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IB Chemistry HL 1.4.3 Molar Mass M Questions

Use a formula to obtain molar mass, then apply n=m/M and Avogadro constant to convert between mass, amount and specified particles.

Syllabus
First assessment 2025
Course
Chemistry HL
Level
HL

Exam points

  • Calculate molar mass in g mol⁻¹ from a chemical formula, including hydrates and organic compounds.
  • Use n=m/M to convert between mass and amount in mol, then combine with stoichiometric coefficients in reaction calculations.
  • Convert amount or mass to specified particles using molar mass and Avogadro constant, checking units and significant figures.

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Study 1.4.3—Molar mass (M) conceptsOpen the corresponding Concept lesson for explanations, examples and exam connections.

IB Chemistry HL 1.4.3 Molar Mass M Questions question 1

[Maximum number: 1]

Phosphine (IUPAC name phosphane) is a hydride of phosphorus, with the formula PH3\mathrm{PH}_{3}.

2.478 g of white phosphorus was used to make phosphine according to the equation:

P4( s)+3OH−(aq)+3H2O(l)→PH3( g)+3H2PO2−(aq)\mathrm{P}_{4}(\mathrm{~s})+3 \mathrm{OH}^{-}(\mathrm{aq})+3 \mathrm{H}_{2} \mathrm{O}(\mathrm{l}) \rightarrow \mathrm{PH}_{3}(\mathrm{~g})+3 \mathrm{H}_{2} \mathrm{PO}_{2}^{-}(\mathrm{aq})

Calculate the amount, in mol, of white phosphorus used.

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