92: The accompanying photo shows the reaction between a solution of Cd(NO3)2 and one of Na2S. (a) What is the identity of the precipitate? (b) What ions remain in solution? (c) Write the net ionic equation for the reaction, (d) Is this a redox reaction?
Solution: Here, we are going to identify the precipitate and ions in the given solution. Also, we are going to write the net ionic equation for the reaction and identify whether it is a redox reaction or not. Step1: a) Cadmium nitrate[Cd(NO ) ] reacts wi3 2dium sulfide(Na S) to form cadmium 2 sulfide(CdS) and sodium nitrate(NaNO ). The balanced molecular equation for the 3 above reaction is : Cd(NO ) 3 2+ Na S(aq)2------> CdS(s) + 2NaNO (aq) 3 Using the guidelines of solubility, we can say that CdS in insoluble in water and will be precipitated out. Thus, the precipitate formed is CdS. Step2: b) In the above reaction CdS is precipitated out and thus only the ions of NaNO remains 3 in solution. + - Thus, Na and NO ions are3emained in the solution. Step3: c) While writing the ionic equation, we write out all the soluble compounds as ions and eliminate ions common to both the reactants and products. This will give us the net ionic equation. So, the balanced ionic equation for the above reaction is: 2+ - + 2- + - Cd + 2NO + 2Na3+ S ------------> CdS + 2Na + 2NO 3 (CdS beng insoluble cannot be converted into ions) Eliminating common ions on both sides of the equation, we get the net ionic equation as follows: 2+ 2- Cd + S ------------> CdS Step4: d) Redox reactions are the reactions which involve both oxidation and reduction. One element undergoes oxidation and the other element undergoes reduction. Since, in the above reaction, no such oxidation or reduction is taking place, hence, it is not a redox reaction. ----------------------------