Answer:
1. 6.50mL
2. pH = 13.097
Explanation:
1. The neutralization of HCl with Al(OH)₃ is:
3HCl + Al(OH)₃ → Al(Cl)₃ + 3H₂O
40.0mL ≡ 0.0400L of 0.500M HCl are:
0.0400L × (0.500mol / L) = 0.0200 moles of HCl
Based on the neutralization, 3 moles of HCl react with 1 mole of Al(OH)₃, thus, the moles of Al(OH)₃ that react with 0.0200 mol of HCl are:
0.0200mol HCl × (1mol Al(OH)₃ / 3mol HCl) = 0.00667 moles of Al(OH)₃. In grams:
0.00667 moles Al(OH)₃ × (78g / 1mol) = 0.520g of Al(OH)₃ ≡ 520mg
As 5.00mL of milk magnesia contain 400mg of Al(OH)₃, the mL of milk magnesia required for a complete reaction are:
520 mg Al(OH)₃ × (5.00mL / 400mg) = 6.50mL
2. The reaction of lithium hydroxide (LiOH) with perchloric acid (HClO₄) is:
HClO₄ + LiOH → LiClO₄ + H₂O
The reaction is 1:1.
Moles of LiOH and HClO₄ are:
LiOH: 0.0500L × (0.350mol / L) = 0.0175 moles of LiOH
HClO₄: 0.0300L × (0.250mol / L) = 0.0075 moles of HClO₄
Assuming the reaction goes to completion, moles of LiOH that remains are:
0.0175 mol - 0.0075 mol = 0.0100 moles of LiOH. The total volume is 80.0mL, 0.0800L. Thus, molarity of LiOH is:
0.0100 mol / 0.0800L = 0.125 M of LiOH
It is possible to obtain the pOH of the solution thus:
pOH = -log (OH) = -log 0.125M = 0.903
As pH = 14- pOH,
pH = 14 - 0.903 = 13.097
I hope it helps!
