Hydrochloric Acid

[jowrose]

Ok, I'm trying to figure out the volume of one mole of HCl in muriatic acid, but I don't know how they measure the HCl content. The bottle says 31.45% HCl, but what is this in relation to? Does this mean that 31.45% of the mass of the muriatic acid is HCl, or that 31.45 particles out of every 100 particles in the bottle are HCl?

[jdurg]

It will say it someplace on the bottle as in w/w or w/v. w/v means that in one liter of solution, 31.45% of the weight is from HCl and other 68.55% of the weight is from water. If it states w/w, then it means for every 100 grams of solution, 31.45 grams are HCl.

[jowrose]

What's the difference? Just units of measurement?

[RyanJ]

What's the difference? Just units of measurement?

 

Yup, they are different measurents

 

Cheers,

 

Ryan Jones

[jdurg]

Exactly. Let's take a look at how the interpretations could be different. Let's say you have a solution that's 37% HCl w/v. As the density of 37% HCl is about 1.19 g/mL, a 37% w/v designation means that in 1.00 Liters of solution you will have a total mass of HCl of 440.3 grams. That's equal to about 12.06 moles making your molarity 12.06 Molar.

 

Now if the designation was 37% w/w, that means that in 100 grams of solution we have 37 grams of HCl. With this information we could figure out the molality of the solution then convert it to molarity. 37 grams of HCl is about 1.014 moles. So we take 1.014 and divide it by the kg of solvent (water) which would be 0.063 kilograms. This gives us a MolALity of 16.095. Now we can convert that readily to molARity and we get a value of about 12.07 molAR. So while the difference isn't much, there is a difference which could affect any volume precise experiments you are doing.

 

(BTW, chemicals such as acids and bases are typically denoted in the w/w %).

[jowrose]

Ah ok. Thanks. I searched the muriatic acid bottle and couldn't determine whether it was w/v or w/w. Should I just assume it's w/w then?

[jdurg]

Ah ok. Thanks. I searched the muriatic acid bottle and couldn't determine whether it was w/v or w/w. Should I just assume it's w/w then?

 

Yup.

[spudpeel]

I got in big trouble with a certain teacher for questionning this once! Im a moles man myself, and 2% glucose solution completely confused me. I got into a big argument because of it.

[dorucalinciobanu]

Exactly. Let's take a look at how the interpretations could be different. Let's say you have a solution that's 37% HCl w/v. As the density of 37% HCl is about 1.19 g/mL, a 37% w/v designation means that in 1.00 Liters of solution you will have a total mass of HCl of 440.3 grams.

 

Sorry, but the density of 1.19 g/mL has a HCl solution of 37% w/w. If You have a solution of 37% w/v, You'll have 37 g / 100 mL or 370 g / 1.00 Liters!!