8/22 mcat help

[ejay1518]

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Hello, I took the mcat on 8/22. While reading one of the chemistry passages I saw some thing which I had never seen before. I wanted to know if you guys could shed some light on it.

"x% of w/w [insert formula of chemical compound]"

what does w/w mean? In all of my mcat prep I have never seen anything like it (maybe I was half asleep when it came by, idk.) 😴

 

[BloodySurgeon]

w/w is an abbreviation for "by weight," used in chemistry to describe the concentration of a substance in a mixture or solution. Properly speaking, 2% w/w means that the mass of the substance is 2% of the total mass of the solution or mixture. The metric symbol g/g has the same meaning as w/w.

 

[Vihsadas]

Yup, another common one is 2% "v/v", which means that 2% of the volume of the total solution is made up of the first substance, and 98% is the second substance.

So when you see something like a 1L "90% Ethanol solution v/v" that means that 900ml out of 1000ml is pure EtOH, and the other 100mls is usually water.

 

[ashish89]

I don't the w/w note had any effect on the corresponding question in that passage...as the density for the soln. was provided.

 

[sunny1]

Thanks for posting this. I was annoyed because I've never seen this notation before. I guessed it meant "water with" but apparently it's the other way around. Greeeeeat...