PURITY OF SODIUM BICARBONATE Objective To determine the percentage of purity of
ID: 944588 • Letter: P
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PURITY OF SODIUM BICARBONATE Objective To determine the percentage of purity of sodium bicarbonate by conversion to sodium carbonate Discussion Sodium bicarbonate is converted to sodium carbonate, when heated at a temperature above 100 °C as shown in the equation. 2 moles The carbonic acid is unstable and will undergo thermal decomposition into CO2 gas and H20 vapor as shown in the equation. 1 mole 1 mole 1 mole 1 mole 1 mole The amount of mass loss by the heated sample of NaHCO3 is equal to the mass of CO2gas and H20 vapor released into the air. If the NaHCO3 sample is impure, the percentage of purity can be calculated by using this mass loss and the theoretical yield of carbonic acid. Procedure Review the PowerPoint program, Purity of Na,CO, Sample. Obtain a test tube with an impure sample of NaHCOs, RECORD UNKNOWN Clean and dry by flame brushing two 18 X 150 mm test tubes, cool and weigh each test NUMBER(1) tube on the Top-loading balance to the nearest 0.01 g., RECORD WEIGHTS OF EACH TUBE.(2) Place into each test tube. 1/2 of the impure sample of NaHCO, and weigh the test tubes with sample, RECORD WEIGHTS OF EACH TUBE WITH NaHCO3 SAMPLE.(3) Now use your test tube clamp to hold the tube with your sample, begin heating sample 1 first over the flame of your burner. (Slowly move the sample back and forth in flame when heating) As NaHCOs undergoes decomposition, water vapor will form on the cooler part of the tube; move the upper part of tube into flame to drive off the water as vapor. Tun the tube over and heat on the opposite side so that all the NaHCO, will be decomposed. Continue heating in this manner until there is no formation of water on the cooler part of tube. Remove the test tube with sample from the flame and cool on a ceramic pad to room temperature. While, the first sample is cooling, repeat this process with the second sample. When the first sample has cooled to room temperature weigh the test tube and sample 1, RECORD THE WEIGHT -a, OF THE TEST TUBE AND Na2COs after 1 heating.(4) Now carry out a second heating and cooling on sample 1, using the above steps forExplanation / Answer
The first question is correct, but you got wrong in the second question, the overall reaction it's not what you put in there, it's the reaction in the first sheet.
the moles are fine, but to get the moles of H2CO3, you have to divide the moles of NaHCO3 by 2:
0.0357 / 2 = 0.01785 moles
And the mass: 0.01785 * 62 = 1.1067 g
So correcting this now to do part 4:
If from 3 grams, it only reacts 1 gram means:
% = 1/3 * 100 = 33.33% of purity, while the other 66.67% didn't react because it's impure.
Hope this helps.
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