I have to find the weight percent of Na2Co3 for my lab report that's due tomorrow but I have no idea how to do it. In the lab I had to wdight 0.4 g of the unknown soda ash sample into an erlenmyer flask and add about 50 mL of deionized water. Then I had to add 2 drops of phenolphthalein and titrate with standard 0.1 M HCl until the pink color disappears. Recorde the volume of HCl added. Then add 4 drops of methyl orange indicator. The solution should now be olive green. Continue to titrate with 0.1 M HCl. The endpoint will be a grayish color. Record the volume of HCl added.

Question

I have to find the weight percent of Na2Co3 for my lab report that's due tomorrow but I have no idea how to do it. In the lab I had to wdight 0.4 g of the unknown soda ash sample into an erlenmyer flask and add about 50 mL of deionized water. Then I had to add 2 drops of phenolphthalein and titrate with standard 0.1 M HCl until the pink color disappears. Recorde the volume of HCl added. Then add 4 drops of methyl orange indicator. The solution should now be olive green. Continue to titrate with 0.1 M HCl. The endpoint will be a grayish color. Record the volume of HCl added.

The overall reaction to the 2nd endpoint is
2HCl+Na2CO3-2NaCl+H2CO3-H2O+CO2+2NaCl
I'm totally clueless on how to get the %Na2Co3. Is that soda ash or am I calculating the %of Na2Co3 in soda ash. Help would be greatly appreciated

For every two moles of HCL you used, you had one mole of sodium cargonate. How many moles of HCl did you use?

MolesHCL=volumeHCLin liters*.1M

Then half that number of moles is the moles of sodium carbonate.

Percetn= masssodiumcarbonate/.4g

I added what you see in bold face type.
Percetn= [(masssodiumcarbonate)/.4g] x 100 = %Na2CO3

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