Question

Magnesium reacts with acid according to the equation: Mg + 2 H+ yields Mg2+ + H2 If 0.883 g of magnesium is added to 25.5 mL of 1.809 M HCl solution at 25°C and 1.00 atm, how many liters will be occupied by the dry hydrogen which is produced? The vapor pressure of water at 25°C is 3.2 kPa

Answer 1

: Mg + 2 H+ yields Mg2+ + H2

First calculate the number of moles of Mg as follows:

0.833 g /24.305 g/mol = 0.0342 mol Mg

Now moles of HCl as follows:

25.5 ml * 1.809 mol /1000 ml = 0.0461 mol HCl

here HCl is a limiting agent

HCl is limiting agent due to following reasons:

1. It completely reacted in the reaction.
2. It determines the amount of the product in mole.

Now calculate the moles of H2 as follows:

0.0461 mol HCl *1 mol of H2/ 2 mol HCl

= 0.02305 mol H2

According to gas law volume of gases is calculated as follows:

PV=nRT

V = nRT /P

Here R= 0.08206 (L*atm)/(mol*K) , P= 1.0 atm L, T = 298 K

V = nRT /P

V = 0.02305mol *0.08206 (L*atm)/(mol*K) *298K / 1.0 atm

V=0.564 -L