Question

Calcium reacts with a polyatomic ion to form a compound with the general formula Ca(X). What would be the most likely formula for the compound formed between potassium and the polyatomic ion X?

A) K X
B) K2X
C) KX2
D) K2X3
E) K3X2

Answer 1

Answer:

B) K2X

Explanation:

In an uncharged compound, the total oxidation state must be zero. The oxidation state of the calcium is +2, thus we get the following formula, where x is the oxidation state of the polyatomic ion X:

$x + 2 = 0 \\ x = 0 - 2 \\ x = - 2$

Also, it is known that potassium has an oxidation state of +1. Since the new compound also has a total oxidation state equal to zero, we get the following equation, where k is the number of K atoms:

$k \times 1 + ( - 2) = 0 \\ k - 2 = 0 \\ k = - ( - 2) \\ k = 2$

That's how it is found that the compumd consists of 2 K+ ions and one X ion.