Recently I was preparing a citric acid buffer. Most literature describes the process of mixing citric acid and sodium citrate in a specific proportion. Is there a reason why I cannot just use Citric Acid of a desirable molar concentration and then just adjust the pH to what I need it to be using NaOH ? Is there a reason why the acid /corresponding salt mixture better than the simple alkalization of the acid?
Convenience and safety, mainly - you will have to add a lot of NaOH and the reaction is exothermic. Stirring failure may result in a small but violent geizer.
It is just for simplicity. I prepare my buffers the way you say it. You just need to adjust the pH before making the volume up to the mark.
I dont think there is any difference. Anyways it's going to make conjugate base by itself when we add NaOH. Just take care that you don't overshoot NaOH concentration beyond your required pH, otherwise you will have to add Citric acid to lower the pH and that will change the molarity of your buffer ions.
If you require a final concentration of the buffer reagent ( in this case citric acid) of , for example, 0.1M and a defined pH , for example pH 5.0. and for example a sodium counter ion ( Na+), then the buffer is defined precisely as '0.1M sodium citrate buffer pH 5.0'. Whether you make it by neutralising citric acid with NaOH and adjusting the volume to the required citric acid concentration, or by mixing 0.1M citric acid with 0.1M sodium citrate until the pH is pH5.0., you will have exactly the same buffer solution formulation. As indicated previously, I have also found that mixing the acid form and the sodium salt ( both solutions having the same concentration) is the safest and most convenient method. There is no need to adjust the volume of the buffer after the correct pH has been reached and the solution heats up much less than when using strong base solution for neutralisation.
Also if you make a stock solution of buffer you can dilute it with water to a lower buffer ion concentration with little or no change in the pH unless you dilute by a large amount. Check the pH after dilution.
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