One of the alkali metals reacts with oxygen to form a solid white substance. when this substance is dissolved in water, the solution gives a positive test for hydrogen peroxide, h2o2. when the solution is tested in a burner flame, a lilac-purple flame is produced. what is the likely identity of the metal?

Potassium (K)

Explanation:

First, you need to know the possible alkali metals, which are:

Sodium (Na), Litium (Li), Potassium (K) and Cesium (Cs), rubidium (Rb).

Now, the reaction that is taking place is the following:

M + O2 > M2On

Where n should be the oxidation state of the metal. In this case, most of the alkalin metals have an oxidation state of +1, so, this number should be 1. However some elements can produce the peroxyde, like litium, sodium and potassium.

The following reaction would be:

M2O + H2O > MOH

Now, the hint here is that the solution is tested with a flame. This, would be, the final hint to know which element this is.

In the case of sodium, litium and potassium, the reactions being held are as following:

Li + O2 > Li2O2         Li2O2 + 2H2O > 2LiOH + H2O2

Na + O2 > Na2O2         Na2O2 + 2H2O > 2NaOH + H2O2

K + O2 > K2O2         K2O2 + 2H2O > 2KOH + H2O2

Now, all of these elements throw a different color in the flame. Litium is a red or crimson. Sodium is usually yellow, and finally the potassium is always purple.

Therefore the identity of this metal would have to be potassium.

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