Hey there! Sign in to join this conversationNew here? Join for free
x Turn on thread page Beta
    • Thread Starter
    Offline

    8
    ReputationRep:
    Hi everyone,

    I've been given this question, and I have a answer which is definitely wrong:

    "In a TOF mass spectrometer, ions are accelerated to the same kinetic energy. Each ( 25Mg+ ) ion is accelerated to a kinetic energy of 4.52x10^-16 J, and the time of flight is 1.44x10^-5 seconds.

    Calculate the distance travelled, in meters, in the TOF drift region.

    Avogadro constant = 6.022x10^23 "

    Can someone please help or give a rough outline of what steps I need to do?
    • Thread Starter
    Offline

    8
    ReputationRep:
    I have tried the answer again, would I be right in saying that the distance is about 2.1 meters?
    • Community Assistant
    • Study Helper
    Offline

    17
    ReputationRep:
    Community Assistant
    Study Helper
    (Original post by Electrogeek)
    Hi everyone,

    I've been given this question, and I have a answer which is definitely wrong:

    "In a TOF mass spectrometer, ions are accelerated to the same kinetic energy. Each ( 25Mg+ ) ion is accelerated to a kinetic energy of 4.52x10^-16 J, and the time of flight is 1.44x10^-5 seconds.

    Calculate the distance travelled, in meters, in the TOF drift region.

    Avogadro constant = 6.022x10^23 "

    Can someone please help or give a rough outline of what steps I need to do?
    Kinetic energy = 1/2mv2

    mass = 25/L = 4.15 x 10-26 kg

    2 x 4.52 x 10-16/4.15 x 10-26 = v2

    v = 147591 ms-1

    TOF = 1.44x10-5 s

    distance = vt = 2.13 m
    • Thread Starter
    Offline

    8
    ReputationRep:
    Thanks! I'm glad that I had the right answer.
    • Community Assistant
    • Study Helper
    Offline

    17
    ReputationRep:
    Community Assistant
    Study Helper
    (Original post by Electrogeek)
    Thanks! I'm glad that I had the right answer.
    It's more physics than chemistry IMHO
    Offline

    2
    ReputationRep:
    (Original post by charco)
    Kinetic energy = 1/2mv2

    mass = 25/L = 4.15 x 10-26 kg

    2 x 4.52 x 10-16/4.15 x 10-26 = v2

    v = 147591 ms-1

    TOF = 1.44x10-5 s

    distance = vt = 2.13 m
    Could you explain how you calculates the mass please?
    • Community Assistant
    • Study Helper
    Offline

    17
    ReputationRep:
    Community Assistant
    Study Helper
    (Original post by Barbie1998)
    Could you explain how you calculates the mass please?
    You are told that it is a 25Mg+ ion. The '25' represents the relative mass on a scale in which an atom of the 12C isotope = 12.00000.

    Hence an Avogadro number of atoms of 25Mg have a mass of 25g

    To find the mass in kg of one atom you must divide by 6.0223 x 1023 and then by 1000.
    Offline

    2
    ReputationRep:
    (Original post by charco)
    You are told that it is a 25Mg+ ion. The '25' represents the relative mass on a scale in which an atom of the 12C isotope = 12.00000.

    Hence an Avogadro number of atoms
    of 25Mg have a mass of 25g

    To find the mass in kg of one atom you must divide by 6.0223 x 1023 and then by 1000.
    Thanks so much!
    Offline

    2
    ReputationRep:
    (Original post by charco)
    Kinetic energy = 1/2mv2

    mass = 25/L = 4.15 x 10-26 kg

    2 x 4.52 x 10-16/4.15 x 10-26 = v2

    v = 147591 ms-1

    TOF = 1.44x10-5 s

    distance = vt = 2.13 m
    Could you explain what formula you used to get the mass of the molecule? Thats the only part i do not understand
    Offline

    2
    ReputationRep:
    (Original post by AnIndianGuy)
    So Mass in grams is RFM/avogadro constant

    Then divide by 1000 again cos it's in kg.
    Oh right, got it now, I kept getting 4.14x10^-23 because i didnt realise its in kg.

    Thanks
    • Community Assistant
    • Study Helper
    Offline

    17
    ReputationRep:
    Community Assistant
    Study Helper
    (Original post by derpz)
    Could you explain what formula you used to get the mass of the molecule? Thats the only part i do not understand
    divide the mass of one mole of the molecules (the relative mass expressed in grams) by Avogadro's constant.

    This gives the mass of 1 molecule in grams.

    However, you need the mass in SI units (kg) so you now have to divide by 1000.
    Offline

    17
    ReputationRep:
    When oh when oh when will physics admit that they got the unit of mass wrong and re-write all their textbooks?
    • Community Assistant
    • Study Helper
    Offline

    17
    ReputationRep:
    Community Assistant
    Study Helper
    (Original post by Pigster)
    When oh when oh when will physics admit that they got the unit of mass wrong and re-write all their textbooks?
    The day they realise that electric current flows in the reverse direction ...
    Offline

    0
    ReputationRep:
    what paper is this question from??
    • Thread Starter
    Offline

    8
    ReputationRep:
    (Original post by JiaS)
    what paper is this question from??
    This is one of the specimen papers from AQA for this year's new A level specification. 😊
    Offline

    0
    ReputationRep:
    (Original post by Electrogeek)
    This is one of the specimen papers from AQA for this year's new A level specification. 😊

    Oh okay, thanks
 
 
 
Reply
Submit reply
Turn on thread page Beta
Updated: May 20, 2016
Poll
Do you agree with the proposed ban on plastic straws and cotton buds?

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.