What are H+ ions?

Question

What are H+ ions?

Noah Aldrich · Accepted Answer

#H^+# ions represent the characteristic cation of water. I will try to explain what I mean.

Two typical illustrations of autoprotolysis in water are as follows: #H_2O rightleftharpoons H^+ + OH^-# And, #2H_2O rightleftharpoons H_3O^+ + OH^-# I write representations because that's exactly what they are: a molecular understanding of water that may or may not represent reality but is chemically reasonable and undoubtedly useful. We know that at #298# #K#, #K_w# #=# #10^(-14)# #=# #[OH^-][H^+]#, and for most acid/base problems this will suffice. But what is this species, which is also represented as #H_3O^+#, the acidium ion? As far as anyone knows this is a cluster of water molecules with an extra proton associated; so #H_7O_3^+# or #H_9O_4^+#, 3-4 water molecules with an extra #H^+# tacked on. If you have ever played rugby, think of a maul where the forwards bind together and pass the pill from hand to hand. This may not be realistic, in that within a cluster of water molecules (unlike within a pack of forwards), proton transfer can tunnel across water clusters; it is the movement of charge rather than protons. This explains the ionic mobility of #H^+# and #OH^-# in comparison with other ions. At undergraduate level, it is probably useful to think of the acidium ion as an actual entity. You must be able to use #K_w# in some form in your calculations, and use #[H^+]# and #[H_3O^+]# to determine #pH# and #pOH#. I apologize if this is information I have already written somewhere else; I was unable to locate the link.

Henry Antrim · Answer

undefined H+ ions, also known as hydronium ions or hydrogen ions, are positively charged ions consisting of a single proton. They are formed when a hydrogen atom loses its electron, resulting in a lone proton with a positive charge. In aqueous solutions, H+ ions are often accompanied by water molecules to form hydronium ions (H3O+), which play important roles in acid-base chemistry and various biochemical processes.