Practical:- Pharmaceuticals (1 Viewer)

[Kat92]

Hey guys,

We have to do this practical for the pharmaceuticals option.

And I was just wanting to know how I can get a constant light purple colour change in my solution?

The following equipment that we are using include, pipettes, conical flask, retort stand, boss head and clamps, beaker, hydrochloric acid, sodium hydroxide, phenolphthalein, paper and filter funnel.

Have done practice runs for this experiment following the teacher's notes and doesn't work.

Seeing as we will be assessed on this in the next couple of weeks, if anyone has any suggestions it would be mostly appreciated.

Thanks!:wave:

 

[missanonymous7]

Hi, I might be able to help but I don't quite understand, what exactly are you trying to test?

From what you've written, I can tell you that phenolphthalein will turn a pinkish purple colour when the solution is basic. But I don't see how what you've described relates to the pharmaceuticals option. More info maybe?

 

[Kat92]

From what I gather, our teacher is relating the phenolphthalein and hyrdochloric acid to the absorption within the blood stream and how drugs break down. Personally I am thinking the same thing, what does this really have to do with the pharmaceuticals option, it is more lifestyle chemistry. As we need to have the acid and the base combine to make the pinkish/purplish solution at the 20 mark on the dripper. Although on numerous runs when he said 25mls of hcl and then 15 mls phenolphthalein and sodium hydroxide it doesn't work. Well not until the 30ish mark or until the dripper is empty.

 

[missanonymous7]

Do you think you might be able to post the method or whatever instructions you've been given? Because this still doesn't sound like anything we ever did when I did the pharmaceuticals topic! It almost sounds like you're trying to do some kind of titration (I don't know if you've done any chemistry or not (besides 'lifestyle chemistry'), but that's where titrations come from). But I really don't see how that relates to drug absorption/breakdown.

However I think if you can get the pH of the solution to be approximately 10, you should get that pinkish/purplish colour...although you'd only need a few drops of phenolphthalein (I'm assuming that's what you mean by 'penophaline' right?), not 15mLs...but yeah, sorry, I'm still a bit at the moment!

If all else fails though, just ask your teacher.

 

[Kat92]

We have to set up the retort stand with the boss head and clamps to hold the pipette. Fill the conical flask with 25 mls sodium hydroxide, add 3 drops phenolphthalein. Then get a filter funnel attach to the pipette and pour in hydrochloric acid until it reaches 0 on the pipette. Then slowly open the valve and let the liquid drip into the conical flask and turn the valve off at the 20ish mark and have a solid light purple solution once swirled. As when in the practices even working in pairs I ended up with a slight result at around the 30ish mark, but the solution didn't stay a solid purple, it went back to clear after a few seconds.

PS> Like you said if we can't figure anything out, might have to ask my teacher. As I have been able do all the other pracs succesfully and worksheets getting full marks each time. However, this prac doesn't seem to interrelate to anything in my notes

 

[missanonymous7]

OK, I'm just going to assume you haven't done any chemistry (sorry if you have and I sound a bit teacherish, lol). What you've just described is called a titration, which is where you gradually add one substance (the hydrochloric acid in this case) to another substance (the sodium hydroxide) until it reaches a certain 'point' and the colour of the solution in the conical flask changes (because you've added some kind of indicator that will show you when this change happens - in this case, the phenolphthalein changes from pink/purple to clear). This is usually done when you're trying to figure out what the concentration is of the solution in the pipette.

But there's absolutely no need for you to be doing titrations in senior science; that's for (I think?) HSC chemistry, and first-year chem at uni. And I have no idea how it fits into pharmaceuticals! Unless there are other parts to this experiment that I (or you) don't know about.

Also, there's a pretty good reason why the solution is changing from pink/purple to clear - by adding more hydrochloric acid, you are gradually making the solution in the conical flask more acidic, or you're lowering the pH. This means the phenolphthalein in the bottom solution will change from pink to clear, rather than from clear to pink. If you're trying to make it change from clear to pink, you would need to have the hydrochloric acid in the conical flask, with phenolphthalein added to it, and put the sodium hydroxide in the pipette.

At least, I think that's what's happening, anyway. I could be wrong. But I hope that's helped you a bit. I think you should definitely ask your teacher about it, and maybe also ask how it relates to pharmaceuticals (or even ask what dot point it relates to).

 

[Kat92]

No, I haven't done much chemistry before. Although, like you said it would be more logical to have the hydrochloric acid in the conical flask, with phenolphthalein added to it, and put the sodium hydroxide in the pipette. As if the sodium hydroxide was in the conical flask and phenolphthalein was added it would turn purple straight away and the hydrochloric acid would change the PH.

Thank You for your help, it has cleared some things up.

I will ask my teacher today before we have to do the prac tomorrow and see what he says. As maybe he made a mistake when writing it up on the board.