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# Water consists of hydrogen and oxygen, and the approximate

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Manager
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Water consists of hydrogen and oxygen, and the approximate [#permalink]  18 Jan 2008, 11:33
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Question Stats:

58% (02:25) correct 42% (00:05) wrong based on 11 sessions
Water consists of hydrogen and oxygen, and the approximate ratio, by mass, of hydrogen to oxygen is 2:16. Approximately how many grams of oxygen are there in 144 grams of water?

(A)16
(B)72
(C)112
(D)128
(E)142

-thanx
Director
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Re: water [#permalink]  18 Jan 2008, 11:36
portion of hydrogen in water is 2/(2+16) = 1/9.

weight of hydrogen = 144*1/9= 16.

SVP
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Re: water [#permalink]  18 Jan 2008, 11:36
H and O are in a 1:8 ratio per gram of water

Therefore, in 144 gms of water, their ratio will be 16:128

Therefore, D.

vermatanya wrote:
Water consists of hydrogen and oxygen, and the approximate ratio, by mass, of hydrogen to oxygen is 2:16. Approximately how many grams of oxygen are there in 144 grams of water?

(A)16
(B)72
(C)112
(D)128
(E)142

-thanx
Senior Manager
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Posts: 308
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Re: water [#permalink]  18 Jan 2008, 11:37
2x+16x=18x=144
x=8
8*16=128. D.
Director
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Re: water [#permalink]  18 Jan 2008, 11:41
If the ratio, by mass, of hydrogen to oxygen is 2:16 then the total weight of water is 2+16=18 where oxygen is 16/18 and hydrogen makes up the other 2/18.

If we are looking at 144 grams of water let's divide it by 18.

144/18 = 48/6 = 8

So we have 8 units of water (where each unit is made up of 16 oxygen and 2 hydrogen). To find the amount of hydrogen we multiple the units of water (8) by the units of hydrogen in each unit of water (16).

16*8=128 grams of oxygen.

Manager
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Re: water [#permalink]  18 Jan 2008, 11:43
eschn3am wrote:
If the ratio, by mass, of hydrogen to oxygen is 2:16 then the total weight of water is 2+16=18 where oxygen is 16/18 and hydrogen makes up the other 2/18.

If we are looking at 144 grams of water let's divide it by 18.

144/18 = 48/6 = 8

So we have 8 units of water (where each unit is made up of 16 oxygen and 2 hydrogen). To find the amount of hydrogen we multiple the units of water (8) by the units of hydrogen in each unit of water (16).

16*8=128 grams of oxygen.

yeah thanx for explaining.
Manager
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Re: water [#permalink]  18 Jan 2008, 12:04
eschn3am wrote:
If the ratio, by mass, of hydrogen to oxygen is 2:16 then the total weight of water is 2+16=18 where oxygen is 16/18 and hydrogen makes up the other 2/18.

If we are looking at 144 grams of water let's divide it by 18.

144/18 = 48/6 = 8

So we have 8 units of water (where each unit is made up of 16 oxygen and 2 hydrogen). To find the amount of hydrogen we multiple the units of water (8) by the units of hydrogen in each unit of water (16).

16*8=128 grams of oxygen.

hey but in the end y u multiplied it with the amount of oxygen instead of hydrogen
Director
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Re: water [#permalink]  18 Jan 2008, 12:23
oops, i calculated the amount of hydrogen, not oxygen. I should be more careful next time.
Director
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Re: water [#permalink]  18 Jan 2008, 13:09
vermatanya wrote:
eschn3am wrote:
If the ratio, by mass, of hydrogen to oxygen is 2:16 then the total weight of water is 2+16=18 where oxygen is 16/18 and hydrogen makes up the other 2/18.

If we are looking at 144 grams of water let's divide it by 18.

144/18 = 48/6 = 8

So we have 8 units of water (where each unit is made up of 16 oxygen and 2 hydrogen). To find the amount of hydrogen we multiple the units of water (8) by the units of hydrogen in each unit of water (16).

16*8=128 grams of oxygen.

hey but in the end y u multiplied it with the amount of oxygen instead of hydrogen

The question is asking for the amount of oxygen. Always make sure you know exactly what the question is asking for before you answer it.
Manager
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Re: water [#permalink]  30 Oct 2010, 02:56
great thread .. i was getting 16 all the time .. just that i mixed up water and hydrogen
)
Re: water   [#permalink] 30 Oct 2010, 02:56
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