I only need the answers (lol).. I got these questions wrong, but I want to see w
ID: 834303 • Letter: I
Question
I only need the answers (lol).. I got these questions wrong, but I want to see where I can find my own mistake.
1. How many pounds of sulfur react with 14.7 pounds of zinc to form zinc sulfide, ZnS?
2. Calculate the mass of Na2SO4 needed to prepare 0.273 L of a 0.343 M solution.
3. Oxalic acid reacts with the chromate ion in acidic solution as follows.
3 C2H2O4(aq) + 2 CrO42-(aq) + 10 H+ ? 6 CO2(g) + 2 Cr3+(aq) + 8 H2O(l)
Calculate the molarity of the oxalic acid (C2H2O4) solution if 15.7 mL of the solution consume 45.0 mL of 0.0214 M CrO42-.
4. Calculate the concentration of an aqueous KCl solution if 32.30 mL of this solution give 0.382 grams of AgCl when treated with excess AgNO3.
KCl(aq) + AgNO3(aq) ? AgCl(s) + KNO3(aq)
Explanation / Answer
1)
Balanced reaction:
Zn + S = ZnS
l lb = 453.59 g
Moles of Zn = 14.7 lbs x 453.59 g/1 lb x 1 mol/65.38 g = 101.98 moles
Moles of S = 101.98 moles (ratio of Zn:S is 1:1)
Mass of S = 101.98 moles x 32.07 g/mol x 1 lb/453.59 g = 7.21 lbs
2)
Moles of Na2SO4 = 0.273 L x 0.343 moles/L = 0.0936 moles
Mass of Na2SO4 = 0.0936 moles x 142.04 g/mol = 13.3 g
3)
Moles of CrO4^2- = 45.0 mL x 1 L/1,000 mL x 0.0214 moles/L = 0.000963 moles
Moles of C2H2O4 = 0.000963 moles of CrO4^2- x 3 moles of C2H2O4 / 2 moles of CrO4^2-
Moles of C2H2O4 = 0.00144 moles
Molarity of C2H2O4 = 0.00144 moles / 0.0157 L = 0.0917 M
4)
Moles of AgCl = 0.382 g x 1 mol/143.32 g = 0.00267 moles
Moles of KCl = 0.00267 moles (ratio of AgCl to KCl is 1:1)
Molarity of KCl = 0.00267 moles / 0.0323 L = 0.0827 M