Really short question, please and thank you

[yellowjellybean]

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What is the pH of 100mL of 0.030 M HBr?
Answer is 1.52

I don't understand why we don't multiple 100 mL/.1L with 0.030M (the solution doesn't)

 

[Gauss44]

What is the pH of 100mL of 0.030 M HBr?
Answer is 1.52

I don't understand why we don't multiple 100 mL/.1L with 0.030M (the solution doesn't)

The molarity alone indicates the ph of a strong acid. It's not being mixed with anything so volume doesn't matter.

 

[yellowjellybean]

I still don't get it. If there are 0.03 moles per liter, then wouldn't you have less moles in 100mL, and then wouldn't you have a higher pH?

 

[Gauss44]

I still don't get it. If there are 0.03 moles per liter, then wouldn't you have less moles in 100mL, and then wouldn't you have a higher pH?

The volume is irrelevant.

 

[sp808]

The definition of pH is based on concentration of hydronium, not the absolute number of moles. 100 ml of a 0.3 M solution has the same concentration as a liter of 0.3 M solution.

 

[LoLCareerGoals]

The volume is irrelevant.

Super helpful answer repeating what someone else said after OP still said he didn't get it. The guy is clearly confused about what is used in the formula.


OP, formula for ph is:
ph = -log10([H+]), where [H+] is already in M, not moles. Acidity in Arrehnious sense is about how concentrated a solution is with [H+]s or [OH-] not how many moles of these ions there are.

 

[yellowjellybean]

Oh thank you! That was driving me crazy.

 

[BerkReviewTeach]

Oh thank you! That was driving me crazy.

This is another question you've posted from handouts that are from the BR lecture course. Why aren't you utilizing the teacher's office hours or email? It would be much more effective and that's what they're there for.

 

[Jepstein30]

This is another question you've posted from handouts that are from the BR lecture course. Why aren't you utilizing the teacher's office hours or email? It would be much more effective and that's what they're there for.

Could be he got the materials second-hand and doesn't have access to the office hours, etc... I've seen a few copies floating around Ebay.

 

[yellowjellybean]

What are you talking about? I'm not taking a course and I don't have any handouts. These questions are from the books.

 

[BerkReviewTeach]

What are you talking about? I'm not taking a course and I don't have any handouts. These questions are from the books.

I'm really sorry if I offended you, because that was not at all the intention. It's completely my bad, because I've seen a couple questions posted from those lately and the question you posted is in the rapid-fire questions in the in-class handout as well as the in the book, but with different answer choices. I mistakenly thought it was the class version of the question.

My point was simply that for anyone in the class, they have a great resource available to them as part of the class tuition when it comes to getting their questions answered. I mistakenly thought you might have been a student, so please accept my apology.

 

[Gauss44]

Super helpful answer repeating what someone else said after OP still said he didn't get it. The guy is clearly confused about what is used in the formula.


OP, formula for ph is:
ph = -log10([H+]), where [H+] is already in M, not moles. Acidity in Arrehnious sense is about how concentrated a solution is with [H+]s or [OH-] not how many moles of these ions there are.

LOLCareerGoals: Check your facts. I reworded what I said to clarify. Please don't criticize me for trying to help someone on this forum.

OP: It's the same concept of ordering a small orange juice and a large orange juice. The small size has the same concentration as the large. Hopefully this is more clear.

 

[yellowjellybean]

No worries 🙂