I'm not sure how to do these...I keep getting the wrong answers... Please help someone...
Mg(s) + 2 HCl(aq)= MgCl2 (aq) + H2(g)
a. What volume of 15.7 M hydrochloric acid will react with 2.1 grams of Mg?
b. What mass of magnesium will react with 8.5 liters of 0.7 M hydrochloric acid?
c. How many liters of hydrogen will you make (at STP) if you react 1.90 L of 0.030 M hydrochloric acid with excess magnesium?
It would much easier and certainly simpler for you to show how you solve them. That way we can find the error and understand where you're going wrong instead of us working all of them and you comparing your answers with ours.
a. To calculate the volume of hydrochloric acid needed to react with a certain amount of magnesium, you can use the equation's balanced coefficients as conversion factors. Let's break it down step by step:
Step 1: Calculate the number of moles of magnesium (Mg) using its molar mass. The molar mass of magnesium is 24.31 g/mol, so 2.1 grams of Mg would be:
2.1 g / 24.31 g/mol = 0.0863 mol of Mg
Step 2: Use the balanced equation to determine the mole ratio between magnesium and hydrochloric acid. From the equation, we know that 1 mol of Mg reacts with 2 mol of HCl.
Step 3: Use the molarity (concentration) of the hydrochloric acid to convert moles of HCl to volume (liters). The molarity (M) represents the number of moles of a substance per liter of solution. In this case, we are given 15.7 M hydrochloric acid.
0.0863 mol of Mg * (2 mol HCl / 1 mol Mg) * (1 L / 15.7 mol HCl) = 0.0109 L or 10.9 mL of 15.7 M HCl
Therefore, you would need 10.9 mL of 15.7 M hydrochloric acid to react with 2.1 grams of Mg.
b. To calculate the mass of magnesium required to react with a certain volume of hydrochloric acid, we'll follow similar steps:
Step 1: Convert the volume of hydrochloric acid from liters to moles. The molarity (M) of the acid (0.7 M) tells us that there are 0.7 moles of HCl per liter of solution.
8.5 L * 0.7 mol/L = 5.95 mol of HCl
Step 2: Use the balanced equation to determine the mole ratio between magnesium and hydrochloric acid. From the equation, we know that 1 mol of Mg reacts with 2 mol of HCl.
Step 3: Convert moles of HCl to moles of Mg:
5.95 mol HCl * (1 mol Mg / 2 mol HCl) = 2.97 mol of Mg
Step 4: Calculate the mass of Mg using its molar mass:
2.97 mol * 24.31 g/mol = 72.4 g of Mg
Therefore, you would need 72.4 grams of magnesium to react with 8.5 liters of 0.7 M hydrochloric acid.
c. To calculate the volume of hydrogen produced, we'll follow these steps:
Step 1: Convert the given volume of hydrochloric acid to moles using its molarity (M = 0.030 M):
1.90 L * 0.030 mol/L = 0.057 mol of HCl
Step 2: Use the balanced equation to determine the mole ratio between hydrogen gas (H2) and hydrochloric acid. From the equation, we know that 1 mol of Mg reacts with 1 mol of H2.
Step 3: Convert moles of HCl to moles of H2:
0.057 mol HCl * (1 mol H2 / 2 mol HCl) = 0.0285 mol of H2
Step 4: Convert moles of H2 to volume using the ideal gas law, assuming standard temperature and pressure (STP). At STP, 1 mole of any gas occupies 22.4 liters.
0.0285 mol * 22.4 L/mol = 0.6396 L or 639.6 mL of H2
Therefore, 1.90 L of 0.030 M hydrochloric acid reacting with excess magnesium would produce 639.6 mL of hydrogen gas at STP.