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Chemistry 104 Laboratory |
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This Week |
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á
Expt 4: Understanding and Predicting
Acid-Base Behavior |
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Next Week |
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Expt 5: Identification of an Unknown by pH Titration á
Quiz 3: Experiment 1 |
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Notes for
Today |
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What is pH? á
A combination
of p for the word power, H for hydrogen ion á
A measure of acidity o pH = -log10[H+] or -log10[H3O+] o Most aqueous solutions have pH values in the
range 0-14: How is pH
Measured? á
Use an
Indicator o H2O + HIn
<--> H3O+ + In- o color depends on pH á
HIn and In-
are different colors á
e.g., for bromthymol blue, HIn = yellow
and In- = blue á
when both
are present, transition color (green) occurs á
transition occurs
over a fairly wide range (~2 pH units) á
Use a pH Meter
o measures potential difference (voltage) between two
electrodes á
potential of sensing
electrode (glass electrode) depends on [H+] á
reference electrode
potential does not á
potential difference
(voltage) depends on [H+] of solution o measures to +/- 0.01 pH
unit o combination electrode (glass
+ reference in one unit) is common How Can a Salt
Affect pH? á Add
NaNO3 to water; pH = 7 á Add
CH3NH3NO3 to water; pH
<7 á How
to explain the difference? o Step
1: Identify ions in solution o Step
2: Identify ions that do/don't hydrolyze (react with water) o Step
3: Write a net ionic equation to explain why the pH in CH3NH3NO3
soln is <7 á reactants = ion + H2O
á 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 |
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