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    Hi,

    So i've been doing my chemistry investigation on Esters.

    Those of you who are familiar with the production of esters, you'll know there is a washing process, wherein you rid the impurities of the ester you have distilled by washing it with dilute sodium carbonate (0.1moldm-3)
    (Usually in a seperating funnel)

    I stupidly used a higher concentration through out my whole c.w say about 10moldm-3,
    I wanted to know what impact this has on the ester (if anything?)

    I produced quite a decent set of results, with a good trend.
    My investigation is now over, and im in the writeup stage!

    Do you think its worth mentioning I STUPIDLY got my calculations wrong and used a higher conc?
    Tried googling what impact a higher conc. of sodium hydrogen carbonate has.. but no luck

    I could do with some help
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    Is it acid catalysed using carboxylic acids, or using acid anhydrides, or using acyl chlorides?

    The sodium hydrogen carbonate would react with unreacted carboxilic acid and neutralise the acid used to catalyse the reaction (for carboxylic acids) or produced as a biproduct (organic acids for acid anhydrides, HCl for acyl chlorides) , preventing any hydrolysis to break the ester down again (weak acid catalyses the hydrolysis) and taking these components out of the organic layer, assisting purification.

    I would assume dilute sodium hydrogen carbonate is specified as you dont need conc. to get the job done, also it's cheaper by a factor of 100x to use the same volume of 0.1M as 10M...... Otherwise it shouldn't cause any harm.

    I'm sure your lab techs loved you!
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    (Original post by gingerbreadman85)
    Is it acid catalysed using carboxylic acids, or using acid anhydrides, or using acyl chlorides?

    The sodium hydrogen carbonate would react with unreacted carboxilic acid and neutralise the acid used to catalyse the reaction (for carboxylic acids) or produced as a biproduct (organic acids for acid anhydrides, HCl for acyl chlorides) , preventing any hydrolysis to break the ester down again (weak acid catalyses the hydrolysis) and taking these components out of the organic layer, assisting purification.

    I would assume dilute sodium hydrogen carbonate is specified as you dont need conc. to get the job done, also it's cheaper by a factor of 100x to use the same volume of 0.1M as 10M...... Otherwise it shouldn't cause any harm.

    I'm sure your lab techs loved you!


    Thank you so much that really helped!
    I was using just plain old carboxyllic acid + alcohol
    No fancy acid anhydrides or acyl chlorides (as I'm trying to determine the equilibrium constant)

    My lab techs absolutely adored me:

    • Broke a £100 relfux condenser
    • Stunk out the WHOLE lab room, using butanoic acid...went home smelling like vomit.
    • Soaked people with leaking water pipes
    • Skin started peeling after constant use of Methanoic acid with no gloves


    All in all I would say I am a rather fantastic chemist ;D
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    Yeah, you aren't going to be getting a Christmas card of them, that's for sure.

    We all start somewhere.

    At least you haven't set the fire alarm off yet. One of my university colleagues managed to get the entire block (8 stories + basement) evacuated, coated my back in burning ether (thank God for lab coats) and her face in concentrated sodium hydroxide. I managed to break a mercury thermometer, then in the process of cleaning it up end up holding a round bottom flask full of burning, boiling, overflowing 98% nitric acid.

    When you get more experienced that just ensures when you do **** it up, your ****-ups are all the larger.
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    I absolutely adore your colleague. She sounds bloody amazing.
    I mean wow, I honestly rate her.

    My vomit smelling experiment was probably what made me a household name.
    People on the bus were coughing and opening windows, absolutely mortified I was.
    Luckily all my friends who had been working next to me smelt just as gorgeous going home.
    The following day the chemistry lab was closed off, becuase it smelt horrific and the students were refusing to attend lesson.
    All my doing

    I am such a klutz its unbelievable, and i'm dreading Uni..
    I'm assuming you're studying chemistry?
    If you don't mind me asking, where? and whats it like?
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    I studied at Imperial, it's a few years back now.

    Great fun but nutso hard work. It's no doss degree either with regards to the level of the work or the amount of it. I recon i did around 3000hrs of lab work throughout the degree AT LEAST (4yr MSci) which was generally good fun. Lectures were mixed, depending upon the lecturer and my aptitude for that area of chemistry. The level of scientific complexity is mindblowing compared to the simplistic models you learn at GCSE and A-level.

    Was an enjoyable experience overall.
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    (Original post by gingerbreadman85)
    I studied at Imperial, it's a few years back now.

    Great fun but nutso hard work. It's no doss degree either with regards to the level of the work or the amount of it. I recon i did around 3000hrs of lab work throughout the degree AT LEAST (4yr MSci) which was generally good fun. Lectures were mixed, depending upon the lecturer and my aptitude for that area of chemistry. The level of scientific complexity is mindblowing compared to the simplistic models you learn at GCSE and A-level.

    Was an enjoyable experience overall.
    oh WOW. That sounds so intense, and so WOW.
    I can only imagine what its like :/
    I've applied to Imperial, ha.. waiting for my rejection any day now

    If you don't mind me asking, what are you doing now?
    I'm always curious to know what graduates end up doing, so very few people I know have actually entered their field.
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    I'm a teacher, GCSE & A-level
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    i've actually quoted you in my coursework! Thanks for the help again
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    (Original post by gingerbreadman85)
    I'm a teacher, GCSE & A-level
    Sorry to bother you again, but I did start a thread about something and no one has replied.
    If you don't mind could you please help me on this?

    Heres what i posted:

    I did a chemistry investigation based around the production of esters by varying acid/alcohol conc. to see what impact this would have.

    alcohol+carboxylic acid = ester+water

    Im aware this is an equilibrium reaction,
    And i've spoken about Le chateliers principle in my c.w

    In my particular case, increasing concentration of reactants shifts equilibirum to the right.

    But this ONLY happens when you're increasing the conc. of a reaction thats already started- by say for example adding more reactants a few minutes into the reaction?

    I've not been doing this, instead I BEGIN with higher/lower concs. of acid/alcohol. So theres not really a shift in equilibirum?

    ALSO:

    i've worked out the equilibrium constant for each experiment and they're all different.
    My teacher said the equilibrium constant should remain the same for every reaction, regardless of higher/lower conc of acid/alcohol.

    Why is this?

    AND ONE FINAL THING: Any suggestions anyone can offer are much appreciated/any other chemical based principles i should add etc


    thanks so much
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    (Original post by Sifr)
    Sorry to bother you again, but I did start a thread about something and no one has replied.
    If you don't mind could you please help me on this?

    Heres what i posted:

    I did a chemistry investigation based around the production of esters by varying acid/alcohol conc. to see what impact this would have.

    alcohol+carboxylic acid = ester+water

    Im aware this is an equilibrium reaction,
    And i've spoken about Le chateliers principle in my c.w

    In my particular case, increasing concentration of reactants shifts equilibirum to the right.
    No, it pushes the reaction to the RHS, that's not the same as the equilibrium.

    (Original post by Sifr)


    But this ONLY happens when you're increasing the conc. of a reaction thats already started- by say for example adding more reactants a few minutes into the reaction?

    I've not been doing this, instead I BEGIN with higher/lower concs. of acid/alcohol. So theres not really a shift in equilibirum?
    Nothing changes the position of equilibrium except temperature

    (Original post by Sifr)


    ALSO:

    i've worked out the equilibrium constant for each experiment and they're all different.
    My teacher said the equilibrium constant should remain the same for every reaction, regardless of higher/lower conc of acid/alcohol.

    Why is this?
    Ahh the joys of experimental data...

    Your experiments are

    A. inaccurate... or
    B. imprecise... or
    C. full of errors...

    choose any one from three!

    That's just the way it goes. You will never get exact results from an experiment, and that's the beauty of science.


    (Original post by Sifr)
    AND ONE FINAL THING: Any suggestions anyone can offer are much appreciated/any other chemical based principles i should add etc
    thanks so much

    Rather than look at your data from the point of view of equilibrium try looking at the percentage yield based on your limiting reagent.
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    (Original post by charco)
    Rather than look at your data from the point of view of equilibrium try looking at the percentage yield based on your limiting reagent.
    Yes I've done that, I've calculated theoretical yields..limiting reagent etc.
    And plotted graphs against the yields I got, compared the theoretical yields (they wernt too bad)
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    (Original post by Sifr)
    Im aware this is an equilibrium reaction,
    And i've spoken about Le chateliers principle in my c.w

    In my particular case, increasing concentration of reactants shifts equilibirum to the right.

    But this ONLY happens when you're increasing the conc. of a reaction thats already started- by say for example adding more reactants a few minutes into the reaction?

    I've not been doing this, instead I BEGIN with higher/lower concs. of acid/alcohol. So theres not really a shift in equilibirum?
    You aren't changing the equilibrium position, which is defined as the proportion of products vs reactants. It's just as you have MORE products you will get MORE reactants in the same proportion.

    Same thing if you remove products, the reaction will cease to be at dynamic equilibrium but the balance point itself remains the same.
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    (Original post by gingerbreadman85)
    You aren't changing the equilibrium position, which is defined as the proportion of products vs reactants. It's just as you have MORE products you will get MORE reactants in the same proportion.

    Same thing if you remove products, the reaction will cease to be at dynamic equilibrium but the balance point itself remains the same.

    So this is the reason I should have a constant, Equilibirum constant, as in the same value?

    what is the position of equilibrium then? Or does it not have one?

    Sorry for the ignorance :/
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    any equilibrium reaction has an equilibrium constant (Kc).
    http://www.chemguide.co.uk/physical/equilibria/kc.html

    The size of this constant defines the "position" of the equilibrium. A large Kc will result in more products and less reactants at equilibrium (equilibrium lies to the right), a small Kc will results in an equilibrium that lies to the left.

    Thus the concentrations of the starting materials doesn't effect the Kc. You can in fact use the Kc to predict the equilibrium concentrations of products and reactants from given starting concentrations.
 
 
 
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