# Foo - Chemistry Help

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View Full Version : Chemistry Help

anthonaut
03-20-06, 04:04 AM
Hey guys and gals,

I need help with a chemistry problem! Normall i would go to "science access" to get help but i have a meeting on at the same time which i need to be at, so any help would be greatly appreciated. (or you could just do it for me :) )

Ok heres the problem:

What weight of P4O10 would i have to add to a litre of water to achieve a solution of pH of 2.0?

Thanks to anyone who helps!

shikaka
03-20-06, 05:21 AM

EJ123
03-20-06, 05:46 AM
Wheres cabbage man?

jschen
03-20-06, 09:50 AM
"cabbage man" checking in. I will never do anyone's homework for them, but I'm happy to help.

You need to figure out what exactly happens to P4O10 when you place it in water. P4O10 itself is not a Bronsted acid. (This is very clear since it lacks hydrogen atoms, and a Bronsted acid is by definition a donor of H+.) So something must happen to it in water to form an acid. And since the only other thing around in water, clearly, you are hydrating it, or adding (H2O)x. So try to write a balanced equation and figure out what acid you are forming.

The acid you form happens to have multiple acidic protons of different pKa's. You must decide what the state of this species is at pH 2. You can do this by comparing the pKa's of the protons (something you should be able to readily look up) with the pH of the solution you're trying to make. And the equation(s) you use to do so will help you figure out just how much of this acid you need for pH 2. And looking back at your balanced equation, you can determine just how much P4O10 you need.

Good luck. If you start working on it and have further questions, post what you've got figured out so far and we'll go from there.

anthonaut
03-21-06, 03:27 AM
"cabbage man" checking in. I will never do anyone's homework for them, but I'm happy to help.

You need to figure out what exactly happens to P4O10 when you place it in water. P4O10 itself is not a Bronsted acid. (This is very clear since it lacks hydrogen atoms, and a Bronsted acid is by definition a donor of H+.) So something must happen to it in water to form an acid. And since the only other thing around in water, clearly, you are hydrating it, or adding (H2O)x. So try to write a balanced equation and figure out what acid you are forming.

The acid you form happens to have multiple acidic protons of different pKa's. You must decide what the state of this species is at pH 2. You can do this by comparing the pKa's of the protons (something you should be able to readily look up) with the pH of the solution you're trying to make. And the equation(s) you use to do so will help you figure out just how much of this acid you need for pH 2. And looking back at your balanced equation, you can determine just how much P4O10 you need.

Good luck. If you start working on it and have further questions, post what you've got figured out so far and we'll go from there.

Wow! Thanks very much for the help, I've got it worked out now.