 Now we're going to look at the reaction between acids and metal sulfides. The general formula is acids plus metal sulfide, goes to salt again, and hydrogen sulfide. Okay, let's look at some examples. So first we're going to react zinc sulfide to an S with hydrochloric acid. Now, the salt that we're going to produce, the positive part of the base in this case is the zinc sulfide. The negative part of the acid, that's going to be the chloride. So zinc chloride, problem with that. So zinc has a charge of two plus, chloride has a charge of one minus. So Chrissy Crossy's at NCO2 plus hydrogen sulfide H2S. So now let's check balancing. Got one chlorine, two chlorine, so double that one. So two hydrogens, two hydrogens, one sulfur, one sulfur, one zinc, one zinc, two chlorine, two chlorine. So now that's balanced. So in our next example, we're going to react nitric acid with iron sulfide. So iron-2 sulfide, so ferrous sulfide. Now we need to figure out what the name of the salt is going to be. So the positive iron from the acid is the ferrous iron. So iron-2, our negative part from the acid is going to be the nitrate iron. So we've got a problem because ferrous iron has a charge of two plus nitrate iron, has a charge of one minus. So again, we need to Chrissy Crossy. We get FeNO32, so two nitrates, plus hydrogen sulfide. Let's check for balancing. So one Fe, one Fe, so one iron, one iron. Two nitrates, only one nitrate, so we need to double that one. Two hydrogens, two hydrogens, one sulfur, one sulfur. So I think we're balanced now.