Clarification for Sampling #7

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VanessaZhu2L
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Clarification for Sampling #7

Postby VanessaZhu2L » Sun Jan 24, 2021 10:57 pm

HClO is a weak acid ( ka=4.0×10−8 ) and so the salt NaClO acts as a weak base. What is the pH of a solution that is 0.085 M in NaClO at 25 °C?

In this problem, is it because they ask specifically about NaClO that you have to find kb first to solve the problem? I used ka and it was wrong so I just wanted to double check and make sure that that was the reason why you had to find kb first to answer the question. Thank you!

SophiaJenny3I
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Re: Clarification for Sampling #7

Postby SophiaJenny3I » Sun Jan 24, 2021 10:59 pm

Hi! You're correct you do have to find the kB value first. This is because you're specifically looking for the pH of the salt NaClO, which is identified in the problem as a weak base. So yes, you have to convert to Kb from Ka!

JoshMoore2B
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Re: Clarification for Sampling #7

Postby JoshMoore2B » Sun Jan 24, 2021 11:00 pm

VanessaZhu2L wrote:HClO is a weak acid ( ka=4.0×10−8 ) and so the salt NaClO acts as a weak base. What is the pH of a solution that is 0.085 M in NaClO at 25 °C?

In this problem, is it because they ask specifically about NaClO that you have to find kb first to solve the problem? I used ka and it was wrong so I just wanted to double check and make sure that that was the reason why you had to find kb first to answer the question. Thank you!


Yes, you need to find Kb first to answer this question, since NaClO is said to act as a base and the question asks about NaClO.

You can use Ka x Kb = 1 x 10^-14 to convert between them.

Hope this helps!

Sarah Salam 1J
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Re: Clarification for Sampling #7

Postby Sarah Salam 1J » Sun Jan 24, 2021 11:07 pm

Yes, because they are asking about the pH of the weak base, you'll need to find Kb first, and then solve the way you would have with Ka.

VanessaZhu2L
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Re: Clarification for Sampling #7

Postby VanessaZhu2L » Sun Jan 24, 2021 11:17 pm

ahh okay! That makes a lot of sense. Thank you guys so much!

Isaias Gomez D3A
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Re: Clarification for Sampling #7

Postby Isaias Gomez D3A » Sun Jan 24, 2021 11:21 pm

Yes! since its asking for the weak base :)

Geethika Janga 1L
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Re: Clarification for Sampling #7

Postby Geethika Janga 1L » Sun Jan 24, 2021 11:21 pm

Since they identify NaClO as a weak base in the problem, that is why you would need to use Kw=KaxKb to calculate the value of Kb. If I remember correctly there was another sapling problem similar to this one concerning a weak acid, in that case we would need to find Ka instead.

Jaclyn Schwartz 1I
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Re: Clarification for Sampling #7

Postby Jaclyn Schwartz 1I » Sun Jan 24, 2021 11:25 pm

Yep! A general rule is if its an acid use Ka, and if its a base use Kb. And to convert between the two you can use this equation Ka x Kb = 1 x 10^-14! Hope that helps!

Hasan Mirza 3F
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Re: Clarification for Sampling #7

Postby Hasan Mirza 3F » Sun Jan 24, 2021 11:27 pm

Remember that you can use the Kw=1.0x10^-14 to switch between Ka and Kb as Ka*Kb=Kw

Chinmayi Mutyala 3H
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Re: Clarification for Sampling #7

Postby Chinmayi Mutyala 3H » Sun Jan 24, 2021 11:34 pm

It identifies it as a weak base so you would need to find Kb. You can do this by using the formula Ka x Kb = Kw so you would just divide 1.0 x 10^-14 by the given Ka.

joshtully
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Re: Clarification for Sampling #7

Postby joshtully » Sun Jan 24, 2021 11:41 pm

Yes, you have to calculate the Kb value from Ka in this problem, because your are finding the pH of a weak base.


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