For each of the following errors, indicate whether the calculated molarity of hy
ID: 899374 • Letter: F
Question
For each of the following errors, indicate whether the calculated molarity of hydrochloric acid oul bo higher or lower than the real value or unaffected Briefly explain your? Answer. The sodium carbonate is not dried before use. The sodium carbonate fe dissolved in 80 ml of water (rather than the 40 ml. indicated in the procedure). The buret, wet with water, is not rinsed with HCI solution before filling The titration solution is not boiled at the appropriate step in the procedure. Why should a primary standard have a high molecular mass? When you finished the titration, you may have noticed that the green end-point color changed gradually to yellow after several minutes. What is a possible cause for this change?Explanation / Answer
1) if the sodium carbonate is not dried the moisture present in the sodium carbonate will lower the concentration of the sodium carbonate solution prepared .
therefore the volume required to titrate the Na2CO3 solution will be lowered
calculation for molarity of HCl
Molarity of HCl = 2(mass of Na2CO3)/(106)(Vol. of HCl)
from the above equation Molarity of HCl is inversely proportional to the volume of HCl.
Therefore the Molarity of HCl will be more than the actual value
b) If the sodium hydroxide is dissolved in 80ml of water which is 40ml more than the volume of water indicated in the procedure.
The Molarity of HCl remains uneffected.
c) The buret wet with water is not rinsed with HCl before filling.
If the burette is not rinsed with HCl solution and has water in it, there will an error in the volume calculation of HCl, which will show more volume than the actual volume required for neutralization.Therefore as explained in Part a, the volume of HCl is inversely proportional to Molarity of HCl.
Therefore the Molarity of HCl will decrease than the real value.
The molarity of the HCl will be lowered because it will react with the water present .
d.The titration solution is not boiled at the appropriate step when required.
in the experiment the titration solution is Na2CO3 solution.The Na2CO3 solution when boiled will release all the carbondioxide present in it.
When Na2CO3reacts with HCl, carbon dioxide (CO2) is produced. This will give us an incorrect endpoint. To correct this, we must remove the CO2 by boiling the solution when it first starts to turn green.
The Na2CO3 solution when boiled will turn back to blue and then can be used for titration to get to the correct endpoint.
Due to this the HCl will react with CO2 and lower its Molarity than the real value.
2. why should a primary standard have a high molecular mass.
Primary standards should have high molar masses that allows them to be easily and accurately weigh on a balance with minimal error. This property facilitates accurate calculation of the molar concentrations of solutions when they are prepared in volumetric flasks
3. green end point might have changed to yellow due to oxidation.
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