Question

In a reaction of an unknown metal that follows the generic reaction (unbalanced) given below,

M(s) + HCl(aq) → MCl2 (aq) + H2 (g)

a. 0.0900 g of metal is reacted with 50.00 mL of 0.100 M HCl. Once the reaction is complete, the reaction mixture is titrated with 0.1375 M NaOH. It requires 16.35 mL of NaOH to reach the endpoint. What is the molecular weight of the metal that was reacted?

b. What is the identity of the metal that was reacted?

Answer 1

(a)given reaction is:

M(s) + HCl(aq)   MCl₂(aq) + H₂(g)

Balanced reaction is:

M(s) + 2HCl(aq)   MCl₂(aq) + H₂(g)

Molarity of Hcl added = 0.100M = 0.100mol/L

Volume of HCl added = 50 mL = 0.050L

Moles of HCl added = Molarity * Volume = 0.100mol/L*0.050 L = 0.005 moles

Similarly moles of NaOH = 0.1375 M * 0.01635 L = 0.002248 moles

Thus, Moles of HCl in excess = Moles of Hcl that reacts with NaOH = moles of NaOH = 0.002248 moles

Moles of Hcl that reacts with metal = Total moles of HCl added - moles of HCl in excess

= 0.005 moles - 0.002248 moles = 0.002752 moles

From reaction 1 mol of Metal reacts with 2 moles of Hcl

So,Moles of Metal = Moles of HCl reacted/ 2 = 0.002752 moles/ 2 = 0.001376 moles

Mass of metal that reacts = 0.0900g

Molar mass of metal = mass/ Moles = 0.0900g/ 0.001376 moles = 65.4 g/mol

(b) Molar mass of metal = molar mass of zinc

Thus, Metal is Zinc