 Today, welcome to the second lesson of NSSCO physical science in a series of two lessons. The topic of this lesson is identification of cations. The objectives of this lesson are to use qualitative analysis in the identification of cations. Describe the use of the following tests to identify aqueous cations like ammonium, zinc, copper 2, iron 2 and iron 3 using aqueous sodium hydroxide and aqueous ammonia as appropriate. Let's switch over to hear what Mary and her mom discussed about this topic. How have you been? We don't have the whole day. Sorry mom. Okay, now the last time we tested for negative ions. Today we are going to test for positive ions. Do they have a special name? Yes, they are called cations. Today we will test for the following cations. Iron 2 ions, iron 3 ions, zinc ions, copper 2 ions and ammonium ions. Now, before we start, please have your record book and pen ready. To test for cations, we use aqueous sodium hydroxide and aqueous ammonia. To test for iron 2 plus ions, we add a couple of drops of sodium hydroxide and shake it. What do you see? A green precipitate. Yes, this is a green precipitate. Don't forget to record that in your notebook. Next, I will add excess sodium hydroxide and see if the precipitate dissolves. No, it doesn't. Okay. The precipitate is insoluble in excess sodium hydroxide. Okay. Now, to test for iron 3 ions, I will add a few drops of aqueous sodium hydroxide and then I will shake it. What do you see? A red-brown precipitate. Yes. Now, I will add excess aqueous sodium hydroxide and see if the precipitate will dissolve. Now, let's see if it dissolves. No, it doesn't dissolve. Okay. Next, we will test for zinc ions. I will add a couple of drops from the aqueous sodium hydroxide and then I will shake it. What do you see? A white precipitate. Okay. Now, I will add excess sodium hydroxide to see whether the precipitate will dissolve. Now, let's see if the precipitate will dissolve. Yes, it does, but it's getting a little bit lighter. Okay. Now, to the test tube with copper 2 ion solution, I will add a few drops of aqueous sodium chloride hydroxide. And then shake it. What do you see? A light blue precipitate. Now, I will add excess sodium hydroxide to see whether the precipitate will dissolve. No, it doesn't. Okay. Now, I will test the other portion of aqueous ion to ions with aqueous ammonium. I will add a few drops of aqueous ammonium and shake it. What do you see? A green precipitate. Good. Now, I will add excess ammonia to see whether the precipitate will dissolve. What do you see? No, it doesn't. Good. Now, I will add a couple of drops to the ion 3 ions with aqueous ammonia. Shake it. What do you see? A red brown precipitate. Okay. Now, what happens? Open. What happens when I add excess ammonia? The precipitate doesn't dissolve. Good. Now, I will add a couple of drops of aqueous ammonia to the zinc ion solution. Shake it. What do you see? A white precipitate is formed again. Now, what happens when I add excess ammonia? The white precipitate dissolves to form a colorless solution. Good. Now, to the copper to ions, I will also add a few drops of aqueous ammonia. Shake it. What do you see? A light blue precipitate. Now, what will happen if I add excess ammonia? The light blue precipitate changes color to deep blue precipitate. You see, what happens is that the light blue precipitate dissolves to form a deep blue solution. Oh, I see. Okay. Now, we will test for ammonium ions. What I'm going to do is that I'm going to heat the test tube of ammonia salt, and it will produce ammonia gas. How can I know that the gas produces ammonia? By holding the litmus paper over the opening of the test tube. Wow, the litmus paper is turning blue. That confirms the presence of ammonium ions. And that is also the end of our test for the identification of ions. Thanks, mom. It was great to observe all the color changes. I will definitely remember them since I saw them better myself. It's a pleasure, my dear. Let's now recap what we've learned today. Cat ions are positively charged ions. Here is a complete summary of all the tests for the different cat ions. Let's go through them again. To test for ion-2 ions, aqueous sodium hydroxide will produce a green precipitate. Excess aqueous sodium hydroxide will produce an insoluble green precipitate. To test for ion-2 ions with aqueous ammonia, a green precipitate will also appear. Excess aqueous ammonia will produce an insoluble green precipitate. To test for ion-3 ions with aqueous sodium hydroxide, a red-brown precipitate will appear. Excess aqueous sodium hydroxide will produce an insoluble red-brown precipitate. To test for ion-3 ions with aqueous ammonia, a red-brown precipitate will appear. Excess aqueous ammonia will produce an insoluble red-brown precipitate. To test for zinc ions with aqueous sodium hydroxide, a white precipitate appears. With excess aqueous sodium hydroxide, it will produce a soluble white precipitate giving a colorless solution. To test for zinc ions with aqueous ammonia, a white precipitate appears. With excess aqueous ammonia, a soluble white precipitate forms giving a colorless solution. To test for copper-2 ions with aqueous sodium hydroxide, a light blue precipitate appears. With excess aqueous sodium hydroxide, an insoluble light blue precipitate appears. To test for copper-2 ions with aqueous ammonia, a light blue precipitate appears. With excess aqueous ammonia, a light blue precipitate appears giving a dark blue solution. To test for ammonium ions, heat the solution, red litmus paper will turn blue to confirm the production of ammonia gas. This brings us to the end of today's lesson. Goodbye.