need help with an easy titration question (1 Viewer)

[kooltrainer]

what is the difference between an equivalence point and an end point? is equivalence point one where first sign of colour change occurs or is it equal moles of H+ and OH- being added together?





4) A mass of 0.665g of sodium carbonate is used to prepare a solution in a 250ml
volumetric flask. This solution is delivered from a burette into 20ml of HCl. Three accurate titres were obtained as shown.
titre1 - 27.5ml
titre2 - 27.3ml
titre3 - 27.4ml (note the average is 27.4ml)
a) Calculate the concentration of the standard solution of sodium carbonate
b) calculate concentration of HCl solution

 

[namburger]

equation:
Na2CO3 + 2HCl -> 2NaCl + CO2 + H2O

Concentration of sodium carbonate:
0.665 grams of Na2CO3
n=m/M
n = 0.665/106
= 6.27 x 10^-3

C = n/v
= 6.27 x 10^-3 / 0.25
= 0.025 mol/L

concentration of HCl solution :

C (Na2CO3) = 0.025
V (Na2CO3) = 27.4

C (HCl) = ?
V (HCl) = 20

C1V1 = C2V2
0.025 x 27.4 = 20 x ?
but since there is 2 moles of HCl per one mole of Na2CO3, therefore you multiply by 2 and you get 0.0685 Mols/L

 

[cameron0110]

An end point is where the first sign of colour change is observed. The equivalence point is where there are just enough moles of acid to completely react with the number of moles of base (or vice versa).

Ideally in a titration you want both to be around the same point (i.e. choose the indicator so that it will change colour around the equivalence point).