ST ICHI METRY LAB EXPERIMENT PLANNING

Transcription

1 ST IHI METRY B EXPERIMET PIG P I G RESERH QUESTIO How is the amount (g) of Sodium cetate produced dependant on the amount (g) of Sodium Bicarbonate (Baking Soda) used in a reaction with Vinegar? VRIBE IDEPEDET (x) mount of Sodium Bicarbonate (g) DEPEDET (y) mount of Sodium cetate (g) OTROED VRIBES Flask Vinegar Desiccator Baking Soda ir onditions Electronic Weighing Scale Spatula Water Sticker abel Filter Paper VRIBES MIPUTIO s the sodium bicarbonate is the limiting reactant, we will add 4 grams, 5.4 grams, and 6.3 grams of it to the reaction, and add vinegar freely. We will measure the amount (g) of sodium acetate produced by evaporating water and then weighing it. SPEIFITIOS 250m Erlenmeyer Flask 5% cetic cid with water Vinegar 70 at full setting oncentrated Baking Soda Room temperature, slight current from 300grams Electronic Scale accurate to 0.01 g Standard metallic flat-ish spatula Tap water Standard Sticker abel, 0.62 grams Standard Filter Paper, 0.81 grams

2 P I G HYPOTHESIS IF we react 4 grams of Sodium Bicarbonate (SBc) with vinegar in excess THE 3.90 grams will be the theoretical yield of Sodium cetate (Sc) BEUSE 4 grams x 1 mol x 1 mol SBc x g = grams g 1 mol Sc 1 mol of Sc IF we react 5.4 grams of Sodium Bicarbonate (SBc) with vinegar in excess THE 5.27 grams will be the theoretical yield of Sodium cetate (Sc) BEUSE 5.4 grams x 1 mol x 1 mol SBc x g = g g 1 mol Sc 1 mol of Sc IF we react 6.3 grams of Sodium Bicarbonate (SBc) with vinegar in excess THE 6.15 grams will be the theoretical yield of Sodium cetate (Sc) BEUSE 6.3 grams x 1 mol x 1 mol SBc x g = g g 1 mol Sc 1 mol of Sc MTERIS 3 Goggles 1 Electronic Weighing Scale 1 Bunsen Burner m Erlenmeyer Flasks 1 Gauze Mat 1 Tripod 20g of Baking Soda 1 Bottle of Vinegar 2 Spatulas 1 Box of Matches/1 ighter 1 Desiccator 6 Sticker abels a few pens/pencils Filter Paper PROEDURE 1. Gather the Materials 2. Place a sticker on the flask identifying it 3. Weigh the flask itself and record the weight in grams 4. Measure 4g of Baking Soda and put it in the Flask 5. Slowly but continuously add Vinegar and continue to add it until the reactions stops and there are no more bubbles. 6. Once the reaction has stopped place the flask in the desiccator 7. Desiccate the mixture until all of the liquid has evaporated and the remaining sodium acetate is dry and has crystallised 8. Remove the flask from the desiccator 9. Weigh the flask with the sticker and the sodium acetate in it 10.Record the (weight of the flask with the sodium acetate) - (the weight of the flask only) 11.lean the flask and all used materials 12.Repeat steps 2-11 with 5.4g and 6.3g of Baking Soda 13.Repeat steps 2-12 another time for a total of 2 trials

3 DT RW DT the amount of Sodium cetate produced (g) with increasing amounts of Sodium Bicarbonate (g) in a reaction with vinegar Sodium Bicarbonate (g) Yield Weights (g) Flask Weight Flask + Sc Weight Sodium cetate Yield D T OBSERVTIOS The bottom of the flask always had slightly darker powder along with the fine white of the rest of the flask, possibly indicating contamination. When we used acetic acid instead of vinegar in our second and third trials, the reaction lasted much longer. DT PROESSIG the amount of Sodium cetate produced (g) with increasing amounts of Sodium Bicarbonate (g) in a reaction with vinegar Sodium Bicarbonate (g) (input) Sodium cetate Theoretical Yield (g) Sodium cetate ctual Yield (g) Percent Yield % % % Percentage Yield (%) Percentage (%) Yield of 3 different trials Sodium Bicarbonate Input (g)

4 O EV O - E V OUSIO The data clearly shows that there is a direct correlation between the amount of Sodium Bicarbonate used in the reaction in the beginning and the amount of Sodium cetate produced from it. We created 3.88, 5.00, and 6.14 grams of Sodium cetate for 4, 5.4 and 6.3 grams of Sodium Bicarbonate respectively. Our hypothesis was close to right and we achieved over 90% yield for all of our trials (99.5%, 94.9%, 99,8%). However, our hypothesis has to be right, because it predicts (using stoichometry) the amount that should be created in a perfect lab. I used the balanced chemical equation below to find my yields. SOURES OF ERROR ERROR SIGIFIE IMPROVEMET The scale was poorly calibrate and continuously changed the weight it was showing. We used acetic acid and the faster reaction had the foam spill outside the flask, wasting material. There was contamination in the flasks that we used, which could have been chemicals that react with the chemicals we used, affecting the yields. While trying to isolate the right amount of baking soda and put it in the flask, we spilled it Some measurements were taken when the Sodium cetate wasn't completely dry yet. aho3 + H2H3O2 a2h3o2 + H2O + O2 It is of a low significance because the scales are completely accurate to at least one decimal point. This has a medium level of significance because quite a bit of wastage can occur like this. We observed some black coloured powder mixed with the white sodium acetate, which could have changed our yields/ data high significance. Spillage was only of minimal quantities so this is of low significance. This is a significant error because measurements are the most important part of a stoichiometry experiment. Use better scales, or predict using one less significant figure than the scales. Use the slower reacting vinegar only. Use clean flasks, and if there are no clean flasks, thoroughly clean the flask you have, until there is no trace of the contaminating chemicals. Use a smaller beaker instead of filter paper as a container use a better spatula Use the desiccator for far longer, such as another 24 hours beyond the observation that the Precipitate is dry.

5 O - E V EVUTIO I think these results are reliable, but they don t really matter, because we didn t have enough trials. We did get pretty good results as all of our yields being above 90%, which indicates good lab procedure with minimal error. I also believe we did our stoichiometry correctly so this is a good lab. The only major error could be that the substance is not wholly Sodium cetate, as some of the contaminants could have reacted with acetic acid and sodium bicarbonate as well. However, it is practically impossible to actually get 100% yield of a 100% pure substance. This is because there are always minute errors in measurements, especially when we are trying to calculate down to the atom, and measuring in 2 decimal points of grams. There is always human error in any complex, specific, and systematic procedure. If we were to do this lab again, I would try to reduce error by using proper equipment instead of what we improvised. I would also use completely clean flasks to avoid contamination, as well trying to use a better scale. I would let the solution properly dry and take its time in the desiccator. Finally, I would definitely add more trials, as that s what s stopping this experiment from being reliable. EXT TESTBE QUESTIOS ext testable questions beyond this would be changing the limiting reactant and the excess, possibly switching the vinegar and baking soda around. We could also apply stoichiometry to other experiments, or have seen how multiple trials affect results. nother future experiment could involve adding a catalyst or an extra reactant later on in the reaction and seeing the effect on theoretical calculations. Finally, we could do an experiment that looks into the creation and breaking of bonds, which is another theoretical aspect of chemistry.

6 ST IHI METRY B QUESTIOS PRE B 1.If we mix 25 grams of sodium bromide with a large amount of potassium chloride, what will our theoretical yield of sodium chloride be? abr + Kl = al + KBr P R E - B 25g abr x 1 mol 1 mol abr g x x g 1 mol al 1 mol al = g 2. If our actual yield from this reaction was 18 grams of sodium chloride, what would our percent yield for this reaction be? 18 g g = = % 3.Is the answer in question 2 reasonable? If so, explain why you think this was a reasonable answer. If not, explain what is wrong with it and discuss possible reasons you might get this answer in the laboratory. This is not reasonable and is impossible because you cannot get more than 100% output from the given input, and in a lab it is nearly certain that you will get below 100%. Unless there was a lab error in either adding more of the limiting reactant (abr), or of getting rid of the KBr, there is no way it s possible for you to magically produce substance out of nothing. 4.What are some factors that might cause our percent yield to be greater than 100%? What are some factors that might cause it to be less than 100%? Make sure you discuss specific cases of how both might happen. Greater than 100% - Incorrectly measured limiting reactant, other compounds not completely removed or evaporated, incorrectly calibrated weighing machines ess than 100% - Spilt limiting reactant, inaccurate weighing machines, vinegar not in excess, ontamination causes a separate reaction.