Chapter 2 NotesQualitative/Quantitative

Precision/AccuracySig Figs

Error/Percent Error

What do you know?1. What is a hypothesis?2. What is the difference between

an control and a variable?3. What is the difference between

an independent and dependent variable?

ExperimentsSystem: Matter that you’ve chosen

to observe and the region of space selected for study.

Surroundings: the area around the system.

DemoDraw a picture of what happened!

Write a couple of sentences regarding what we will discuss.

What is the System? Surroundings?

Measurements-

Why do you think measurements might be important to the study of chemistry?

What kind of measurements are you familiar with?

Day 1 of Measurement Activity

Splash of Color-

Accuracy and Precision Activity-

Group WorkEverybody is on task and working at all

times. Everyone is responsible for handing in a completed assignment!

Jobs:1. Leader- Reads all the instructions (out loud) and keeps everyone on task2. Scientist 1- Reviews instructions and does the task.3. Recorder- Keeps careful record of all observations to share with other group members.

Debrief the Activities:1. What is the difference between

quantitative and qualitative observation?

2. Which is most helpful to scientists?

3. What is the problem with using qualitative measures?

Debrief4. Was it a chemical or physical change?

Types of MeasurementsQualitative-

descriptionsno numbersdetermined using sensesvary depending on observer

Quantitativemore definiteuse numbers (with units)only as good as the instrument used

Quantitative MeasureQuantity- a measure of magnitude, size or

amount.

Units- “Le Systeme International d’Unites.

Adopted in 1960- agreed on world-wide

7 base units

SI Base UnitsQuantity Symb

olName abbreviati

on

Length l Meter m

Mass m kilogram kg

Time t Second s

Temperature

T Kelvin K

Amount of substance

n Mole mol

Non-Si Units Used in Chemistry

Physical Quantity

Unit Name Symbol

Volume Liter L

Pressure AtmosphereMillimeters of mercuryTorr

Atm

mmHgTorr

Energy CalorieJoule

CalJ

Derived SI UnitsYou already know two of these from

Math!

AreaWhat formula would

you use to determine the area of this rectangle?

What would the units be?

VolumeWhat formula would

you use to determine the volume of this box?

What would the units be?

Using a Graduated Cylinder

Another way of determining volume is using this fabulous tool.

1ml = 1cm3

Always keep track of your Derived SI Units in any

calculation! Quantity Unit Abbreviatio

nDerivation

Area Meter squared

m2 L x W

Volume Meter cubed m3 L x W x H

Density Kilograms per cubic meter

Kg/ m3 Mass/volume

Molar Mass Kilograms/mol

Kg/mol Mass/amt of substance

DensityWhat formula do we

use to calculate density.

What do we need to measure?

DensityDensity = Mass/Volume

Density is a useful way of determining the identity of a substance!

Is it a chemical or physical property?

Try a practice problem!!

A sample of aluminum metal has a mass of 8.4g. The volume of the sample is 3.1 cm3. Calculate the density.

What is the difference between accuracy and precision?

The Accuracy/Precision Activity looks at

How “Good” is the measurement?

Accuracy- how close are we to the real value?

Precision- how reproducible are the results?

Were your measurements in the activity accurate, precise or

both.

Why was it important to use the same measuring tools for each

trial?

How could you have gotten better results?

Accurate or Precise??

Let’s look at some data!Accurate? Precise?

Shadows’ weight (experimental)

62.7 lbs62.0 lbs62.5 lbs

Her weight according to the vet (accepted)

67.4 lbs

Miles to school (experimental)

3.9 miles3.8 miles3.9 miles

Mapquest (accepted)3.98

In Our Dream Life—All our measurements would be BOTH

Accurate and Precise!

Scientists strive for correct measurements that are reproducible.

With No Error!

Experimental Measurements are seldom

perfectWe often compare experimental

values to known, widely accepted values and calculate the error.

You learned about this during the measurement activity!!

ErrorExperimental value is measured in the

lab

Accepted value is based on reliable references

Error = lAccepted - Experimentall

What formula did you use to calculate percent error?

Percent error is an indication of how well the lab went… if you have a low percent error, it means that there were few lab errors.

Calculate the percent error!

Shadows’ weight (experimental)

62.7 lbs62.0 lbs62.5 lbs

Her weight according to the vet (accepted)

67.4 lbs

Miles to school (experimental)

3.9 miles3.8 miles3.9 miles

Mapquest (accepted)3.98

Percent Error

What are some lab mistakes you could have made that would effect your accuracy and precision?

Gen Chem- Homework… percent error WS.

Warm Up: How did you do on %Error WS?

Front Side1.4.62%2.24.3%3.12%4.0.9%5.0.3%

Back Side1. 5.6%2. 2.6%3. 1.8%4.10.%5.0.519 mL6.5.6%

Warm Up- Friday1. What is the density of a substance with a

length of 3.5 cm a width of 2.1cm and a height of 4.5 cm and a mass of 261 g. What is the substance?

Known Densities Zinc 7.14 g/cm3

Iron 7.89 g/cm3

Copper 8.92 g/cm3

Gold 19.39 g/cm3

2. The density of aluminum is 2.7g/cm3. What mass of aluminum takes up 1.2 cm3 of space?

Warm Up Answers1. Iron

2. 3.24 g

Work on the density WS… we will fix your answers for SF on Monday

Measurement Activity- 3 and 4

Same groups as previous class.

Change jobs!1. Leader- Reads all the instructions (out loud) and keeps everyone on task2. Scientist 1- Reviews instructions and does the task.3. Recorder- Keeps careful record of all observations to share with other group members.

You have 25 minutes to complete these two tasks!

Warm Up- Monday/Tuesday

How would you determine the volume of an irregular shaped object?

General Chem

Collect the “Why I need to study Chemistry” assignment.

Debrief Activities

1. So, what is a significant figure?2. Why is it important that we use

them?3. How hard was it to “estimate” the

last digit on the ruler? How about the beaker?

Sig Figs

Significant figures include all the known digits plus a last digit that is

estimated.

Significant FiguresDepends on the instrument being used-

The better the instrument (read more expensive)

the more significant figures.

Which was a better measuring tool?The beaker, the cylinder or the volumetric flask?

Rules for Zeros:

1. All non zero digits 2. Zero’s in between digits3. Zero’s in front are not sig4. Zero’s in back are not sig unless it is a known measured value (there is a decimal point).5. Unlimited sig figs

When something is countedExactly defined quantities (constants)

Every calculation in this class, you need to look at the Sig Figs.

When you multiply or divide: count the SF and round your answer to

the lowest number of SF.

The rule is a little different when you add and

subtract…

Do the addition or subtraction…

Look at the numbers and round to the measurement with the least number of decimal places.

RoundingIf the number after the last sig fig is

5 or greater– round up.

If the number after the last sig fig is less than 5– keep it the same!

Look at the Sig Fig WS.

Do a few of these… yes, you can use your calculator!

Get the answer… and round your answer to the correct number of SF.

How did you do on %Error WS?

Front Side1.4.62%2.24.3%3.12%4.0.9%5.0.3%

Back Side1. 5.6%2. 2.6%3. 1.8%4.10.%5.0.519 mL6.5.6%

What about the SF???

How did you do on the Density WS?

Check your significant

How do I do conversions Using Dimensional

Analysis