Author Topic: What is meant by "percent solution"?  (Read 591 times)

0 Members and 1 Guest are viewing this topic.

ning

  • Guest
What is meant by "percent solution"?
« on: October 24, 2003, 06:51:00 PM »
Ning is a little confused.
with TFSE, it seems that with solids (i.e. NaOH), "percent" means "grams of solid per grams of solution", weight/weight.
But with nominally gaseous things (ammonia), Strange, hard to isolate things (NaOCl), what does "percent" mean?
Ning has heard the term "w/v" fly around, but how can a weight divided by a volume give a percentage?
And what is the "weight" of dissolved gasses like ammonia?
Ning knows these are simple-minded questions, but for a newbee, they are essential. Perhaps ning could be directed to a suitable FAQ?

Ning wants an algorithm to convert:  percent solution --> molarity
With w/w, it is relatively easy.
but....

Thanks in advance, bees.

Flippie

  • Guest
solution percentage
« Reply #1 on: October 24, 2003, 07:49:00 PM »
Ning has heard the term "w/v" fly around, but how can a weight divided by a volume give a percentage?


The term "w/v" is not used for gasses but for fluids. The weight of a gas can be calculated starting from "the Ideal Gas Law" - if you really want to know how you do this just ask me - but I don't think you need it.

The weight of dissolved gasses can be measured by subtracting the weight of the solution after gassing with the one before gassing. The difference is the dissolved gas  ;) .


Weight percent = weight of solute (g) x 100
                         weight of solution (g)

Weight/Volume percent = weight of solute (g) x 100
                                    volume of solution (mL)


Because of the different units in the numerator and denominator (in case of w/v), this type of concentration is not a true percentage. It is used as a quick and easy concentration unit because volumes are easier to measure than weights and because the density of dilute solutions is generally close to 1 g/mL. Thus, the volume of a solution in mL is very nearly numerically equal to the mass of the solution in grams.

molarity =  moles of solute
               liter of solution

Some useful definitions

Solution: a mixture consisting of a solute and a solvent

Solute: component of a solution present in the lesser amount

Solvent: component of a solution present in the greater amount

Concentration: amount of a solute present in a solution per standard amount of solvent



The following link contains more theory and examples

http://dl.clackamas.cc.or.us/ch105-04/





ning

  • Guest
thanks guys
« Reply #3 on: October 26, 2003, 03:58:00 AM »
that w/v was killing me.
So when household chemicals like bleach and ammonia give percent, they are usually meaning w/w or w/v?

Flippie

  • Guest
houshold chemicals
« Reply #4 on: October 26, 2003, 10:03:00 AM »
Houshold chemical manufacturers probably use w/v for their convenience.
The product concentration has not to be that accurate for houshold use (draincleaner, bleach, ammonia,...).
I guess if you make a dilute ammonia solution to clean your windows it doesn't matter how they calculated its concentration   :P .