Turn on thread page Beta
    • Thread Starter
    Offline

    2
    ReputationRep:
    Boron trichloride (BCl3) can be prepared as shown by the following equation.B2O3(s) + 3C(s) + 3Cl2(g) 2BCl3(g) + 3CO(g) A sample of boron oxide (B2O3) was reacted completely with carbon and chlorine. The two gases produced occupied a total volume of 5000 cm3 at a pressure of 100 kPaand a temperature of 298 K. Calculate the mass of boron oxide that reacted. Give your answer to 3 significant figures. (The gas constant R = 8.31 J K–1 mol–1)I have tried to work this out and I looked on the mark scheme which is :P = 100 000 (Pa) and V = 5.00 x 10-3 (m3)n = PV/RT = 100 000 x 5.00 x 10-3/8.31 x 298 = 0.202 moles (of gas produced)Therefore 0.202/5 = 0.0404 moles B2O3 Mass of B2O3 = 0.0404 x 69.6= 2.81 (g)I understand all of this except i don't understand why you divide 0.202 by 5. Why do i divide by 5?
    Offline

    1
    ReputationRep:
    In this reaction, 0.202 moles of gas are produced. If you look at the equation 2BCl3 and 3CO are produced which in total give 0.202 moles. The ratio of these gases to the moles of B2O3 produced is 5:1. (2 of BCl3 and 3 of CO) Therefore the moles of B2O3 must be 0.202/5 mol.
 
 
 
Reply
Submit reply
Turn on thread page Beta
Updated: May 15, 2015

University open days

  1. University of Cambridge
    Christ's College Undergraduate
    Wed, 26 Sep '18
  2. Norwich University of the Arts
    Undergraduate Open Days Undergraduate
    Fri, 28 Sep '18
  3. Edge Hill University
    Faculty of Health and Social Care Undergraduate
    Sat, 29 Sep '18
Which accompaniment is best?

The Student Room, Get Revising and Marked by Teachers are trading names of The Student Room Group Ltd.

Register Number: 04666380 (England and Wales), VAT No. 806 8067 22 Registered Office: International House, Queens Road, Brighton, BN1 3XE

Write a reply...
Reply
Hide
Reputation gems: You get these gems as you gain rep from other members for making good contributions and giving helpful advice.