Strength and Weakness

[sharonvivianv]

How do I compare the strength of two acids?

[Cienna Henry 1J]

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

[davidbakalov_lec2_2L]

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]

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]

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]

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

[Abhi Vempati 2H]

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 K_a or pK_a, 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 K_a or pK_a 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]

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]

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]

compare ka values

[Tyler Angtuaco 1G]

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).

[RoshniVarmaDis1K]

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

[Megan_1F]

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.