## Strength and Weakness

sharonvivianv
Posts: 63
Joined: Fri Apr 06, 2018 11:05 am

### Strength and Weakness

How do I compare the strength of two acids?

Cienna Henry 1J
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Joined: Fri Sep 28, 2018 12:15 am
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### Re: Strength and Weakness

Compare their K values. The larger the value of Ka, the stronger the acid.

davidbakalov_lec2_2L
Posts: 61
Joined: Fri Sep 28, 2018 12:23 am

### Re: Strength and Weakness

The main way to compare is to look at their corresponding Ka values. Higher values mean that the forward reaction is more favored, which thereby means that the acid dissociates to a greater extent and is therefore stronger.

Aili Ye 4L
Posts: 58
Joined: Fri Sep 28, 2018 12:16 am

### Re: Strength and Weakness

Look at the Ka, the larger the Ka the more favored the dissociation into H3O+ and the stronger the acid. Or look at pKa- the smaller the pKa the stronger the acid.

Ray Guo 4C
Posts: 90
Joined: Fri Sep 28, 2018 12:15 am

### Re: Strength and Weakness

If possible, you can compare their X-H bond strength to see which one is more likely to lose protons. That would be the stronger acid.

Katherine Chhen 3I
Posts: 53
Joined: Fri Sep 28, 2018 12:15 am

### Re: Strength and Weakness

Would the pKa and Ka values be given or would we have to calculate that ourselves?

Abhi Vempati 2H
Posts: 104
Joined: Fri Aug 09, 2019 12:17 am

### Re: Strength and Weakness

Katherine Chhen 3I wrote:Would the pKa and Ka values be given or would we have to calculate that ourselves?

You only need one value to make the comparison, so if you're given either the Ka or pKa, you can tell which one is the stronger acid. However, sometimes you may not be given either of these values. If this is the case, we would do something similar to what we did in Wednesday's lecture. We would compare the bond lengths involving the protons and we would also look for any electron-pulling molecules, allowing us to compare the relative acidities of multiple acids. I believe we haven't learned how to calculate Ka or pKa yet, which means that we probably will not be tested on it. Professor Lavelle may teach this to us next week, though, and if he does, it will probably be tested. Hope this helps!

chrischyu4a
Posts: 52
Joined: Thu Jul 25, 2019 12:16 am

### Re: Strength and Weakness

the strength of an acid is indicated by its Ka. The higher the Ka, the more it dissociates which means that it is a stronger acid

andrewcj 2C
Posts: 102
Joined: Thu Jul 11, 2019 12:17 am

### Re: Strength and Weakness

I feel like this is obvious, but it hasn't been mentioned so I'll say it. You can also compare pH (lower pH means stronger acid).

Callum Guo 1H
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Joined: Fri Aug 02, 2019 12:15 am
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### Re: Strength and Weakness

compare ka values

Tyler Angtuaco 1G
Posts: 130
Joined: Wed Sep 11, 2019 12:16 am

### Re: Strength and Weakness

For strong acids (no kA value provided), observe bond length. For weak acids, the stronger acid is the one with a higher kA value (concentration of the products divided by the concentration of the reactants).

Posts: 51
Joined: Sat Aug 24, 2019 12:16 am

### Re: Strength and Weakness

An acid that dissociates more easily (longer bond length) is a stronger acid and will have a higher KA value.

Megan_1F
Posts: 49
Joined: Thu Jul 25, 2019 12:16 am

### Re: Strength and Weakness

You would look at the Ka value. If the Ka is a higher number, that implies the numerator is larger than the denominator, and thus more products are dissociated so it is more acidic.

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