AS chemistry please help!

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Starmock99
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#1
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#1
Our bodies are approximately 60% water. Using the assumption that our bodies are completely water, and the average person weights around 75kg, how many molecules are there in the human body?
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troubadour.
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#2
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(Original post by Deval)
Our bodies are approximately 60% water. Using the assumption that our bodies are completely water, and the average person weights around 75kg, how many molecules are there in the human body?
Think about the following equations:

1. moles = mass/Mr.

2. moles = number of molecules/Avogadro's constant.

Not allowed to give straight answers, sorry.
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Sophie7699
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#3
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#3
use the equation

number of particles = mass of substance / Molar mass (this is equal to the relative atomic mass)
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ETbuymilkandeggs
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#4
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#4
- What's the molecular mass of water? (think about what water actually is in terms of the respective elements)

- How do I find the number of moles of something? (this will come in handy for the next equation.)

- What do I multiply the number of moles of a substance by to find the number of molecules? (rhymes with 'avocado')
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Starmock99
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#5
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(Original post by Hydeman)
Think about the following equations:

1. moles = mass/Mr.

2. moles = number of molecules/Avogadro's constant.

Not allowed to give straight answers, sorry.
Can I just ask, would I have to convert 75kg to 75,000g??
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troubadour.
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(Original post by Deval)
Can I just ask, would I have to convert 75kg to 75,000g??
Yes, you would.
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troubadour.
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(Original post by ETbuymilkandeggs)
- What do I multiply the number of moles of a substance by to find the number of molecules? (rhymes with 'avocado')
Avocadro you mean.
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troubadour.
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#8
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(Original post by Deval)
Is the answer .. 2.509541539x10^27 ? :P
Approximately, yes. I'm guessing you used 18 for the Mr value of water rather than 18.02? My answer is off by only a few decimal places so your answer would still be accepted unless the examiners had supplied the Ar of each element in the question and you failed to use it correctly.
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Maker
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#9
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#9
This question is so easy its embarrassing.
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Starmock99
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#10
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(Original post by Hydeman)
Approximately, yes. I'm guessing you used 18 for the Mr value of water rather than 18.02? My answer is off by only a few decimal places so your answer would still be accepted unless the examiners had supplied the Ar of each element in the question and you failed to use it correctly.
Yap I used 18 :^_^: And no the Ar wasn't given ! Thanks for your help !!!! :shakehand:
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turquoisecat
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#11
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#11
what is the molecular mass of 2Fe?
The question is calculate atom economy to make iron from iron oxide?

Fe2O3+3CO=2FE+3CO2
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