I think the mass the mass was less than the original because a gas was released into the atmosphere. The mass in a chemical reaction is constant in a closed system according to conservation of mass law. However, if a chemical reaction is completed in an open system, mas changes may occur. In our case i think the change in mass was due to the release of hydrogen gas from the reaction to the atmosphere.
Molarity is mole divided by volume in litres.
0.5mol divide by 0.5L = 1M
The two dimensions of aluminum foil are given 13.72 cm and 8.63 cm respectively with mass 3.1 g.
The density of aluminum is 
. It is defined as mass per unit volume thus, volume of aluminum can be calculated as follows:
Putting the values.
The volume of cuboid is 
, the length and breadth are given, height can be calculated as follows;
Putting the values,
Or, approximately 9.7\times 10^{-3}cm
Therefore, thickness of aluminum foil is 
