Hi could anyone help me solve this question?
A 1.00g sample of a mixture of sodium carbonate and sodium hydrogen carbonate was titrated with 0.200 mol/dm3 hydrochloric acid using phenolphthalein as indicator. If 17.50 cm3 of HCL were required, what is the percentage by mass of sodium hydrogen carbonate in the mixture?
Answer: 62.9 %
This is my solution but I was stuck somewhere and my answer is wrong:
Mol of HCL: (0.2x 17.50)/1000 = 0.0035 mol
Na2CO3 + 2HCL ---> 2 NaCl + H2O + CO2
2 mol of HCL ---> 1 mol of Na2CO3
NaHCO3 + HCL ---> NaCl + CO2 + H2O
1 mol of HCL ---> 1 mol of NaHCO3
total mol of HCL required: 3 mol
0.0035 / 3 = 0.00116666...
0.00116666....x Mr of NaHCO3 = 0.00116666....x (23 + 1 + 12 + 3 x16)
= 0.098g
0.098/1 x 100% = 9.8 % ???
is there a ph curve graph?
no i dont think so it is given in this question....
I think you have 1 assumption that is wrong from your working: You assumed equal amount of Na2CO3 and NaHCO3
I think need to use algebra. Let x be mass of NaHCO3. Then (1-x) g is mass of Na2CO3. Continue from there and see if you can get the ans.
okay thanks!