Calculating salt concentration in water (1 Viewer)

[sugaryblue]

Let's say, you use 100ml of water mixes with 1 teaspoon of salt. How do you calculate the concentration? I try to use the mole thingy but I am hopeless and lost

 

[jims]

depends on the salt.
lets say u use NaCl and a tablespoon holds 10g:

moles = 10/NaCl = 10/(22.99+35.45) = 0.1711 moles

thats in 100ml so in 1L theres 0.1711x10 = 1.711M

 

[sugaryblue]

Originally posted by jims
depends on the salt.
lets say u use NaCl and a tablespoon holds 10g:

moles = 10/NaCl = 10/(22.99+35.45) = 0.1711 moles

thats in 100ml so in 1L theres 0.1711x10 = 1.711M

Thanks

so does that mean that in order to calculate the concentration of salt (NaCl) in water, then I just have to calculate the mole of salt, then that's the no of mole in the amount of water I used? then I just have to change it back to out of 1 L?

 

[jims]

yup. simple.

 

[inasero]

well u havent really specified what units of concen tration you are using...but jims is correct in his (or her) use of molar concentration...

other types of concentration might include grams/litre (the easiest since there is no conversion)
ppm
ppb
etc etc...

 

[Giant Lobster]

omg i feel like such an idiot asking this... what is ppb?

 

[inasero]

parts per billion...
so 1 ppm (parts per million) is equivalent to 1000 ppb

 

[Giant Lobster]

lol ppb.. how come its never mentioned in my text books? ... did u make it up? *hmmm*

 

[inasero]

no way man! this is a standard term

edit: i think this term is used in relation to some gases in the atmosphere which are present in minute amounts...also in roland smith in relation to the greatness of AAS in monitoring ions in our waterways

 

[Giant Lobster]

i didnt know AAS can measure anything below 0.01 ppm...

 

[sugaryblue]

i don't really understand the stuff about ppm and ppb

 

[McLake]

Originally posted by sugaryblue
i don't really understand the stuff about ppm and ppb

1 ppm means that for every 1 "part" (which could be gram, litre, "handful" or 300mL bottle of COke, any measurment works) there is 1,000,000 parts of other "stuff". Similar for ppb.

So If I know there is 5ppm of Hg in my water supply, then if I take 1,000,000 buckets of water then 5 of them will contain mecury (well not exactly, but you get the idea) ...

 

[Giant Lobster]

cept in gases, ppm and ppb are v/v insted of m/m
so 1 ppm of a gas means 1 mL in 1000L

 

[ruski_gal]

i dont really understand ppm either. how do you convert moles in to ppm???

 

[McLake]

Originally posted by ruski_gal
i dont really understand ppm either. how do you convert moles in to ppm???

OK, this follows from what I was saying above. ppm can be of ANY ammount, including moles.. So if I have 5 moles of NaCl and 1,000,000 moles of water then the calcium is 5ppm.

 

[Constip8edSkunk]

uh

i thought in solution, ppm is m/m, ie mass of solute/mass of solution *10^6 and if it is aqueous, the standard unit is taken as being mg/L

5mol of NaCl/1000000mol of H2O will not give u a mass ratio 2 give 5ppm. instead u should devide 11700000 by 18 to see how many mol of H20 (molar mass of NaCl being 58.5g) per 5 mol of NaCl

correct me if im wrong plz

 

[McLake]

No, I'm probably wrong ...