Assalamu alaikum students this practical session is about experiment number three regarding the type of chemical reactions and as you have understood in the theoretical class that the chemical reactions can be classified into different types based on the rearrangement of reactant to give a product so what what kind of a product we're going to get it will actually place rules here in the classification of chemical reaction this is one objective the second objective in this experiment is to be able to identify some of the evidence of chemical reaction so you will see which type of evidence is associated with each of the chemical reaction and the third one is to be able to write down the chemical equation and balance the chemical equations so we will start first with the combination reaction but we need to To look into our safety concern, as you know I'm wearing gloves and lab coat and also safety shoes. And the chemicals that we are going to use today, we have the magnesium ribbon as you can see here. And we have also copper ribbon here. Right, and chemicals. silver nitrate is there, Hydrolytic acid, sodium hydroxide, nitric acid and the indicator.
And regarding the glassware mostly we are going to use a test tube simple one and the test tube holder get this one simply by holding the stick like that right and we use the the clipper here is to hold you know the ribbon during the performance of chemical reactions so we will start first with experiment with the chemical reaction number one To start with the chemical reactions we are going to observe the combination reaction now here. The combination reaction means to combine two or more chemical reactants to produce one product. In order to show this practical experiment we are going to demonstrate burning of magnesium ribbon in the air with oxygen. So I'm going to burn this magnesium using this crucible tongue.
I'm holding it. To start the reaction of course heat is the condition needed for this. So I'm going to light the lighter and you can see what's going to happen.
Now what's happening the oxygen in the air is coming to combine with the magnesium ribbon at this high temperature and it's going to start the reaction you can make the clear observation it's giving you a very bright white light with some smoke and at the end there will be product and we can observe the color of the product also of course you see the light was very bright it's not good for direct eyes for some people you can avoid okay let me put the product down and now you can see what happened to the magnesium Now the product is completely white color and it's in the form of powder. And in this product, magnesium has combined with oxygen to give you magnesium oxide product. So this is a combination reaction. So the second chemical reaction that we're going to perform here is called replacement reaction.
and this replacement reaction require one element react with a compound as you can see here we have the copper react with silver nitrate and when the reaction happens the product is copper replacing the silver ion in this solution so producing copper 2 nitrate plus element of silver. Watch out for the evidence of chemical reaction here. It will be light blue solution due to the presence of copper ion in the solution. solution to change into blue but the second evidence also you can see precipitation of silver element it's like a gray precipitate on the what's left from the copper wire in the solution of silver nitrate so i will perform the experiment for you so we have the the copper wire right and i'm going to take i'm going to take an amount of silver nitrate you need to watch for the alignment of these two so you can easily make the liquid you know the chemical to drop in so here you go hold nicely and safely holding this stopper here holding it and then nicely just turn it to allow the liquid to come in to put an amount of silver nitrate inside here I think this will be you know almost enough for for the for the experiment so next we're going to drop the copper wire into the silver nitrate and test it you so after allowing enough time for the reaction to take place we can see clearly the color change in the solution this is due to the releasing of copper ion into the solution this is one type of evidence reactions the other evidence is the precipitation of silver element so if i shake it a little bit you can clearly see the the silver there So here we go, we got the product evidence you got here silver and also the copper 2 nitrate as light blue solutions.
The second replacement reaction is between magnesium and HCl hydrochloric acid. So what actually happening here? magnesium replaces the hydrogen and the hydrogen come out as a gas and the the MGCL become as a solution here so if you look to this drawing just to show the hydrogen coming out due to the reaction due to the replacement of magnesium ribbon here so i will perform the experiment Taking a test tube but this time because this is a Exothermic reaction so I have to use the test tube holder right and then I will add an amount of HCl to the test tube an amount just an amount to satisfy the need of today's experiment we will add the magnesium ribbon as you can see here right so drop it in and you will see reaction happen immediately as you can see here the reaction taking place by evolution of gas hydrogen is coming out and because it is it is hot here we are using the test tube holder Now one of the evidence of today of this type of reaction is the evolution of heat. So by although the heat is not much I can I can actually hold it myself like that. I can feel the heat is already there.
So we have the heat and we have evolution of gas as evidence of chemical reaction. Next we are moving on to the third type of chemical reaction which is known as acid. base reaction which is also known as a neutralization reaction in which we react a base and an acid that will produce salt and water.
In this experiment, we are going to use sodium hydroxide as the base, hydrochloric acid as the acid, which will produce sodium chloride, salt, and the water. Of course, you are going to see that this acid-base reaction will not produce clear observation. Therefore, we have to use an indicator that will help us to get the observation. This is phenolphthalein indicator and this will give you colorless in acid and this will be pink in base.
We are using two chemicals one is sodium hydroxide of course I am going to use the acid not the hydrochloric acid but it is nitric acid. Let me show you the reaction now. Ok here I have the test tube.
and in which I am going to add the nitric acid you can see it's a colorless solution okay now the next step I will add the phenolphthalein indicator just one drop enough for this reaction you so just one drop i'm adding it you can see that it does not produce any color so we can conclude the phenolphthalein indicator is colorless in the acid okay now we will continue with the addition of the base sodium hydroxide now i will add the sodium hydroxide drop wise You can see here, just I add one or two drops and see that the solution is still colorless, which means the sodium hydroxide is reacting with the acid in the test tube and still extra acid molecules are present. So there will be a point, enough sodium hydroxide when it is added, they will completely react with the acid. You can see that it appears some pink color but when you shake it goes.
When you add enough sodium hydroxide to react with all the acid molecules, so there is no more acid, it's completely neutralized and additional drops of sodium hydroxide remaining there to give you the pink color indicating the end of the reaction. So this way we can study the direction between an acid and base. Of course indicator plays a major role.
in this experiment. The fourth type of chemical reaction that we are going to study is known as precipitation reaction. The precipitation reaction in which when we mix two aqueous chemicals like you can see AX aqueous and the BY is aqueous. When you mix aqueous chemical it will happen a type of maybe what type of reaction maybe the replacement or double replacement whatever it is.
One of the product will be a solid you can see here bx the product is solid so for this we are taking that example of the reaction between hydrochloric acid aqueous and silver nitrate aqueous and when we react them they produce two products one is nitric acid which is soluble so we mark it aqueous and the other one is silver chloride of course this is a solid product since the reaction is producing a solid product this reaction is known as precipitation reaction and also if you look at carefully it is also a double replacement and where hydrogen is replacing the silver and joining with nitrate and the silver is coming back to join with the chlorine and that's the second replacement so silver chloride so it's a double replacement also let me demonstrate the reaction now Here I have a clean test tube and this is hydrochloric acid. Let me add the hydrochloric acid which is a colorless solution. Okay, hope it's enough. Let me now add Silver nitrate. You can see the silver nitrate, AGM-NO3, is normally kept in dark bottle because silver nitrate chemical is photosensitive.
So they are normally kept in dark bottle. Let me add just one or two drops. You can see it is producing a white color cloudy precipitate.
So, since the reaction is producing a precipitate we call it a precipitation reaction. Even though the solution looks milky if we leave it for long time of course, all the white color solid will come to the bottom it will clearly indicate the formation of solid particles. The last reaction that we are going to observe is redox reaction and this is only for the demonstration purpose we are performing it. Redox reaction is really a combination of two process here you see red means reduction the ox means oxidation.
So, we have a reaction in which both reduction and oxidation takes place we call it a redox reaction. In order to demonstrate this experiment, we have a setup like this, you can see here, which normally we call it voltaic cell, you can see here the voltaic cell, in which we have a zinc electrode immersed into zinc sulfate solution, and then a copper electrode is immersed into copper sulfate solution. And when we try to connect them through an external wire, And you will see the flow of electron that goes from zinc to the copper. The reason here, zinc, the reactivity is higher than copper. So the zinc atoms loses electron to the circuit and those atoms become zinc ions, they come to the solution.
And those electrons from the zinc, they move toward the copper electrode. Of course the copper electrode in which These copper 2 plus ions, they will reach there and they will gain this electron. So they undergo reduction to produce copper solid. It will be deposited here. Of course, in order to observe this reaction, we have to make the connection between these two solutions.
So to make the circuit complete. So for that, we have to create a salt bridge here. Of course, you are going to see when I show you the demonstration.
And also we can use a multimeter. To show the flow of current as observation. Let me go to the demonstration part.
Here we have a small voltage cell in which you can see here we have two electrodes. This one is the zinc electrode and this one is the copper electrode. We are going to place them.
In this voltage cell you can see the voltage cell is divided separated internally here and so to keep the two solution not connected at the beginning. Okay first I am going to fill this voltage container voltage cell container by this copper sulphate solution to one side. You can see that this copper sulfate solution is blue in color because it has copper 2 plus ions.
Okay fine. Then other half of the vortex cell will be filled with zinc sulfate solution. You can see the zinc sulfate solution is colorless.
Okay, now what I am going to do is, before I immerse these two electrodes into the solution, I will try to connect these two solutions by a short bridge, in which I am going to use a paper and fold it. You can see, I just will place them here. And, we can... Here now I have placed the salt bridge which means try to connect the two solution through this paper. It will allow the movement of the ions to complete the circuit.
Then I am placing see the copper goes to the copper solution and the zinc will go to zinc sulphate solution. so now what's going to happen the zinc is going to lose electron and become zinc ions it will go to the solution here therefore the electrons will be left in the zinc electrode it will be rich of electron then what will happen here the copper electrode the copper solution It has copper 2 plus iron. It will go to the copper electrode and take the electron to become copper deposited.
So, therefore, this electrode will become positively charged. Okay, but in order to make the observation, we are using a multimeter to prove that we have electron in the zinc and the copper. So, if we connect them externally, it will allow the flow of the current.
and we should be able to see that one and here you can see i i'm connecting the zinc let me switch it on okay it should be dc current okay and if when i connect them you may observe the flow of current and will create a voltage You can see it's clearly when I connect them it's giving you a voltage. This indicates there is a flow of current from one electrode to another. In this case you can see it's minus reading. So voltage cannot be minus which means maybe the way I have connected is wrong.
So if I just exchange this connection you can see now we get almost similar voltage. but now it will be positive reading so you have to record this voltage