QUESTIONS Laboratory Experiments 91 1. Why is it necessary to use a blank when u
ID: 1040097 • Letter: Q
Question
QUESTIONS Laboratory Experiments 91 1. Why is it necessary to use a blank when using the spectrophotometer? 2. Why do you have to uea volue fak instcad of amn Erlenmger fask or beasker when prepuring the solutions in this experiment? 3. If you need to prepare 100.0 mL of a 0.080 M solution, how much of a 1.6 M stock solution do you need to use? (Show your calculations) 4 If you need to prepare 100.0 mL of a 0.12 M solution, how much of a 0.80 M stock solution do you need to use? (Show your calculations) 5 For the dilution equation, Mc Vc - Md Vd, what can be said about the relative values of the concentrations and the relative values of the volumes? Use "less than" or "greater than" in your answers. The value of Vc is alwaysthe value of Vd because The value of Mc is alwaysthe value of Md becauseExplanation / Answer
In order to subtract and eliminate any possible contribution of solvent and any unknown impurity, or systematic error on the absorption spectra of a compound. In other words, if you do a blank, the spectra that you are measuring for a particular sample is exclusively from that sample and no contribution from solvent or other impurities. The volumetric flask is also known as standard flasks since you can make the final volume to very high accuracy usually to a tolerance of a few hundredths of a millilitre, about 0.1% of the flask's capacity. But with Erlenmeyer flasks, the tolerance value may be 1-5 % of the total volume. Using the dilution equation, Mc.Vc = Md.Vd, Mc = 0.080 M, Vc = 100.0 mL, Md = 1.6 M, Vd = Mc.Vc/Md = 0.080 M x 100 mL/1.6 M = 5.00 mL. Using the dilution equation, Mc.Vc = Md.Vd, Mc =0.12 M, Vc = 100.0 mL, Md = 0.80 M, Vd = Mc.Vc/Md = 0.12 M x 100 mL/0.8 M = 15.00 mL. The value of Vc is always greater than the value of Vd because the value of Mc is less than the value of Md. The value of Mc is always less than the value of Md because the value of Vc is greater than the value of Vd.