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Tschermigite is a hydrated, water-soluble mineral, with relative formula mass of 453.2 - AQA - A-Level Chemistry - Question 2 - 2022 - Paper 3
Question 2
Tschermigite is a hydrated, water-soluble mineral, with relative formula mass of 453.2. The formula of tschermigite can be represented as M·xH₂O, where M represents... show full transcript
Worked Solution & Example Answer:Tschermigite is a hydrated, water-soluble mineral, with relative formula mass of 453.2 - AQA - A-Level Chemistry - Question 2 - 2022 - Paper 3
Step 1
Calculate the empirical formula of tschermigite and the value of x in M·xH₂O.
Answer
To find the empirical formula, we first determine the number of moles of each element in one mole of tschermigite based on its mass percentages.
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Calculate Moles:
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Nitrogen (N):
n(N) = rac{3.09}{14.01} ext{ mol} \
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Hydrogen (H):
n(H) = rac{6.18}{1.01} ext{ mol} \
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Aluminum (Al):
n(Al) = rac{5.96}{26.98} ext{ mol} \
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Sulfur (S):
n(S) = rac{14.16}{32.07} ext{ mol} \
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Oxygen (O):
n(O) = rac{70.61}{16.00} ext{ mol} \
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Simplifying Moles:
- Divide all moles by the smallest number of moles obtained.
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Determining the Formula:
- The ratio of elements will give the empirical formula of the mineral.
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Finding x in M·xH₂O:
- Calculate moles of water based on the molecular weight of water (18.02 g/mol). Compare the hydrated compound's weight to find the value of x.
Step 2
Describe the tests, with their results, including ionic equations, that would confirm the identities of the ions present.
Answer
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Test for Ammonium Ion (NH₄⁺):
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Add a few drops of sodium hydroxide (NaOH) solution and gently heat the mixture.
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Observed Result:
- If ammonia gas (NH₃) is released (smelly gas), it confirms the presence of ammonium ions.
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Ionic Equation:
ext{NH}_4^+ + ext{OH}^- ightarrow ext{NH}_3(g) + ext{H}_2O
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Test for Aluminum Ion (Al³⁺):
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Add sodium hydroxide (NaOH) until it is in excess.
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Observed Result:
- A white precipitate of aluminum hydroxide (Al(OH)₃) forms, and it will dissolve in excess NaOH, indicating the presence of aluminum ions.
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Ionic Equation:
ext{Al}^{3+} + 3 ext{OH}^- ightarrow ext{Al(OH)}_3(s) \ ext{Al(OH)}_3 + ext{OH}^- ightarrow ext{[Al(OH)}_4]^-
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Test for Sulfate Ion (SO₄²⁻):
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Add barium chloride (BaCl₂) to the solution acidified with hydrochloric acid (HCl).
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Observed Result:
- A white precipitate of barium sulfate (BaSO₄) confirms the presence of sulfate ions.
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Ionic Equation:
ext{Ba}^{2+} + ext{SO}_4^{2−} ightarrow ext{BaSO}_4(s)
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