Question

Zinc hydroxide, Zn(OH)2, is precipitated from the tailings ponds of zinc mining operations before the water is released into local rivers. This reduces the concentration of Zn2+ ions in the wastewater. 5.00 kg of sludge containing zinc hydroxide is titrated against HCl solution and 1.50 L of 2.0 M acid is required to reach the endpoint and neutralize the zinc hydroxide. What mass of zinc is contained in the 5.00 kg sludge?

Answer 1

First, we need to find the number of moles of HCl used in the titration:

moles HCl = M x V = 2.0 mol/L x 1.50 L = 3.00 mol

Since zinc hydroxide and HCl react in a 1:2 molar ratio according to the balanced chemical equation:

Zn(OH)2 + 2 HCl → ZnCl2 + 2 H2O

we know that twice as many moles of HCl are required to react with each mole of Zn(OH)2. Therefore, the number of moles of zinc hydroxide in the 5.00 kg sludge can be calculated as follows:

moles Zn(OH)2 = 1/2 x moles HCl = 1/2 x 3.00 mol = 1.50 mol

Finally, we can use the molar mass of Zn(OH)2 to convert the number of moles to mass:

mass Zn(OH)2 = moles Zn(OH)2 x molar mass Zn(OH)2

= 1.50 mol x 99.39 g/mol

= 149.1 g

Therefore, the mass of zinc contained in the 5.00 kg sludge is 149.1 grams.

Step-by-step explanation: