Amphoteric and Amphiprotic (1 Viewer)

[Sparcod]

Hey. Two questions today.
1. I don't get the difference between these two similar-sounding words. What is the difference between amphoteric and amphiprotic?

2. What if a 1M strong acid (take HCL) was to be diluted to 10^2, it's pH rises from 0 to 2 using the formula .. pH= -log10 [H+]. What if it was to be diluted to 10^8 mol/L. It would be very watery but it's pH would be 8. Shouldn't an acid's pH be less than 7. Please explain. What's going on?

Thanks.

 

[Dreamerish*~]

Hey. Two questions today.
1. I don't get the difference between these two similar-sounding words. What is the difference between amphoteric and amphiprotic?

2. What if a 1M strong acid (take HCL) was to be diluted to 10^2, it's pH rises from 0 to 2 using the formula .. pH= -log10 [H+]. What if it was to be diluted to 10^8 mol/L. It would be very watery but it's pH would be 8. Shouldn't an acid's pH be less than 7. Please explain. What's going on?

Thanks.

1. First of all, you might be relieved to hear that the term amphoteric is not in the syllabus, therefore you can just stick with amphiprotic. Amphiprotic substances are able to both donate and accept protons (H⁺), and proton-transfer reactions are not always acid-base reactions, whereas amphoteric substances are substances that can act both as an acid or a base. They might sound exactly the same, but the term amphoteric restricts itself to acid-base reactions, while amphiprotic covers a wider range of substances.

2. Remember k_w = 1.00 x 10^-14, which means:
[H₃O⁺] x [OH^-] = 1.00 x 10^-14.

When the concentration of H₃O⁺ is so low, that is, a 1 M solution that has been diluted to 0.00000001 M solution, the concentration of OH^- would equal to (1.00 x 10^-14)/0.00000001. When [OH^-] > [H₃O⁺], the solution is alkaline. Therefore you have a pH of 8.

 

[bmc]

amphiprotic means it can act as an acid or base

 

[Dreamerish*~]

amphiprotic means it can act as an acid or base

No, it doesn't.

It means a being able to both donate and recieve protons - hence amphiprotic. Your definition is of amphoteric substances.

 

[Sparcod]

Does that mean the acid (eg HCL) becomes a base if diluted? That's what the mathematics says.

 

[Dreamerish*~]

Does that mean the acid (eg HCL) becomes a base if diluted? That's what the mathematics says.

I don't really know how to answer that. From the k_w formula and the above calculations you can see how it works, but logically it's quite confusing. If I didn't know better I would have assumed that the pH would be 7.0.

 

[insert-username]

Does that mean the acid (eg HCL) becomes a base if diluted? That's what the mathematics says.

If you add an acid to water, it cannot become more basic. Check out this site.

When you were first introduced to the concept of pH you invariably neglected the role of water dissociation in determining the pH. For example, we can imagine a game where I shout out acid concentrations (lets assume it is HCl) and you in turn shout out the pH. The game might go something like this:

(Flick) 1*10^-8

(You - tentatively) 8?

The problem of course is that we are adding [very small amounts of] an acid to water (at a pH of 7) and then saying that the solution becomes more basic (less acidic). That counterintuitive result arises because we neglected the water dissociation.

They then multiply through and all sorts of stuff with the K_w formula, but in the end, you have to include the fact that water self-ionises in the calculation for very dilute acids.

It all ends up with very dilute acids ([H₃O⁺] less than 1*10^-6) having pH levels extremely close to, but less than 7.

What if it was to be diluted to 10^8 mol/L. It would be very watery but it's pH would be 8. Shouldn't an acid's pH be less than 7. Please explain. What's going on?

Conveniently enough, that site used that exact number. It calculated the pH to be 6.98, not 8. Check out the link above for the full working.


I_F

 

[Riviet]

An easy way to remember it is the pro in amphiprotic, and amphiprotic substances can donate and accept protons.

 

[hydrobiont]

Hey, what tool or software do u guys use to type chemical symbols and equations?

 

[.ben]

hey guys what's wrong with this statement (if anything)

"However, there are exceptions to this rule with some oxides exhibiting both acidic and basic properties, that is, acting as a base in the presence of an acid and behaving as an acid in the presence of a base. These species of oxides are termed amphoteric and include elements such as Al, Zn, Sn, Pb, and Be."

thnaks

 

[Riviet]

If I'm not mistaken, that's an extract from Conquering Chemistry (3rd/4th edition?) and nothing is wrong with it.

 

[.ben]

ok cool thanks!

 

[XcarvengerX]

Hey, what tool or software do u guys use to type chemical symbols and equations?

Do you mean how to write CO₂ or CO₃^2-?
Type in CO<sub>2[/sub*] and CO3[/sub*]<sup>2-[/sup*] without the stars (*).

I think we use = sign for equilibrium and minus greater than signs (->) for forward reaction.

I hope that's what you are asking for.</sup></sub>

 

[Riviet]

I think hydrobiont was referring more to specific software or program that produces these super scripts and sub scripts, as well as chemical symbols.

 

[tofuking]

You can have a pure water solution with a pH of 8. [H3O+] x [OH-] = 1.00 x 10-14 at 25 C. You can't have a concentration of 10^-8 M for hydronium at 25 C however you can at lower temperatures.

 

[okhan90]

sorry but i had too say something...

WHEN DILUTING AN ACID.. THE PH DOES NOT CHANGE... IT STAYS CONSTANT.. concentration changes not the pH.. why because as the syllabus dot point about strong and weak acids tells us to talk about is that no matter how much u dilute acids.. ph is the same

 

[brenton1987]

WHEN DILUTING AN ACID.. THE PH DOES NOT CHANGE... IT STAYS CONSTANT.. concentration changes not the pH.. why because as the syllabus dot point about strong and weak acids tells us to talk about is that no matter how much u dilute acids.. ph is the same

You are joking arent you?

The definition of pH is the negative log of the proton concentration. Change the concentration and the pH changes.

If I have a 1 M solution of HCl
pH = -log (1)
= 0

If I take 10 mL of that solution and dilute it to 100 mL I now have a 0.1 M solution of HCl
pH = -log (0.1)
= 1

Dilute that solution 1 in 10 again to get a 0.01 M solution
pH = -log (0.01)
= 2

 

[chousta]

You are joking arent you?

The definition of pH is the negative log of the proton concentration. Change the concentration and the pH changes.

If I have a 1 M solution of HCl
pH = -log (1)
= 0

If I take 10 mL of that solution and dilute it to 100 mL I now have a 0.1 M solution of HCl
pH = -log (0.1)
= 1

Dilute that solution 1 in 10 again to get a 0.01 M solution
pH = -log (0.01)
= 2

lol yea i agree with the post above...its absurd that way it was defined 2 posts above....contradicting even

 

[kooliskool]

gg lol

 

[jlnWind]

Hey. Two questions today.
1. I don't get the difference between these two similar-sounding words. What is the difference between amphoteric and amphiprotic?

Firstly, props to insane-username that was the most f*cking cool proof ive ever seen in chemistry rofl, as if you the quadratic formula to find concentration haha.

umm I guess its easier to explain amphiprotic first

Amphiprotic substances (NaHCO3) which act as either a proton donator (acid) or proton acceptor (base)
Amphiprotic substance come under the umbrella term of amphoteric.

Amphoteric substances are within the scope of the syllabus because they more strictly apply to substances can act as a base and an acid.

The greatest source of our confusion is that from the syllabus our model for the definition of acids and bases is restricted to the Bronsted-Lowry theory. Instead amphoteric encompasses that of the Lewis Theory (some of you may come across lewis bases describing ligands in Chemistry of Art)

A Lewis acid is therefore any substance, such as the H⁺ ion, that can accept a pair of nonbonding electrons. In other words, a Lewis acid is an electron-pair acceptor. A Lewis base is any substance, such as the OH^- ion, that can donate a pair of nonbonding electrons. A Lewis base is therefore an electron-pair donor.

This is why amphoteric substance include amphoteric oxides. Amphoteric oxides
such as ZnO react with NaOH as an acid but do not donate a proton. For this reason amphoteric is beyond the syllabus as it requires the Lewis Theory.

For the sake of HSC Chemistry, usually it refers to substances known as amphoteric oxides such as ZnO PbO and Al2O3 which react with both acids and alkalis to form salts.