A isotope is atoms of the same element with different amount of neutrons to change the mass. They can become more stable by sharing or giving away electrons to have a stable electron shell
Molarity: M = #moles of solute / liters of solution
# moles = mass / molar mass
Molar mass calculation
Barium hydroxide = Ba (OH)2
Atomic masses
Ba = 137.4 g/mol
O=16 g/mol
H=1 g/mol
Molar mass of Ba (OH)2 = 137.4 g/mol + 2*16g/mol + 2*1 g/mol = 171.4 g/mol
# mol = 25.0g/171.4 g/mol = 0.146 mol
For the volume of water use the fact that the density is 1g/ml., so 120 g = 120 ml = 0,120 liters.
M = 0.146mol / 0.120 liters = 1.22 mol/liter
