# Help working out concentration

Found 22nd Mar 2010
If I add 20g of salt to 150ml of water does that make a 8% solution?

Thanks

Groups

Do you mean would that be a 8% solution of sodium?
If so remember you need to know the concentration of what the salt is. I believe salt in sodium is 2.5x its mass in grams.

If you just want the solution of salt in water then surely that would be 13.3% not 8%?

awoodhall2003;8173356

Do you mean would that be a 8% solution of sodium?If so remember you need … Do you mean would that be a 8% solution of sodium?If so remember you need to know the concentration of what the salt is. I believe salt in sodium is 2.5x its mass in grams.If you just want the solution of salt in water then surely that would be 13.3% not 8%?

this ^

are you trying to calculate the concentration of salt in water?

150ml of pure water weighs 150 grams.

Therefore, 20grams of salt added to 150 grams of water would give a ratio of 20:150 in 170grams of solution.

This equates to 11.76% salt & 88.24% water.

cammy69;8173526

150ml of pure water weighs 150 grams.Therefore, 20grams of salt added to … 150ml of pure water weighs 150 grams.Therefore, 20grams of salt added to 150 grams of water would give a ratio of 20:150 in 170grams of solution.This equates to 11.76% salt & 88.24% water.:p

Yeah i forgot to add the salt, nice one. But still you often find people are actually trying to work out the sodium ratio not the salt. Thus would be a different value, so you would divide the salt by 2.5 to get the sodium concentration.

I'm not a chemist but i was going about to find the concentration i'd find the number of moles 1st

moles= mass/molar mass
mass of salt (NaCl) = 20g from your question
molar mass = 23+ 37.5 = 60.5 gmol

so mole = 20/60.5 =0.331 mol

Concentration = moles/ volume

150ml = 0.15L

concentration = 0.331/0.15 = 2.207 mol/L

Original Poster

OK, thanks so if I wanted to make an 8% salt solution I would mix 20g of NaCl with 250ml of water right?

Banned

Civic EG6;8173781

OK, thanks so if I wanted to make an 8% salt solution I would mix 20g of … OK, thanks so if I wanted to make an 8% salt solution I would mix 20g of NaCl with 250ml of water right?

you making crystalmeth brah?

Civic EG6;8173781

OK, thanks so if I wanted to make an 8% salt solution I would mix 20g of … OK, thanks so if I wanted to make an 8% salt solution I would mix 20g of NaCl with 250ml of water right?

That would make a 7.4% sodium chloride solution. :thumbsup:

cammy69;8173526

150ml of pure water weighs 150 grams.Therefore, 20grams of salt added to … 150ml of pure water weighs 150 grams.Therefore, 20grams of salt added to 150 grams of water would give a ratio of 20:150 in 170grams of solution.This equates to 11.76% salt & 88.24% water.:p

This

Civic EG6;8173781

OK, thanks so if I wanted to make an 8% salt solution I would mix 20g of … OK, thanks so if I wanted to make an 8% salt solution I would mix 20g of NaCl with 250ml of water right?

i guess so cos mass/volume x100 = the % solution
20/250 x 100 = 8%

chesso;8173849

This

lol you know better than me chesso :oops::oops:

Original Poster

So your also counting the mass of the salt as part of the total volume, so (mass/total volume x 100) right?

awoodhall2003;8173838

That would make a 7.4% sodium chloride solution. :thumbsup:

20/(x+20) = 8/100
200 = 0.8 (x+20)
= 0.8 x +16
200-16 = 0.8x
184 = 0.8x
x=230g water

20g salt in 230 g water gives a % solution of 20/250 = 8%

Civic EG6;8173925

So your also counting the mass of the salt as part of the total volume, … So your also counting the mass of the salt as part of the total volume, so (mass/total volume x 100) right?

yeah as it will make up part of the total mass.

Original Poster

Thanks people rep for all.

chesso;8173945

20/(x+20) = 8/100200 = 0.8 (x+20) = 0.8 x +16200-16 = 0.8x184 = … 20/(x+20) = 8/100200 = 0.8 (x+20) = 0.8 x +16200-16 = 0.8x184 = 0.8xx=230g water20g salt in 230 g water gives a % solution of 20/250 = 8%

i moreorless said that in my prev post

ilovelilac;8174049

i moreorless said that in my prev post

That's true (more or less):-D
but almost right answer, wrong reason!!:w00t: