1.1 CHEMICAL AND IONIC EQUATIONS

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Hi there! In today's post I am going to tell you all about chemical and ionic equations. We are going to learn how to balance them and write them out, as well as the definitions.

So, let's start with some definitions. What are chemical equations?

CHEMICAL EQUATIONS- they describe the equation. The easiest way to think about them is that they sum up or summarise what is going on in an equation. For example, if we get aluminium and combine it with oxygen, we get aluminium oxide and this is what a chemical equation will tell us (aluminium+oxygen--> aluminium oxide). However, this is not everything. Chemical equations also tell us what is the state of an element or a compound in a given equation, like so in the image above. There are four states that you need to be familair with for the A-level course and they all have their symbols so that you don't have to write them all out every time. These are:

(g)- gas

(l)- liquid

(s)- solid

(aq)- aqueous (meanig it's a solution)

Balancing equations is another very important aspect when writing chemical equations. This is because nothing is created or destroyed in a reaction, so there must be the same number of atoms at the beginning as there are at the end.

Let's start with something easy (example on the image above). We have magnesium and oxygen added together to give us magnesium oxide. The way I always balance chemical equations is simple:

1. Write out the equation with chemical symbols instead of words.

2. Write out all the different elements that are present on both sides, next to the equation.

3. Write how many of each there are on both sides.

4. Now, use trial and error technique, unitl there is the same amount of each element on either side. Remember to start with low numbers!

Now, go back to the eaxmple from above: there is one magnsium on either side but there are two oxygens on the left compared to one oxygen on the right. I know it is very tempting to just put a little two after oxygen in MgO or just completely rub out the little two on the LHS from O, but this would completely change the formulae of the substance and the equation would simply not make sense anymore. The only way you can 'change', or actually I should say, balance the equation is by adding big numbers in front of the substances. Now, everything stays the same but there is more of each substance which finally leaves us with the same amount of each element on either side.

Trust me, this is easy! You just need to take some time and remember the steps. I know some of the equations are easier than the others and sometimes it is difficult to see what number is missing to balance the equation. But practice makes it perfect! I know you can manage it! :)

Let's give a go two more examples. One of them is extra hard, just to get you thinking about it. Feel free to just write the equations down, try doing them yourself and then check it with me. I also prepared more past paper questions for you on my youtube channel for which I left a link at the top of this page.

What do you think? Are you still with me? All the steps are here: write it out, check how many of each element there are, trial and error, until you get there. There is nothing more I can help you with on that one. You just need to think positively and believe you will find the right number. Just to make you feel better, this type of questions are usually one markers on an exam, so if you really struggle with it, leave until the last, and try it once more if you have time.

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IONIC EQUATIONS- this type of equations involve ions in solutions. An ionic equation helps you see what is happening with the ions and which ones do not take part in a chemical change. These are usually precipitation and displacement reactions, but you will see what I mean in a second.

How about we start with some more definitions and you will understand my terminology later on this post.

SPECTATOR ION- doesn't take part in a chemical change.

HALF EQUATIONS- they are two equations, where each equation describe half of a redox equation. This means one describes oxidation that it taking place and the other describes reduction that is taking place in a redox equation.

As you can see above on the image, copper is oxidised (o.n. goes from 0 to +2) and silver has been reduced (o.n. goes from +1 to 0).These two HALF EQUATIONS can be combined together to form one big equation. The electrons can be cancelled out from the equation, as they are SPECTATOR ions.

We are going to write ionic equations now. As for everything, I have couple of steps for you to follow to successfully write an ionic equation. I will then provide you with two examples that I will fully exaplin and go through with you. I hope this will help and after this post, you will master writing ionic equations. To the point then, these are the steps that I always follow:

1. Check the equation is balanced.

2. Write the state symbols.

3. Look for all elements that are in aqueous state because they can be split into ions.

4. Look for spectator ions and cancel them out.

5. Write out half equations.

6. Combine half equations (if there are two).

1. We've got equation for a reaction but it needs to be balanced before we can go further. If you're not sure how to do it, scroll up and read how to do this.

2. Now, that the equation is balanced, we have to write down the state symbols of each element. If you're not sure how I know what state symbol each substance has, it is usually written in the question. For example they may say, 'a solution of ...... combines with solutions of .....' meaning it has an aqueous state. Or they say, that '....... forms a white percipitate' meaning it has a solid state. It's not magic, you just have to read the question carefully. Magnesium ribbon is a solid metal and hydrochloric acid is aqueous, when they react an aqueous solution of magnesium chloride and hydrogen gas is produced.

3. When you finally recognise which substances are aqueous, you can split the substance into ions ( ions dissociate in solutions ). In this example, hydrochloric acid dissociates into hydrogen and chloride ions and magnesium chloride dissociates into magnesium and chloride ions. Cancel out the spectator ions ( ions that do not change in the reaction).

4. Now, we've got two half equations. One of them shows oxidation, which is magnesium and the other shows reduction, which is hydrogen.

5. Lastly, you just have to combine the two half equations and get the final ionic equation. As you can see we have 2 electrons either side, so we can just cancel them out.

Here is another example, but I think you can manage working this one out without my explanations. Just go number by number, step by step and I am sure, you will understand what I've done.

Thank you soo much for staying with me. If you want some more practice questions visit my youtube channel (link at the top of the page) and carry on with revision. If you would like a copy of the past paper questions on my youtube channel please either email me (link on the top of the post) or comment here or on youtube.

PS. Please remember, I am only a student, and as anyone, I can make mistakes. If you think you can see one, don't hesitate and comment (either here on on my youtube channel) Thank you!