Discussion
I have a long-term, from before my time, bottle of 0.1M hydrochloric acid. I've topped it up over the years using an inaccurate dilution that I titrated to get a good number, then diluted. And diluted again. And again.
So today the ~14yr old chemists were learning about titration. They've made standard solutions (particularly precise solutions of a very stable alkali) to balance against my "0.1M" acid, to get a really accurate measurement.... (1/n)
And now they know *WHY* we do titrations too. When I get a delivery of "38% hydrochloric acid" it might be 35% or 40% (roughly 12M) so I dilute it down to "4M" for lower hazard handling and *then* do a titration to get an accurate value of 3.72M or whatever.
That gets diluted down to 2M, which gets diluted to 1M, then to 0.5M etc etc.
@_thegeoff thank you for letting your students find out.
We had a number of obviously rigged experiments thrown at us, and it was always disappointing
@scruss I'm particularly proud of having turned several "we rig it because it doesn't work" experiments into ones that actually work. But prouder of the one a 6th year student decided to fix after hearing me complain about it.
The teacher asks me to double check the sums in front of the class, because every one of 5 groups of students measured the acid at ~0.2M, about double what it should be.
And there's a factor of 2 in the reaction. But nope, the sums were right.
So I tell the class, yup, you got me, at some point I've messed up on the multiple dilutions. That's how science works, eliminate the errors and then trust the data, ego has to go out of the window.