CHEM 1040 Lecture Notes - Lecture 21: Chief Operating Officer, Ammonia, Rice Chart

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CHEM 1040 Lecture 21 pH Calculations
Strong Acid/ String Bases
Total dissociation will occur.
EX.1: Calculate the pH of a 0.10mol/L HCl solution.
pH = -log[H+]
pH = -log[0.10]
pH = 1.00
EX.2: Calculate the pH when 0.80 grams of NaOH are placed in 200mL of water
Step 1: Find the moles of NaOH
0.80g / 40.0gmol-1 = 0.02 mol
Step 2: Find the concentration of NaOH
0.02mol / 0.200L = 0.10molL-1
Step 3: Calculate the pOH
pOH = -log[OH-]
pOH = 1.00
Step 4: Calculate the pH
pH = 14 pOH
pH = 13
EX.3: Calculate the pH of a 0.10molL-1 Ba(OH)2 solution.
Step 1: Find the concentration of OH-
0.10mol/L * 2 = 0.20mol/L
Step 2: Calculate the pOH
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pOH = -log(0.20)
pOH = 0.70
Step 3: Calculate the pH
pH = 14 0.70
pH = 13.30
Weak Acids / Weak Bases
Whenever you place a weak acid or base in water, there are 3 things that are related.
1. KA or KB
2. Initial concentration (Cx)
3. Final pH ([x])
This relationship is shown as;
K = [x][x] / (Cx [x])
NOTE:
If K is smaller than 10-3, we can assume that the x in the denominator is negligible and can be
dropped.
EX.1: Calculate the pH of a 0.10molL-1 CH3COOH solution. KCH3COOH = 1.8E -5
Step 1: Write out the equation.
CH3COOH + H2O ↔ CH3COO- + H3O+
Step 2: Make an ICE table.
CH3COOH
CH3COO-
+
H3O+
Initial
0.10
0
Change
-x
+x
Final
0.10 x
x
X
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Document Summary

Chem 1040 lecture 21 ph calculations. Strong acid/ string bases: total dissociation will occur. Ex. 1: calculate the ph of a 0. 10mol/l hcl solution. ph = -log[h+] ph = -log[0. 10] ph = 1. 00. Ex. 2: calculate the ph when 0. 80 grams of naoh are placed in 200ml of water. Step 3: calculate the poh poh = -log[oh-] poh = 1. 00. Step 4: calculate the ph ph = 14 poh ph = 13. Ex. 3: calculate the ph of a 0. 10moll-1 ba(oh)2 solution. Step 2: calculate the poh poh = -log(0. 20) poh = 0. 70. Step 3: calculate the ph ph = 14 0. 70 ph = 13. 30. Whenever you place a weak acid or base in water, there are 3 things that are related: ka or kb, initial concentration (cx, final ph ([x]) If k is smaller than 10-3, we can assume that the x in the denominator is negligible and can be dropped. Ex. 1: calculate the ph of a 0. 10moll-1 ch3cooh solution.

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