Acid bases

[silverice]

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What's the ph of 10^-8 M of HCl

 

[milski]

[H] in water is 10^-7
HCl will dissociate completely, so you'll have [H]=10^-7+10^-8=1.1*10^-7
-log(1.1*10^-7)=6.96

If you need just a quick estimate, it's safe to assume that it's 7 or just a bit below that.

 

[Temperature101]

[H] in water is 10^-7
HCl will dissociate completely, so you'll have [H]=10^-7+10^-8=1.1*10^-7
-log(1.1*10^-7)=6.96

If you need just a quick estimate, it's safe to assume that it's 7 or just a bit below that.

Can you explain more how you get that 10^-7...( I know it's water)...The OP did not say that HCl dissociates in water. I would think the pH is 8.

 

[ljc]

Can you explain more how you get that 10^-7...( I know it's water)...The OP did not say that HCl dissociates in water. I would think the pH is 8.

Theoretically, it should be. But you have to dissolve it in something, so you need to add in water's acidity. When they say "HCl is a strong acid because it dissociates completely," they mean in water.

I honestly don't know what would happen if you dissolved it in like diethyl ether or something. But unless it says otherwise, assume the solvent is water.

 

[silverice]

[H] in water is 10^-7
HCl will dissociate completely, so you'll have [H]=10^-7+10^-8=1.1*10^-7
-log(1.1*10^-7)=6.96

If you need just a quick estimate, it's safe to assume that it's 7 or just a bit below that.

Quick estimate is what I'm looking for! Thx!

 

[milski]

Quick estimate is what I'm looking for! Thx!

Water is acidic enough that the pH will stay 7, minimal amounts of HCl won't change it.

Theoretically, it should be. But you have to dissolve it in something, so you need to add in water's acidity. When they say "HCl is a strong acid because it dissociates completely," they mean in water.

I honestly don't know what would happen if you dissolved it in like diethyl ether or something. But unless it says otherwise, assume the solvent is water.

Ether has pKa significantly higher than 8 which means that HCl will be the major source of H+ and the pH should be 8. Unlike aqueous solutions, pH of 8 will not indicate a basic solution here - neither Cl-, nor ether are good proton acceptors.

 

[MedPR]

Water is acidic enough that the pH will stay 7, minimal amounts of HCl won't change it.



Ether has pKa significantly higher than 8 which means that HCl will be the major source of H+ and the pH should be 8. Unlike aqueous solutions, pH of 8 will not indicate a basic solution here - neither Cl-, nor ether are good proton acceptors.

Can you explani why a pH of 8 doesn't indicate a basic solution? I mean, I know HCl is a strong acid...

I would never have expected a situation where HCl has a pH of anywhere near 7-8

 

[milski]

Can you explani why a pH of 8 doesn't indicate a basic solution? I mean, I know HCl is a strong acid...

pH=7 is the 'border' between acidic and basic in aqueous solutions because anything higher than 7 would give you more OH- which is a very good base. If the solvent is diethyl ether, you have only H+, Cl- and the ether itself - none of these is a good proton acceptor (pKa for HCl is negative, and so is pKa C2H5OC2H5H+)

I would never have expected a situation where HCl has a pH of anywhere near 7-8

It's all about how much of it you have. If it is the only source of [H] and you have only 10^-8 M of HCl, pH will be 8.

 

[ljc]

Ether has pKa significantly higher than 8 which means that HCl will be the major source of H+ and the pH should be 8. Unlike aqueous solutions, pH of 8 will not indicate a basic solution here - neither Cl-, nor ether are good proton acceptors.

This makes sense, and I probably should have realized this on my own.

Thanks!