what is your source of motivation: monetary gain, loves research, enjoy teaching at university?

One of my postgraduate tutor loves teaching. He finds it a fulfilling job that he decided to pursue a PhD so that he may become a university academic, to teach undergraduates.

I have a friend who is doing his chem eng PhD now because during the year he completed his undergraduate degree, all the major oil companies weren't recruiting. He had a first class honours in chemical engineering FYI.

I havent met anyone who wants to do a PhD because he wants to be scientist. Perhaps you are the first. It's your calling whether you want to do a MS in Chemistry. There's always other attractive options such as pharmacy or MBA or a graduate chemical engineering degree. Nowadays, pharmatical manufacturing requires engineers with specialised chemistry knowledge and vice versa.

What is the question you are asking yourself:
(1) Do I want to go grad school? OR
(2) Do I want to do a Master in Chemistry?

PS: If you wonder why I quote all chem eng examples.. I study chemical engineering

Grad school for chem is very different than for chem E.  Engineers don't need grad school to go out into the work force.  A BS chemist doesn't either, but can expect to earn less and not really be involved in much research, especially the higher-up project design.  If you have a PhD, you are much more likely to be involved in the research planning, and also execution.

As a friend once told me:
A BS chemist will do one process all day long.
A MS chemist will run the same machine all day long.
A PhD tells the BS and MS what to do.

That's a little cynical and supposed to be humorous, but you've got a lot more job opportunities with a PhD in chemistry.  Ironically, if you have a higher degree in chem E, you've got less job opportunities, as you are mostly employable in academics.

I will not kid you either, if you go to a grad school for chemistry, it will not be easy.  If your school is worth its salt, it is one of the hardest PhD programs out there.

I would also warn you about P-Chem, but it seems though you might be ready for it if you were a Chem E--it's a lot of math.  Evil math.  Best of luck.

jd1828, you must be kidding. I love my ChE thermodynamics class. It's the most interesting subject (although I must say it is very mathematical). My ChE department is very research-focused and surprisingly most of the staff here are not PhD chemical engineers but physical chemists.

Geodome, you're a ChemE.  Of course you'd like thermo.  I'm a chemist.  I hate it.

Its funny that I was actually sitting in that thermo class when I decided that I didnt want to be a ChE anymore.   I realized that I hate this class and need to do anything I can to avoid taking it.  

It really wasnt that bad of a class it was more the bad the prof.  I have had some boring teachers but this guy made my brain go numb.  

BTW, a lot of chem grad schools don't offer an MS program.  You have to at least apply as a PhD student, although you can usually leave after a year or two with an MS.

Also, your overall grades don't matter all that much when applying to grad school as long as you did well in your major subject.  It's certainly helpful to have good grades all around, but definitely not imperitive.

I agree with your statement that says to make sure you really really want a PhD, but I disagree a little with your statement that it's harder to get a job with a PhD in chemistry than a BS.  While your specific field, medicinal chemistry, that may be true, when you look at synthetic chemistry jobs, that's not the case.  I can't speak to physical chemistry, biochem, physics, or medicinal chemistry, but if you take a look through Chemical and Engineering News, almost all the job opportunities are for those with a PhD and experience.  That's hard to come by.  Academia of course requires a PhD, but industry likes them a lot, too.  Again, this is very specific to the field.  There's a huge difference between ChemE, biochem, and synthetic chemistry, I know for sure.  I have worked for three different companies through internships, etc., and all of them told me that it's easier to get hired if you have a PhD--it's what the look for.  It is one of the major reasons that I'm getting a PhD.  Also, if you want a government job at a national lab, you better have a PhD.  They used to hire a lot more BS and MS chemists, but they're headed toward the all PhD route.  Anyway, those people that I know leaving with a PhD are getting good jobs, many in pharmaceuticals and consulting, and few have trouble finding a job.  Conversely, almost all those that I went to undergrad with who left with a BS have been unable to find a job in industry.  Several of them I know wound up working the food service industry at my old dorm because the pay was better.

You should read this article by Katz (physicist) about pursuing advanced degrees in science.  http://wuphys.wustl.edu/~katz/scientist.html  Pretty much everything he said is true, no matter how many people don't want to believe it.  

I'm somewhere between pharmaceutical (research) and computer science (research  also).

Try doing some computational chemistry.  Computational chem is starting to become huge in the pharm industry.