Question

I need help writing an overall equation for the acid-base reaction that would be required to produce the following salt:
MgCl2

Answer 1

I think it can basically be anything where one has Mg2+ as the cation and another having Cl- as its anion. Can you come up with two? Google will make it easier.

Answer 2

I'm not sure I understand, It can be anything? What would I search for?

Answer 3

Since Acids have H+ and you need Cl-: look up acids with Cl;
and since Bases have OH- and you need Mg2+: look up bases with Mg instead of the mixed.
Get me so far?

Answer 4

yes.

Answer 5

Alright so, can you list 2 reactants you can use to obtain MgCl2?

Answer 6

Would Magnesium Hydroxide be right? Mg(OH)2

Answer 7

For the base, yes. What about the acid? Remember that to obtain a salt, you must react an acid with a base.

Answer 8

Perchloric Acid HClO4?

Answer 9

You might want to try something simpler at this level. Something with just H+ and Cl-?

Answer 10

HClO, Hypochlorous Acid?

Answer 11

Try HCl, hydrochloric acid. It's the most common acid people use.

Answer 12

Ok. I just found that one!

Answer 13

Sry, I'm just learning this.

Answer 14

It's fine. :) Now, we have \[HCl+Mg(OH)_{2}\rightarrow \] Can you finish that? Do you know how to form ionic compounds?

Answer 15

No, I don't.

Answer 16

Can I ask you to read this first?: http://www.occc.edu/kmbailey/chem1115tutorials/formulas_ionic.htm

Answer 17

Yes. Thank you.

Answer 18

OK. So, I need to identify the cation and the anion. I believe that the Mg is the cation and the HCl is the anion?

Answer 19

Close. The anion will be Cl- and cation Mg2+. See, anions and cations are ions so they will have a charge on them. Do you know how to get what their charges are?

Answer 20

I think so. All charges have to equal zero?

Answer 21

Yes.

Answer 22

If Cl is negative, then it is -1. For it to equal zero, we would have to change it to 2? would that be positive 2 though?

Answer 23

You are adding Cl- to Mg2+. For the charge to be zero, you will need to add 2- to 2+, right? In short, they must have the same magnitude of charge.

Answer 24

Ok. Thank you. So, Cl + Mg2+ = Mgcl2

Answer 25

Do we always put the Cation in front of the anion?

Answer 26

Right! But don't forget the charge on Cl-. And yes, the cation in front of the anion. :) Now, you have one part of the product. You took Cl- from HCl leaving H+, and took Mg2+ from Mg(OH)2 leaving OH-. Those two combine as well. What do they become?

Answer 27

(OH-) + (H+) = OH2?

Answer 28

Close, but notice how that can be rearrange to be something very familiar :)

Answer 29

H2O? or 2H2O?

Answer 30

H2O, water :) So in general, reactions between acids and bases will produce a salt and water. So next time you can write the equation faster. What will our full equation be now?

Answer 31

MgCl2 + H2O

Answer 32

Those are the products. Can you write the full equation including the reactants we found earlier?

Answer 33

HCl+Mg(OH)2→ MgCl2 + H2O

Answer 34

Yes! Now here comes the balancing part. Basically, what you want is the same number of elements on the left side as the right side. What you can do is multiply any compound with a constant.

Answer 35

So, I multiply the 2's?

Answer 36

Or, maybe because there is a MgCl2 we have to give H2O a 2?

Answer 37

If you want to multiply, you have to multiply is by the whole compound. For example, here we see that we have 2 Cl on the right side, so you multiply whatever compound that has Cl on the left side by a number to make have 2 Cl. So we will have\[2HCl+Mg(OH)_{2}\rightarrow MgCl _{2}+H _{2}O\] Now we have 2 Cl on both side. Notice that this also makes us have 4 H on the left side instead of just 3.

Answer 38

OH, ok. So, it's almost like just placing 2 there. I get confused easy

Answer 39

Yeah. Now we only need to balance out the Mg, H, and O. Can you do it?

Answer 40

Mg(OH)2 + 2 HCl --> 2 H2O + MgCl2
That is multiplying to achieve 2's?

Answer 41

It doesn't necessarily have to achieve 2's. It depends on what and how many elements you have. Here is an example of a non-2 equation: 2C2H6 + 7O2 ---> 4CO2 + 6H2O
But either way, your equation here is correct but not because you achieved 2's. It's because now you have equal number of elements on each side.

And so you I have shown you what you asked for. :)

Answer 42

I really can't thank you enough!
I'm trying to learn these chem equation rules.
Could I ask you for help in the future, about chem equations?

Answer 43

Sure. Let me know if you have any other questions about this. I will try to help. A key to mastering balancing equations is practice.

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Answer 44

o_0

Answer 45

Oh. My. Goodness. lol

Answer 46

What? O.o

Answer 47

I understood nothing of that xD