Ask Question
3 November, 00:16

An unidentified compound contains only phosphorous and fluorine, meaning we could write its formula as PxFy. Heating 0.2324 g of the compound in a 378-mL container converted all of it to gas with a pressure of 97.3 torr at 77°C. The gaseous PxFy was then reacted with an aqueous solution of calcium chloride, and all of the fluorine was converted to 0.2631 g of CaF2. Find the molecular formula of the compound.

+3
Answers (1)
  1. 3 November, 01:14
    0
    The molecular formula of the compound is P2F4

    Explanation:

    Step 1: Data given

    Mass of the compound = 0.2324 grams

    Volume of container = 378 mL

    Pressure at 77 °C = 97.3 torr

    The gaseous PxFy was then reacted with an aqueous solution of calcium chloride, and all of the fluorine was converted to 0.2631 g of CaF2.

    Molar mass CaF2 = 78.07 g/mol

    Step 2: Calculate moles CaF2

    Moles CaF2 = 0.2631 g / 78.07 g/mol=0.003370

    Step 3: Calculate moles F

    For every 1 mol CaF2 we have 1 mol Ca2 + and 2 moles F-

    moles F - = 2 * 0.003370=0.006740

    Step 4: Calculate mass of F

    mass F = 0.006740 mol * 19.00 g/mol=0.1281 g

    Step 5: Calculate mass of P

    mass P = mass of compound - mass of F = 0.2324 - 0.1281 = 0.1043 g

    Step 6: Calculate moles P

    moles P = 0.1043 g / 30.97 g/mol=0.003368 moles

    Step 7: Calculate mol ratio

    We divide by the smallest amount of moles

    P: 0.003368/0.003368 = 1

    F: 0.006740 / 0.003368 = 2

    The empirical formula is PF2

    The empirical formula has a molar mass of 68.97 g/mol

    Step 8: Calculate moles of compound

    p*V = n*R*T

    n = (p*V) / (R*T)

    ⇒ with p = the pressure of the gas = 97.3 torr = 97.3/760 = 0.128 atm

    ⇒ with V = the volume of the gas = 0.378 L

    ⇒ with R = the gas constant = 0.08206 L*atm/K*mol

    ⇒ with T = the temperature = 77.0 °C = 350 Kelvin

    Number of moles = (0.128 * 0.378) / (0.08206*350)

    Number of moles =

    moles gas = pV/RT = 0.128 atm x 0.378 dm^3 / 0.08206x350 K=0.00168

    Step 9: Calculate molar mass

    Molar mass = mass / moles

    Molar mass = 0.2324 grams / 0.00168 moles

    Molar mass = 138 g/mol

    Step 10: Calculate the molecular formula

    138.0 / 68.97 = 2

    2 * (PF2) = P2F4

    The molecular formula of the compound is P2F4
Know the Answer?
Not Sure About the Answer?
Find an answer to your question ✅ “An unidentified compound contains only phosphorous and fluorine, meaning we could write its formula as PxFy. Heating 0.2324 g of the ...” in 📘 Chemistry if you're in doubt about the correctness of the answers or there's no answer, then try to use the smart search and find answers to the similar questions.
Search for Other Answers