Question

in my chem lab brass and nitric acid reacted to form copper ions and I had to calculate the percent copper in the brass. I came out with a percentage of 36%. It was expected that the copper int he brass percentage would be higher. So what could be some likely causes of experimental error for the percentage of copper in brass to be much lower?

Answer 1

% of copper in brass can be calculated by calorimetry as well as by titration.

In calorimetry possible errors could be:

1 : Water used is contaminated (means normal tap water used instead of distilled water) this will lead to presence of other elements in sample which change the absorbance value and error occur in result.

2: other error could be due to loss of sample amount while transferring sample to test tubes and cuvettes.

3: if test tubes and cuvettes are not clear.

Another method is titration:

Before titration brass is digested in nitric acid for getting free copper for further experiment

1: First error could be due to over digestion of sample and because of evaporation of the sample liquid.

2:After that if while making standard solutions amount of sample is not transferred completely.

3: Iodometry titration used for calculating amount of copper in standard solution,if there is loss of iodine from solution than there would be error in result.Also loss of iodine can be due to acidic solution due to oxidation of iodine ion this can be controlled by instant titration .

4:if starch used for Iodometry is not fresh there would be experimental error.