The unbalanced equation below shows the reaction between sodium and water. In the reaction, hydrogen gas is given off and sodium hydroxide is formed. The gas is collected and there is found to be
1.8 grams of hydrogen. What mass of sodium would have been used in this reaction?

Na + H2O + NaOH + H2

41.4 g

Explanation:

2Na(s) + 2H2O (l) > 2NaOH ( aq) + H2 (g)

According to the above balnced chemical equation the ratio between moles of H2 gas formed to moles of Na used up is 1:2

Molar mass ( Mass of 1 mol) Of H2 gas is 2 gmol-1

So in 1.8 g of H2 0.9 mol should be present

Therefore no. of moles of Na used should be 2× 0.9 = 1.8 moles

Molar mass of Na= 23 gmol-1

So mass of 1.8 mol of Na = 1.8× 23 g = 41.4g

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