chem lab report and calculation
Lab 3: The Stoichiometry of a Chemical Reaction
2018
Overview
Introduction to:
Balanced chemical equations
Stoichiometry
Titrations, Neutralization
Parts:
3 titration trials
Calculation of equation coefficients
Oxalic Acid
Found in rhubarb leaves
Formula: (C2H2O4)
Weak acid with two acidic hydrogens
Titration
Involves a reaction between two reagents:
Analyte – substance being analyzed
Titrant – standard solution with known molarity
Two completely reacted at equivalence point
Determined by stoichiometry of balanced equation
Most common titration reaction: neutralization!
Neutralization Reaction
Double-replacement reaction between acid and base
H+ from acid and OH- from base react
Products: water and an ionic compound
Example: oxalic acid and sodium hydroxide
+ NaOH H2O +
Titration Set-Up
Titrant in buret
e.g. NaOH
Added incrementally to flask
Analyte in flask:
e.g. oxalic acid
Precise amount measured out
End signaled with color change
Indicator!
Buret Reminders
Always handle with care
Keep on ring stand
Keep waste container under tip
Keep stopcock closed when not in use
Horizontal = closed
Before use, clean with DI water
Then rinse with desired solution x2
Fill using funnel
Open!
Reading the Buret
Read from the top down
Bottom of the meniscus
Watch significant figures, uncertainty +/- 0.05 mL
Two decimal places!
Indicator
Substance that indicates pH by its color
Our indicator: phenolphthalein
Stop when solution is a very faint pink!
| pH Range | Color |
| <8.0 | Colorless |
| >8.0 | Pink to magenta |
Good
Not Good
Terrible
Calculations
The titrant:
Find volume of titrant dispensed (mL)
Convert to L
Use molarity to find moles
The analyte:
Use molar mass to find moles
Plug moles into the equation and balance:
__H2C2O4 + __NaOH __Na2C2O4 + __H2O