Here is the procedure:
1. By difference weight 1.0g of the unknown metal carbonate into a 250 ml volumetric flask
2.Dissolve it and dilute it to volume with distilled water
3. Into each of three erlynmeyer flask pipet 20 ml of your unknown metal carbonate
4. Pipet 15 ml of HCL solution (record the exact molarity) into each of the three erlenmeyer flasks and gently sgake for about 7 minutes
5.Add two drops of phinolphtalein to each of the three flasks
6. Set up a buret. Clean and rinse the buret with a few mililitres of standart NaOH solution. Record the exact molarity of the standart NaOH solution. Fill the buret with the standart NaOH solution
7. Titrate and excess HCl in each flask with standart NaOH solution until you reach the end point. The end point is reached when the solution remains barely pink for at least 15 seconds
8. Record the volume of NaOH used in the back titration for each of the three samples.
Questions:1. If all of your CO2 gas is not driven out of solution in the shaking process how will it affect the final result for your molar mass of the metal carbonate? Explain your answer (Hint: if CO2 remains dissolved in water it forms a weak acid, carbonic acid (H2CO3)
2. Explain why the pink colour obtained at the end point of the titration in this experiment gradually dissapears over time?
3. A sample of BaCO3 (molar mass=197.33 g/mol) has 25.00 ml of HCL (0.2120 M) added:BaCO3+2HCL ---- BaCl2+CO2+H2OA back titration of the excess HCL required 22.48 ml of NaOH (0.1082 M) Determine the mass of BaCO3 which was originally present