A monovalent metal with a mass of 3.5 g was treated with water, and hydrogen was released

| February 9, 2021 | education

A monovalent metal with a mass of 3.5 g was treated with water, and hydrogen was released in a volume of 5.6 liters. Define metal.

By the condition of the problem, we write the equation schematically:
Let’s denote the unknown metal-R
2R + 2H2O = H2 + 2ROH – OBP, hydrogen is evolved;
Let’s calculate the number of moles of hydrogen:
1 mol of gas at normal level – 22.4 liters;
X mol (H2) -5.6 l. hence, X mol (H2) = 1 * 5.6 / 22.4 = 0.25 mol.
We make a proportion according to the equation:
X mol (R) – 0.25 mol (H2);
-2 mol       -1 mol hence, X mol (R) = 2 * 0.25 / 1 = 0.5 mol.
Let’s calculate the molar mass of an unknown metal using the formula:
m (R) = Y * M;
M = m / Y = 3.5 / 0.5 = 7 g / mol;
M (Li) = 6.9 = 7 g / mol.
Answer: Li is a monovalent metal of the first group.



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