Stochiometry- Balanced equation
K2CrO4+BaCl2 --> 2KCl+BaCrO4
Table 1: Showing the results obtained during the experiment
Graph1: Showing the relation between the average height and the volume of BaCl2
Conlcusion:
The graph is consistent with the expected results. The height increases
when the volume of BaCl2 is lower than the volume of K2CrO4, then it stays the
same when there is equal amount of both substances and finally, the height
decreases again as the is more BaCl2 than K2CrO4. The height was the highest
when there was the same amount of BaCl2 and K2CrO4. Whe can also see that we
must balance the equation K2CrO4+BaCl2 → BaCrO4+KCl by adding a 2 in front of
KCl = K2CrO4+BaCl2 → BaCrO4+2KCl. We need to balance the equation because
of the law of conservation of mass: matter can be changed from one form into
another, mixtures can be separated or made, and pure substances can be
decomposed, but the total amount of mass remains constant. (Chem.wisc.edu,
2016)
Evaluation:
The first thing that could have varied a bit the results and made them less accurate was the fact that when the test tubes came out of the centrifuge, we had to measure the centimetres of solid that were concentrated at the bottom, but the amount wasn’t at the same level, so we had to smoothly hit it against the table, so that it came down and all of it was more or less balanced, but though we did this, it didn’t fully balance, therefore we had to search for a point between the lowest and the highest so that it is as accurate as possible, it wasn’t though, because we can’t know the exact point. We believe this is a random error, because each one of it has a different change in level, which is unpredictable.
A solution we propose for this is to let the test tubes in the same place for a day, so that all of the solid comes down the test tubes and rests on the bottom, just the same that the centrifuge does in less time, but this way we know that everything will be at the same level and that we will be able to measure it accurately.
Another thing that could have varied our results, was the difficulty that caused measuring with such a big pipette, sometimes it wasn’t really accurate because a few drops were spilled in the process of transporting the solution from the beaker to the test tube. A solution to this is to use a small beaker next time.
It’s very probable we haven’t filled the tube exactly with the amount needed each time, so we have to take into account a parallax error. Also, the tube was filled by a different member of the group each time, so can be the cause of the mistake.This could have maybe originated a mistake because not all humans have the same view. Maybe, one of my partners filled more or less the tube than I did and saw the meniscus differently every time, this could be considered as a random error. We could solve this by making sure the tube is filled by the same person every time and to get rid of the parallax error we could be careful and consider the meniscus to make the measuring precise.
Another thing that could have made our result less precise is that we believed the substances that were given to us were really BaCl2 and K2CrO4 but maybe there weren’t as the containers weren’t labelled. If the substances weren’t the ones they were supposed to be, our results will be completely imprecise. A solution to this is to make sure the containers containing the substances are labelled.
We should have repeated each individual experiment a few times to reduce random errors.
As we can see, there are lots of things that could be improved for the next time we repeat the experiment by carrying out the solutions we have proposed and receive more accurate results.
References:
Chem.wisc.edu,. (2016). Retrieved 26 January 2016, from http://www.chem.wisc.edu/deptfiles/genchem/sstutorial/Text1/Tx14/tx14.html
Using the pipette, put 0.5 mL of potassium chromate in the first tube,
1.0 mL in the second, and so on up to the ninth.
Repeat the process filling the tubes with barium chloride making sure that finally each tube has 5 ml in total
Use the centrifuge to settle the solid to the bottom of the test tube.
Finally, measure the height of the remaining substance and collect all the data in a table
