The element forms a higher oxide of the composition R2O5. The volatile hydrogen compound contains

The element forms a higher oxide of the composition R2O5. The volatile hydrogen compound contains 8.82% hydrogen. Define the element.

Given:
R2O5 – higher oxide
ω (H in hydrogen compound) = 8.82%

To find:
R -?

Decision:
1) Since R2O5, the highest valence of the element will be equal to V, therefore the element is located in group 5 of the periodic system of D.I.Mendeleev, which means:
H3R is its hydrogen compound;
2) Mr (H3R) = N (H in H3R) * Ar (H) * 100% / ω (H in H3R) = 3 * 1 * 100% / 8.82% = 34;
3) Mr (H3R) = Ar (H) * N (H) + Ar (R) * N (R);
1 * 3 + Ar (R) * 1 = 34;
Ar (R) = 31 – phosphorus (P).

Answer: The unknown element is phosphorus (P).