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Which amount of sodium hydroxide would react exactly with 7.5 g of a diprotic acid, H₂A (Mₐ = 150)? A 50 cm³ of 0.05 mol dm⁻³ NaOH(aq) B 100 cm³ of 0.50 mol dm⁻³ NaOH(aq) C 100 cm³ of 1.0 mol dm⁻³ NaOH(aq) D 100 cm³ of 2.0 mol dm⁻³ NaOH(aq) - AQA - A-Level Chemistry - Question 6 - 2019 - Paper 3

Question 6

Which-amount-of-sodium-hydroxide-would-react-exactly-with-7.5-g-of-a-diprotic-acid,-H₂A-(Mₐ-=-150)?--A-50-cm³-of-0.05-mol-dm⁻³-NaOH(aq)-B-100-cm³-of-0.50-mol-dm⁻³-NaOH(aq)-C-100-cm³-of-1.0-mol-dm⁻³-NaOH(aq)-D-100-cm³-of-2.0-mol-dm⁻³-NaOH(aq)-AQA-A-Level Chemistry-Question 6-2019-Paper 3.png

Which amount of sodium hydroxide would react exactly with 7.5 g of a diprotic acid, H₂A (Mₐ = 150)? A 50 cm³ of 0.05 mol dm⁻³ NaOH(aq) B 100 cm³ of 0.50 mol dm⁻³ Na... show full transcript

Worked Solution & Example Answer:Which amount of sodium hydroxide would react exactly with 7.5 g of a diprotic acid, H₂A (Mₐ = 150)? A 50 cm³ of 0.05 mol dm⁻³ NaOH(aq) B 100 cm³ of 0.50 mol dm⁻³ NaOH(aq) C 100 cm³ of 1.0 mol dm⁻³ NaOH(aq) D 100 cm³ of 2.0 mol dm⁻³ NaOH(aq) - AQA - A-Level Chemistry - Question 6 - 2019 - Paper 3

Step 1

Calculate the amount of substance of the acid

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Answer

To find the amount of substance (in moles) of the diprotic acid, we use the formula:

$n = \frac{m}{M}$

where:

$m$ = mass of the acid = 7.5 g
$M$ = molar mass of the acid = 150 g/mol.

Calculating:

$n = \frac{7.5 \, \text{g}}{150 \, \text{g/mol}} = 0.05 \, \text{mol}$

Step 2

Determine moles of NaOH needed

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Answer

Since the acid is diprotic, it can donate 2 moles of H⁺ ions for every mole of acid. Thus, for 0.05 moles of the acid, the required moles of NaOH will be:

$n_{NaOH} = 2 \times n_{H₂A} = 2 \times 0.05 \, \text{mol} = 0.1 \, \text{mol}$

Step 3

Calculate the volume of NaOH solution required

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Answer

We need to find out which option provides exactly 0.1 moles of NaOH. Using the concentration formula:

$C = \frac{n}{V}$

rewriting for volume gives:

$V = \frac{n}{C}$

For:

Option C: 0.1 mol in 1.0 mol/dm³:

$V = \frac{0.1 \, \text{mol}}{1.0 \, \text{mol/dm}^3} = 0.1 \, \text{dm}^3 = 100 \, \text{cm}^3$

This shows that 100 cm³ of 1.0 mol dm⁻³ NaOH(aq) is the correct answer.

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Calculate the amount of substance of the acid

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Calculate the volume of NaOH solution required

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