#### Papabravo

Joined Feb 24, 2006
14,833
You seem to forget that muriatic acid (aka "HCl") is not a gas. As a gas, which you seem to assume, the standard volume for a gas is 22.4 L per mole (there is some discussion about changing that). It is in solution. Solutions of HCl in water deviate from "ideal" solutions significantly.
I never said HCl was a gas. It is a liquid. A liter is a measurement of liquid volume in case you failed chemistry. It stands to reason that a liquid is going to have more moles per liter than a gas.

I did make a mistake in my previous post. The 6 moles/L figure is for the 20% solution, commonly referred to as Muriatic Acid. The maximum concentration in which HCl is produced is about 38% or 12.39 moles/L. Higher concentrations are possible but the evaporation rate is sufficient to require special storage and handling precautions.

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#### psoke0

Joined Mar 31, 2017
131
okay thank you
I never said HCl was a gas. It is a liquid. A liter is a measurement of liquid volume in case you failed chemistry. It stands to reason that a liquid is going to have more moles per liter than a gas.

I did make a mistake in my previous post. The 6 moles/L figure is for the 20% solution, commonly referred to as Muriatic Acid. The maximum concentration in which HCl is produced is about 38% or 12.39 moles/L. Higher concentrations are possible but the evaporation rate is sufficient to require special storage and handling precautions.
so my acid is 6 moles lower then required strengt right ? can i use 3% of strength hydrogen peroxide to make it work ?
because i know making more pure acid is hard and dangerous its beyond me

#### psoke0

Joined Mar 31, 2017
131
This is a really good point. what you REALLY need to know is how many moles of HCl you have along with how many moles of H2O to make a particular concentration of acid in solution
1 mole of HCl is about 36.4 grams. and a liter of HCl would be about 6 moles. So a liter of 100% HCl should be about 218 grams.
Every acid is different, and for example a liter of Sulfuric acid is about 18 moles for one liter

One thing you always remember in dealing with concentrated acid is to NEVER EVER under ANY CIRCUMSTANCES dilute a pure acid by adding water to it. Your injuries will be painful, extreme, and life threatening. You always add the pure acid to a suitable quantity of water which you have computed ahead of time.

This is also a good practice to follow when diluting a solution that is less than 100% acid. Just for the consistency it encourages.
so 100 ml of my acid should be 21.8 grams if its actually 6 moles right ?

#### jpanhalt

Joined Jan 18, 2008
10,923
I never said HCl was a gas. It is a liquid. A liter is a measurement of liquid volume in case you failed chemistry. It stands to reason that a liquid is going to have more moles per liter than a gas.

I did make a mistake in my previous post. The 6 moles/L figure is for the 20% solution, commonly referred to as Muriatic Acid. The maximum concentration in which HCl is produced is about 38% or 12.39 moles/L. Higher concentrations are possible but the evaporation rate is sufficient to require special storage and handling precautions.
1) HCl is a gas. It is commonly used as a solution in water or other liquids.
2) Thank you for clarifying that your original statement (below) was wrong.
1 mole of HCl is about 36.4 grams. and a liter of HCl would be about 6 moles. So a liter of 100% HCl should be about 218 grams.
Since you did not say the HCl was in water and later referred to "100% HCl," the only reasonable interpretation is that you were referring to HCl (gas). There is no such thing as 100% HCl in water. In its condensed phase, pure HCl has a density of 1.49, which equates to about 41 molar. A liter of 100% HCl (liquid) would weigh about 1490 grams.
3) "Muriatic acid" is older and still common nomenclature for solutions of HCl in water. It does not define any specific concentration of HCl in water. Wikipedia says it can be "5% to 32%" HCl.
4) 20% (approx) HCl in water is very common and is approximately 6 molar.
5) Since the TS is using solutions and has no way to measure weight accurately, I suggest using molarity (i.e., moles of HCl per liter of solution) in discussions of concentration here as it is less ambiguous than composition by percentage. For example, if his "muriatic acid" is 6 molar (about 20% by weight), then a 1:3 dilution by volume would be 2 molar, and so forth. If his muriatic acid is more concentrated, say 37% by weight, then the molarity is about 12 molar. Wikipedia (https://en.wikipedia.org/wiki/Hydrochloric_acid ) has a table that compares various concentration terms used for HCl and molarity (see: Physical Properties).

papabravo said:
A liter is a measurement of liquid volume in case you failed chemistry.
Your personal attack is unwarranted. Please respect the privacy you extended by putting me on your ignore list.

#### jpanhalt

Joined Jan 18, 2008
10,923
so my acid is 6 moles lower then required strengt right ? can i use 3% of strength hydrogen peroxide to make it work ?
because i know making more pure acid is hard and dangerous its beyond me
Is the acid you used labeled with a percentage of HCl? Is that 20%? If so, then it has approximately 6 moles (about 219 g) of HCl per liter. Hydrogen peroxide concentrations are even more confusing to interpret. However, your 6 M (20%) HCl should work with the 3% hydrogen peroxide. (The greatest difference in nomenclature for hydrogen peroxide is between concentrations based on weight as used for antisepsis and concentrations based on"volume percentage" as used is cosmetics to lighten hair. That volume refers to the amount of oxygen (gas) it can produce. As I recall, "40% volume" for bleaching hair is about 3% by weight.)

That mixture of HCl and H2O2 for etching is common. The used liquid is mostly CuCl2 (cupric chloride) , which is a good etchant in its own right, if of sufficient concentration. As mentioned earlier, I used ferric chloride or cupric chloride for etching. They perform about equally. In my limited experience, I found cupric chloride to work a little faster, and it was a bit harder to control the endpoint. I preferred ferric chloride for PCB's that had finer details. I have very little experience with HCl/peroxide as I found that mixture damaged the resist mask I used. That resist was a photoresist, which apparently is no longer available.

#### Papabravo

Joined Feb 24, 2006
14,833
so 100 ml of my acid should be 21.8 grams if its actually 6 moles right ?
Almost. As I pointed out in my correction I was thinking that 6 moles of HCl was at 100% concentration. This was an error on my part. The 6 molar solution is the 20% HCl (commonly known as Muriatic acid). That solution is 20% Hcl and 80% water. You have to take the water into account. If you take 100 ml of 6 molar HCl it will have about 21.8 grams of HCl, the rest will be water. Here is a page with some info on computations with solutions of acids

https://mason.gmu.edu/~sslayden/Lab/sws/acid-calc.htm

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#### Chris65536

Joined Nov 11, 2019
254
Actually the riddle for me is how man may spend a minimum day-long of valuable work time...
Sometimes getting there is half the fun! I just recently started collecting chemical elements, and I got a nice chunk of Germanium. Maybe I could make my own diode?

#### Chris65536

Joined Nov 11, 2019
254
so 100 ml of my acid should be 21.8 grams if its actually 6 moles right ?
Plus 100g for the 100ml of water = 121.8g total.