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# Help working out concentration

6y, 8m agoPosted 6 years, 8 months ago
If I add 20g of salt to 150ml of water does that make a 8% solution?

Thanks
6y, 8m agoPosted 6 years, 8 months ago
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(18)
1 Like #1
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%?
#2
awoodhall2003
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 ^
#3
are you trying to calculate the concentration of salt in water?
1 Like #4
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
#5
cammy69
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.
1 Like #6

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
#7
OK, thanks so if I wanted to make an 8% salt solution I would mix 20g of NaCl with 250ml of water right?
banned#8
Civic EG6
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?
#9
Civic EG6
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:
#10
cammy69
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
#11
Civic EG6
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%
1 Like #12
chesso
This

lol you know better than me chesso :oops::oops:
#13
So your also counting the mass of the salt as part of the total volume, so (mass/total volume x 100) right?

awoodhall2003
That would make a 7.4% sodium chloride solution. :thumbsup:
1 Like #14
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%
#15
Civic EG6
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.
#16
Thanks people rep for all.
#17
chesso
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%

i moreorless said that in my prev post :p
#18
ilovelilac
i moreorless said that in my prev post :p

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