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

Answer 1

To calculate the weight percent of Na2CO3 in your unknown soda ash sample, you need to use the information provided. Here are the steps:

1. Calculate the moles of HCl used for the first endpoint:
MolesHCL1 = volumeHCL1 in liters * 0.1 M

2. Calculate the moles of HCl used for the second endpoint:
MolesHCL2 = volumeHCL2 in liters * 0.1 M

3. Calculate the total moles of HCl used:
TotalMolesHCL = MolesHCL1 + MolesHCL2

4. Since the reaction between HCl and Na2CO3 is a 1:1 ratio, the moles of HCl used are equal to the moles of Na2CO3 in your sample.

5. Divide the moles of Na2CO3 by the total moles of the sample:
PercentNa2CO3 = (MolesNa2CO3 / TotalMoles) * 100

Where:
- MolesHCL1 is the number of moles of HCl used for the first endpoint
- MolesHCL2 is the number of moles of HCl used for the second endpoint
- volumeHCL1 is the volume of HCl added for the first endpoint
- volumeHCL2 is the volume of HCl added for the second endpoint
- TotalMolesHCL is the total number of moles of HCl used
- MolesNa2CO3 is the moles of Na2CO3 in your sample
- TotalMoles is the total moles of the sample

The weight percent of Na2CO3 can be calculated by dividing the mass of Na2CO3 by the total mass of the sample and multiplying by 100:

PercentNa2CO3 = (massNa2CO3 / total mass) * 100

Make sure to substitute the appropriate values into the formulas and divide the moles and masses by the correct amount of sample used (0.4 g) to obtain accurate results.