Experiment 2

DensityCalibration of Pipet & grad. Cylinder

Thickness of Aluminum Foil

Reminders

ALL pages in the notebook must be numberedNEVER tear pages out of the notebookMake corrections by placing a single line through itemAnything with a line through it (including entire pages) is not looked at during grading

Goals To determine the average density of

water To determine average volumes

delivered by 10mL Volumetric Pipet and Graduated Cylinder (using previously determined DensityH2O value) and compare the associated errors

Use previously determined value (DensityH2O) to determine the thickness of aluminum foil

Using a Pipet What is a Pipet?

Long narrow open glass (or plastic) tube used to deliver liquids

Types Volumetric vs. Graduated TD vs TC

Use Clean first until water sheething occurs (no

beading) Use pipet bulb, never mouth Use forefinger, not thumb (because not as

controllable)

What is a Meniscus?

Water binds stronger to glass than it does to itself and forms a smile

Mercury binds to itself better and forms a frown

Bottom of meniscus indicates where liquid level is at

Take bottom of meniscus to fiduciary line of vol. pipet

Part One

Density of Water

Density Intensive Property vs. Extensive Prop

Intensive- Extensive-

D=mass/volume =

So what do you need to measure?

Why do we use corks?

Why use 25.00mL instead of 1mL or 5mL?

Reminder

The analytical balance is a very precise instrument. It will consistently give the same values if used the same way every time. But, accuracy of mass measurements is dependent on you using the balance appropriately (zeroing, closing doors, etc.).

Tables in the Notebook Put DESCRIPTIVE titles on all

tables Pair data and results for each trail

together It is easier to find and compare

data/results if all paired data is kept together in tables with descriptive titles

Density Data

Items Mass (g)

Container

Container + H2O

Calc. Mass H2O

Calc. DensityH2O

Class Avg DH2O

Water Density Determination by Mass

Part Two

Calibration of Pipet and Cylinder

Critical Measurements/Steps What are they?

How can you tell?

Calibration DataExperimental Values for Pipet

CalibrationItems Weighed Trial 1 Trial 2 Trial 3 Avg

Mass (g)container

Container+ H2O mass (g)

Calc massH2O (g)

Calc. Vol.Delivered (mL)* Similar Table for Grad Cylinder Calibration

Calculations D=mass/Volume = g/mL Volume = Mass/Density (Use class Avg

value) Calculate Avg Calculate Std. Dev.

What does this tell us?

Compare values for Pipet and Cylinder When would it be most appropriate to use each?

Part Three

Thickness of Aluminum Foil

How???? Area of irregularly shaped piece of foil

cannot be measured directly Use ideas of Density (DAl =

2.702g/mL) and Thickness*Area (A= l*w) = Volume D=mass/volume = mass/(A*thickness)

Thickness = mass/(A*D) So, how do you get area of irregularly shaped

object?

How Continued Measure WHOLE sheet of paper

and calculate area Awhole paper=Lwhole paper*Wwhole paper

Trace foil shape on paper

How Continued Weigh beaker (mbeaker)

Weigh beaker + foil shape (mbeaker+foil)

mfoil= mbeaker+foil – mbeaker

Weigh beaker+paper shape (mbeaker+paper

shape)

mpaper shape = mbeaker+ps- mbeaker

Add cut-off paper & weigh (mbeaker+whole paper)

mwhole paper = mbeaker+whole paper - mbeaker

The Comparisons mpaper shape= Dpaper*Vpaper shape

= Dpaper*Apaper shape*Tpaper

mwhole paper = Dpaper*Vwhole paper

= Dpaper*Awhole paper*Tpaper

mpaper shape Dpaper*Apaper shape*Tpaper

mwhole paper Dpaper*Awhole paper*Tpaper

Comparisons Continued Then, do algebra:

mpaper shape Apaper shape Apaper shape mpaper shape* Awholepaper

mwhole paper Awhole paper mwhole paper

We can now determine Afoil

Afoil = Apaper shape

Final Substitutions Tfoil = mfoil/(Afoil*Dfoil)

mfoil = mbeaker+foil – mbeaker

Dfoil = 2.702g/mL (given, handout) Afoil = Apaper shape

Hazards: Understanding MSDSs

What is it?

What does it tell us?

Where can they be found?

What is a Hazardous Material?

Corrosive Water sensitive/reactive MSDS warns of ecological effects Flammable Carcinogen – may cause cancer Mutagen – may cause mutations Teratogen – may cause reproductive effects or harm

fetus Toxic – may kill you or cause harm to a major organ Inhalation hazard/lachrymator - must use protective

equipment to protect Which ones do we have to collect?

How will the MSDS Tell Us? Will clearly state the hazard “May cause burns” = corrosive “May cause damage to “major organ”” =

toxic “Studies in mice have indicated

“hazard”” Regulated by Clean Water Act or Clean

Air Act = environmental hazard “Harmful by inhalation/ingestion”

Other Confusing Phrases Target Organs

Where the substance will go when it enters the body Does not mean that it harms that organ unless otherwise

noted Irritant

May irritate the skin (cause rash, etc.), eyes, nose, lungs if you are sensitive to the material

Chronic Not a hazard – means repeated exposure

NFPA Ratings You will not need to know, at this level, what each number

represents Follow this rule: if it is a value 3, definitely include it as a

primary hazard