Please scroll to question 21. near the end of the paper. The answer is A.
To set up an experiment where rate of reaction of sodium thiosulfate and hydrochloric acid is analysed. We add sodium thiosulfate to a conical flask with acid in it. we can measure the rate of reaction by recording the time taken for a cross to disappear beneath the conical flask due to a precipitate forming.
Why is rinsing the conical flask with acid likely to decrease the accuracy of the experiment? I would imagine that stirring the solution introduces error as the rate of stirring is difficult to control
I could see closure as unclear what you're asking, due to failure to include key details in the post itself.
But this is not a 'problem dump' question -- OP has a reasonable question about the answer to a test question about an experimental procedure. IMO the community should have worked with OP here rather than just homework-closehammering him.
In fact, I have taken the time to rework the question, and invite 10k+ rep users to consider voting to undelete.
Given the above, and various other occurrences around the site, I propose we formally dial the homework close reason waaaaaaay back. Based on the results of last year's experiment, this sort of philosophical change seemed to have salutary effects, so how about let's move forward with a formal change to site policies in this direction? There's been a lot of discussion about what to do about HWVTC, with little action actually resulting. Mostly it seems like there's difficulty reaching consensus about exactly how to define what's homework/homeworky and what's not.
So, how about we change the homework VTC reason to only cover questions that are explicitly posts containing the text of homework problems/exercises; either with no additional comments, or with requests for help without mention of any technical concept that they're having difficulty with?
We've already deprecated the homework tag, and are thus in the process of minimizing "homework" as a category on the site. We seem to have received an appreciable influx in new askers and answerers to the site in the last few weeks; if we want to welcome these new people in and grow the community, we probably are sending exactly the wrong message by summarily closing a bunch of posts, instead of engaging their authors and helping orient them to the site philosophy/policies.
Implications and recommendations if this were to be implemented:
Posts that "feel homeworky" but do not include an explicit problem statement are not closeable as homework. Downvote and move on, or engage the OP in comments if desired.
"Insufficient research" posts (AKA, "Three seconds of Googling" questions) are not closeable as homework. Downvote and move on, optionally leaving a suitable comment.
Posts that include a problem statement and do ask a technical question are not closeable as homework. If the question is poor, downvote and move on; or, engage OP in comments; or, vote to close as unclear or too broad if appropriate.
AMIRITE questions are not closeable as homework. (This is the implication I'm least happy about, but I think it's necessary.)
If there is no useful exposition to be made and the only reasonable response is a trivial "yes", then provide that trivial "yes" in a comment, downvote the question as being poor for the site, preferably leave a comment indicating this motivation for the downvote, and move on.
If the answer is correct but there is some useful exposition to be made, make it in an answer. The appropriateness of a downvote here is somewhat less clear; likely I would not upvote, though.
If the answer is not correct, write an answer explaining why. As above, the appropriateness of a downvote here is unclear, since the question represents a real confusion someone had about a problem, and thus may be helpful to others.
Posts that are laden with misconceptions are not closeable as homework (if they ever were).
If the misconceptions are sufficiently few, post an answer addressing them. Probably do not downvote or upvote.
If there are too many to address, downvote and leave a comment to that effect.
Posts that address basic concepts are not closeable as homework (if they ever were / should have been)
- Check for possible duplicate targets for these, either through site search or The Giant List of Duplicates. If no dupe target is forthcoming, consider writing a detailed answer that can then become a dupe target for other questions. (If the particular question is insufficiently general, then create a new, general, self-answered Q&A and then close the particular question as a duplicate of the newly-created one.)
This proposal is just to feel out the general opinion of the community on this course of action. Appropriate changes to the wording of the close reason and of the relevant Meta (here, at minimum) and possibly Help Center pages would have to be drafted and approved down the line.