If not all the alum dissolves in the water before adding the Ba(NO3)2 solution, what effect will this have on the sulfate percent error determination?
I don't think the problem is stated very well. You know without any reasoning that the percent error will increase. Surely this isn't the answer you want.
It appears to me that you want an answer that is based on the final result. If all of the alum is not dissolved, then less will be in solution, the amount of BaSO4 will be less, that leads to a smaller mass Alum calculated than it should.
If not all the alum dissolves in the water before adding the Ba(NO3)2 solution, it will have an effect on the sulfate percent error determination. The percent error is a measure of the accuracy of an experimental measurement compared to the true value.
When attempting to determine the sulfate content in a sample using the Ba(NO3)2 solution, the assumption is that all the alum dissolves completely in the water. This is necessary because the reaction between the sulfate ions in the alum and the Ba(NO3)2 solution is a precipitation reaction. The sulfate ions react with the barium ions in the solution to form insoluble barium sulfate precipitate.
If not all the alum dissolves, it means that some of the sulfate ions will not react with the Ba(NO3)2 solution and will remain in the undissolved residue. As a result, the measured amount of sulfate in the sample will be lower than the actual amount, leading to an underestimation of the sulfate content.
To calculate the percent error, you would compare the measured sulfate content (which is lower due to undissolved alum) with the expected sulfate content (based on the assumption that all the alum dissolves). The formula for percent error is:
Percent Error = |(Measured Value - Expected Value) / Expected Value| x 100%
In this case, the measured value is lower than the expected value, resulting in a negative percent error. The greater the amount of undissolved alum, the larger the negative percent error will be.
To minimize this effect and obtain more accurate results, it is crucial to ensure that all the alum dissolves completely before adding the Ba(NO3)2 solution. Additionally, thorough mixing and agitation of the solution can help improve the dissolution process.