A 0.500 L solution of 1.250 M hydrochloric acid is used to neutralize a 75.0 g sample of magnesium hydroxide in a coffee-cup calorimeter. Magnesium hydroxide solution, also known as milk of magnesia, is a common ingredient of antacids. The temperature in the calorimeter was observed to rise from 20.07deg;C to 25.1°C during the neutralization. Assume the density of the hydrochloric acid solution is 1.00 g/mL and that the specific-heat capacity of the system is the same as that for water, 4.18 J/g-K. Assume only water is available to absorb or release heat, and that the reaction is at constant pressure. (25 points)
2 HCl(aq) + Mg(OH)2(aq) -> MgCl2(aq) + 2 H2O(l)
a. How many moles of HCl are there? Use that number to calculate the maximum yield of MgCl2. How many moles of Mg(OH)2 are there? Use that number to calculate the maximum yield of MgCl2. Is HCl or Mg(OH)2 the limiting reagent? (7 points)
b. How many moles of Mg(OH)2are neutralized by HCl? How many moles of excess reagent
were left over? To find the moles left over, subtract the number of moles of Mg(OH)2neutralized from the original number of moles of Mg(OH)2. (5 points)
c. If 12.3 g of magnesium chloride were obtained after the neutralization was complete, what was the percent yield? Determine how many moles of MgCl2 should theoretically be produced from the reaction. Convert that to grams, and determine the percent yield. (4 points)
d. What was the enthalpy change for the system in the coffee-cup calorimeter? ?H = -mcp?T. Figure out how many grams of hydrochloric acid there are, assuming its density is 1.00 g/ml. Don’t forget about the mass of Mg(OH)2. Make sure to convert the temperature from °C to K. Assume the specific-heat capacity of the system is the same as that for water, 4.18 J/g-K. (5 points)
e. What was the heat of reaction per mole of water produced? You already have figured out how many moles of HCl are consumed. Use this number to figure out how many moles of water are produced, then use your answer to part d to figure out the heat of reaction if a mole of water was produced. (4 points)
2 HCl(aq) + Mg(OH)2(aq) -> MgCl2(aq) + 2 H2O(l)
a. How many moles of HCl are there? Use that number to calculate the maximum yield of MgCl2. How many moles of Mg(OH)2 are there? Use that number to calculate the maximum yield of MgCl2. Is HCl or Mg(OH)2 the limiting reagent? (7 points)
b. How many moles of Mg(OH)2are neutralized by HCl? How many moles of excess reagent
were left over? To find the moles left over, subtract the number of moles of Mg(OH)2neutralized from the original number of moles of Mg(OH)2. (5 points)
c. If 12.3 g of magnesium chloride were obtained after the neutralization was complete, what was the percent yield? Determine how many moles of MgCl2 should theoretically be produced from the reaction. Convert that to grams, and determine the percent yield. (4 points)
d. What was the enthalpy change for the system in the coffee-cup calorimeter? ?H = -mcp?T. Figure out how many grams of hydrochloric acid there are, assuming its density is 1.00 g/ml. Don’t forget about the mass of Mg(OH)2. Make sure to convert the temperature from °C to K. Assume the specific-heat capacity of the system is the same as that for water, 4.18 J/g-K. (5 points)
e. What was the heat of reaction per mole of water produced? You already have figured out how many moles of HCl are consumed. Use this number to figure out how many moles of water are produced, then use your answer to part d to figure out the heat of reaction if a mole of water was produced. (4 points)