Milk of magnesia, a widely used antacid, is an aqueous suspension of Mg1OH22. How would you prepare Mg1OH22 from magnesium metal?

Video transcript

All right. Hi, everyone. So this question says that slate lime or calcium hydroxide is a commonly used flocculate. How can you prepare calcium hydroxide from calcium metal? Here we have four different answer choices. But the first thing I want to point out here is that options A and B propose a series of two reactions whereas options C and D propose only one reaction. Now, in case you were curious, a flocculent is a substance that causes smaller particles of something to create larger clusters. So with that out of the way, let's go ahead and get started. In this case, our target product, calcium hydroxide is of course a hydroxide and hydroxides if you recall can be combined or can be produced from the reaction of h2o with either an oxide, a super oxide or a peroxide. So all this is to say is that this is actually going to be a two step process because calcium metal first has to react to create either an oxide, a peroxide or a super oxide. And then that intermediate reacts further with water to generate the intended hydroxide. So because of this, we can actually go ahead and eliminate option C and D because we know that it's not going to be one single reaction. So the question is, what type of intermediate are we going to see? Well, to understand this, we have to recall that calcium is a metal in group two a of the periodic table because recall the metals in group two A, they don't react to form super oxides which means that they can only form either an oxide or a peroxide. So now the question is simply which of the two is going to form. Well, recall that there is a pneumonic device to help answer this question or a memory tool. And that is that peroxides or bananas. And I want to draw special attention here to B A and N A in the word bananas because those are the chemical symbols for barium and sodium respectively. And so this means right or this indicates that barium and sodium are the metals that react to create peroxides. So because calcium is not on the list, so to speak, this means that calcium can only react the form an oxide. So if I scroll down here to open up some room for myself, the first reaction is going to involve calcium metal. So calcium is a solid reacting with oxygen gas to form an oxide. Now recall that an oxide is a compound in which oxygen has an oxidation state. Therefore a charge of negative two. So calcium has a charge of positive two to counteract the negative two charge. This means that there's going to be a 1 to 1 ratio of calcium to oxygen, which means that the chemical formula of the resulting oxide is simply going to be cao and that will be assault. So now as for the second reaction, our calcium oxide is going to go ahead and simply react with water to create the hydroxide that we discussed in the beginning, right, specifically caoh two and notice how the ratio changes, right, because hydroxide has a charge of negative one, whereas calcium has a charge of positive two. So because of this, there is a 1 to 2 ratio of calcium to hydroxide to balance out their charges. And there you have it. If I scroll up here one more time, the answer is going to be option being in the multiple choice because calcium hydroxide can be produced from calcium metal through the following series of reactions. Part one is calcium metal reacting with oxygen gas to create calcium oxide. And part two is calcium oxide reacting with water to generate calcium hydroxide. And with that being said, thank you so very much for watching and I hope you found this helpful.