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Titration Calculation

 So... next set of never ending calculations is.... the titration calculation. Fun times right? Lets get this on the road! What is a titration? Simply put it is the neutralization of an acid by an alkali or vice versa to an immensely accurate scale - not flawless though mind, just saying (problematic I know but it is 2020!).  Be careful when measuring values in the burette, it needs to be read from the meniscus - this is the dip of the solution in the burette.

Also just to annoy you that little bit more, you have to record and record and record and record and record and record and record.... oh sorry lost myself there! (it is true though!) ... until you get two results that are concordant with one another (within 0.1 of each other).

So lets get down to the ever so enjoyable maths...

Ca(OH)₂ + HNO₃ ---> Ca(NO₃)₂ + H₂O

So here we have our lovely little equation. Now I recommend simply balancing this out - having issues? check this out- as balancing this out as soon as possible makes everyone's life a little bit easier.

Ca(OH)₂ + 2HNO₃ ---> Ca(NO₃)₂ + 2H₂O

Now for the question itself...

18.30cm³ of calcium hydroxide was needed to neutralize 25.0cm³ of nitric acid. The concentration of the alkali was 1.5 mol/dm³. What is the concentration of the hydroxide?

Lets recognize which is our acid and which is our alkali. If you recognized Ca(OH)2 as the alkali (calcium hydroxide) then go you! If not don't worry, the acid itself is pretty simple to spot and when you know which is the acid then you know which is the alkali!

Lets set this out in a way that could just make this entire calculation easier for you-

                Ca(OH)₂         +         2HNO₃ ---> Ca(NO₃)₂  +  2H₂O
Volume:
Concen:
Moles:

Notice the extra space given for the reactants? Bet ya think its to give you more space when truthfully I'm just trying to annoy you with the uneven spacing between all of the elements in the equation! Ok I'm kidding, you do need a fair bit of space between the lot so you can work some stuff out. Lets fill in the gaps though first -

                                 Ca(OH)₂        +         2HNO₃ ---> Ca(NO₃)₂  +  2H₂O
Volume (cm³):            18.3                            25.0
Concen (mol/dm³):                                         1.5
Moles:

That's all the info we know but for that extra step to push us is this calculation we need to use the equation below-

      n                                   n-moles   c-concentration   v/1000- volume dived by 1000 to get to dm3.
_________
c x v/1000

So lets do that!

n= c x v/1000
n= 1.5 x 25/1000
n=0.0375

Lets put that in then shall we!

                                Ca(OH)₂         +         2HNO₃ ---> Ca(NO₃)₂  +  2H₂O
Volume (cm³):            18.3                          25.0
Concen (mol/dm³):                                       1.5
Moles:                                                        0.0375


Now this I where the balanced equation helps as you need to make a ratio from the amount of both the acid and the alkali.

Two lots of nitric acid to one calcium hydroxide and you can write it like this:

1 : 2

So that means we need to divide the moles from the nitric acid by 2:

0.0375/2= 0.01875

                                Ca(OH)₂         +         2HNO₃ ---> Ca(NO₃)₂  +  2H₂O
Volume (cm³):            18.3                            25.0
Concen (mol/dm³):                                         1.5
Moles:                      0.01875                       0.0375

Now using that same equation we used earlier we can figure out the concentration of the calcium hydroxide.

c= n / (v/1000)
c=0.01875/(18.3/1000)
c=1.02 (to 3 sig. fig.)

And that is your answer of course it needs its units so it is:

1.02 mol/dm³

Did you find this helpful? Feel free to drop a comment and let me know what you liked and if I have missed something!


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