Quick Question

[Edward Elric]

Hey AN members

I would like to know how the increase in temperature decreases the hydronium ions and subsequently decreasing the ph. Without using the proportionality rules of maths, that v is inversely proportional to the amount and the amount is directly proportional to concentration, can someone concisely and logically explain the theory that is happening without relying on maths formulas.

This might sound like a stupid question but all my teacjcer was able to explain to me was the mathematical component of whats happening not the chemistry involved.

Thanks

[keltingmeith]

Let's try this:



So, we have an acid. Some kind of acid - it doesn't matter what acid. For any kind of acid, when it dissociates in water, we get an exothermic reaction. If we want to find pH, we need to use K_a to find the concentration of hydronium using this reaction.

Here's the thing - if we increase the temperature, the equilibrium is going to shift (as we know by Le Chatelier's principle). Hopefully, you know that it'll shift to the left, so we're going to get a decrease in the amount of hydronium ions being produced in our reaction. So, the concentration of hydronium ions will decrease, and so will the pH.

Does that make a little more sense to you?

[Edward Elric]

Let's try this:



So, we have an acid. Some kind of acid - it doesn't matter what acid. For any kind of acid, when it dissociates in water, we get an exothermic reaction. If we want to find pH, we need to use K_a to find the concentration of hydronium using this reaction.

Here's the thing - if we increase the temperature, the equilibrium is going to shift (as we know by Le Chatelier's principle). Hopefully, you know that it'll shift to the left, so we're going to get a decrease in the amount of hydronium ions being produced in our reaction. So, the concentration of hydronium ions will decrease, and so will the pH.

Does that make a little more sense to you?

Hmm, that kind of makes sense  but i have a couple of questions.
1) how is ionisation of an acid exothermic?
2) and if we increase the temp, how do we know the position of equilibium shifts to the left?

But the rest i understand thanks.

[keltingmeith]

ARGH my equation messed. Okay, so:

1. It's not very exothermic - only slightly. So, it's not like you'll see things catching fire, or possibly even steam. Think about it, though - acids are corrosive. So, if you mix them with water, wouldn't you expect the acid to make it hotter and release heat? How do things corrode? Are neutralisation reactions normally exothermic or endothermic? If you want a better answer, I'm not the person to ask, sorry.

2. Okay, so here's our reaction, with something very wrong added in:



So, heat is produced on the right side. So, if we put MORE heat in (increase the temperature), the system is going to want to make less heat (by Le Chatelier's principle), so we're going to have a net backwards reaction (or a shift to the left).

[Edward Elric]

ARGH my equation messed. Okay, so:

1. It's not very exothermic - only slightly. So, it's not like you'll see things catching fire, or possibly even steam. Think about it, though - acids are corrosive. So, if you mix them with water, wouldn't you expect the acid to make it hotter and release heat? How do things corrode? Are neutralisation reactions normally exothermic or endothermic? If you want a better answer, I'm not the person to ask, sorry.

2. Okay, so here's our reaction, with something very wrong added in:



So, heat is produced on the right side. So, if we put MORE heat in (increase the temperature), the system is going to want to make less heat (by Le Chatelier's principle), so we're going to have a net backwards reaction (or a shift to the left).

Thanks for clearing that up, I think I get it now

[Bestie]

hello,
quick question here...
what would you need to rinse the conical flask with in an acid - base titration? NOTE: acid will be in the conical flask and base in the burette
thank you