Calculate the formula weights of the following substances

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  1. Calculate the formula weights of the following substances: (a) BaCl2 · 2H2O, (b) KHC2O4 · H2C2O4, (c) Ag2Cr2O7, (d) Ca3(PO4)2.
  2. Calculate the number of millimoles contained in 500 mg of each of the following substances: (a) BaCrO4, (b) CHCl3, (c) KIO3 · HIO3, (d) MgNH4PO4, (e) Mg2P2O7, (f) FeSO4 · C2H4(NH3)2SO4 · 4H2O

The Correct Answer and Explanation is :

To address your queries, we’ll first calculate the formula weights (molar masses) of the specified substances and then determine the number of millimoles in 500 mg of each compound.

1. Formula Weights:

The formula weight (molar mass) of a compound is the sum of the atomic masses of all atoms present in its formula.

(a) BaCl₂·2H₂O (Barium chloride dihydrate):

  • Barium (Ba): 1 atom × 137.33 g/mol = 137.33 g/mol
  • Chlorine (Cl): 2 atoms × 35.45 g/mol = 70.90 g/mol
  • Water (H₂O): 2 molecules × (2 × 1.01 g/mol + 16.00 g/mol) = 36.04 g/mol

Total Molar Mass: 137.33 + 70.90 + 36.04 = 244.27 g/mol

(b) KHC₂O₄·H₂C₂O₄ (Potassium hydrogen oxalate and oxalic acid):

  • Potassium (K): 1 atom × 39.10 g/mol = 39.10 g/mol
  • Hydrogen (H): 3 atoms × 1.01 g/mol = 3.03 g/mol
  • Carbon (C): 4 atoms × 12.01 g/mol = 48.04 g/mol
  • Oxygen (O): 8 atoms × 16.00 g/mol = 128.00 g/mol

Total Molar Mass: 39.10 + 3.03 + 48.04 + 128.00 = 218.17 g/mol

(c) Ag₂Cr₂O₇ (Silver dichromate):

  • Silver (Ag): 2 atoms × 107.87 g/mol = 215.74 g/mol
  • Chromium (Cr): 2 atoms × 52.00 g/mol = 104.00 g/mol
  • Oxygen (O): 7 atoms × 16.00 g/mol = 112.00 g/mol

Total Molar Mass: 215.74 + 104.00 + 112.00 = 431.74 g/mol

(d) Ca₃(PO₄)₂ (Calcium phosphate):

  • Calcium (Ca): 3 atoms × 40.08 g/mol = 120.24 g/mol
  • Phosphorus (P): 2 atoms × 30.97 g/mol = 61.94 g/mol
  • Oxygen (O): 8 atoms × 16.00 g/mol = 128.00 g/mol

Total Molar Mass: 120.24 + 61.94 + 128.00 = 310.18 g/mol

2. Millimoles in 500 mg:

To find the number of millimoles in 500 mg (0.500 g) of each substance, use the formula:

Millimoles (mmol) = (mass in grams / molar mass in g/mol) × 1000

(a) BaCrO₄ (Barium chromate):

  • Molar Mass: 137.33 (Ba) + 51.996 (Cr) + 4 × 16.00 (O) = 253.326 g/mol
  • Millimoles: (0.500 g / 253.326 g/mol) × 1000 ≈ 1.97 mmol

(b) CHCl₃ (Chloroform):

  • Molar Mass: 12.01 (C) + 1.008 (H) + 3 × 35.45 (Cl) = 119.37 g/mol
  • Millimoles: (0.500 g / 119.37 g/mol) × 1000 ≈ 4.19 mmol

(c) KIO₃·HIO₃ (Potassium iodate and iodic acid):

  • Molar Mass: 39.10 (K) + 126.90 (I) + 3 × 16.00 (O) + 1.01 (H) + 126.90 (I) + 3 × 16.00 (O) = 389.01 g/mol
  • Millimoles: (0.500 g / 389.01 g/mol) × 1000 ≈ 1.29 mmol

(d) MgNH₄PO₄ (Magnesium ammonium phosphate):

  • Molar Mass: 24.31 (Mg) + 14.01 (N) + 4 × 1.01 (H) + 30.97 (P) + 4 × 16.00 (O) = 137.33 g/mol
  • Millimoles: (0.500 g / 137.33 g/mol) × 1000 ≈ 3.64 mmol

(e) Mg₂P₂O₇ (Magnesium pyrophosphate):

  • Molar Mass: 2 × 24.31 (Mg) + 2 × 30.97 (P) + 7 × 16.00 (O) = 222.55 g/mol
  • Millimoles: (0.500 g / 222.55 g/mol) × 1000 ≈ 2.25 mmol

(f) FeSO₄·C₂H₄(NH₃)₂SO₄·4H₂O (Iron(II) sulfate complex):

  • Molar Mass: 55.85 (Fe) + 2 × 32.07 (S) + 12 × 16.00 (O) + 2 × 12.01 (C)

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