-- Posted by Uhhello at 12:25 pm on Jan. 2, 2009 The answer is 5cm but i can't seem to get it...:( 10cm of hydrogen is burnt in oxygen to form water. What volume of oxygen is needed for the hydrogen to burn completely? Thanks for any help :) -- Posted by yyyt at 12:26 pm on Jan. 2, 2009 do you mean cm cubed? -- Posted by agerask at 12:26 pm on Jan. 2, 2009 use dimensional analysis. -- Posted by Z o E at 12:26 pm on Jan. 2, 2009 isnt it something to do with the ratio of hydrogen to oxygen. -- Posted by wallopwoop at 12:26 pm on Jan. 2, 2009 Dude water's two parts hydrogen and one part oxygen.  Everybody learned that in like kindergarten. -- Posted by Lord Cat at 12:26 pm on Jan. 2, 2009 Well there is twice as much hydrogen then oxygen So if there is 10cm of H then there is 5cm of O -- Posted by Leannbby at 12:27 pm on Jan. 2, 2009 Quote: from Lord Cat at 3:26 pm on Jan. 2, 2009 Well there is twice as much hydrogen then oxygen So if there is 10cm of H then there is 5cm of O im pretty sure thats it -- Posted by senior09 at 12:27 pm on Jan. 2, 2009 There are two hydrogens so you have to use half of the oxygen -- Posted by marshmellowman at 12:28 pm on Jan. 2, 2009 The reaction is H2 + 1/2O2 -> H2O So you had 1 mole of Hydrogen + 1/2 mole of Oxygen making one mole of water. Therefore the volume of oxygen will be half the volume of hydrogen needed, 10/2 = 5cm^3. -- Posted by sicosys at 12:28 pm on Jan. 2, 2009 Quote: from Lord Cat at 12:26 pm on Jan. 2, 2009 Well there is twice as much hydrogen then oxygen So if there is 10cm of H then there is 5cm of O I know this is it haha -- Posted by Uhhello at 12:29 pm on Jan. 2, 2009 Quote: from yyyt at 12:26 pm on Jan. 2, 2009 do you mean cm cubed? Yea -- Posted by Frubeling at 12:29 pm on Jan. 2, 2009 Everyones giving the most simple method, are you expected to use moles? -- Posted by Uhhello at 12:30 pm on Jan. 2, 2009 Quote: from Frubeling at 12:29 pm on Jan. 2, 2009 Everyones giving the most simple method, are you expected to use moles? Well i was trying top use like 1 mole of gas occupies 24dm volumne... I think i was over complicating it. Thankyou everyone. -- Posted by Frubeling at 12:31 pm on Jan. 2, 2009 Quote: from Uhhello at 8:30 pm on Jan. 2, 2009 Quote: from Frubeling at 12:29 pm on Jan. 2, 2009 Everyones giving the most simple method, are you expected to use moles? Well i was trying top use like 1 mole of gas occupies 24dm volumne... I think i was over complicating it. Thankyou everyone. You did over complicate it, alot -- Posted by Just Waiting Here at 12:35 pm on Jan. 2, 2009 It's really just stoichiometry. H2 + O2 -->  H2O That's the skeletal equation, so you need to balance it. 2H2 + O2 ---> 2H20 So... you need twice as much hydrogen as you do oxygen.