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

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

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

0

Change

-x

+x

+x

Final

0.10 – x

x

X

## 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.