Unknown Alkali Metal Carbonate Lab Report

Finally ensure that your results are accurate. You should have a light blue precipitate remaining when the sodium carbonate reacts with the copper chloride and when sodium sulphate ionises with copper chloride no precipitate should have formed.

The probable identification of the unknown crystalline hydrate given in class, which was unknown A, is ZnSO4 • 7H2O (Zinc Sulfate Heptahydrate). After completing all the calculations, the percent water of the Unknown hydrate A was 41.997% based on the information gathered during the experiment. By dividing the mass of water lost by the mass of the hydrate, 41.997% was calculated as the percent water. The percent water for CuSO4 • 5H2O and ZnSO4 • 7H2O was also calculated, the conclusion of which hydrate is the unknown was based on the comparison of all three percentages.

In experiment A the results from the precipitation of CaC2O4 H2O from the salt mixture were obtained by weighing the items listed on Table 1 on a scale.

One error for the experiment could be from the popping and spritzing of the hydrate when heating it, which could have caused a slight decrease in mass of the whole compound. Since some of the hydrate spritz out of the crucible, the mass decreased. This directly affected the results of the experiment because the mass that spritzed out of the crucible caused the mass to be weighted differently when remeasured on the scale. Another error of the experiment was that there was some hydrate that stuck to the stirring rod when stirring the hydrate.

We then proceeded in testing for excess Ca2+ by adding two drops of .5 M K2C2O4 to test tube two and attentively observed to see if a precipitate formed, which it did. This meant that Ca2+ was in excess and C2O42- was the limiting reactant in the original salt mixture. We then cleaned up. Upon returning to our next class, we took the filter paper, with the precipitate on it, and took its mass.

Purpose: used in gravimetric analysis for analysis of a substance by mass of a precipitate it produced (solid collected in paper or fritted-glass filters)

The pre-test helped us decide the exact details of our experiment. We started off with testing 25cm³ of 3-molar hydrochloric acid to 2g of calcium carbonate medium size chips (we decided a medium size chips before we started our pre-test as we had a choice of 3, small, medium, large). We saw that this reacted too quickly as we used 10 second intervals and we couldn't get 6 results this is because our burette could only hold 100cm³ of water, which would make our results reliable. We then decreased the amount of Calcium Carbonate to 1g and kept the same 25cm³ of 3 molar hydrochloric acid and 10 second intervals. We could get the right amount of results of this, so we then tested the other extreme - the lowest molarity.

After conducting experimentations to find the best fit ratio that will produce the most amount of magnesium carbonate and highest percent yield, having a procedure was very helpful. The procedure used was very effective in helping the group collect and record precise results. The procedure was effective in the way that it was easy to follow with short, straightforward- to the point steps. In addition, the procedure included all the masses of the substances needed to collect for each trial, as well as the other materials that needed to be weighed. However, even with a competent procedure, one can’t predict what will go well and what will go wrong. An example of something that went well would be having all the materials that was needed before

It is very difficult to get an exact amount measured for whatever substances is being used, in particular the water. Measuring exactly 100 mL is difficult as seeing where the water is in the graduated cylinder can be hard. Also, there is a possibility the magnetic stir bar could not have stirred the solution fully or equally, causing a dissonance in temperatures and how the energy is distributed throughout the solution. Finally, the mass we recorded could have slight inaccuracies due to there being a chance grains of whatever salt we were using falling onto the scale itself and not the weighting boat, causing the balance to show a heavier mass than what there actual is. In the calculations, rounding and sig fig errors can be prevalent, though keeping them as precise as possible is something I tried my best in doing.

Just from looking at the aim of the investigation I already know that a salt would be formed because a carbonate with an acid forms a salt. In this investigation the substance that is formed is Calcium Chloride, Water and Carbon Dioxide. The symbol equation for this is:

This created a distance from the hot surface of the crucible from the Bunsen burner thus, not allowing the experiment to conduct. With the magnesium not touching the hot surface, there is a lack of energy for the chemical reaction to happen and not produce magnesium oxide. Another possible experimental error is that when crushing the magnesium oxide to a fine powder with a glass rod, water was used to wash off the magnesium oxide on the rod to get a more accurate mass. However, due to the solution being hot from the Bunsen burner, adding water created evaporation and also resulted in the solution to spill on to the lab bench which affected the mass and calculations. Also, connecting to this experimental error could be that the glass rod was not washed properly with the distilled water leaving some of the fine powder thus, leading to an approximate mass rather than an exact mass.

In Section B, we evaporated our samples to give total dissolved solids. To do this I placed a piece of aluminum onto a hot plate and set it on medium temperature. Then I placed a drop of my sample, a drop of distilled water, and a drop of 1x10-3 M Ca2+ onto the foil, each 0.5 cm away from each other. After the water evaporates, you are able to see white solids left behind which is the total dissolved solids.5

Results In the part 2 of the experiment conducted, another salt was used, called Calcium Chloride. Calcium chloride is created from the ionic bonds that form between calcium cations and chloride anions. Calcium ions have a charge of +2, while chloride ions have a charge of -1, thus making its structure like this: Table 2. The table shows the data obtained from the experimental set-up.

In class, we did some lab work using a sample of sodium bicarbonate undergoing a chemical change through heat temperature. By looking at the baking soda, we did not see any visual changes occurring because the substance by no means was harmed or altered by the fire. It was the same solid white powdery substance as it was before. Nevertheless, what happened was that the weight of the baking soda decreased from 3.2 grams from when it start to 2 grams at the end of the lab. However, when we checked one more time as we let it stay overnight, the mass was 2.42 grams. Therefore, there was not much of a difference except that the mass increased by a bit. This got me thinking that, it wasn’t going to be a good idea to use it for the actual mass as

Mark Steven R. Santiago and Kristiene B. Sadiwa Institute of Chemistry, University of the Philippines, Diliman, Quezon City 1101 Philippines Date/s Performed: July 13, 2012; Date Submitted: July 19, 2012 Results and Discussions A mixture of carbonate (CO32-), bicarbonate, (HCO32-) and hydroxide (OH-) ions can be analysed and determined by titration with strong standard acid solution. Volumetric titrimetry can be employed to compute percent compositions of sodium carbonate (Na2CO3), sodium bicarbonate (NaHCO3), and sodium hydroxide (NaOH) in a soda ash sample through the application of neutralization concepts and titrimetric analyses. Volumetric titrimetry has been utilized in