chemistry question

Question

The following chemical equation has NOT been balanced.

 

Na + H₂O --> NaOH + H₂

 

How many grams of sodium are needed to produce 0.250 moles of hydrogen gas?

Answer 1

The first step to answering this question is to balance the chemical equation. If you count the elements on both sides the Na and O are balanced, but there are 2 H on the left and 3 H on the right. Adding a second water to the left means that there are now 1 extra O and H on the left. That can be balanced by adding a second NaOH to the right. To balance the extra Na on the right side now you add a second equivalent of Na to the left. That gives us the following balanced chemical equation

2 Na + 2 H2O ---> 2 NaOH +H2.

With the balanced equation we can use the stoichiometry of the reaction to find out how many moles of Na we need. We would need twice as many moles of Na as H2 produced or 0.250x2 = .500 moles of Na. To find the mass we need to multiply the amount in moles by the molecular mass.

.500 mol * 22.990 g/mol = 11.5 g of Na. I limited the answer to three digits because there were three significant digits in the original question.