As badapple has indicated, the sodium carbonate solution is 0.1106 mol/L. For the second part, we need to dilute this solution to be 500.0 mL and 0.100 mol/L, so use the diltuion formula (C_1 * V_1 = C_2 * V_2) with
C_1 = 0.1106 mol/L, V_1 = ? L, C_2 = 0.100 mol/L, and V_2 = 0.5000 L, which gives V_1 = 0.45207... L. So, you need to place 452 mL (3 sig fig) of the sodium carbonate solution into the 500.0 mL volumetric flask, and then fill to the graduation mark (dropwise near the end), then shake to mix, to produce 500.0 mL of 0.100 mol/L sodium carbonate solution.
Originally posted by kimmeh
what does it mean when the solution reaches end point? is that the point where 55.3 ml of HCl actually "neutralised" the the solution?
Originally posted by badapple
yes. 55.3mL of HCl neutralised 25mL of Na2CO3
Firstly, make sure that you understand the difference between
equivalence point and
end point, as they are not the same thing, and there is a horrible tendency for these terms to be used interchangeably. Hopefully, the following will make the difference clear
:
Equivalence Point: The point in a titration where the reactants are present in their stoichiometric ratio. That is, just enough titrant has been added from the burette to completely react all of the material in the conical flask, and thus neither is present in excess.
End Point: The point in a titration when the first
permanent colour change of the indicator occurs.
Now
if the indicator is appropriate, then the end point should occur just after (say half a drop after) the equivalence point. Since a drop is about a twentieth of a mL, we can take the end point (which is what we find) as a very good approximation to the equivalence point (which is what we seek), and use the end point as if it were the equivalence point in calculations.
This is the reason that the approriateness of the indicatot is so important. If an inappropriate indicator is used, then the end point may be quite different from the equivalence point, and so the assumption that we can approximate the equivalence point with the end point is invalid.
Secondly, avoid using the word
neutralise in the context of acid / base titrations, as whether the equivalence point is neutral (ie pH = 7 at 25 C) depends on what chemicals are involved. The pH at the equivalence point will depend on the
nature of the salt formed (acidic, basic or neutral), and this in turn will determine what indicators are approriate in a given experiment.
As it turns out, the equivalence point for this titration will be neutral - NaCl is a neutral salt - provided that all of the CO2 produced is evolved as gas. However, the term is still dangerous. Try to stick with equivalence point / end point, or if you must speak of pH, make sure you also talk about the nature of the salt.
