Friday, February 5, 2010

Help with designing an experiment to test if it's true that if you increase by 1 on the ph scale...?

could someone please help me with ideas for an experiment. i have to test if it's true that if you increase by 1.00 on the ph scale , the concentration of hydrogen ions will decrease by a tenfold.Help with designing an experiment to test if it's true that if you increase by 1 on the ph scale...?
It's really not difficult at all. Start with some stock acid, HCl at 1M, for instance. Then make up multiple dilutions, and measure the pH of each. Plot on graph to see the trend. You will need 10 mL pipette and multiple 100 mL graduated cylinders. Pipette 10 mL from the more concentrated dilution, transfer to 100 mL volumetric flask and dilute to 100 mL to make the 10-fold dilution.





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Trevor's transferring of 100 mL of acid and diluting to 1000 mL is a bit extreme, in terms of the total volumes, and the need for 1L volumetric flasks. 10 mL transfers to 100 mL flasks is more reasonable.Help with designing an experiment to test if it's true that if you increase by 1 on the ph scale...?
1) prepare a dilute solution of HCl.


2) check the pH using pH meter - if necessary, adjust concentration of solution to give pH approx 2.0


3) record the pH of the solution, say this is 2.15


4) Now remove 100ml of this solution and dilute it to 1000ml. This is a 10X dilution.


5) measure pH of this second diluted solution. It should be 3.15





Do the calculations:





Ist solution, pH = 2.15


[H+] = 10^-pH


[H+] = 10^-2.15


[H+] = 7.079*10^-3





2nd solution, pH = 3.15


[H+] = 10^-pH


[H+] = 10^-3.15


[H+] = 7.079*10^-4





You have shown that if you increase the pH by 1 unit, the concentration of hydrogen ions will decrease by tenfold.

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