Chapter 9 Review

Question

Magnesium hydroxide, Mg(OH)2, is often present in antacids to neutralize stomach acid, HCl. Each antacid tablet contains 0.675 g of magnesium hydroxide. How many grams of HCl get neutralized by one antacid tablet? _____ Mg(OH)2 + _____ HCl 🡪 _____MgCl2 + _____ H2O

Upon heating, aluminum carbonate decomposes to produce aluminum oxide and carbon dioxide. _____Al2(CO3)3 🡪 _____ Al2O3 + _____ CO2 Determine the theoretical yield of CO2 if 75.0 g of Al2(CO3)3 is heated. What is the percent yield of CO2 if 39.7 g of CO2 is collected during an experiment?

Cell respiration reactions in green plants use glucose, C6H12O6, and oxygen gas, O2, to produce carbon dioxide and water. A plant has 25.0 g of glucose and 17.0 g of oxygen gas available for cell respiration. Determine the mass of water produced. What is the limiting reactant? What reactant is in excess? How much excess reactant is left over? _____ C6H12O6 + _____ O2 🡪 _____CO2 + _____ H2O

Answer 1

Hello, Mkc,

Looking at question 1, the first thing is to balance the equation.

_____1 Mg(OH)2 + ____2 HCl 🡪 ____1 MgCl2 + ____2 H2O

Now we know that 1 mole of Mg(OH)₂ will neutralize 1 mole of HCl. So it is a 1 to 1 ratio. Now let's find the number of moles in 0.675g of Mg(OH)₂. Determine the molar mass of Mg(OH)_{2 ,} which I calculate to be 58.3g/mole. (24.3 + 2x16 + 2x1). We can the number of moles by:

0.675g/(58.3g/mole) = 0.0116 moles Mg(OH)₂.

We know from the balanced equation that 0.0116 moles of Mg(OH)₂ will neutralize/react with 0.0116 moles of HCl (a 1 to 1 ratio).

To determine the number of grams in 0.0116 mole HCl, multiply by the molar mass of HCl (1 + 35.5 = 36.5g HCl/mole HCl).

(0.0116 mole HCl)*(36.5 g/mole HCl) = 0.423 g HCl, to 3 sig figs.

The other questions can be answered in a similar manner. Question 2 requires you calculate a result based on the complete decomposition of Al₂(CO₃)₃ and then use the actual yield of 39.7 g to calculate a percentage yield, based on the theoretical amount, expressed as a percentage. Question 3 requires that you determine which reagent is limiting after balancing the equation. The calculations are based on that reagent.

I hope this helps you get started,

Bob