Question

part a
what is the correct formula for potassium dichromate?
kcr₂o₇
k₂cr₂o₇
k₂cro₄
k(cro₄)₂
none of the above

Explanation:

Step1: Recall ion charges

Potassium ion (\(K^+\)) has a charge of +1. Dichromate ion is \(\text{Cr}_2\text{O}_7^{2-}\) (charge -2).

Step2: Balance charges

To balance the charges, the number of \(K^+\) ions needed is 2 (since \(2\times(+1) + (-2) = 0\)). So the formula is \(K_2\text{Cr}_2\text{O}_7\).

Step3: Check options

• \(K\text{Cr}_2\text{O}_7\): Charge imbalance (K is +1, dichromate -2; 1+(-2)≠0).
• \(K_2\text{Cr}_2\text{O}_7\): Matches the balanced formula.
• \(K_2\text{CrO}_4\): This is potassium chromate (chromate is \(\text{CrO}_4^{2-}\)), not dichromate.
• \(K(\text{CrO}_4)_2\): Incorrect ion combination (dichromate is \(\text{Cr}_2\text{O}_7^{2-}\), not two \(\text{CrO}_4^{2-}\) with K+).

Answer:

B. \(K_2\text{Cr}_2\text{O}_7\)