in the titration between Na2CO3 and HCl...
1) at the first end point what reaction is stoiciometrically complete?
2)At the start of titration where HCl=0 is the solution acidic or basic. ExPlain?
3) At the 2nd end point what reaction is stiociometrically complete?
4)Propose a suitable indicator to use in the lab for each end point. Explain your choices.
i've tried to di it.
1)Na2CO3 + HCl---> NaCl+NaHCO3
2)Basic as Na2CO3 is a base and amount of HCl =0
3)NaHCO3+HCl--->NaCl+CO2+H2O
4)phenolphthalein for eq pint point 1 as it will indicate change in basicity and methyl orange for secong equivalnce point as it will indicate change in acidity. (Don't know how to explain it can any one do it better than me?
All of your answers look ok to me. As for the indicator one,
The pH at the 1st equivalence point is that of a NaHCO3 solution which is pH = 1/2(k1k2) = about 8 or so and phenolphthalein changes between 8 and 10 (approximately). The second equivalence point is about pH 3.5 or 4.0 and methyl orange changes about 3-4.5. I prefer to boil the solution to expel the CO2 and that gives a sharper end point with methyl red indicator (4.2-6.3 or mid point about 5.0)
1) At the first endpoint of the titration between Na2CO3 (sodium carbonate) and HCl (hydrochloric acid), the stoichiometrically complete reaction is the neutralization reaction between the acid and the carbonate ion. The balanced chemical equation for this reaction is:
2HCl + Na2CO3 -> 2NaCl + H2O + CO2
In this equation, one mole of HCl reacts with one mole of Na2CO3 to produce two moles of NaCl, one mole of water, and one mole of carbon dioxide. At the first endpoint, the amount of HCl added is sufficient to react completely with all the carbonate ions present in the solution, resulting in the formation of NaCl, water, and carbon dioxide.
2) At the start of the titration when HCl = 0, the solution is basic. This is because Na2CO3 is a basic salt that dissociates into sodium ions (Na+) and carbonate ions (CO3^2-) when dissolved in water. The carbonate ion can accept protons (H+) from water, leading to the formation of hydroxide ions (OH-) and bicarbonate ions (HCO3-) through the following reactions:
CO3^2- + H2O -> HCO3- + OH-
Therefore, in the absence of HCl (which is an acidic solution), the concentration of hydroxide ions increases, making the solution basic.
3) At the second endpoint of the titration between Na2CO3 and HCl, the stoichiometrically complete reaction is the neutralization reaction between the remaining bicarbonate ions (HCO3-) and the excess HCl that has been added. The balanced chemical equation for this reaction is:
HCl + HCO3- -> H2O + CO2 + Cl-
In this equation, one mole of HCl reacts with one mole of HCO3- to produce one mole of water, one mole of carbon dioxide, and one mole of chloride ion. At the second endpoint, all the bicarbonate ions that were initially formed from the carbonate ions are consumed, resulting in the production of water, carbon dioxide, and chloride ions.
4) Suitable indicators for each endpoint of the titration can be chosen based on their color change at a specific pH range.
- At the first endpoint (where HCl is reacting with carbonate ions), an indicator that undergoes a color change around pH 8.2-10 would be suitable. Phenolphthalein is commonly used for this purpose. It is colorless in acidic solutions but turns pink in slightly alkaline solutions.
- At the second endpoint (where HCl is reacting with bicarbonate ions), an indicator that undergoes a color change around pH 3-4 would be suitable. Methyl orange is commonly used for this purpose. It is red in acidic solutions but turns yellow in slightly alkaline solutions.
These indicators are chosen because their pH range of color change matches the pH range at which the stoichiometric reactions occur, allowing for a clear indication of the endpoints.