Gravimetric Analysis Prelab

7/30/2019 Gravimetric Analysis Prelab

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Gravimetric Analysis Prel



General Lab Safety



General Lab Safety

You willnot

be allowed to perform the lab (and will therget a zero) if you do not adhere to the following guideli

Wear safety goggles

Wear closed-toe shoes

No bulky, baggy, or loose fitting clothes

Remove jewelry, including necklaces and rings No gum, food, or drinks

Tie back long hair and roll up sleeves



General Lab Safety

Once you are in the lab doing the experiment, please ato the following guidelines: Notify me of any chemical spills, accidents, and brok

glassware; do not attempt to do something on your unless I explicitly instruct you to do so

Do not use chipped or cracked glassware

To avoid contamination, do not return unused chema reagent bottle; if you have extra, set aside in a cleabeaker

Read and reread all of the directions for a laboratoryprocedure before attempting it

Wash your hands with soap and water at the end of



What is Gravimetric Analysis?

• A laboratory technique that allows for the determinatithe unknown mass of a substance

• Many ways of doing gravimetric analysis, the method

doing involves a precipitation reaction (i.e. a reaction

results in the formation of a solid, insoluble precipitate

• Once we have the mass of the precipitate, we can us

stoichiometry to work backwards and determine the m

the original substance



What Are We “Gravimetrically” Analyz

• All groups will be given a 15 mL sample of copper(II)chloride solution, i.e. CuCl2 (aq)

• The problem is that the concentration of the sample i

unknown to everyone (except me of course)

• The challenge is for your groups to determine:1) the concentration of the copper(II) chloride soluti

2) the amount of copper(II) ions in your 15 mL samp



General Strategy for Gravimetric Ana

• Step 1: Find a chemical that will react with CuCl2 (aq>>> Are there other considerations besides reactivity

• Step 2: Using a known concentration of that chemica

it with CuCl2 (aq) to form a precipitate

>>> What needs to happen next?

• Step 3: Separate the precipitate from solution

>>> What would be good techniques for separating t

mixture?



General Strategy for Gravimetric Ana

• Step 4: Dry then weigh the precipitate>>> Is drying even necessary?

• Step 5: Use stoichiometry to determine the mass of th

desired substance in the original, unknown sample

>>> How do we even use stoichiometry with solutions



Chemicals

• Everyone will get 15.0 mL of ??? M CuCl2 (aq

)• With your assigned lab group, decide which one of th

following chemicals you would like to use:

• Be prepared to explain why you chose that chemical

0.500 M NaC2H3O2 0.500 M KBr

0.500 M Na2CrO4 0.500 M KNO3

0.500 M Na2SO4 0.500 M KOH

0.500 M Na3PO4 0.500 M K2CO3



Exit Ticket

• Do #1-3 on the Prelab with your group right now (it w

checked before you leave today)

• Do #4 on the Prelab (setting up a data table) for hom

• NOTE: If you do not have a completed Prelab hando

formatted data table tomorrow, you will be docked po



ChemCatalyst 3/14/13

• Take out your completed Prelab handout and formatt

table from yesterday for a quick spot-check

• Write 2 –3 sentences explaining which chemical your

chose yesterday, and why your group chose it. Be pre

to share with the class.



Gravimetric Analysis Prel



Safety Information about Chemica

General rule of thumb:Call for help, and then wash affected area with lots of wa

• Na2CrO4:

Very hazardous to skin,eyes, and lungs

Carcinogenic and mutagenic

• Na3PO4:

Very hazardous to skin,eyes, and lungs

• KOH

Very hazardous to skeyes, and lungs

• K2CO3:

Irritates, skin, eyes, alungs



Steps 2 –4: Funnel and Filter Set-u



Steps 7 –8: How Much Chemical to U

• I did a trial run of all four chemicals, and tried to use t

minimum of each

>>> Why the bare minimum?

0.500 M Na2CrO4 15 –25 mL

0.500 M Na3PO4 10 –20 mL

0.500 M KOH 30-35 mL

0.500 M K2CO3 15 –25 mL



Step 9: Stir then Settle!

• Why would you want to stir the precipitate into the so

especially if you want it to settle in the first place?



Steps 10 –11: Rinse and Repeat

• Use distilled water (dH2

O) for rinsing your beaker and

• All rinses should be poured over your precipitate/filte

>>> Why?

• I did not do step 11 and got mixed results…it’s up to y

group if you want to do it (make sure you note whethenot your group chooses to do it)

>>> What’s the point of this step anyways?



Solution Stoichiometry

• We will be discussing this more in-depth when you st

working on the Postlab and formal lab report

• For now, think about what you ultimately end up with

doing this experiment:

1) balanced chemical equation describing your reacti

2) grams of your precipitate



Exit Ticket

• The experiment will go long if you’re unprepared, so

efficiency and accuracy!

• Get back into your assigned lab groups, and form an

plan” to help make your experiment go smoother

• Potential ideas to strategize about: – Which steps can be done independently?

– Which steps can be done simultaneously?

– Who should do which step, and when?

Gravimetric Analysis Prelab

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