Is my experiment plan okay? (1 Viewer)

[Interdice]

Okay. Luckily, the teacher told us EXACTLY what we'll be doing in the practical.

What he said:

Part 1: We'll be given hydrocloric acid with known concentratoin, and we're to use this to find the concenation of sodium hydroxide.

Part 2: We'll use use the derived concentration of the sodium hydroxide from the previous part, to find if another acid is monoprotic, dioprotic, or trioprotic. We have to create the standard solution ourseles. We're given molar mass and mass.

My calculation procedure:

titrate to find the volume at which the HCL titrates with NaOH.

CV = CV to find concentration

Part 2:

titrate Sodium hydroxide with acid.

find volume at which indicator turns pink.

find moles of sodium hydroxide. n = cv
find moles of acid. n = m/mm

compare moles to see which is monoprotic, dioprotic and trioprotic.

Any issues?

 

[Eagle Mum]

I’m uncertain from the words/phrases you use whether you have the right plan or not.
For example, you use the phrase ‘find moles of acid. n = m/mm’, which suggests that this will be determined through measurement which is incorrect - the correct step is to calculate the number of moles required, from the given molar mass of the unknown acid, to make up the solution for titration.

You’ve correctly stated that in part 1, your aim is to determine the concentration of NaOH.

In part 2, since you will be given the molar mass of the unknown acid, you can prepare the solution of the unknown acid to be the same concentration as NaOH (which you determined in part 1).

For example, if you’ve determined the concentration of NaOH to be X (eg. 0.5 mM) and you’re given the molar mass of the unknown acid to be Y (eg. 204), then to make up the acid solution to the same concentration, you would dissolve X*Y (ie. 0.5 x 204) grams of the unknown in 1L (or part thereof if you are making the solution to a final volume of less than one litre).

If you prepare the unknown acid to the same concentration as NaOH, then if the same volume of NaOH is required to neutralise the acid, it is monoprotic. If the volume of NaOH required for neutralisation is twice the volume of the acid, then the unknown acid is diprotic and if three times the volume is required, then it is triprotic.