% error =

x 100%
Experimental: 2.85
Actual (theoretical): 2.70
% error =

x 100% = .055555 x 100% = 5.56%
The physical explanation is that increasing temperature increases the kinetic energy of the gas molecules. Hence, their random motion breaks more intermolecular bonds and the gas is less dissolved in the solvent. In contrast, solid solutes in water have increased solubility with increased temperatures.
Before proceeding, we should write the reaction equation to better understand what is happening:
2AgNO₃ + Na₂S → Ag₂S + 2NaNO₃
Now, we may apply the law of conservation of mass, due to which the total mass before a chemical reaction is equivalent to the total mass after a chemical reaction. Therefore:
Mass of silver nitrate + mass of sodium sulfide = mass of silver sulfide + mass of sodium nitrate
Mass of silver nitrate + 156.2 = 595.8 + 340
Mass of silver nitrate = 779.6 grams