Okay, this is the topic 6 of PIPC1. Introduction to ionic equilibrium. So what is ionic equilibrium or ionic equilibrium?
Actually, ionic equilibrium is a chemical balance established between the molecules and their ions in a solution. It looks like a bit hard to understand, right? So I can use a very simple example to explain.
just for example we got a water solution in a beaker so i draw a beaker first the beaker like that then inside we got water solution then i put a formic acid into the water solution uh can you write down the chemical structure of formic acid yes is H COOH. You can see the two hydrogens right. Then you put the formic acid into the water, what happen? They will fully dissociate or partially dissociate. Yeah just partially dissociate into a hydrogen ion H plus and another one is what?
Yeah it's a formic ions. How to write down the formic ion structure? Is H COO minus.
Yes. So now tell me in this water solution, how many major substance we have? Some students say, oh three.
One, two, three. No, no, no. H3 is four. We got water. So I put water and call it H2O, right?
We got a lot of water inside. So how about this solution? We can say in this solution, the formic acid and their ions, hydrogen ions and formic ions form an equilibrium. We call this equilibrium is ionic equilibrium. Okay this is the first part of topic six.
In this part, we need to talk about the acids and bases. But what is acid and what is a base? actually there are three different theories to define the acids and the bases i will show here three different types of acid and base theories the first one is iron news acid and base theory second one is the bronze that lori acid and base the last one is the lewis acid and base actually in the pipc one we are more focused on second one bronze that lori acid and base and i think you will learn the lewis acid and base in uni so based on the brownstack-laurie acid and base theory what is acid you can see the definition here an acid is a proton donor proton here means H plus hydrogen ions and proton donor means what acid can give up the proton give up the hydrogen ions so we here we have two different types of acids the first one is monoprotein acid and second one is polyprotein acid monoprotein acid gives up one proton per molecule for example like hydrochloric acid hcl they can only generate one proton here right then polyprotein acid like sulfuric acid H2SO4 they generate the two protons or two hydrogen ions here so that's why we call polyprotein acid.
I will give you an additional question like CH4, methane, is the methane an acid or not? Can you answer this question? Methane in the acid or not?
Before we answer this question, we must take a look at the structure of the methane. Can you draw the structure of methane? Yes right, we just put the carbon in the middle, then the carbon will link to hydrogen.
How many hydrogens we have? Four right. So we draw the structure like that.
Based on this structure, we can see all the hydrogen are directly linked to the carbon. So the CH bond here, you see, carbon hydrogen bond here is really really stable. So the methane is very hard to donate the proton. donate the proton or give up the proton so methane is not a proton donor and methane is a not acid based on the brown stat lorry acid-base theory okay let's take a look the general properties of acids first one solutions of acids have a sour taste some students will laugh haha you taste the acids yes i taste the acid huh you taste the acid yes actually i drink a coke you know what acid in the coke phosphoric acid yeah i also like the lemon juice so what's the acid in the lemon juice citric acid without sugar if you don't put the sugar into the lemon juice don't put sugar into the coke the the coke and the lemon juice will be very very sour so the sour taste actually is the taste of the acid the second one is the pH value pH value of the acid is normally less than seven of course you learn this one in secondary school and third one is acid turn acids turn the blue limus paper to red you can see here if you put the acid here then you put the blue limus paper into the acid will show the red color and the last one is acids react with the bases to form the salt and water just for example hydrochloric acid hcl and react with sodium hydrochloride NaOH will generate the sodium chloride in the salt and finally it's water here we call this one is a neutralization reaction I think we learned this one in second grade school already. In this page we talk about the strong acids and the weak acids.
What is a strong acid? Strong acids are acids dissociate completely in the water or fully dissociate in the water. What this means?
Fully dissociating in the water means that the acid no more keep in the molecular form but generate ions with opposite charges. I can use hydrochloric acid as an example HCl. So initially I put 1m or 1 mol of HCl into the water and there are no more hydrogen ions no more chloride ions right. After reaction what happened? After reaction you can see oh there are no more HCl in the water.
What happened? Because HCl is strong acid. Strong acid will fully dissociate or 100% dissociate into the hydrogen ions 1m and chloride ions 1m. And you also need to notice since this one is 100% dissociate, you can see the arrow here is one direction arrow right one direction arrow means this reaction only happens forward happens forward We have a lot strong acid just like the hydrochloric acid, nitrate acid, sulfuric acid.
The second acid is wheat acids. So what is a wheat acid? Wheat acids are acids dissociated partially in the water. A lot of organic acids are wheat acids. For example, formic acid, acetic acid, benzoic acid.
I use acetic acid as example can you write down the acetic acid structure CH3COOH yes so initially i also put one molarity or one moles of CH3COOH into the water and there are no more hydrogen ions no more acetic ions right after the reaction what happened oh the reaction happened you see well still got 0.99m 0.99 molarity of acetic acid in the water and maybe only generate 0.01m of hydrogen ions and 0.01m of acetic ions why like that because the acetic acid is a weak acid so the weak acid only partially dissociate how much dissociate we don't know but maybe 1%, maybe 50%, maybe only 0.01%, right? And you can see here we use the different arrows, we call half arrows in this reaction. What this means? Means this reaction can happen either forward or backward, right? That's the difference between the strong acids and weak acids.
In this page, We try to use the Brown-Statt-Lowry theory to define and base. Actually, and base is a proton acceptor. What's the meaning of the proton acceptor?
Proton acceptor means the base can accept or gain the protons. Just like the acid, bases also have the two different types, strong bases and weak bases. Strong bases can fully dissociate in water or completely dissociate in water.
just like sodium hydroxide. You can see put the sodium hydroxide here, you put into water 100% to dissociate into sodium ions and hydroxide ions. We base this, we use ammonia as an example.
Ammonia is NH3. They only can partially dissociate in the water. So you put into water what happen?
They will generate the NH4 plus ammonium ions. and hydroxide ions. Let's take a look at general properties of bases. Actually solutions of the bases have a bitter taste. For example, lime water.
Do you know what is lime water? Lime water actually is calcium hydroxide right. So when we touch the calcium hydroxide, you will feel a bit slippery or soapy on the skin but don't touch don't touch the strong acid and strong base strong acid and strong base are very very dangerous highly corrosive right when you handle the strong acid and base you must wear the gloves wear the goggles and wear the lab coats and you also know in the secondary school the ph value of bases is larger than seven right and basis will turn the limus paper from red to blue.
You can see if you put the limus paper into the basis solution, you'll turn the blue color. And you also know if we use the strong base or base to neutralize the acid, it will generate the salts in the water like that. So some students will ask me in PIPC1 how many acids and bases need to memorize Actually all here so for the strong acids you can see how many strong acids need to memorize seven the first one hydrochloric acid, nitric acid, sulfuric acid, hydroiodic acid, hydrobromic acid, chloric acid, and perchloric acid right seven for wind acids first one hydrofluoric acid anything else some organic acids for example formic acid can you write down the formic acid yes H-COOH second one acetic acid CH3-COOH anyone else benzoic acid yes you must write down a benzene ring first then you put a COOH benzoic acid after that is a strong basis strong basis actually is a group one and group two metal hydroxides for the group one don't tell me water not water so the first one is what lithium yeah lithium hydroxide second one sodium yeah sodium hydroxide after that potassium hydroxide yes then group two metal hydroxides magnesium yes OH2 then after that is calcium calcium hydroxide oh lime water for the weak bases actually PIPC1 i think you only need to remember this one ammonia of course sometimes we'll give you some amine for example like CH3NH2 or you give you amine like that NH2 right don't worry huh just need to memorize the first one ammonia NH3 and you also know if we put it NH2 NH2 here or wheat base