why did the balance record a decrease in mass during the reaction betwwn iron sulphide and hydrochloric acid?
Did you smell anything? If so, a gas was given off, and the balance wont record that as a mass.
Phew. A smelly reaction.
The decrease in mass recorded on the balance during the reaction between iron sulfide (FeS) and hydrochloric acid (HCl) can be explained by the concept of a chemical reaction. When these two substances react, a chemical change occurs, resulting in the formation of new compounds.
In this reaction, iron sulfide reacts with hydrochloric acid to produce hydrogen sulfide gas (H2S) and iron chloride (FeCl2). The reaction can be represented by the following equation:
FeS + 2HCl → H2S + FeCl2
Now, let's consider the mass of the reactants and the products. Initially, on the balance, you have the mass of the iron sulfide and the mass of hydrochloric acid. As the reaction progresses, iron sulfide reacts with hydrochloric acid to form the new compounds, hydrogen sulfide gas, and iron chloride.
The decrease in mass recorded on the balance is due to the conversion of solid reactants (iron sulfide and hydrochloric acid) into gaseous products (hydrogen sulfide gas). Since gas has a much lower density than solids, the loss of mass is observed on the balance.
To calculate the precise decrease in mass, you would need to know the balanced chemical equation and the molar masses of the substances involved. You can determine the molar mass of each substance by adding up the atomic masses of each element in the compound. Then you can use stoichiometry (mole-to-mole ratios) to convert between mass and moles.
It's important to note that the decrease in mass observed in this particular reaction is due to the formation of a gas as one of the products. However, in other reactions, mass changes may occur due to other factors like the formation of a precipitate or the consumption of a reactant.