# How to turn a weak acid into a strong acid

Nick tringali
TL;DR Summary
Turning .1M HCL into a high molarity strong acid.
so my question is how do I turn .1M HCL into a super strong acid like 10M or higher HCL. What is the highest M ever recorded for HCL? At what Molarity do I have to wear gloves and avoid skin contact?

## Answers and Replies

Homework Helper
Gold Member
That makes NO SENSE. NONE!

Homework Helper
Gold Member
Summary:: Turning .1M HCL into a high molarity strong acid.

At what Molarity do I have to wear gloves and avoid skin contact?
If this is still regarding a strong mineral acid such as the mentioned HCl, handling any of strength 0.0001M or higher, WEAR GLOVES; and GOGGLES.

I do not really know what the lower limit is, so in case any member recommends greater care or a lower concentration, then follow that advice!

Nick tringali
Nick tringali
That makes NO SENSE. NONE!
So my understanding is that the strength of an acid depends on what molar it is. For example 0.1 Molar HCl is not as strong as 1 Molar HCl. My question would be how do you increase molarity of an acid. Does that make sense?

Mentor
My question would be how do you increase molarity of an acid.

Depends on the acid. No simple way in the case of hydrochloric.

Nick tringali
Homework Helper
Gold Member
So my understanding is that the strength of an acid depends on what molar it is. For example 0.1 Molar HCl is not as strong as 1 Molar HCl. My question would be how do you increase molarity of an acid. Does that make sense?
We may have differences about word usage. We might loosely say "strength" when what is meant is "concentration", but when discussing hazardous materials, we should use wording with precise meaning for the proper purposes. Glacial Acetic Acid may be a WEAK acid, but I sure as he__ would not want to handle it around foods or beverages nor handle it without wearing goggles & gloves. One might be handling a STRONG acid like Sulfuric and it might be in use in a situation that it be 0.01M (a measurement of CONCENTRATION), but in case any drip of it spill or fly onto your hand or skin, it needs to be rinsed with water immediately - and the person should STILL have been wearing glooves and goggles!

Nick tringali
Nick tringali
Okay got it, so I am referring to concentration. Let's use your sulfuric acid example. 0.01 M sulfuric acid spills onto your hand, you rinse it off. That is much different than a 10.00 M Sulfuric acid spilling onto your hand, correct? Wouldn't the 10 Molar acid burn right through your hand while the .01 M may just sting a bit? Would I be correct to also say that the .01 M sulfuric acid would dissolve steel at a slower rate than 10.00 Molar sulfuric acid? Lastly, is there a concentration of Glacial Acetic Acid (being that its a weak acid) where it can be equal to the dissolving rate of a strong acid at a more mild concentration? I am not sure if that last part makes sense.

Nick tringali
Depends on the acid. No simple way in the case of hydrochloric.
Well diluting an acid is easy as you can just add water to it right? I figured then concentrating would be just as simple. Couldn't you just pull out water to increase the molarity? Thats the way I see it.

DrStupid
Couldn't you just pull out water to increase the molarity?

That is easy with sulfuric acid but not with hydrochloric acid.

Nick tringali
Nick tringali
That is easy with sulfuric acid but not with hydrochloric acid.
Whats the difference?

Homework Helper
Gold Member
Lastly, is there a concentration of Glacial Acetic Acid (being that its a weak acid) where it can be equal to the dissolving rate of a strong acid at a more mild concentration? I am not sure if that last part makes sense.
Glacial Acetic Acid is 100% Acetic Acid.

Also, you and any less knowledgeable readers, be aware that this and some of the following posts would in practice present or describe possible safety hazards.

Mentor
HCl is a gas at room temperature, it stays a gas until cooled below the boiling point.

Boiling point is -121.1°F (-85.05°C), really low. So distillation is difficult and requires special equipment, for starters. Lots of upfront cost. You can but fairly strong HCL at any swimming pool supply place in the US.
It also is available at building supply places, for cleaning off mortar on brick - it is called muriatic acid most places that sell it. It is not expensive.

What exactly do you want? Strong acids by themselves are not terribly useful.

symbolipoint
Homework Helper
Gold Member
ATTENTION: Moderators may decide to remove this posting.

Nick Tringali,
You may be interested in reading to learn about the existence and meaning of Acetic Anhydride, and Fuming Sulfuric Acid, to improve your understanding.

Homework Helper
Gold Member
Nick Tringali,
Just by curiosity, I do not require you to answer:
Are you a high school student, or college or university student, studying Chemistry?
Are you reading about or studying Chemistry on your own while not enrolled in any Chemistry course?

Gold Member
There’s a lot going on in this thread.

Best practice is to wear PPE (gloves, safety glasses, lab coat) whenever handling any pure chemicals, regardless of their concentration. Volatile compounds like HCl require good ventilation as well.

Glacial acetic acid is not well-described as a weak acid. “Weak” in a chemical context means that dissociation in solution is incomplete, whereas “strong” means that dissociation is complete. Hydrochloric acid, being a strong acid, is completely dissociated in water:
$$HCl \longrightarrow H^++Cl^-$$
When acetic acid is dissolved in water, some undissociated ##CH_3COOH## remains; hence, it is referred to as a weak acid. Glacial acetic acid has no water (and people don’t generally talk about its self-ionization), so calling it a weak acid is misleading.

A more concentrated acid will undergo reaction at a faster rate than a less concentrated acid. This is true for basically all chemical reagents, not just acids: reaction rate is generally proportional to concentration.

Sulfuric acid is an oxidizer and has an enormous enthalpy of hydration in addition to being an acid, so the reactions it undergoes are more varied. Concentrated sulfuric acid will damage tissue, but not (mainly) because of its acidity.

HCl forms an azeotrope with water at around 6 M, so you can get there with distillation (from either direction). Gaseous HCl can dissolve in water up to a concentration of 12 M or so. Above that, two phases are formed (12 M HCl liquid and HCl vapor). In the solid state, you can get significantly higher HCl concentration via a variety of cocrystal phases.

Pure HCl is a gas and is easily obtained in the lab by adding concentrated sulfuric acid to NaCl, but as @jim mcnamara noted, it has a low boiling point, and pure liquid HCl isn’t great fun to work with.

ATTENTION: Moderators may decide to remove this posting.

Nick Tringali,
You may be interested in reading to learn about the existence and meaning of Acetic Anhydride, and Fuming Sulfuric Acid, to improve your understanding.
Why in the world would moderators remove that?

DrClaude, Nick tringali and etotheipi
snorkack
Notice that distilled water is a pure chemical, too - and it does NOT require any personal protective equipment tap water does not. Unless you are trying to protect the distilled water from you, not vice versa.

Gastric acid is 0,16 M hydrogen chloride in glands. Somewhat diluted in stomach, but when you have as little as 0,01M, you are suffering from indigestion.
Gastric acid can certainly damage stomach (gastric ulcers), gullet (hearburn) and does some damage to teeth, but you do not normally use gloves to vomit.
(Eyes, of course, are more sensitive)

Among foods, lime juice is ph 2,0...2,5. Several sour tasting foods are around 3. So if the acid is not a poisonous one like HF, there should be no problem drinking a strong but dilute mineral acid at 0,0001 M.

Strong acids are actually easier to neutralize for equal pH than weak acids - because the strong acids have less buffering capacity. At pH 2,5, HCl solution is 3 mM, and that´ s it - neutralize those and it is done. But with the same pH, citric acid (first pKa 3,13) is around 16 mM - you have to neutralize both the dissociated citric acid (3 mM) and 13 mM undissociated acid, and then also the 2nd and 3rd acid hydrogens. And expend much more body fluids on neutralization.

Now about properties of HCl: at 1 bar, HCl is not miscible with water, because a solubility gap lies from about 48 % HCl to quite close to 100 %. Also, 100 % HCl is not actually a strong acid, because it has low polarity: dielectric permittivity just about 12 at boiling point.

Of course HCl can be concentrated by distillation. Its volatility complicates matters here. Pure distillation at constant pressure would only give you azeotrope - and that given unlimited theoretic plates. Because water vapour and HCl vapour being both gases are naturally miscible.

A theoretically better approach would be crystallization. Effectively nothing is miscible in ice save heavy water. Practically, you also need to precipitate water in large clear crystals, to avoid trapping mother liquor in slush.
Crystallization also cannot pass melting point extrema - eutectics and hydrates - but melting point extrema generally won´ t match boiling point extrema.

Nick tringali
Nick tringali
There’s a lot going on in this thread.

Best practice is to wear PPE (gloves, safety glasses, lab coat) whenever handling any pure chemicals, regardless of their concentration. Volatile compounds like HCl require good ventilation as well.

Glacial acetic acid is not well-described as a weak acid. “Weak” in a chemical context means that dissociation in solution is incomplete, whereas “strong” means that dissociation is complete. Hydrochloric acid, being a strong acid, is completely dissociated in water:
$$HCl \longrightarrow H^++Cl^-$$
When acetic acid is dissolved in water, some undissociated ##CH_3COOH## remains; hence, it is referred to as a weak acid. Glacial acetic acid has no water (and people don’t generally talk about its self-ionization), so calling it a weak acid is misleading.

A more concentrated acid will undergo reaction at a faster rate than a less concentrated acid. This is true for basically all chemical reagents, not just acids: reaction rate is generally proportional to concentration.

Sulfuric acid is an oxidizer and has an enormous enthalpy of hydration in addition to being an acid, so the reactions it undergoes are more varied. Concentrated sulfuric acid will damage tissue, but not (mainly) because of its acidity.

HCl forms an azeotrope with water at around 6 M, so you can get there with distillation (from either direction). Gaseous HCl can dissolve in water up to a concentration of 12 M or so. Above that, two phases are formed (12 M HCl liquid and HCl vapor). In the solid state, you can get significantly higher HCl concentration via a variety of cocrystal phases.

Pure HCl is a gas and is easily obtained in the lab by adding concentrated sulfuric acid to NaCl, but as @jim mcnamara noted, it has a low boiling point, and pure liquid HCl isn’t great fun to work with.

Why in the world would moderators remove that?
Thank you!

Gold Member
just add water to it right

No. You should always add the acid to the water.

BoB

Nick tringali and symbolipoint
Mentor
figured then concentrating would be just as simple.
Just add an acid with a higher concentration to it. That would be the equivalent process. It's kind of trivial, of course. "Produced 0.01 M HCl out of 0.001 M HCl by adding 10% 0.1 M HCl".

Mayhem
So my understanding is that the strength of an acid depends on what molar it is. For example 0.1 Molar HCl is not as strong as 1 Molar HCl. My question would be how do you increase molarity of an acid. Does that make sense?
Be careful with your choice of words. Acid "strength" is usually quantified in terms of pKa and qualitatively on its ability to how much it dissociates in water (strong acids tend to dissociate entirely). Molarity relates to amount of substance per unit volume. This gives us a better estimate of the pH of the acid, which isn't a constant, but the pKa is constant (under constant conditions)!

0.1 M HCl has the same pKa as 1 M HCl, but the pH of a given solution would be different, and therefore its chemical properties also vary.

Gold Member
No. You should always add the acid to the water.

BoB
It's water to acid...

Homework Helper
Gold Member
It's water to acid...
NO! The typical and long-taught and practiced way of mixing acids or acids & water, emphasized for SAFETY is to add the acid to the water. (Or the higher concentrated to the less concentrated, and in many cases, with mixing/agitation.)

rbelli1, Ygggdrasil, mfb and 1 other person
Gold Member
NO! The typical and long-taught and practiced way of mixing acids or acids & water, emphasized for SAFETY is to add the acid to the water. (Or the higher concentrated to the less concentrated, and in many cases, with mixing/agitation.)
For safety reasons we rinse acid spills with water and we add water to sulfuric acid in cars as well as any lead acid batteries used for backup power storage.

Homework Helper
Gold Member
For safety reasons we rinse acid spills with water and we add water to sulfuric acid in cars as well as any lead acid batteries used for backup power storage.
First you need to understand why water to acid is bad. Dilution of sulphuric acid is a strongly exothermic reaction. Adding a small amount of water to a large amount of acid would generate heat around the diminishing water droplets and could be enough to boil them. The steam could blow acid around.
I don't *know* why the reverse process is safer. It also generates heat, but the nucleus is a diminishing drop of concentrated acid, which if it boils (BP much higher than water), maybe likely to blow water and diluted acid around. Still, I'd pour cautiously, pausing frequently, looking, listening and feeling (indirectly!) for signs of heating. (Not to mention goggles and other PPE.)

Spills - you want to get rid of the acid, so you can hardly do that by adding more concentrated acid. You have to add water. Undesirable and potentially harmful, but necessary. And you add massive amounts of water very quickly, hopefully overwhelming the heating effect with a small quantity of acid.

If there were a large spill, you would need to be very careful. Perhaps use a large hosepipe from a good distance?? (I'really don't know. Just thinking what I might try if I absolutely had to.)

Batteries - Again, you're stuck with the necessity of adding water, so must just try to do it carefully. I think the sulphuric acid gets up to about 4M (but not sure). I can only assume that this is low enough to allow topping up with water, without boiling. One could make a point of adding the water when the battery is at a low state of charge, when the acid is less concentrated.

symbolipoint
Gold Member
First you need to understand why water to acid is bad. Dilution of sulphuric acid is a strongly exothermic reaction. Adding a small amount of water to a large amount of acid would generate heat around the diminishing water droplets and could be enough to boil them. The steam could blow acid around.
I don't *know* why the reverse process is safer. It also generates heat, but the nucleus is a diminishing drop of concentrated acid, which if it boils (BP much higher than water), maybe likely to blow water and diluted acid around. Still, I'd pour cautiously, pausing frequently, looking, listening and feeling (indirectly!) for signs of heating. (Not to mention goggles and other PPE.)

Spills - you want to get rid of the acid, so you can hardly do that by adding more concentrated acid. You have to add water. Undesirable and potentially harmful, but necessary. And you add massive amounts of water very quickly, hopefully overwhelming the heating effect with a small quantity of acid.

If there were a large spill, you would need to be very careful. Perhaps use a large hosepipe from a good distance?? (I'really don't know. Just thinking what I might try if I absolutely had to.)

Batteries - Again, you're stuck with the necessity of adding water, so must just try to do it carefully. I think the sulphuric acid gets up to about 4M (but not sure). I can only assume that this is low enough to allow topping up with water, without boiling. One could make a point of adding the water when the battery is at a low state of charge, when the acid is less concentrated.
My experience is with large lead acid storage batteries kept at float voltage, therefore in a fully charged state. These batteries have see through cases allowing for views of any boiling or extreme chemical reactions. In maintaining proper electrolyte level no violent reactions were ever observed. Certainly not a lab setting, this is why your statement baffled me.

Mayhem
My experience is with large lead acid storage batteries kept at float voltage, therefore in a fully charged state. These batteries have see through cases allowing for views of any boiling or extreme chemical reactions. In maintaining proper electrolyte level no violent reactions were ever observed. Certainly not a lab setting, this is why your statement baffled me.
I doubt lead-acid batteries contain highly concentrated sulfuric acid anyway. The reason you should always add acid to water is to reinforce a safety mindset so when you are working with 18 M sulfuric acid, you don't do the opposite and risk getting yourself hurt. But if you add water to 0.1 M acetic acid ... yeah, nothing will happen.

First you need to understand why water to acid is bad. Dilution of sulphuric acid is a strongly exothermic reaction. Adding a small amount of water to a large amount of acid would generate heat around the diminishing water droplets and could be enough to boil them. The steam could blow acid around.
I don't *know* why the reverse process is safer. It also generates heat, but the nucleus is a diminishing drop of concentrated acid, which if it boils (BP much higher than water), maybe likely to blow water and diluted acid around. Still, I'd pour cautiously, pausing frequently, looking, listening and feeling (indirectly!) for signs of heating. (Not to mention goggles and other PPE.)

Spills - you want to get rid of the acid, so you can hardly do that by adding more concentrated acid. You have to add water. Undesirable and potentially harmful, but necessary. And you add massive amounts of water very quickly, hopefully overwhelming the heating effect with a small quantity of acid.

If there were a large spill, you would need to be very careful. Perhaps use a large hosepipe from a good distance?? (I'really don't know. Just thinking what I might try if I absolutely had to.)

Batteries - Again, you're stuck with the necessity of adding water, so must just try to do it carefully. I think the sulphuric acid gets up to about 4M (but not sure). I can only assume that this is low enough to allow topping up with water, without boiling. One could make a point of adding the water when the battery is at a low state of charge, when the acid is less concentrated.

Adding water to sulfuric acid and adding sulfuric acid to water are equally exothermic. However, adding acid to water allows the heat to disperse throughout the solution so nothing exciting happens. This won't cause acid to spray around.

FactChecker and symbolipoint
Mentor
The heat capacity shouldn't be that different between the two liquids, but splashes from a container with water are safer than splashes from a container of concentrated acid.

Mayhem
snorkack
For properties of hydrogen cloride, such as heat of solution/dilution, see:
https://www.jsia.gr.jp/data/handling_02e.pdf
If you add 1 g of water to 1 l of hydrogen chloride, would hydrogen chloride be spilt from the bottle, or would air be sucked in?

Gold Member
The heat capacity shouldn't be that different between the two liquids, but splashes from a container with water are safer than splashes from a container of concentrated acid.
The specific heat capacity is not likely to be different between the two liquids, but often one would be diluting a small quantity of concentrated acid in a larger volume of water, so heat capacity would be another reason to add acid to water (in addition to the point you bring up about the concentration of acid in splashes). For example, a drop of water in 1 mL of concentrated acid would cause a larger temperature change than a drop of concentrated acid in 10 mL of water.

Homework Helper
Gold Member
For properties of hydrogen cloride, such as heat of solution/dilution, see:
https://www.jsia.gr.jp/data/handling_02e.pdf
If you add 1 g of water to 1 l of hydrogen chloride, would hydrogen chloride be spilt from the bottle, or would air be sucked in?
I've not done that. But when dissolving hydrogen chloride in water, we used an inverted funnel to avoid the water being sucked back into the HCl generator.
So I'd expect air to be sucked in.

You can see water being sucked in when some is added to a flask containing some HCl. This is the HCl fountain experiment

Hillbillychemist
The basic confusion here is between acid strength and acid concentration. A strong acid has a weak bond between hydrogen and the atom to which it is attached and a weak acid has a strong bond. The dividing or reference bond is the strength of the hydrogen-oxygen bond in water. Molarity is a measure of concentration not strength and is defined as the number of moles (one gram molecular weight) dissolved in one liter of solution.
In terms of acid strength it would be necessary to change the structure of the acid molecule in such a way as to weaken the hydrogen bond to the atom to which it is attached. One example would be to replace the hydrogens attached to carbon in acetic acid with a more electronegative element such as chlorine. The resulting trichloroacetic acid is a strong acid.
Looking at the concentration aspect, glacial acetic acid is a weak acid but is pure acetic acid so its concentration is 100% and its molarity is 17.4 meaning that one liter of glacial acetic acid contains 17.4 moles of acetic acid.
Fuming sulfuric acid is not pure sulfuric acid but is sulfuric acid containing dissolved sulfur trioxide.
When looking at the issue of adding acid to water, as stated, when a small amount of water is added to concentrated sulfuric acid the highly exothermic dissolution causes the small amount of water (boiling point 100 celsius) to boil splattering the sulfuric acid. When adding the sulfuric acid (boiling point 377 celsius) to water the sulfuric acid does not boil and the heat generated is readily absorbed by the large amount of water.

Merlin3189, BillTre and symbolipoint
Gold Member
The easy thing to remember is that acids are generally denser than water. HCl acid has a specific gravity of 1.18; water is, of course, 1.0.

If you have acid in the bottom of a container and add water, the water floats on the acid. You then have a large exothermic reaction at the interface surface which causes both to boil... and spatter acid far and wide.

Conversly, when adding acid to water, the acid migrates downward through the water, distributing the heat and avoiding the boiling.

That's why the recommendation is to SLOWLY add acid to water.

Hope this helps.

Cheers,
Tom

Merlin3189 and symbolipoint
snorkack
The easy thing to remember is that acids are generally denser than water. HCl acid has a specific gravity of 1.18; water is, of course, 1.0.

If you have acid in the bottom of a container and add water, the water floats on the acid. You then have a large exothermic reaction at the interface surface which causes both to boil... and spatter acid far and wide.

Conversly, when adding acid to water, the acid migrates downward through the water, distributing the heat and avoiding the boiling.

That's why the recommendation is to SLOWLY add acid to water.
That seems to be the better insight!
Sulphuric acid being high boiling is not applicable to acids in general. At azeotrope (98 %), sulphuric acid does boil at 337 (not 377) Celsius, but sulphur trioxide itself releases even more heat on dilution (duh! all the same heat sulphuric acid would release plus the reaction heat to sulphuric acid) and boils at +45 Celsius. Suitably concentrated HCl of course boils at room temperature. As does HF.

But the abovesaid substances still form aqueous solutions that are denser than water, sink to bottom and confine bubbles and spray.
Of acids, the ones that are less dense than water include carboxylic acids starting with propanoic acids. But simple carboxylic acids don´ t have large heats of dilution.
A strong acid might be organic sulphonic acids. But sulphonic acid groups also add density: C2H5CO2H density is 0,99, but C2H5SO3H density is 1,35. Higher aliphatic sulphonic acids and sulphuric acid esters would have to be lighter than water (hard to find actual data), and still strong acids (due to nature of group), with possibly large heat of transferring the proton to water - but the organic tail would participate in diluting the heat of dilution!

Hillbillychemist
That seems to be the better insight!
Sulphuric acid being high boiling is not applicable to acids in general. At azeotrope (98 %), sulphuric acid does boil at 337 (not 377) Celsius, but sulphur trioxide itself releases even more heat on dilution (duh! all the same heat sulphuric acid would release plus the reaction heat to sulphuric acid) and boils at +45 Celsius. Suitably concentrated HCl of course boils at room temperature. As does HF.

But the abovesaid substances still form aqueous solutions that are denser than water, sink to bottom and confine bubbles and spray.
Of acids, the ones that are less dense than water include carboxylic acids starting with propanoic acids. But simple carboxylic acids don´ t have large heats of dilution.
A strong acid might be organic sulphonic acids. But sulphonic acid groups also add density: C2H5CO2H density is 0,99, but C2H5SO3H density is 1,35. Higher aliphatic sulphonic acids and sulphuric acid esters would have to be lighter than water (hard to find actual data), and still strong acids (due to nature of group), with possibly large heat of transferring the proton to water - but the organic tail would participate in diluting the heat of dilution!
The functional factors are boiling points and heat capacity. Water has a very high heat capacity so adding a small amount of acid to a large amount of water results in a small temperature rise. Density is not a factor as any acid with a high heat of dilution has a very high solubility in water and would dissolve far faster than any possible segregation due to density.
Sulfuric acid does not boil at 45 celsius. Adding sulfuric acid to water RAISES the boiling point of the mixture. If I said 377 celsius, that was a typo I did not catch. Hydrochloric acid DOES NOT boil at room temperature. Otherwise, all those lab reagent bottles would have to be pressure containers and muriatic acid would not be sold in one gallon plastic containers at retail outlets. Sulfur trioxide in fuming sulfuric acid would immediately react with any water to form more sulfuric acid: SO3 + H2O --> H2SO4. This multi-step reaction is used in the industrial production of sulfuric acid.
In any event, the question was about the strength of acids not the hazards of their dilution.

snorkack
Sulfuric acid does not boil at 45 celsius. Adding sulfuric acid to water RAISES the boiling point of the mixture. If I said 377 celsius, that was a typo I did not catch.
45 Celsius is the boiling point of pure (and non-polymerized) sulphur trioxide.
Hydrochloric acid DOES NOT boil at room temperature. Otherwise, all those lab reagent bottles would have to be pressure containers and muriatic acid would not be sold in one gallon plastic containers at retail outlets.
I specified sufficiently concentrated.
Boiling point of concentrated hydrochloric acid drops rapidly with concentration:
20 % - 108 C
30 % - 90 C
32 % - 84 C
34 % - 71 C
36 % - 61 C
38 % - 48 C
42 % - 20 C
45 % - 0 C
48 % - -18 C
The hydrochloric acid sold by retail seems to go to 32 %, which boils at 90 %.
Scroll up at the post where hydrogen chloride generator is used to feed a funnel... there filled with NaCl/H2SO4 mixture, and heated.
Well, you can use the same arrangement to generate gaseous hydrogen chloride by heating hydrochloric acid above 20 %! Say, 32 % acid would give off mostly HCl and little water Thus you can distil one portion of 32 % acid down to 30 % and absorb the fumes into the other portion of 32 % acid which you are cooling. So you can get from two portions of 32 % acid a portion of 30 % and a portion of 34 % acid. Or if the portions are different size and you are using enough cooling of the second portion, as much as 48 % acid.