SSCE VCE Chemistry Measuring Solubility and Concentration: A solution of sodium hydroxide (

A solution of sodium hydroxide (NaOH) has a pH of 10 - VCE - SSCE Chemistry - Question 12 - 2005 - Paper 1

Question 12

A solution of sodium hydroxide (NaOH) has a pH of 10. 10 mL of this solution is mixed with 990 mL of water. The pH of the diluted solution is closest to A. 8 B. 9 C.... show full transcript

Worked Solution & Example Answer:A solution of sodium hydroxide (NaOH) has a pH of 10 - VCE - SSCE Chemistry - Question 12 - 2005 - Paper 1

Step 1

Calculate the initial concentration of NaOH

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Answer

The pH of the NaOH solution is 10. This means that the concentration of hydroxide ions [OH⁻] can be calculated using the formula:

$[OH⁻] = 10^{-pOH}$

where pOH = 14 - pH = 14 - 10 = 4. Therefore:

$[OH⁻] = 10^{-4} ext{ M}$

Since NaOH fully dissociates, the concentration of NaOH is also $10^{-4}$ M.

Step 2

Calculate the number of moles of NaOH in 10 mL

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Answer

The volume of the NaOH solution is 10 mL, which is 0.01 L. The number of moles of NaOH is:

$ext{moles NaOH} = [NaOH] \times \text{volume} = 10^{-4} \text{ M} \times 0.01 ext{ L} = 10^{-6} ext{ moles}$

Step 3

Determine the total volume after dilution

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Answer

The total volume after mixing 10 mL of NaOH with 990 mL of water is:

$\text{Total Volume} = 10 ext{ mL} + 990 ext{ mL} = 1000 ext{ mL} = 1 ext{ L}$

Step 4

Calculate the new concentration of NaOH after dilution

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Answer

After dilution, the concentration of NaOH in the total volume is:

$[NaOH] = \frac{\text{moles of NaOH}}{\text{total volume}} = \frac{10^{-6} \text{ moles}}{1 \text{ L}} = 10^{-6} ext{ M}$

Step 5

Calculate the pOH and then pH of the diluted solution

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Answer

To find the pOH of the diluted solution:

$pOH = -\log[OH⁻] = -\log(10^{-6}) = 6$

Now, to find the pH:

$pH = 14 - pOH = 14 - 6 = 8$

Step 6

Final answer

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Answer

The pH of the diluted solution is closest to 8. Therefore, the correct answer is:

A. 8

A solution of sodium hydroxide (NaOH) has a pH of 10 - VCE - SSCE Chemistry - Question 12 - 2005 - Paper 1

Worked Solution & Example Answer:A solution of sodium hydroxide (NaOH) has a pH of 10 - VCE - SSCE Chemistry - Question 12 - 2005 - Paper 1

Calculate the initial concentration of NaOH

Calculate the number of moles of NaOH in 10 mL

Determine the total volume after dilution

Calculate the new concentration of NaOH after dilution

Calculate the pOH and then pH of the diluted solution

Final answer

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