chemistry Q!

[tris-]

if i want to make a 0.5M concentration of KCl in 5 litres of water, is this the correct route to work out the mass of KCl needed -

0.5 * 5 = 2.5moles

2.5 * 74.5 = 188.75grams

(188.75/100) * 500 = 943.75grams needed for 1 litre

 

[Ormorof]

mmmm it seems like quite a high number, could you not just work it from the figures you have?

moles = conc/1000 * volume

so 0.5/1000 * 5000 = 2.5 moles, then the rmm of KCl = 74.5513

so mass = moles * rmm, 2.5 moles * 74.5513gmol-1 = 186.37825g

thats what i would do anyhoo

edit: which i see now you have done, dont get what the last part is all about though

 

[tris-]

beecause i want it in 5 litres. i assume 1 litre is just going to be 100% of the mass, but 5 litres is going to be 500%.
?

 

[Ormorof]

but you have already worked out how many moles you have in 5 litres

 

[swords]

What he said ^^
Remember that you are actually dissolving a mass of power into a fixed volume of liquid! Imagine you are weighing everything out and for the love of god dont take moles too seriously

 

[tris-]

cheers me dears

 

[crispy]

100% of the mass?

What do you mean?

Didnt get the last part of your calculations hehe

 

[swords]

Thats because it is a brain fart ofc!

 

[crispy]

How do they smell btw?

 

[tris-]

Thats because it is a brain fart ofc!

i was taking the advice of some guy at uni but he only knows as much as me, which is why i doubted it. i did this last yr but i forgot it and threw all my notes out thinking id never need them again :\.

i ask you, who goes into a law based degree thinking theyd need chemistry

 

[Bugz]

Chemistry is incredibly hard I find.

And I want a law degree too.

Oh no!

 

[Tilda]

Jonny was a Chemists son,
but jonny is no more,
cause what he thought was H2O
was H2SO4!

Bugz, in terms of difficulty for me, chemistry was 1000 times harder than most of the stuff on my degree.
message me if you want my msn to chat about law degrees or something.

 

[tris-]

Chemistry is incredibly hard I find.

And I want a law degree too.

Oh no!

this is down to the forensic investigations element of mine. which i never expected to be in as much detail. we do nearly the same amount of FI work as people studying CSI and applied science for FI :\

tilda is correct though. chemistry IS harder than law by far. sadly i need leet knowledge of both

 

[Agrigo]

RMM :
1)K=39g
2)Cl=35.5g

RMM of KCL = 39g+35.5g = 74.5g

This means that to make a 1molar solution of KCl in 1000cm^3 water you need 74.5g of KCl

74.5g = 1Molar
? = .5Molar

Cross Multiply

74.5(.5) =1(?)

?= 37.25g is needed to make a .5molar soultion of KCl in 1000CM^3

To get this in 5liters (5000CM^3) you just multiply 37.25g X 5 (as 5000CM^3 / 1000CM^3 = 5)

186.25g of KCl is needed to make a .5Molar soultion of KCl.


Hope that helps.

 

[Fatload BoysDoCry]

Chemistry is incredibly hard I find.

And I want a law degree too.

Oh no!

Law isn't hard Bugz

 

[Fatload BoysDoCry]

i was taking the advice of some guy at uni but he only knows as much as me, which is why i doubted it. i did this last yr but i forgot it and threw all my notes out thinking id never need them again :\.

i ask you, who goes into a law based degree thinking theyd need chemistry

I did a degree in Forensic Science and it had 1 year of Psychology and 2 years of criminal law and vice versa for the law students from what i heard off fellow students.

 

[psyco]

booo... i remember my old science lessons now

 

[Nate]

RMM :
1)K=39g
2)Cl=35.5g

RMM of KCL = 39g+35.5g = 74.5g

This means that to make a 1molar solution of KCl in 1000cm^3 water you need 74.5g of KCl

74.5g = 1Molar
? = .5Molar

Cross Multiply

74.5(.5) =1(?)

?= 37.25g is needed to make a .5molar soultion of KCl in 1000CM^3

To get this in 5liters (5000CM^3) you just multiply 37.25g X 5 (as 5000CM^3 / 1000CM^3 = 5)

186.25g of KCl is needed to make a .5Molar soultion of KCl.


Hope that helps.

ofc it doesn't, no one can work it backwards other then your kin! you damn irishgoatman!! ;p

 

[Serbitar]

don't you think its a it cruel to the moles when you cut one in half to get the .5 mole?

note: searching for 'mole' on images.google.co.uk gives a NSFW picture on the first row, as i just found out much to my horror

 

[rayzor]

note: searching for 'mole' on images.google.co.uk gives a NSFW picture on the first row, as i just found out much to my horror

uke:

Man, I wish I hadn't been so keen to check that pic

 

[crispy]

note: searching for 'mole' on images.google.co.uk gives a NSFW picture on the first row, as i just found out much to my horror

Just asked myself:

People wanna save lions, shitty hippos and whales, but it that there were an endangered species i dont think environmentalists would even try to save it ^_^

But that says more about biased environmentalists than it does about that animal hehe