The flowchart shown outlines the process used to determine the amount of sulfate present in a sample of lawn fertiliser. Step 1 Fertiliser weighed Dissolved + filtered + rinsed Filtrate Residue discarded Step 2 Addition of Ba$^{2+}$ Precipitation Step 3 Filtered Filtrate discarded Step 4 Rinsed Dried and weighed (a) What assumptions were made and how do these affect the validity of this process? (b) It was found that 4.25 g had a sulfate content of 35%. What is the mass of the dried precipitate at Step 4? Include a chemical equation in your answer.

SSCE HSC Chemistry Using Quantitative Analysis: The flowchart shown outlines the

The flowchart shown outlines the process used to determine the amount of sulfate present in a sample of lawn fertiliser - HSC - SSCE Chemistry - Question 29 - 2010 - Paper 1

Question 29

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The flowchart shown outlines the process used to determine the amount of sulfate present in a sample of lawn fertiliser. Step 1 Fertiliser weighed Dissolved + filte... show full transcript

Worked Solution & Example Answer:The flowchart shown outlines the process used to determine the amount of sulfate present in a sample of lawn fertiliser - HSC - SSCE Chemistry - Question 29 - 2010 - Paper 1

Step 1

What assumptions were made and how do these affect the validity of this process?

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Answer

Several assumptions were made during this process:

Complete Dissolution: It is assumed that the fertilizer dissolves entirely in the solvent. If any of the sulfate remains undissolved, it will lead to an underestimation of the sulfate content.
No Loss of Sulfate: The process assumes no loss of sulfate occurs during filtration and rinsing. Any loss would similarly lead to inaccurate results.
Complete Precipitation: The addition of Ba $^{2+}$ should ensure that all sulfate ions present precipitate out as BaSO $_4$ . Incomplete precipitation can result in lower measurements of sulfate.

These assumptions are crucial for the validity of the process; any deviations can lead to errors in quantifying the sulfate content.

Step 2

What is the mass of the dried precipitate at Step 4? Include a chemical equation in your answer.

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Answer

To find the mass of the dried precipitate at Step 4, we first determine the amount of sulfate in the original sample. Given that the sample weighs 4.25 g and contains 35% sulfate:

$ext{Mass of sulfate} = 4.25 ext{ g} imes 0.35 = 1.4875 ext{ g}$

When Ba $^{2+}$ is added, it reacts with sulfate ions to form barium sulfate (BaSO $_4$ ) according to the following chemical equation:

ightarrow ext{BaSO}_4 $$ From this reaction, we see that the mass of the resultant precipitate (BaSO$_4$) is equivalent to the amount of sulfate calculated. Therefore, the mass of the dried precipitate is approximately 1.49 g.

The flowchart shown outlines the process used to determine the amount of sulfate present in a sample of lawn fertiliser - HSC - SSCE Chemistry - Question 29 - 2010 - Paper 1

Worked Solution & Example Answer:The flowchart shown outlines the process used to determine the amount of sulfate present in a sample of lawn fertiliser - HSC - SSCE Chemistry - Question 29 - 2010 - Paper 1

What assumptions were made and how do these affect the validity of this process?

What is the mass of the dried precipitate at Step 4? Include a chemical equation in your answer.

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