Alkali metals react with water to form hydrogen gas and the hydroxide of the metal. When 3.55 grams of an alkali metal reacts with excess water, 1020ml of hydrogen gas, measured at STP, are evolved. What is the alkali metal?

Answer 1

2X + 2H20 = 2XOH + H2
So two moles of X reacts with water to produce 1 mole of hydrogen.
Let R = relative atomic weight of the alkali metal.
1.020 l /22.4 l = 3.5 g /2R
R=(3.55/2)*22.4/1.02
=39.0

The alkali metal with a RAM closest to 39.0 is.....