The concentration of phosphate ions in washing machine waste water can be determined using colourimetry. A sample of washing machine waste water was collected and diluted by quantitatively transferring 1.00 mL of the solution to a volumetric flask and making up the volume to 1.000 L with distilled water. Standard phosphate solutions were prepared and analysed with a colourimeter using an accepted method. The standard calibration graph is shown. The diluted sample solution was then analysed using the same method as the standard solutions. The absorbance of this solution was found to be 0.64. Determine the concentration of phosphate ions in the sample of washing machine waste water, in mol L⁻¹.

SSCE HSC Chemistry Alcohols: The concentration of phosphate i

The concentration of phosphate ions in washing machine waste water can be determined using colourimetry - HSC - SSCE Chemistry - Question 25 - 2024 - Paper 1

Question 25

The concentration of phosphate ions in washing machine waste water can be determined using colourimetry. A sample of washing machine waste water was collected and d... show full transcript

Worked Solution & Example Answer:The concentration of phosphate ions in washing machine waste water can be determined using colourimetry - HSC - SSCE Chemistry - Question 25 - 2024 - Paper 1

Step 1

Concentration of diluted sample

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Answer

The absorbance of the diluted sample is given as 0.64. From the calibration graph, we can identify the concentration that corresponds to this absorbance value. Upon analysis of the graph, we find that the concentration of the diluted sample is 0.78 mol L⁻¹.

Step 2

Concentration of phosphate ions in original sample in mg L⁻¹

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Answer

To find the concentration of phosphate ions in the original sample in mg L⁻¹, we use the dilution factor. Since the diluted solution is 1.00 mL made up to 1.000 L, the concentration in mg L⁻¹ can be calculated as:

$1000 ext{ mL} imes 0.78 ext{ mol L}^{-1} = 780 ext{ mg L}^{-1}$

Step 3

Molar mass of PO₄³⁻

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Answer

The molar mass of phosphate ions (PO₄³⁻) is calculated as:

$30.97 + 4 imes 16.00 = 94.97 ext{ g mol}^{-1}$

Step 4

Concentration of phosphate ions in mol L⁻¹

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Answer

Finally, we calculate the concentration of phosphate ions in mol L⁻¹:

$\text{Concentration in mol L}^{-1} = \frac{0.78}{94.97} = 0.0082 \text{ mol L}^{-1}$

The concentration of phosphate ions in washing machine waste water can be determined using colourimetry - HSC - SSCE Chemistry - Question 25 - 2024 - Paper 1

Worked Solution & Example Answer:The concentration of phosphate ions in washing machine waste water can be determined using colourimetry - HSC - SSCE Chemistry - Question 25 - 2024 - Paper 1

Concentration of diluted sample

Concentration of phosphate ions in original sample in mg L⁻¹

Molar mass of PO₄³⁻

Concentration of phosphate ions in mol L⁻¹

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