Chemistry A Level Planning

chocolates-xed SG

Need help with this SPA Planning qn... its my first attempt without guidance and so need some help! thanks :)

_________

The basicity of an acid can be determined by a titration method. With a known molar mass of an unknown organic acid, it can be neutralized by standard solution of an alkali as shown :

H⁺ + OH^- → H₂O

You are to design an experiment in which the amount of acid can be determined by its reaction with an alkali through titration.

Acid given is a weak acid while the alkali given is a strong hydroxide.

From the data collected in the experiment you should be able to determine the basicity of the organic acid.

(a) Outline a titration method by which you may determine the basicity of organic acid with M_r of 90, starting with 1.0g of the anhydrous acid.

In your procedure you should include a justification of the amounts and concentrations of any other chemicals used.

(b) From the data collected, work out the basicity of organic acid

UltimaOnline SG

Exactly what kind of help are you looking for? Is there something about the question, procedure or calculations you don't understand?

Try writing out your draft answer here, and have others comment on it.

Note that you can control the molarities of both the acid (since you have sample mass and molar mass) and alkali used.

What the question means by "basicity" of the acid, refers to the proticity of the acid, eg. monoprotic (or "monobasic") or diprotic (or "dibasic") and so on.

chocolates-xed SG

actually i don't really understand also. our teacher hasn't even taught us and expects us to submit tmr.

anyway this is what i wrote:

1. 1.0g of anhydrous organic acid is dissolved in distilled water and made up to 1dm3

2. x moldm-3 of the strong hydroxide is made up to 1dm3

3. Pipette 25.0cm3 of the strong hydroxide into a concial flask.

4. Add a few drops of methyl orange indicator.

5. Titrate with organic acid in the burette

the part (b) i totally do not know how... and my ans to (a) doesn't really make sense too. :(

UltimaOnline SG

Your answer is fine, but here are a few points to consider :

Given sample mass and molar mass, you can find the no. of moles. Hence by controlling the volume of solvent, you can control and/or know the molarity of the weak acid.

If possible, use the same molarity of the strong alkali, for convenience of volumetric calculations.

Since a weak acid and a strong alkali, will at equivalence point, generate a salt that undergoes hydrolysis to generate hydroxide ions, the pH at equivalence point will be alkaline. So choose a suitable indicator such as bromothymol blue or phenolphthalein.

http://en.wikipedia.org/wiki/PH_indicators

If, using equal molarities of acid and alkali, to reach equivalence point (approximated by endpoint); equal volumes of acid and alkali were used, the acid is monoprotic. If volume of alkali required (to reach endpoint or equivalence point) was twice that of the acid, then the acid is diprotic. If thrice the volume, the acid is triprotic.

You may also refer to the following page for more info on the Titration process :

http://en.wikipedia.org/wiki/Titration

Remember, as a self-motivated, self-learning resourceful academic student, Wikipedia is your best friend. Take full advantage of the capacities of the Internet Age.

chocolates-xed SG

ok thanks for the advice :) ... have searched the internet for help also on assignments on organic chem and etc before... but sometimes wikipedia not reliable right?