There are several arsenic minerals, two of which are claudetite (As2O3) and orpiment (As2S3). Wrtie a balanced half cell reaction between these two minerals, in an aqueous solution. The half cell reaction is: As2O3 + 3 SO4^2- + 30H+ +24e- <--> As2S3 + 15H2O How do you know that As2O3 will be on the left side of the equation than the right? How do you know to add SO4^2- to the equation? How do you know to add the 24e- to the left side of the equation? If someone could show me steps to explain these questions, it\'d help me out a lot. Thank you. Solution The half cell reaction is: As 2 O 3 + 3 SO 4 2- + 30H + +24e - <--> As 2 S 3 + 15H 2 O How do you know that As 2 O 3 will be on the left side of the equation than the right? Ans:- As 2 O 3 is soluble in dilute acids and this reaction takes place in acidic condition that is why As 2 O 3 is on left hand side. As 2 S 3 is not soluble in acid at room temperature that is why this will be on right hand side of the equation. How do you know to add SO 4 2- to the equation? Ans:- As this reaction takes place in acidic medium ,in the presence of sulphuric acid (H 2 SO 4 ) that is why ionised form of sulphuric acid i.e.SO 4 2- is added to the solution. How do you know to add the 24e- to the left side of the equation? Ans:- To balance the charge of the half cell reaction.There is no charge on the right hand side and a (24H + ) + 3(-2) = (30+) - 6 = 24+ charge on the left side of the equation.so to balance this charge add 24 e - to the equation.Now equation become neutral. .