Chemistry 161 Intro 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 Experiment How 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 m?pic=45246.jpg  Analytical Balance  Measures Accurately  Picture From nalytical_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  =  Multiplying and Dividing  Use least # of sig. figs.  *1.0=  ( )*10.05 = 4 sig figs  =  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  Average  Normal  S=  (  (x i -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