Chemistry 161Intro Lab

Monique Wilhelm

NEVER MISS LAB!!!!! One hour lecture Remaining time in lab 1credit class = at least 3 hours spent outside of

class on class preparation Classroom Environment

Lecture-open discussion style I EXPECT you to talk, too Help answer questions, etc. Do not be turned off if I answer a question with another question; my

job is to show you how to problem-solve

What will we learn?

Methods and equipment used in chem labs How to make decisions about experimentation What types of things are important to be aware of

during experimentation How to draw conclusions about data obtained How to communicate your findings

Safety Overview Remember: Everything in Chemistry Lab has the

potential to be harmful Goggles Gloves Absolutely No Eating or Drinking in Any Lab 5 Senses Attire

Long Hair Tied Back Always wear long pants Never wear loose fitting long sleeved shirts NO sandals, closed shoes

Safety Continued Remember: Everything in Chemistry Lab has the

potential to be harmful Labels Contact Excess Chemicals Material Safety Data Sheets (MSDSs)

Explain the hazards associated w/ substances ALL chemicals have the POTENTIAL to be

harmful

Your Grade

Expectations Follow Directions Be Prepared Only one late

assignment allowed NO make ups

Types of Grading Notebooks

-Observations & Data hand-written Lab Reports- TYPED Computer assignments Quizzes – 2 types Final Project Possible Extra Credit

Today’s ExperimentHow to Use a Balance

&

Comparison of Data to Standards

Difference Between Balance & Scale

Scale Measures weight

Balance Measures mass

Relationship?

Weight = mass*gravity

Difference Between Precision & Accuracy

Precision Multiple readings

giving same measurement

Accuracy How close to real

number

A balance is a relatively precise instrument

In this lab, you are interested in accuracy

How to Get Good Accuracy

Top Loading Balances Used to weigh grossly

Analytical Balances Can weigh very small quantities

Weighing by Difference Expected Error = Relative Uncertainty

(error associated with instrument/measurement)*100%

Two Types of Balances

Top Loading Balance Measures Grossly Picture From

http://www.hitechtrader.com/imagepage.cfm?pic=45246.jpg

Analytical Balance Measures Accurately Picture From

http://www.chem.vt.edu/RVGS/ACT/lab/Analytical_Balance.html

Comparison of Data

Compare your average values to class averages

Which one do you EXPECT to be closer to actual value and why?

Compare to U.S Mint values

Be sure to cite reference for values

Coin Demo

I will demonstrate the use of balances in lab

Significant Figures

Always record data as accurately as you can (as many sig. figs. as method allows)

The last digit of the value that you record should be estimated

Do not round values until calculations are completed

Examples Follow

Sig Figs Examples

Addition and Subtraction Use least # of decimal places 15.287+13.07= 28.36

Multiplying and Dividing Use least # of sig. figs. 0.0387*1.0= 0.039

(100.8+0.524)*10.05 = 4 sig figs 100.8+0.524 = 101.3 101.3*10.05 = 1018

Relative & Absolute %Error Precision Determination

How far are values off from each other Standard Deviation OR Relative % Error = (largest – smallest)*100%/average

Accuracy Determination How far off from real value? Absolute %Error = (|experimental value – real value|)*100%/real value

Standard Deviation Error Analysis-how far the values differ from the averages (related to

%relative error, precision) Normal Distribution Assumed

AverageNormal S= ((xi-x)2)/(N-1) Give values as Average ± Std Dev

Using Excel for Data Analysis in CHM 161

What is Excel?

Computer program by Microsoft Spreadsheet program used to present data and

produce graphs Can also be used to perform calculations

using function “programming” Available on all campus computers

Why use Excel?

Makes for better presentation of results Cleaner, more accurate graphing

Ability to calculate more accurate values from graphs

Lesson 1 Making Tables

X values (independent variables) to the left of Y values (dependent variables)

Use top row to indicate which values you will have in which columns

Be sure to add units to labels Click on cell (rectangle) and type (word or

value)

Lesson 2: Performing Calculations

Click on cell that you would like to have the value for the calculation placed

Type “=“ to let program know that you want it to perform calculation

Select “Insert” on toolbar Scroll down to “Function” and click

Lesson 2: Performing Calculations cont’d

Click on categories to find function desired For this class, most common will be SUM and

AVERAGE Double click on function to select Click on red-white-blue box to select values that you

want program to use for calculation Use cursor to highlight boxes with desired values Click red-white-blue box to accept values Click OK to complete

Lesson 3: Making Graphs

Input data as previously described Use cursor to highlight values to be plotted Select “Insert” on toolbar Scroll down to “Chart” and click Click on type desired (best for this class is “XY

Scatter”) Click on picture to right to choose desired style (Use

points without lines) Click “Next”

Lesson 3: Making Graphs Cont’d

Look to be sure that data is lined up on the right axes If not, Select “rows” or use “series” tab to rearrange data Click “Next” Fill in Title (Descriptive enough to tell what info can be

obtained from graph, not x vs. y, etc.) Example: “Standard Curve for the Determination of

Cobalt Concentration”

Lesson 3: Making Graphs Cont’d Click on tabs to change/remove legend/gridlines,

etc. Click “Next” Select “As New Sheet” and click “Finish” Right click on desired area if changes are

necessary Click on grey area and then the bucket and select

“No Fill” to remove grey and save printer ink

Lesson 4: Best Fit Lines

Used for all standard curve graphs made in this class Make graph as previously described Click on data point Select “Chart” on toolbar Scroll down to “Add Trendline” and click Select box of desired curve (ie “linear”)

Lesson 4: Best Fit Lines cont’d Click on “Options” tab Click “Display Equation on Chart”, “Display R-squared

value”, etc. to turn these options on R-squared tells how well your data fits the line

generated Can be used as indicator of accuracy for data

Click on “OK” Click on Equation, etc. displayed on chart and drag to

desired (visible) location

Adding to Notebook

After you have completed your editing, select “File” on toolbar

Scroll down to “Save” and click and save as you would any other file

Select “File” on toolbar Scroll down to “Page Setup” and click Click on “Chart” tab Select “Custom”

Adding to Notebook cont’d.

Click on “Options” Scroll down to “2” in “Pages per Sheet”

Will print 2 graphs per sheet of paper to fit in notebook

Click “OK” until back to graph Select “File” on toolbar Scroll down to “Print” and click Follow usual printing procedures

Adding to Papers

Click on outer edges to select whole graph Select “Edit” on toolbar Scroll down to “Copy” and click Open program that you desire to use to write paper (ie

MS Word) Click area of report where you wish to insert graph Select “Edit” on toolbar Scroll down to “Paste” and click Click corner and drag to scale to appropriate size