chemistry :P

[evilcow]

quad if u're reading this, go away! hehe.
anyways.. we've got this lab.. acid & bases lab to be more specific for chemistry (it's worth 5%) of our mark.. so i'm going to make the effort.. to do some research before actually making my procedure. This is the criteria we have to meet.

Purpose: to determine the concentration of your unknown strong acid to 4 significant digits.

Materials provided: NaOH(s), 1.00 M HCl, 15mL unknown acid, any glassware found in the lab

Basicall we're trying to find the concentration of this unknown strong acid. Any chemists out here.. can you please tell me how i can find the concentration of the unknown strong acid (note this is a titrations lab).. Can you please tell me the proper method, etc to find an accurate concentration Thanks. (note the mark is based upon your result)

 

[CTho9305]

how (in)accurate do you think normal titration would be? not a chemist, so I dont know how good it can get

 

[Evadman]

Drink it. If it eats your stomach out, and your lunch spills out on the floor, it is a 4 molear acid

In all serousness, you should eb able to take the one molar HCL and dilute it with water to the point where the unknown acid and the diluted HCL will match determined bt the NaOH.

 

[crypticlogin]

<< Materials provided: NaOH(s), 1.00 M HCl, 15mL unknown acid, any glassware found in the lab >>


(Oh god, chemistry. :disgust: )

I hope you're given at least a pH or pOH indicator. I vaguely remember bromothymol blue as being the indicator we used in the presence of a base (I think), but litmus strips work as well, just more tedious.

 

[yomega]

It looks like your teacher is giving you a trick question, it is not possible to be accurate to 4 sig figs if you are only given 1.00 M NaOH solution, which only has 3 sig figs.

Now if you are given 1.000 M NaOH then it is possible.

Note: I think it is imposible, but I am not a chemist.

 

[JeremiahTheGreat]

yomega is right, its not possible to get 4 sig figs as sig figs are counted using the lowest possible one (if that makes sense . The 15ml is only 2 sig figs so your maximum accuracy is with only 2 sig figs.)

It would be a hell of a lot easier if you got some pH indicator that tells you when the solution is basic, otherwise just watching to see if the NaOH reacts with the unknown acid is not very accurate.

Well since i'm bored (and i need to remember this for year 12 ) and want to throw you in the completely wrong track, here you are!

Materials - NaOH(s), Water, Titrator thingo (that long metal spout that allows you to measure the amount of liquid given out), pH indicator (theres a way without this, but not accurate), measuring things.

Note - you may need to adjust some of these values for amount of substances (ml, g) depending on what type of aquipment you have. I cbf doing the maths either.. just want to confuse you.

1) Mix 15g of NaOH(s) with 50ml of water. Work out the molar concentration of this solution. (something like add the molar mass of Na + O + H. Divide 15g by that the answer to get the number of mole. Then time that answer by 0.05L to get molar concentration).

2) Put that NaOH(aq) into the titration thingo.

3) Add a few drops of pH indicator into the unknown mixture of acid.

4) SLowly add drops of NaOH into the mixture until the solution turns pink (if using methyl violet i think, or was it that other stuff?) or green (ph = neurtal).

5) Measure the amount of NaOH solution that was needed to turn that acid soultion neutral. Mark this down! [Alternative, put NaOH until you see it stop reacting.. i don't think it reacts quite enough to see tho]

6) Do some maths!!!

Since you know its a STRONG ACID, you can assume 1 mole of OH- will react with 1 mole of the unknown substance (not sure, but this seems nearly always true eg HCL, sulphruic acid, nitric acid ...). WIth the answer you get for 5, work out how many mole of NaOH was used (n=CV - where n is mole, C is molar concentration, and V is amount of liquid in mole). That answer will be how many mole of unknown acid there is in the 15ml. Using n = CV, divide the answer by the volume (0.015ml) and WHOOOOAALLLA~!!! You get your concentration.



Kekeke.. i know this is not what you are asking for, but i really needed to remember this for myself

 

[Shalmanese]

Okey dokey.

I dont know what level this is at so I am assuming Yr 12 High School (for which 4 sig figs IS reasonable since we assume many things are ideal)

Okay

Aim + Hypothesis: Blah

Apparatus

Pippete
Burette
stand for burette
conical flasks
beakers
apron and eyegoggles
phenopthalene (sp?:confused
unknown Acid
HCL
NAOH
Distilled water

Method:

- Usual procedures for titration, these are unbelievably anal so I wont bother listing them unless you have no clue what they are
- Put some NaOH in the conical flask using pippete
- Put some HCl in the burette using different pippete
- put 3 drops of pheno in the conical flask
- titrate
- repeat 3 times until endpoint is accurately known
- do the math
- repeat exept for NaOH and Unknown acid

 

[JeremiahTheGreat]

hehe.. what he said

 

[arcaneman]

Ok first things first, you need to ask your teacher if your acid is a monoprotic, diprotic, or triprotic acid. (I'll assume it'll be monoprotic as this is probably a highschool lab or first year university lab).

Next since you are given solid NaOH, you need to make a standard solution from it, hence you need to do 2 sets of titrations. First one to standardize your NaOH concentrations and the second to determine your unknown acid's concentration. It is insufficient to just weigh your NaOH and use the mol calculations from the weight to determine concentration of your solution as often solid NaOH is hydrated and you do not know it's hydration level so the # of mol NaOH cannot be determined by simple weight calculations. Also, I would recommend you do each set of titrations at least 3 times to ensure the precision of your experiment. (Heh i know it's a lot but at least you're not in analytical chemistry, where you have to repeat everything 5 times hehe).

For the first set of titrations, weigh out enough NaOH to make approximately a 1 L 1.00 M solution of NaOH (you will find the exact concentration of your solution by titration). Now accurately measure out 25.0 mL of the 1.00 M HCl solution you are given and place it in a flask and add a couple drops of phenolphthalein indicator to the acid. Phenolphthalein is clear in acidic solutions and purple-pink in basic solutions. Fill your burette with the NaOH solution. (you don't have to fill it up to the 0 mark just mark down the point where it was filled to). Now allow the NaOH solution to start dripping rapidly into the HCl solution and swirl the flask while this is happening. You will notice that a purple color will form where the drops fall, but this will rapidly dissapate. Slow the rate of NaOH dripping when the color starts to linger for longer and longer periods. As it gets near the end the color will stay for seconds at a time and now you need to add NaOH drop by drop. The final color of your titration must be a light pink, the fainter the better. If you get a koolaid color purple you have overshot badly and that titration is junk. Now just use the C1V1=C2V2 formula to determine the concentration of the NaOH solution. Repeat this 3 times to get an average. That average is the concentration of your standard NaOH solution. This standardization step is necessary for all solutions that you make from solid crystal compounds, due to the hydration problem I pointed out above.

After this, just use your standard NaOH solution to perform the titrations on the unknown acid and since you know the concentration of the base and it's volume (the titrated volume) and the volume of the acid, the concentration of the acid is a simple calculation away. There you have it chemistry 101 in a nutshell. Damn this brings back memories of when I used to TA first year labs hehe.

Dragonheart

 

[RaynorWolfcastle]

Arcaneman's reasoning is the most accurate and it is probably what they expect you to do...

I think I may even have a similar lab somewhere in my older chemistry labs lemme take a look, I could then just scan the complete procedure. Wait, nm, mine involved a pH probe attached to a computer, that helped accuracy quite a bit. Besides I just remembered chucking all those chemistry labs away. Sorry.

-Ice

 

[evilcow]

totally awesome responses. i'm going to go with arcaneman's suggestion. it seems to be the most accurate one thanks a lot guys

 

[CStroman]

Fractionally distill your unknown acid to make it 100% pure.