AP Chem questions. please help!!?

Question

I need help with these 2 questions if possible:

- An excess of Mg(s) is added to l00. mL of 0.400 M HCl. At 0°C and 1 atm pressure, what volume of H2 gas can be obtained?

- 2 H2O(l) + 4 MnO4-(aq) + 3 ClO2-(aq) →4 MnO2(s) + 3 ClO4-(aq) + 4 OH-(aq)

According to the balanced equation above, how many moles of ClO2-(aq) are needed to react completely with 20. mL of 0.20 M KMnO4 solution?


Thanks in advance!

Answer 1

Mg + 2HCl---->MgCl2 + H2

since Mg is in excess the limitant is HCL. Now you have 0.1L*0.4M HCL = 0.04 moles HCl

each 2 mol of HCl produces 1 mol of H2
so
0.04 will produce 0.02 moles of H2

1 mol of H2 at Normal conditions will have a volume of 22.4L so
0.02 * 22 = 0.448L is your volume

Answer 2

The second one, you need to know how many moles of KMnO4 you have: .020L x .20M KMnO4 = .004 KMnO4 mol

Note: K is neutral in the reaction so I does not show up in the equation.

We will then multiply the equation by .001 to get:
.002 H2O(l) + .004 MnO4-(aq) + .003 ClO2-(aq) →.004 MnO2(s) + .003 ClO4-(aq) + .004 OH-(aq)

Which means we need .003 mol of ClO2-(aq) to fully react.

Sorry too early in the morning and been out of school too long I fixed it...