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Acid/Base Trends

Posted: Thu Dec 05, 2019 1:01 pm
by DTingey_1C
If the strength of binary acids increases with elements across a period because of the increase in electronegativity, why does the strength of binary acids also increase with elements down a group if electronegativity typically decreases down a group? Thanks

Re: Acid/Base Trends

Posted: Thu Dec 05, 2019 1:04 pm
by Veronica_Lubera_2A
Strong acids dissociate completely. When going down a group, the atoms are getting larger (making a bond longer), and therefore making the bond weaker. Therefore, the strength will increase because the bond is easier to break.

Re: Acid/Base Trends

Posted: Thu Dec 05, 2019 1:05 pm
by Rita Chen 1B
I think this is because as you go down a group for binary acids, you are looking at the strength and length of the HA bond, not the polarity, so the weaker the HA bond, the stronger the acid.

Re: Acid/Base Trends

Posted: Thu Dec 05, 2019 1:26 pm
by Annie Ye
Why is HF a weaker acid than HI?

Re: Acid/Base Trends

Posted: Thu Dec 05, 2019 1:29 pm
by Daniel Honeychurch1C
I has a larger ionic radius which makes the H-I bond longer and weaker. Therefore, HI dissociates more than HF and is a stronger acid.

Re: Acid/Base Trends

Posted: Thu Dec 05, 2019 1:45 pm
by andrewcj 2C
Annie Ye wrote:Why is HF a weaker acid than HI?

When an acid dissociates, the bond must be broken between the H+ and the conjugate base. If the bond is strong, which it is in the case of HF, this makes it harder and less of the acid dissociates, resulting in less H+ present in the resulting solution and a higher pH by definition of pH.

Re: Acid/Base Trends

Posted: Sun Dec 08, 2019 5:19 pm
by Annie Ye
The trend of acidity increases from left to right across the periodic table but it decreases going from top to bottom.