SSCE HSC Chemistry Alcohols: 150 mL of a 0.20 mol L⁻¹ sodium

150 mL of a 0.20 mol L⁻¹ sodium hydroxide solution is added to 100 mL of a 0.10 mol L⁻¹ sulfuric acid solution - HSC - SSCE Chemistry - Question 29 - 2024 - Paper 1

Question 29

150 mL of a 0.20 mol L⁻¹ sodium hydroxide solution is added to 100 mL of a 0.10 mol L⁻¹ sulfuric acid solution. Calculate the pH of the resulting solution, assuming... show full transcript

Worked Solution & Example Answer:150 mL of a 0.20 mol L⁻¹ sodium hydroxide solution is added to 100 mL of a 0.10 mol L⁻¹ sulfuric acid solution - HSC - SSCE Chemistry - Question 29 - 2024 - Paper 1

Step 1

Calculate moles of NaOH

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Answer

Using the formula for moles, we have:

$n(NaOH) = V imes C = 0.150 ext{ L} imes 0.20 ext{ mol L}^{-1} = 0.030 ext{ mol}$

Step 2

Calculate moles of H₂SO₄

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Answer

For sulfuric acid:

$n(H₂SO₄) = V imes C = 0.100 ext{ L} imes 0.10 ext{ mol L}^{-1} = 0.010 ext{ mol}$

Step 3

Determine moles of NaOH required for reaction

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Answer

The balanced reaction is:

$H₂SO₄ + 2NaOH → Na₂SO₄ + 2H₂O$

From the equation, 1 mol of H₂SO₄ reacts with 2 mol of NaOH. Hence, for 0.010 mol of H₂SO₄, we need:

$n(NaOH) ext{ required} = 2 imes 0.010 ext{ mol} = 0.020 ext{ mol}$

Step 4

Calculate excess moles of NaOH

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Answer

The moles of NaOH in excess:

$n(NaOH) ext{ in excess} = n(NaOH) - n(NaOH) ext{ required} = 0.030 ext{ mol} - 0.020 ext{ mol} = 0.010 ext{ mol}$

Step 5

Calculate concentration of OH⁻ ions

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Answer

The total volume of the solution is 250 mL or 0.250 L. The concentration of NaOH after the reaction is:

$[NaOH] = rac{n(NaOH) ext{ in excess}}{V} = rac{0.010 ext{ mol}}{0.250 ext{ L}} = 0.040 ext{ mol L}^{-1}$

Step 6

Calculate pOH and pH

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Answer

Using the pOH formula:

ightarrow p(OH) ext{ is approximately } 1.40$$ Then, using the relation between pH and pOH: $$pH = 14.00 - p(OH) = 14.00 - 1.40 = 12.60$$

150 mL of a 0.20 mol L⁻¹ sodium hydroxide solution is added to 100 mL of a 0.10 mol L⁻¹ sulfuric acid solution - HSC - SSCE Chemistry - Question 29 - 2024 - Paper 1

Worked Solution & Example Answer:150 mL of a 0.20 mol L⁻¹ sodium hydroxide solution is added to 100 mL of a 0.10 mol L⁻¹ sulfuric acid solution - HSC - SSCE Chemistry - Question 29 - 2024 - Paper 1

Calculate moles of NaOH

Calculate moles of H₂SO₄

Determine moles of NaOH required for reaction

Calculate excess moles of NaOH

Calculate concentration of OH⁻ ions

Calculate pOH and pH

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