A solution containing 2.8 moles of magnesium bromide is combined with a solution containing excess potassium carbonate. This chemical reaction takes place:

MgBr2 (aq) + K2CO3 (aq) → MgCO3 (s) + 2KBr (aq).

If the volume of the resulting solution is 1.33 liters, what's the concentration of potassium bromide? Use the periodic table.

A.

0.24 M

B.

2.1 M

C.

3.7 M

D.

4.2 M

E.

5.6 M

The concentration of potassium bromide (KBr) is 4.2M (answer D)

calculation

MgBr₂ (aq) + k₂co₃ (aq) → MgCO₃ (s) + 2 KBr (aq)

Step 1: use the mole ratio to determine the moles of KBr

From equation above MgBr₂ : KBr is 1:2 therefore the moles of KBr is

=2.8 moles x 2/1 = 5.6 moles

Step 2: find the concentration of KBr (malarity)

molarity = moles / volume in liters

= 5.6 moles / 1.33 L = 4.2 M (answer D)