[KULER]

hello anyone know how to do the attach question and if HCL is added to a solution contain NaOH and Na2CO3. which two will react first and why. please help me .thanks!!

[clownfish]

(Original post by KULER)
hello anyone know how to do the attach question and if HCL is added to a solution contain NaOH and Na2CO3. which two will react first and why. please help me .thanks!!

Hi
In the first titration the following happens:
NaOH + HCl --> NaCl + H₂O
and
Na₂CO₃ + HCl --> NaHCO₃ + NaCl


In the second titration the following happens:
NaHCO₃ + HCl --> NaCl + CO₂ + H₂O

So 2nd titre gives moles of NaHCO₃
Which is equal to the moles of Na₂CO₃

and then the moles of NaOH = moles of HCl in first titre - moles of Na₂CO₃

Then multiply by molar masses and divide by volume used and you have the answers.


This page shows you the titration curve, which should help you understand why the reactions occur in the order they do. Phenolphthalein changes colour at high pH and methyl orange changes colour at low pH: https://docs.google.com/viewer?a=v&q...UIrHDMgHR6NKQg