For some reason i cant get this problem to work out for me: To standardize the H
ID: 794422 • Letter: F
Question
For some reason i cant get this problem to work out for me:
To standardize the HCl, you will obtain a known mass of sodium carbonate and add it to a flask with some water and an indicator that changes color when the solution turns from basic to acidic. You will then slowly add the hydrochloric acid solution from a burette until the end point is reached indicating that the HCl and sodium bicarbonate are in their stoichiometric molar ratio (2HCl:1Na2CO3). Knowing the mass of sodium bicarbonate used, one can calculate the moles of sodium bicarbonate and the moles of HCl. With the volume readings from the burette and the moles of HCl calculated, the molarity of the HCl solution can be found.
The mass of Na2CO3 is .086g in 25ml of water
10.6 mL of HCL was used to reach the end point.
I am trying to find the Molarity of HCL
My attempt: I got the moles of Na2CO3 by using the molecular weight of 105.988 g/mol giving me 8.11E-4 moles of Na2CO4. The problem is saying that it has 1:2 relationship with HCl so i assumed this would mean that HCl would have 4.06E-4 moles. From there i took molarity to be Moles of HCL/Ls of solution but i keep getting the wrong answer. So what am i doing wrong here?
Explanation / Answer
Na2CO3 + 2 HCl => 2 NaCl + H2O + CO2
Moles of Na2CO3 = mass/molar mass of Na2CO3
= 0.086/105.99 = 8.114 x 10^(-4) mol
Moles of HCl = 2 x moles of Na2CO3
= 2 x 8.114 x 10^(-4) = 1.623 x 10^(-3) mol
Molarity = moles/volume of HCl
= 1.623 x 10^(-3)/0.0106
= 0.153 M
(Note that to get moles of HCl, you multiply (and not divide) moles of Na2CO3 by 2)