Chemical Analysis and Stoichiometry Problem Set

 

  1. The routine quality control analysis for an amino acid feedstock in a large chemical production plant returns the following combustion analysis. For each of these samples determine if the amino acid is tyrosine (C9H11NO3), alanine (C3H7NO2) or Valine (C5H11NO2) by calculating the emperical formula using the data provided.
    Combustion Analysis Report
    Mass of sample (mg) 46.87
    Mass of CO2 (mg) 102.42
    Mass of H2O (mg) 25.62
    % N by mass 7.731
    1. From the mass of CO2 find the moles of C.
      1. 102.72 mg
      2. 44.0095 g/mol
      3. 2.334 mmol CO2
      4. 2.334 mmol C
    2. From the mass of H2O find the moles of H
      1. 25.62 mg
      2. 18.0153 g/mol
      3. 1.422 mmol H2O
      4. 2.844 mmol H
    3. From the % N by mass, find the moles of N
      1. 7.731% N
      2. 46.87 mg sample
      3. 3.624 mg N
      4. 14.00674 g/mol
      5. 0.2587 mmol N
    4. Find O from remaining mass of sample
      Element mmole masss (mg)
      Carbon 2.334 28.03
      Hydrogen 2.884 2.907
      Nitrogen 0.2587 3.623
      Subtotal   34.56
      1. subtotal mass 34.56 mg
      2. sample mass 46.87 mg
      3. mass O (difference) 13.30 mg
      4. 15.9994 g/mole
      5. 0.7695 mol
    5. determine mole ratios
      Element mmol ratio
      C 2.334 9
      H 2.844 11
      N 0.2587 1
      O 0.7695 3
    6. Emperical formula is C9H11NO3, which is consistent with tyrosine.
    Combustion Analysis Report
    Mass of sample (mg) 61.48
    Mass of CO2 (mg) 115.65
    Mass of H2O (mg) 52.07
    % N by mass 11.958
    1. From the mass of CO2 find the moles of C.
      1. 115.65 mg
      2. 44.0095 g/mol
      3. 2.628 mmol CO2
      4. 2.628 mmol C
    2. From the mass of H2O find the moles of H
      1. 52.07 mg
      2. 18.0153 g/mol
      3. 2.890 mmol H2O
      4. 5.781 mmol H
    3. From the % N by mass, find the moles of N
      1. 11.958% N
      2. 61.48 mg sample
      3. 7.352 mg N
      4. 14.00674 g/mol
      5. 0.5249 mmol N
    4. Find O from remaining mass of sample
      Element mmole masss (mg)
      Carbon 2.628 31.56
      Hydrogen 5.781 5.827
      Nitrogen 0.5249 7.352
      Subtotal   44.74
      1. subtotal mass 44.74 mg
      2. sample mass 61.48 mg
      3. mass O (difference) 16.74 mg
      4. 15.9994 g/mole
      5. 1.046 mol
    5. determine mole ratios
      Element mmol ratio
      C 2.628 5
      H 5.781 11
      N 0.5249 1
      O 1.046 2
    6. Emperical formula is C5H11NO2, which is consistent with valine.
  2. Write a balanced overall chemical equiation, total ionic equation, and net ionic equation for the following reactions. If you begin with 5.0 g of each reactant and end with 125.0 mL of solution, what is the concentration of each ion in solution?
    1. aqueous sodium hydroxide reacts with aqueous hydrobromic acid
    2. aqueous sodium chloride reacts with aqueous ammonium phospahte
    3. aqueous sodium bromide reacts with aqueous lead chlorate
    4. aqueous phosphoric acid reacts with aqueous potassium hydroxide
    5. aqueous sulfuric acid reacts with aqueous sodium fluoride

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