Question

To answer this question, you will need to write the balanced equation and set up a BCA table. Using appropriate rounding rules, round your answer to the nearest tenth of a decimal (ex: 10.2 g)
Water decomposes when electrolyzed to produce hydrogen and oxygen gas. If 2.5 grams of water were decomposed, how many grams of oxygen gas should be given off?

A. 4.5g
B. 2.2g
C 1.3g
D 0.1g

Answer 1

Water decomposes when electrolyzed to produce hydrogen and oxygen gas. If 2.5 grams of water were decomposed 1.04 grams of oxygen will be formed.

BCA table:

2$H_{2}$O ⇒ $H_{2}$ + $O_{2}$

B  0.13        0 + 0

C  -0.13      0.065 + 0.065

A  0             0.065

Explanation:

Balanced equation for water decomposition into hydrogen and oxygen gases

   2$H_{2}$O ⇒ $H_{2}$ + $O_{2}$

B  0.13        0 + 0

C  -0.13      0.065 + 0.065

A  0             0.065

Number of moles of water = $\frac{mass}{atomic mass of 1 mole}$

mass = 2.5 grams

atomic mass= 18 grams

number of moles can be known by putting the values in the formula,

n = $\frac{2.5}{18}$

  = 0.13 moles

2 moles of water gives one mole of oxygen on decomposition

so, 0.13 moles of water will give x moles of oxygen on decompsition

$\frac{1}{2}$ = $\frac{x}{0.13}$

x = 0.065 moles of oxygen will be formed.

moles to gram will be calculated as

mass =number of moles x atomic mass

        = 0.065 x 16

         = 1.04 grams of oxygen.