Worksheet 6 key: Acids and Bases 1
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1. Write the equilibrium expression for the auto-ionization of water : H2O + H2O ⇌ H3O + OH
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K = [H3O ] [ OH ] This is commonly referred to as Kw.
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2. Unless there is another solute present, [H ] = [OH ] in pure water.
–14
–14
At 20 °C, Kw = 1.0 x 10
At 40 °C, Kw = 3.0 x 10
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What are the [H ] and [OH ] at each temperature?
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For 20 °C: Kw = 1.0 x 10
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= [H3O ] [ OH ] and thus [H3O ] = [ OH ] = 1.0 x 10 M
–14
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For 40 °C: Kw = 3.0 x 10 = [H3O ] [ OH ] and thus [H3O ] = [ OH ] = 1.73 x 10 M The solution is still
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neutral, as [H3O ] = [ OH ], but the pH = 6.76.
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3. Fill in the proper symbol ( =, <, >, ≤, ≥ ) for the relationship between OH− and H at any temperature:
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[H ] =
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[H ] >
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[OH ] >
In neutral solutions,
Acid solutions,
Basic solutions,
4. What is the pH of 0.0054 M HCl?
calculations)
5. What is the pH of 0.0054 M NaOH?
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[OH ]
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[OH ]
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[H ]
pH = –log(0.0054) = 2.27 (recommend using 2 decimal places for most pH
pOH = –log(0.0054) = 2.27 pH = 14 – pOH
pH = 11.73
6. A saturated solution of calcium hydroxide has a calcium-ion concentration of 0.0075 M. What is the pH of the
solution? Is it acidic or basic?
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0.0075 M Ca(OH)2 would have 0.015 M OH due to its formula pH = 14 – [–log(2*0.0075)] = 12.18, Basic.
New for 2013:
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7. Calculate the pH and [H ] values of a solution with an [OH ] of 0.0000170 M.
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pH = 9.23 and [H ] = 5.88 × 10
M.
8. Calculate the pH of a solution that results from mixing 100.0 mL of 0.0245 M NaOH with 200.0 mL of HCl that is
0.0130 M.
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There is a total of 0.00245 mol OH and 0.00260 mol H3O in 0.300 L. This results in 0.00015 mol of H3O (0.000500 M)
The pH = 3.30
9. Calculate the volume (in mL) of 0.125 M NaOH that is needed to titrate 30.00 mL of 0.200 M H2SO4 to the
equivalence point.
0.03000 L H2SO4 × 0.200 mol H2SO4/L × 2 mol NaOH/1 mol H2SO4 × 1 L/0.125 m NaOH = 0.0960 L NaOH