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Plants require trace metal nutrients, such as zinc, for healthy growth - Scottish Highers Chemistry - Question 10 - 2015
Question 10
Plants require trace metal nutrients, such as zinc, for healthy growth. Zinc ions are absorbed from soil through the plant roots. The zinc ion concentration in a so... show full transcript
Worked Solution & Example Answer:Plants require trace metal nutrients, such as zinc, for healthy growth - Scottish Highers Chemistry - Question 10 - 2015
Step 1
(i) Explain fully why the flask was left for 24 hours, without a stopper.
Answer
The flask was left for 24 hours to allow sufficient time for the zinc to fully react with sulfuric acid. During this reaction, hydrogen gas is produced as a byproduct. Without a stopper, the hydrogen gas escapes from the flask, preventing pressure buildup and ensuring the reaction can proceed smoothly.
Step 2
(ii) Explain why the student should use deionised water or distilled water, rather than tap water, when preparing the stock solution.
Answer
The student should use deionised or distilled water instead of tap water because tap water may contain zinc ions, impurities, or other metal ions that could interfere with the accuracy of the zinc ion concentration in the solution.
Step 3
Step 4
(ii) Calculate the concentration, in mg l⁻¹, of the solution prepared by transferring 10 cm³ of the 1 g l⁻¹ stock solution to a 1000 cm³ standard flask and making up to the mark.
Answer
To calculate the concentration of zinc ions in the diluted solution, use the formula:
Where:
- = initial concentration = 1 g l⁻¹ = 1000 mg l⁻¹
- = volume of stock solution transferred = 10 cm³ = 0.01 l
- = final concentration (unknown)
- = final volume after dilution = 1000 cm³ = 1 l
Plugging in the values:
Calculating:
C_2 = rac{10 ext{ mg}}{1 ext{ l}} = 10 ext{ mg l}^{-1}
Step 5
(c) Determine the concentration, in mg l⁻¹, of zinc ions in the solution.
Answer
To determine the concentration based on an absorbance of 0.3, refer to the calibration curve of absorbance vs. concentration (as plotted). By applying the best-fit line or using interpolation based on the given data, the concentration of zinc ions corresponding to an absorbance of 0.3 falls within the range of 4.6 to 4.8 mg l⁻¹.