Calculate Molarities of HCl & NaOH Solutions: Titration Ques

[tipton12]

A 0.4793g sample of primary standard grade Na2CO3 was treated with 40.00mL of dilute HCl. The solution was boiled to remove CO2 and then excess HCl was back-titrated with 8.70mL of NaOH. In a separate experiment, it was established that 27.43mL of the HCl neutralized the hydroxide in a 25.00mL portion of the NaOH solution. Calculate the molarities of the HCl and the NaOH solutions.

I need a starting point or steps. I was thinking about finding the number of moles of the standard Na2CO3 present. But other than that, I'm a little overwhelmed with what to do with all the volumes given. Please help on the homework problem!

 

[chem_tr]

Hello, I see that a lot of people encounter some difficulty in understanding these.

Please remember that molarity has the dimension of $$\frac{mol}{L}$$ or $$\frac{mmol}{mL}$$, while multiplying this with volume gives mol or mmol, respectively.

You can try writing the reaction formula to see how many mols of reactants are required for a complete reaction, and you can find how many moles of HCl are in excess.

A last hint: if someone says that there is a primary standard, you can understand that its purity can be considered as 100%.

 

[ravenprp]

To calculate the molarities of the HCl and NaOH solutions, we need to use the titration data and the molar mass of Na2CO3. Here are the steps you can follow:

1. Calculate the number of moles of Na2CO3 present in the 0.4793g sample using its molar mass (105.99 g/mol). This can be done by dividing the mass by the molar mass.

2. Use the balanced chemical equation for the reaction between Na2CO3 and HCl to determine the mole ratio between Na2CO3 and HCl. This will allow us to calculate the number of moles of HCl used in the titration.

3. Use the volume of HCl used (40.00mL) and the molarity of Na2CO3 (calculated in step 1) to calculate the molarity of the HCl solution.

4. Use the volume of NaOH used (8.70mL) and the molarity of HCl (calculated in step 3) to calculate the molarity of the NaOH solution.

5. Use the titration data from the separate experiment (27.43mL of HCl used to neutralize 25.00mL of NaOH) to calculate the molarity of the HCl solution again. This is done by using the mole ratio between HCl and NaOH.

6. Compare the two values calculated for the molarity of HCl. If they are different, take the average of the two values to get a more accurate result.

7. Repeat step 6 for the molarity of NaOH.

By following these steps, you should be able to calculate the molarities of the HCl and NaOH solutions. It is important to carefully consider the mole ratios and use the correct volumes and molarities in the calculations. I hope this helps and good luck with your homework problem!