The procedure of a first-hand investigation conducted in a school laboratory to determine the percentage of sulfate in a lawn fertiliser is shown. 2.00 g of a sample of fertiliser was ground up and placed in a beaker. It was dissolved in about 200 mL of 0.1 mol L⁻¹ hydrochloric acid, stirred and filtered. Excess barium chloride solution was quickly added to this beaker and a precipitate formed. The precipitate was then allowed to settle, filtered using filter paper and the residue collected. The residue was dried and weighed and had a mass of 2.23 g. (a) Suggest modifications that could be made to the procedure to improve the results of this investigation. Justify your suggestions. (b) Calculate the percentage of sulfate in the original fertiliser sample.

SSCE HSC Chemistry Qualitative Equilibrium: The procedure of a first-hand in

The procedure of a first-hand investigation conducted in a school laboratory to determine the percentage of sulfate in a lawn fertiliser is shown - HSC - SSCE Chemistry - Question 29 - 2015 - Paper 1

Question 29

The procedure of a first-hand investigation conducted in a school laboratory to determine the percentage of sulfate in a lawn fertiliser is shown. 2.00 g of a sampl... show full transcript

Worked Solution & Example Answer:The procedure of a first-hand investigation conducted in a school laboratory to determine the percentage of sulfate in a lawn fertiliser is shown - HSC - SSCE Chemistry - Question 29 - 2015 - Paper 1

Step 1

Suggest modifications that could be made to the procedure to improve the results of this investigation. Justify your suggestions.

96%

114 rated

Answer

Heating the Mixture: After adding barium chloride, the mixture could be heated for some time. This would allow the fine barium sulfate particles to collide and form larger aggregates, which are more easily filtered.
Using a Sintered Glass Filter: Instead of regular filter paper, using a sintered glass filter can prevent fine particles from passing through, ensuring a more complete collection of the precipitate.
Taking Multiple Samples: To achieve more reliable results, multiple samples of the fertiliser could be tested and averaged. This would account for any discrepancies in concentration across the sample.

These modifications would help ensure that the precipitate is maximally collected and that the measurement of sulfate concentration is accurate.

Step 2

Calculate the percentage of sulfate in the original fertiliser sample.

99%

104 rated

Answer

To calculate the percentage of sulfate in the fertiliser, we first note the reaction for the formation of barium sulfate:

$\text{Ba}^{2+}(aq) + \text{SO}_4^{2-}(aq) \rightarrow \text{BaSO}_4(s)$

From the problem, the mass of precipitate (barium sulfate) collected is 2.23 g. Now, we calculate the moles of barium sulfate:

Molar mass of ( \text{BaSO}_4 ): 233.37 g/mol.

Calculating moles:

$\text{moles of BaSO}_4 = \frac{2.23 \text{ g}}{233.37 \text{ g/mol}} = 0.00954\text{ mol}$

Now let's find the mass of sulfate:

Molar mass of ( \text{SO}_4^{2-} ): 96.07 g/mol.

Calculating mass of sulfate:

$\text{mass of SO}_4^{2-} = 0.00954 \text{ mol} \times 96.07 \text{ g/mol} = 0.9175 \text{ g}$

Finally, we can calculate the percentage of sulfate in the original fertiliser sample:

$\text{Percentage of SO}_4^{2-} = \frac{0.9175 \text{ g}}{2.00 \text{ g}} \times 100 = 45.88\%$

The procedure of a first-hand investigation conducted in a school laboratory to determine the percentage of sulfate in a lawn fertiliser is shown - HSC - SSCE Chemistry - Question 29 - 2015 - Paper 1

Worked Solution & Example Answer:The procedure of a first-hand investigation conducted in a school laboratory to determine the percentage of sulfate in a lawn fertiliser is shown - HSC - SSCE Chemistry - Question 29 - 2015 - Paper 1

Suggest modifications that could be made to the procedure to improve the results of this investigation. Justify your suggestions.

Calculate the percentage of sulfate in the original fertiliser sample.

Join the SSCE students using SimpleStudy...