Question

A 2.747g sample of manganese metal is reacted with excess hcl gas to produce 3.22l hydrogen gass at 373 k and 0.951 atm and a manganese chloride compound (mnclx). determine the formula of the manganese chloride produced by this reaction.

Answer 1

1. Find moles! In this case, since we are dealing with H2 gas, we will be using PV=nRT (Where P is pressure, V is volume in liters, n is moles, R is the gas constant specific for the pressure unit and T is temp in Kelvin).
(0.951 atm)(3.22L)=n(.082057)(373K)  
3.062=30.607n  n=0.100 moles H2

Mn (s) +HCl (g)-->  H2 (g)+ Mn(Cl#)

The ratio of HCl to H2 must be 2:1 (Although we do not know the exact number, the ratio must be that so the actual equation can be balanced)
0.100 moles H2* (2 mol HCl/1molH2)=0.200 moles HCl 
0.200 moles HCl * (1mol Cl-/1molHCl)=0.200 moles of chlorine 
2. Find moles of manganese
2.747g Mn * (1 mol Mn/54.938g Mn)=0.05000 moles Mn

3. Mole Ratio
0.05000 moles Mn/0.200 moles chlorine=0.25 (A ratio of 1/4)
The formula should be MnCl₄