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Chemistry 104 Laboratory |
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This Week |
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á Expt 3:
Understanding and Predicting Acid-Base Behavior á Do Part A of Expt 2 (if time permits) á
Check In á
Get check in sheet
now, key in lab á
Wait to do check in
until after you finish Expt 3 |
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Next Week |
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á
Expt
2: A Cycle of Copper Reactions |
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Notes for Today |
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What is pH? á
A combination of
á p for the word power á H for hydrogen
ion á
A measure of acidity á
pH
= -log10[H+] or -log10[H3O+]
á
Most
aqueous solutions have pH values in the range 0-14: How is pH Measured? á
Use a pH Meter
á
measures
potential difference (voltage) between two electrodes o
potential
of sensing electrode (glass electrode) depends on [H+] o
reference
electrode potential is independent of [H+] o
potential
difference
(voltage) depends on [H+] of solution á
can
measure to +/- 0.01 pH unit á
combination
electrode (glass + reference in one unit) is common á
Use an Indicator á
H2O
+ HIn <--> H3O+ + In- á
color
depends on pH o
HIn
and In- are different colors á
e.g.,
for bromthymol blue, á
HIn
= yellow and In- = blue á
when
both HIn and In- are present, transition color (green) occurs á
transition
occurs over a fairly wide range (~2 pH units) How Can a Salt Affect pH? á
Add
NaNO3 to water; pH = 7 á
Add
CH3NH3NO3 to water; pH
<7 á
Why
not the same? o
identify ions in solution o
identify ions that do/don't hydrolyze (react with water) o
write a net ionic equation to explain why the pH in CH3NH3NO3
solution is <7 ¤
reactants
= ion, H2O ¤
products
= H3O+, ??? Practical Details á
Work with a partner á
Safety o
Goggles required
throughout á
Time Management o
Limited number of
pH meters, so you may need to complete lab out of order Expt 3 Report á
Purpose,
Procedure, Data section due
today at end of lab á
See Writing Your
Report for remaining
requirements á
Due in two days, 9 p.m., TA folder outside 184 Need help? See/email KDL or see a TA |
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