a. Describe and explain the effect of adding concentrated sodium sulfate solution (assume saturated) to a sample of the solution taken from a saturated solution of calcium sulfate.
b. Explain, with calculations optional, why this will be effective as a qualitative rather than a quantitative test in the Science classroom, for a 20 mL sample.
How do you do the calculations for part b?
To describe and explain the effect of adding concentrated sodium sulfate solution to a sample of calcium sulfate solution, we need to consider the solubility behavior of these two compounds.
a. When concentrated sodium sulfate solution is added to a sample of the calcium sulfate solution, a double displacement reaction occurs. The sodium ion (Na+) from the sodium sulfate solution replaces the calcium ion (Ca2+) in the calcium sulfate solution, resulting in the formation of insoluble calcium sulfate (CaSO4) precipitate and soluble sodium sulfate (Na2SO4) solution.
This reaction can be represented by the following equation:
CaSO4 (aq) + Na2SO4 (aq) -> Na2SO4 (aq) + CaSO4 (s)
The insoluble calcium sulfate precipitate will appear as a solid, while the sodium sulfate solution will remain clear.
b. Adding concentrated sodium sulfate solution to a sample of calcium sulfate solution can be an effective qualitative test in the science classroom rather than a quantitative test. Here's why:
Qualitative Test: When a qualitative test is performed, the goal is to determine the presence or absence of a particular substance. In this case, adding concentrated sodium sulfate solution to a calcium sulfate solution would result in the formation of a white precipitate of calcium sulfate. This observation would confirm the presence of calcium sulfate in the solution.
Quantitative Test: A quantitative test aims to determine the exact amount or concentration of a substance present in a solution. However, when using the given information, a quantitative test cannot be accurately performed. This is because the concentration of calcium sulfate cannot be determined solely by adding concentrated sodium sulfate solution. To quantitatively determine the concentration, additional information such as the starting concentrations of both solutions and the volume of solution added would be required.
Calculations for Part b (Optional):
In the case of a quantitative test, calculations could be done to determine the concentration of calcium sulfate present in the sample. Here's an example of how the calculations could be done:
1. Determine the number of moles of calcium sulfate:
- Assume the molar mass of calcium sulfate (CaSO4) is 136.14 g/mol.
- Calculate the mass of calcium sulfate precipitate formed by weighing the resulting precipitate.
- Divide the mass of calcium sulfate precipitate by its molar mass to determine the number of moles.
2. Calculate the concentration of calcium sulfate in the sample:
- Use the volume of the sample solution (20 mL) to calculate the concentration in moles per liter (Molarity) by dividing the moles obtained in step 1 by the volume in liters (0.02 L for 20 mL).
These calculations can provide the quantitative information about the concentration of calcium sulfate in the solution. However, without the initial concentrations of both solutions, it would not be possible to accurately calculate the concentration of calcium sulfate.