Urgent: Calculate the minimum mass of hydrobromic acid that could be left over by the chemical reaction.

Question

Aqueous hydrobromic acid HBr will react with solid sodium hydroxide NaOH to produce aqueous sodium bromide NaBr and liquid water H2O.

Suppose 45. g of hydrobromic acid is mixed with 16.6 g of sodium hydroxide.



Calculate the minimum mass of hydrobromic acid that could be left over by the chemical reaction.

Be sure your answer has the correct number of significant digits.

Answer 1

Since the question prompts you to determine how much of one of the reactants remains, you know that the other reactant is the limiting reagent (runs out first, limiting out how much product can be made). Once the limiting reagent and the proportional amount of the other reactant that's needed for the reactant to go to completion is all used up, there is some of that other reactant left over. First, write out your equation and make sure that it is balanced so that you can determine the mol-to-mol ratios. Pick one of the products to determine how much of it can be made. In acid-base reactions like this one, I usually choose the salt that's formed rather than water. Take the grams of the limiting reagent and divide by the molar mass to get to number of moles of the reactant that you have available to use in the reaction. Multiply by the mol-to-mol ratio of the limiting reagent and product from the balanced reaction and that will give you the number of moles of product. Now you can take the moles of product made and the mol-to-mol ratio of the other reactant to see how many moles of the other reactant are necessary to make that amount of product. Use molar mass of the reactant to get back to grams. Now you can subtract this amount from the total amount that you had to start with to get the amount that is left over.

Please let me know if this doesn't make sense or if you need any additional help!