How to determine calcium trioxocarbonate (IV) content in a chalk by back titration
The steps to follow are as follows: First, mass the chalk, and add acid.
a) find the moles of original acid in the 100 mL added (normally on the label)
b) find the moles of NaOH used to titrate the excess acid
c) find the moles of HCl which the NaOH in (b) neutralized (ie. the moles of HCl which were titrated)
d) By subtraction from the total moles of acid in the 100 mL calculate how much acid reacted with the carbonate, hence the moles of CaCO3 and mass of CaCO3.
e) convert that mass of CaCO3 to precentage in the original chalk.
Good
To determine the calcium trioxocarbonate (IV) content in chalk using back titration, you will need the following materials and chemicals:
Materials:
- Chalk sample
- Burette
- Pipette
- Conical flask
- Volumetric flask
- Beakers
- Distilled water
Chemicals:
- Hydrochloric acid (HCl)
- Sodium hydroxide (NaOH)
- Methyl orange indicator
Here is a step-by-step procedure for the back titration method:
1. Weigh a known amount of chalk sample (e.g., 0.5 grams) accurately using a balance and transfer it into a conical flask.
2. Add a known excess amount of hydrochloric acid (HCl) to the flask containing the chalk. The acid should be in excess to ensure complete reaction with the calcium trioxocarbonate (IV) present in the chalk.
3. Swirl the flask to ensure complete mixing and reaction between the acid and chalk. The reaction will produce calcium chloride, water, and carbon dioxide gas.
4. Allow the reaction to proceed until all the carbon dioxide gas has been evolved. You can ascertain this by observation or by connecting a delivery tube to the flask and collecting the evolved gas in a test tube submerged in water. When no more gas bubbles are observed, it indicates that the reaction is complete.
5. Prepare a standard solution of sodium hydroxide (NaOH) by dissolving a known amount (e.g., 0.1 M) in a volumetric flask filled with distilled water. This solution will be used for titration.
6. Transfer the contents of the conical flask into a beaker, and rinse the flask to ensure all the reactants are transferred.
7. Add a few drops of methyl orange indicator to the beaker. Methyl orange changes color from red to yellow at the endpoint of the titration when calcium carbonate is completely neutralized.
8. Slowly titrate the solution in the beaker with the standardized sodium hydroxide (NaOH) solution until the color changes from red to yellow. Record the volume of NaOH solution used.
9. Carry out a blank titration by repeating steps 6 to 8 without adding any chalk sample. This measures the volume of NaOH solution required to neutralize the excess hydrochloric acid used in the reaction.
10. Calculate the volume of NaOH solution used to neutralize the calcium trioxocarbonate (IV) by subtracting the volume of NaOH used in the blank titration from the volume used in the actual titration.
11. Calculate the moles of calcium trioxocarbonate (IV) using the balanced chemical equation, 2HCl + CaCO3 → CaCl2 + CO2 + H2O.
12. Finally, calculate the percentage of calcium trioxocarbonate (IV) in the chalk by dividing the moles of calcium trioxocarbonate (IV) by the mass of the chalk sample and multiplying by 100.
Please note that this is a generalized outline, and exact experimental procedures may vary depending on the specific requirements or apparatus available in your laboratory.
To determine the calcium trioxocarbonate (IV) content in a chalk sample using a back titration method, you will need a few reagents and equipment. Here is a step-by-step guide to performing the analysis:
1. Prepare the necessary reagents:
- Standardized hydrochloric acid (HCl) solution: This should be approximately 0.1 M in concentration.
- Methyl orange or phenolphthalein indicator solution: This will be used to detect the endpoint of the reaction.
- Sodium hydroxide (NaOH) solution: This should also be standardized and approximately 0.1 M in concentration.
2. Weigh a sample of chalk and record the exact mass. Dissolve the sample in excess hydrochloric acid and transfer the solution to a volumetric flask. Dilute the solution to a known volume. This step is necessary to convert the chalk into calcium chloride (CaCl2) in solution.
3. Pipette a known volume (e.g., 25 mL) of the calcium chloride solution into a conical flask.
4. Add a few drops of the methyl orange or phenolphthalein indicator to the conical flask. This will help in identifying the endpoint of the titration.
5. Slowly titrate the calcium chloride solution with the standardized sodium hydroxide solution until a color change occurs. In the case of methyl orange, the color change is from pink to yellow; for phenolphthalein, it is from colorless to slightly pink. This color change indicates the completion of the reaction between calcium chloride and sodium hydroxide.
6. Note the volume of the sodium hydroxide solution required to reach the endpoint. This volume of NaOH will be used in the back titration calculation.
7. Repeat the above steps two more times to obtain accurate and reproducible results.
Calculations:
The back titration method allows us to determine the content of calcium trioxocarbonate (IV) in the chalk sample. Here's how to calculate it:
1. Calculate the moles of hydrochloric acid used in the titration:
Moles of acid = molarity of acid (in mol/L) × volume of acid used (in L)
2. Calculate the moles of sodium hydroxide used in the back titration:
Moles of base = molarity of base (in mol/L) × volume of base used (in L)
3. Determine the moles of calcium trioxocarbonate (IV) in the chalk:
Moles of chalk = moles of base – (2 × moles of acid)
4. Convert moles of chalk to mass (if needed):
Mass of chalk = Moles of chalk × molar mass of calcium trioxocarbonate (IV)
By following these steps and performing the necessary calculations, you can determine the calcium trioxocarbonate (IV) content in the chalk sample using the back titration method.