Question

Water (H2O) forms when hydrogen gas (H2) and oxygen gas (O2) react according to the equation below: 2H2 O2 → 2H2O What mass of water forms when 1. 45 × 10-3 g O2 react completely? (Molar mass of O2 = 32. 00 g/mol; molar mass of H2O = 18. 02 g/mol) 1. 63 × 10-3 g 8. 16 × 10-4 g 1. 29 × 10-3 g.

Answer 1

The mass of water formed in the reaction is $\rm 1.63\;\times\;10^-^3$ g. Thus, option A is correct.

The balanced chemical equation for the formation of water is:

$\rm 2\;H_2\;+\;O_2\;\rightarrow\;2\;H_2O$

From the balanced chemical equation, 1 mole of oxygen forms 2 moles of water.

Computation for the mass of water

The moles of a compound is given by:

$\rm Moles=\dfrac{Mass}{Molar\;mass}$

The moles of oxygen reacted in the reaction are:

$\rm Moles\;O_2=\dfrac{1.45\;\times\;10^-^3\;g}{32\;g/mol} \\Moles\;O_2=0.045\;\times\;10^-^3\;mol$

The moles of water formed is:

$\rm 1\;mol\;O_2=2\;mol\;H_2O\\0.045\;\times\;10^-^3\;mol\;O_2=0.045\;\times\;10^-^3\;\times\;2\;mol\;H_2O\\0.045\;\times\;10^-^3\;mol\;O_2=0.09\;\times\;10^-^3\;mol\;H_2O$

The moles of water formed are $\rm 0.09\;\times\;10^-^3$ mol.

The mass of water is given as:

$\rm Mass=Moles\;\times\;Molar\;mass\\Mass\;H_2O=0.09\;\times\;10^-^3\;\times\;18\;g\\Mass\;H_2O=1.63\;\times\;10^-^3\;g$

The mass of water formed in the reaction is $\rm 1.63\;\times\;10^-^3$ g. Thus, option A is correct.

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