need some help

[kamy]

can someone solve this question:

 

How many electrons are there in a 5000kg elephant?

answer with reasoning please

 

much thanks.................................................

[Skye]

A rough estimate would be to assume an elephant is entirely water, work out how many electrons in a molecule of water, work out how many molecules of water in 5000kg, then multiply those numbers.

[kamy]

can you work it out...and show me the steps

[Darkblade48]

can you work it out...and show me the steps

 

I don't think people are here to do your Fermi problems for you. Skye has already pointed out an interesting way to look at the approach of calculating the number of electrons in a 5000 kg elephant (humans are about 72% water, so you can probably assume an elephant is about the same, and from there, just assume that it's 100% water)

[woelen]

Formula of water is H2O. This is a neutral molecule. How many electrons are there in a H-atom, how many in an O-atom. Sum them up and you have the number of electrons in one molecule of H2O.

 

Now the number of molecules. You know how many molecules there are in 1 mol of water molecules. How many grams is that?

 

How many mols of water are there in 5000 kg of water?

 

If you can answer all these questions, then you can roughly estimate the number of electrons in a 5000 kg elephant.

 

I'll tell you the answer: A LOT

[YT2095]

I`m really glad you guys take this seriously, you Obviosly know something I don`t here (I`de want the compostion of the elephant for a start and not assume a bag of water, unless you want to Cheat!), saves me issuing a Troll warning anyway

 

edit: if you want to cheat, there IS coorelation between Mass and electron count!

you Could for instance take the total mass, and then subtract the percentage of the electron mass from the whole. but this IS cheating!

[Skye]

Oh assuming the body is pure water is standard practice in electropachydermology YT

[YT2095]

but wouldn`t it make more sense to work it out on Ratio.

the Electron is the lightest of all the 3 particles, the Proton and Neutron account for the bulk of all mass, and are Roughly the same mass each.

 

and so, add the weight of a proton and neutron and divide by 2, giving the avg.

you Know that for every proton there is an electron also.

so take this avg you just performed and find the percentage mass difference between that and the electron.

 

that will give you a factor that you must subtract from the overall mass of 5000kg as a percentage.

 

this will give you a number, you then take this number and see how many times the electrons mass will fit into this number.

 

THAT will be your answer

 

 

cheating yes, accurate most certainly!

[woelen]

This is an approximation, which could be used, but it is in no way a better approximation than assuming the elephant is 100% water. The ratio of neutrons to protons is not the same for each element, roughly speaking, one can say that the heavier the element, the more neutrons per proton. By using your approximation, you'll find a slightly lower number of electrons than when assuming 100% water, but both of them are in the same order of magnitude.

 

If you want a really good approximation, then you would need to determine the ratio's in which elements occur in the elephant and then perform a more elaborate computation. But doing that amount of work for such a stupid question is a waste of time .

[kamy]

so what i did was 6.02 X 10>23 ----is 18 g///// therefore 5000/0.018 X 6.02 X 10>23 .....1.7 X10>29.....therefore its 1.7X1030

 

Correct?

[woelen]

Almost correct, the answer should be 1.7*10^29. Your method of reasoning is OK, but you probably did one multiplication by 10 too much.