Achieve W10 #2

[EriMizuguchi2K]

Could someone explain how to think through question #2 on the week 10 achieve homework?

The question is:
Which of these substances is amphoteric, that is, it can act as a Brønsted acid and a Brønsted base?
BrO−2

H2PO−4

HBrO2

PO3−4

H3PO4

[Krutika_Joshi_3I]

Amphoteric essentially means that in a Bronsted equation, the substance can act as a base or an acid. Amongst all the options, H2PO4 is the only compound that will create both a strong acid and a strong base, which makes this the correct option.

[Xuan Lai 1H]

Bronsted acids/bases refer to the movement of hydrogen, so for a species to be an amphoteric bronsted acid and base, it must have a Hydrogen present. That lets you eliminate 2 choices. Next, remember that bronsted bases are proton acceptors, and species with a negative charge can accept H+. Only H2PO4- has both hydrogens and a negative charge so that's your answer!

[carrie_karchmer_3D]

A Brønsted acid must have hydrogen in the formula and a Brønsted base must be able to accept H+. H2PO4- has both H present and a negative charge so it meets both those criteria, therefore it is amphoteric.

[Vicky Tong 3E]

Additionally, you can look at the periodic table for future questions! Elements in/close to the diagonal line of metalloids form amphoteric acids, along with compounds that have hydrogen and an overall negative charge.