Experiment #8 Feedback

Worksheet
Generally well done. Most common issues:
Q2) It is expected that you know these, especially that acids are associated with H+ (or H3O+) and bass with OH-. The only thing you might not know is that they are both electrolytes, that acids are commonly found in foodstuffs and bases in cleaning products
Q5) You have to discuss solutions A, B and C
Q6) You need to know the colour changes of Litmus - it was the whole point of the prac!Also ,anything 'hydroxide' is a base. HF, HCl, HBr & HI are all acids. In fact most covalent compounds containing H (except hydrocarbons and water) are acids. Finally - adding something neutral to an indicator won't change the colour. So if you have red litmus and add a neutral substance it won't shift to the neutral colour, it will just stay red (ditto for blue).

Summary

A) You must include the safety information for all indicators that have an associated risk (Phenolphthalein (PP), Bromothymol Blue (BB), Universal Indicator (UI) and Methyl Orange (MO) all have some risks).

(B) You need to use colour for your final assessment summary

(C) You need to get the pH of the colour changes for these indicators exactly right: Litmus (LS), PP, BB, MO. This information is in your textbook pg 129 (and our 931 handout). You need to present the exact colour CHANGE and the pH it occurs at, noting that each has three distinct colours eg phenolphthalein changes from clear to pink to crimson at pH 8.3 - 10.0

(D) Swimming pool pH - correct pH is needed to ensure the pool equipment isn't damaged, the water isn't cloudy and so the added chlorine can kill pathogens - see here and summarise the first paragraph. In addition, fish tanks do not need to be kept exactly neutral - thye need to be at the CORRECT pH for the fish within it - eg see here & here.
(E) Before disposing high and low pH chemicals they must be neutralised (pH can be checked with an indicator or probe) then flushed down the sink with water

(F) When discussing Le Chateliers Principle (LCP) you MUST correctly define LCP, you must show an example equation and you must specifically refer to the equation in order to explain the effects of changing conditions.
(G) In a risk assessment you need to say what steps or equipment you are using to minimise the risk.

(H) We study the use of indicators titrations in class, so when the syllabus asks for an example from industry it wants you to find another example - eg disposal of chemicals - see textbook.