Question

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

Answer 1

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.

Answer 2

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^(-)`