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Past paper calculation question about moles - help please? Watch

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    When the hydrocarbon was burned 0.20 mol of water were produced. How many moles of hydrogen atoms are there in 0.20 mol of water?

    The markscheme says the answer is 0.4 but I have no idea how to work it out. Would anyone please be able to show me how?
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    The formulae for water is H20 - since there are 2 atoms of hydrogen in 1 molecule if water, there must be 2 moles of hydrogen (and 1 mole of oxygen) in water.
    2×0.2= 0.4

    Hope that helped

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    (Original post by semise)
    The formulae for water is H20 - since there are 2 atoms of hydrogen in 1 molecule if water, there must be 2 moles of hydrogen (and 1 mole of oxygen) in water.
    2×0.2= 0.4

    Hope that helped

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    That's great thank you! So is mol the same as moles or are they different?
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    m is the abbreviation for metres, s for seconds, mol for moles.
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    (Original post by Pigster)
    m is the abbreviation for metres, s for seconds, mol for moles.

    Ok thank you that makes sense now ..... one last thing (which probably sounds like an even more stupid question) how is there 0.4mol of hydrogren in 0.2mol of water when isn't 0.4 greater than 0.2 so how is that possible? Sorry like I said it's probably a really stupid question but I just can't seem to understand this topic arghhhh
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    (Original post by nettogrof)
    Ok thank you that makes sense now ..... one last thing (which probably sounds like an even more stupid question) how is there 0.4mol of hydrogren in 0.2mol of water when isn't 0.4 greater than 0.2 so how is that possible? Sorry like I said it's probably a really stupid question but I just can't seem to understand this topic arghhhh
    You don't understand what moles are by the look of things.

    A mol is a number, that is all. It can be a number of anything.

    I have a set of felt tip pens. Each pen has a barrel and a lid.

    If I have one pen I have one barrel and one lid.

    If I have 12 pens I have 12 barrels and 12 lids.

    If I have 1 mol of pens I have 1 mol of barrels and 1 mol of lids.


    I go to the shop and buy double yoked eggs.

    I buy 6 double yoked eggs. This allows me to make 12 fried eggs.

    I buy 1 mol of double yoked eggs. This allows me to make 2 mol of fried eggs.


    One water molecule is made of one oxygen atom and two hydrogen atoms.

    50 water molecules are made from 50 oxygen atoms and 100 hydrogen atoms.

    1 mol of water molecules is made from 1 mole of oxygen atoms and 2 mole of hydrogen atoms.

    0.2 mol of water molecules is made from 0.2 mol of oxygen atoms and 0.4 mol of hydrogen atoms.
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    Thank you so very much for taking the time to do that - it makes so much more sense now!! Before I just couldn't get my head around it and I tried googling it but none of the revision pages helped and the markscheme only gave me the answer so thank you
 
 
 
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