Which of the following species can be Bronsted-Lowry bases? a- -OH b- Ca2+ c- C2H6 d- PO43- e- -OCl f- MgCO3

2 Answers
Oct 10, 2015

Which of these species can accept a proton, #H^+#?
I count 4!

Explanation:

A Bronsted-Lowry base is any species that will increase the concentration of #OH^-# in water. Hydroxide anion, #OH^-#, fits this description by definition.

So a Bronsted-Lowry base is by this definition a proton acceptor (from #H_2O#), that will increase the concentration of hydroxide anion, #OH^-#, in water. Hydroxide anion, #OH^-#, fits this description by definition. Calcium ion, #Ca^(2+)# ion, will neither affect #[OH^-]# nor #[H^+]#, and is irrelevant to #pH#. Likewise ethane, #C_2H_6#, will dissolve very sparingly in water and will not affect the #pH# of the aqueous solution, i.e. it is neither a Bronsted base nor a Bronsted acid.

Phosphate anion, #PO_4^(3-)#, is a powerful Bronsted base, and will accept protons from water to form #HPO_4^(2-)#, biphosphate ion, and dihydrogenphosphate ion, #H_2PO_4^(-)#, along with equilibrium quantities of #OH^-#, as is required of a Bronsted base. The same is true of hypochlorite anion, #ClO^-#, and the carbonate anion of magnesium carbonate, #MgCO_3#, both of which will hydrolyze water to some extent to form again equilibrium quantities of #OH^-#.

All of these examples I flagged will affect #pH# to some extent. If I have been unclear or waffly, I will certainly attempt to clarify.

Oct 10, 2015

See explanation.

Explanation:

Bronsted-Lowry definition for a base, is any substance that can accept a proton #H^+#.

Let us take a look on the options one by one.

a- #OH^-#
It is a Bronsted-Lowry base because it accepts proton according to the following reaction:
#H^++OH^(-)->H_2O#

b- #Ca^(2+)#
It is not Broasted-Lowry base, since it is a cation and it cannot accept a proton. Two same charge ions will repel.

c- #C_2H_6#
It is not Broasted-Lowry base, since it is an alkane (saturated hydrocarbon) and it cannot accept a proton. Alkenes and alkynes could be considered as Broasted-Lowry bases.

d- #PO_4^(3-)#
This is the phosphate, which is the conjugate base of hydrogen phosphate (#HPO_4^(2-)#). It is a Bronsted-Lowry base because it accepts proton according to the following reaction:
#H^++PO_4^(3-)->HPO_4^(2-)#

e- #ClO^-#
It is the hypochlorite, which is the conjugate base of hypochlorous acid (#HClO#). It is a Bronsted-Lowry base because it accepts proton according to the following reaction:
#H^++ClO^(-)->HClO#

f- #MgCO_3#
Magnesium carbonate is a salt that is made from the magnesium ion (#Mg^(2+)#) and the carbonate (#CO_3^(2-)#). Once it is added to water, it will dissociate into its ions and the carbonate ion (#CO_3^(2-)#) will be a Bronsted-Lowry base because it accepts proton according to the following reaction:
#H^++CO_3^(2-)->HCO_3^(-)#