics for writing scientific notation are easy (hopefully this is review).

1. Shift the decimal point to the left or right to obtain N between 1 and 9.999999. Count the number of shifts to obtain the exponent, n.

2. There are only two cases to consider--numbers > 0 and numbers < 0.

Coefficient(0< N <10)

exponentor power

multiplication sign

N ! 10n

base (10)

Case 1: Numbers > 0Fixed Notation 1246535.7679

6 shifts

1.2465357679 X 106Note exponent positive for n>1

1. To convert to scientific notation we move and count the number of decimal point places until we get a coefficient number between 1 and 9.999999.

2. Count the number of shifts--it’s the value of the exponent.

1246535.7679

Case 2: Numbers < 0

Fixed Notation 0.0000345609

3.45609 X 10-5Note exponent negative for n<1

1. Move the decimal point to the right until we get a coefficient number between 1 and 9.999999.

2. Count the number of shifts--it’s the value of the exponent.

0.0000345609

5 shifts

Try ItFixed Notation Scientific Notation

6098456.323 6.098456323 X 106

0.000345 3.45 X 10-4

607800000 6.078 X 108

4,034,086,784 4.034086784 X 109

0.00002123 2.123 X 10-5

0.00100543 1.00543 X 10-3

0.000345 3.45 X 10-4

More Tools For The Toolbox: What We Measure and what we call it

Density is an intensive physical property of a substance describing the ratio of mass to its volume occupied. SI Unit of Density: kg/L, g/mL or g/cm3

Density =Mass (kg)Volume (L)

Specific Gravity is the density of a substance divided by the density of liquid water 25˚C (Density of Water @ 25˚C =1.000 g/cm3).

Specific Gravity =Density X

Density H2O

Specific gravity tells you the density of a substance at 25˚C!

It is a unitless quantity!

The substances listed at the right are water clear liquids. You have been asked to identify an unknown liquid that is known to be one of the liquids. You transfer 3.50 mL sample of the unknown into a beaker. The empty beaker had a mass of 12.20 g, and the beaker containing the sample weighed 14.96 g.

Liquid Specific Gravity

Glycerol 1.2613

EthyleneGlycol 1.1088

Ethanol 0.7893

Acetic acid 1.0492

Water 0.9997

Sample Problem

Sample Problem 2 A graduated cylinder is filled to the 15.0

ml mark with H2O. It is weighed on balance and gives a mass reading of 27.35 g. An object made of Ag is placed in the cylinder and it is completely submerged. As a result, the water level rises to read 18.3 ml. When

Density =mass g

volume ml

The volume change due to the displacement of water (Archimedes Principle)in the graduated cylinder is just the di!erence in the readings of the graduatedcylinder before and after adding the Ag to the cylinder with water. 18.3 ml -15.0 ml = 3.3 ml.

The mass is also found by the di!erence before and after adding the pieceof silver. Mass = 62.00 g - 27.35 g = 34.65 g

Thus;

Density =34.65 g

3.3 ml= 10.5g/ml = 10g/ml

The metric system, its prefixes, the symbols and the values you have to have at your fingertips!

Derived quantities originate from the 7-basic SI units.

We need to have a good grasp of what these mean

There are five common non-SI Units that will become familiar as we use them.

Quantity Unit Symbol

Volume Liter L

Temperature Celsius ˚C

Pressure Atmosphere Atm

Concentration Molarity M (mol/L)

Length Angstrom A˚

A Liter is a defined as the volume occupied by a 10 cm X 10 cm X 10 cm cube.

1 cm3 = 1 cc = 1 mL

1000 cm3 = 1000 mL = 1 L

Table of Derived UnitsSquare Area = length x width = s x s = s2

Circle

Area = 1/2 x base x height

Area = π x r2

Triangle

Rectangle Area = length x width

Table of Derived Units

Scientists use a tool called Dimensional analysis to convert numbers and units in an organized fashion.

Example: The speed of light in a vacuum is 2.99 X 1010 cm per second. What is this speed in km/hr?

Example: The speed of light in a vacuum is 2.99 X 1010 cm per second. What is this speed in km/hr?

km

hr= 2.99! 1010 !!cm

!!sec! 1""m

102 !!cm! 1 km

103 !!m! 60!!sec

1 ###min! 60!!sec

1 hr

cm

sec! cm

min! cm

hr! m

hr! km

hr

1 m = 100 cm

Let’s divide both sides by 1 m

1 m

1 m=

100 cm

1 m

1 =100 cm

1 m

1 m = 100 cm

Let’s divide both sides by 100 cm

1 m

100 cm=

100 cm

100 cm

1 m

100 cm= 1

Two “conversion factors” can be obtained from any one equality. Pick the one that solves the problem.

Some useful equalities to remember

365 days = 1 year

1000 mg = 1 gram

1000 ms = 1 s

12 in = 1 ft

109 nm = 1 m

1 mile = 5280 ft

1000 m = 1 km

1000 mL = 1 L

453.6 grams = lb1 day = 24 hrs

2.205 lb = 1 kg

1000 cm3 = 1 L

10-12 sec = 1 ps

106 um = 1 m

106 µs = 1 s 1 oz = 28.35 g

100 cm = 1 m

3.78 L = 1 gallon

60 min = 1 hrs60 sec = 1 min

Metric Units

12 in = 1 ft

3 ft = 1 yd

5280 ft = 1 mile

Length Conversions

Metric Units

2,200 lb = 1 metric ton

16 oz = 1 lb

Mass Conversions

Metric Units

4qt = 1 gal

3.78 L = 1 gal 2 pts = 1 qt

16oz = 1 pt

Volume Conversions

Kelvin Celsius Fahrenheit

We have to memorize how convert between temperatures.

We have to memorize how convert between temperatures.

!C =59(!F ! 32) !F =

!!C

95

"+ 32

Kelvin = !C + 273.15

Kelvin is the SI unit for temperature. To convert from ˚C to Kelvin memorize:

Memorize or know how to get between Celcius and Fahrenheit.

PracticeCarry out the following conversions:

1) 10.35 nm to inches

2) 3.44 X 102 m3 to ft3

3) 105˚F to ˚C

4) 1 ton (2000 lbs) to metric ton (1000 kg)

5) How many seconds in 365 days?

Example with volumeThe small block Chevrolet 350 cubic inch race engine is arguably the most famous race engine in US auto racing history. How many liters is the small-block Chevy workhorse?

Example with volumeThe small block Chevrolet 350 cubic inch race engine is arguably the most famous race engine in US auto racing history. How many liters is the small-block Chevy workhorse?

Liters = 350 in3 !!

2.54 cm

1 in

"3

! 1 L

103 cm3= 5.7L

Secretariat’s speed is given but we need to unify units of time. We can convert 1 min 59.4 sec to 119.4 sec (keep the digits until end).

The record for the Kentucky Derby is held by the 1973 Triple Crown winner Secretariat, who ran the 10 furlongs in 1 minute, 59.4 seconds. 1 furlong is 1/8 of a mile in English Units. Calculate this remarkable horse’s average speed in km per hour.

Secretariat’s speed is given but we need to unify units of time. We can convert 1 min 59.4 sec to 119.4 sec (keep the digits until end).

km/hr =10 furlongs

119.4 sec!

!0.125 mi

1 furlong

"!

!1.609 km

1 mile

"!

!60 s

1 min

"!

!60 min

1 hr

"! = 60.64 = 60 km/hr

The record for the Kentucky Derby is held by the 1973 Triple Crown winner Secretariat, who ran the 10 furlongs in 1 minute, 59.4 seconds. 1 furlong is 1/8 of a mile in English Units. Calculate this remarkable horse’s average speed in km per hour.

All measurements, and all instruments used to make measurements, have inherent limitations called uncertainty or error that we account for in reporting data.

Where does the error come from?

Systematic errors - errors that normally affect accuracy in one direction (high or low). Examples: include poor calibration of instruments, human error in reading measurement, incorrect standard.

Random errors- inherent error that can not be anticipated. Lead to values both above and below the true value. More measurements needed to average out. Leads to a decrease in precision.

Scientists use two terms to quantify the uncertainty and validity of a measurement (actually more terms come later). They are:

• Accuracy- how well a measurement or data point agrees to a standard or a true value (validity).

• Precision- how well a large number of repeated independent measurements agree with each another, i.e. reproducibility.

accurate&

precise

precisebut

not accurate

not accurate&

not precise

Suppose the true value of a measurement is the “bulls eye”

Systematic Error Random Error

precise and accurate

precise but not accurate

Precision and accuracy in the laboratory.

25.0 is “true value”

systematic error

random error

Random vs Systematic Error

Example

Which person’s count is the most accurate? Breiana

Which team’s count is the most accurate? Team A

Which team’s count is the most precise? Team A

Team A Team B Miranda: 577 people Spencer: 577 people Brinley: 579 people Taylor: 585 people Breiana: 581 people Brand: 593 people

581 is counted by the electronic gate counter.