Question

Post Lab Questions 1. in a hurry to complete the experiment, the student failed to calibrate the Spectrophotometer. As a result, all absorbance values for the standard solutions that are measured and recorded are too high. How will this affect the following calculations in Part B? a. Will the calculated equilibrium concentrations of FeSCN** be too high, too low, or unaffected? Explain. b. Will the calculated equilibrium constants be too high, too low, or unaffected? Explain. 2. In Part A, one of the standard solutions had an abnormally high absorbance reading, causing a more positive slope for the data plot. a. Will the calculated equilibrium concentrations of FeSCN2* for the solutions in Part B be too high or too low? Explain. b. Will the calculated Key for the equilibrium be too high, too low, or unaffected by the erred data plot? Explain. 3. In Part B, fingerprint smudges are present on the cuvette containing the solution placed into the spectrophotometer for analysis. a. How does this technique error affect the absorbance reading for FeSCN2+ in the analysis? Explain. b. Will the calculated Keg for the equilibrium be too high, too low, or unaffected by the technique error? Explain. 4. In Part B, during the preparation of Test Solution 8, the 2.0 mL of 0.1 M HNO3 is omitted. a. Will this technique error cause the absorbance reading for be too high or too low? Explain. b. Will the calculated Key for the equilibrium be too high, too low, or unaffected by the technique error? Explain.

Answer 1

Ansult feletes Tel As student didnoł calibrate the specterephotomele l before taking absorshance values, etherefore the lowing fras_ may have taken place Lo Wavelength inauuday si Dhotometric | Ci Stray light () Resolutito change inaturally ci)Moite Noise The chemical reaction Felien with SCN ion is given by Fe 31+ scn = Fe ScN²+ 11 Since, absorbance values of the standard Selulions 7 beth Festion and Sex Lion Age measured higher Witherefore absorbance value o Te Senzion mut also wool be heghAs equilibrium Lencentration is depicted by eg bilissium content. zt sy keq = [Fe San Thesefolly equilibrium concentration of Fesen“ will also be high bAs her equation i equilibrium constant is the Iratio of V Fe SCN12 and product of Fest and (SN) Lion and as cher de chaldies ferinciple small ince- tase in concentration & Afrottet alisays leade do _rcadants on

cincrease in concentration d chueducte theleteket equilibrium concentration whereament cause to Ichange un equilibrium constant “ Hence, equilibrium constant rema tns unaffedes- -24). In beet tik ant one s the standard solutions Thad an abnormally high absorbance reading call tring a more politie slope Perethe date plot I o Sonce only one mole di Festion combines Lasith one mell of Sarion, therefore the equie Edibrium concentration > ESCnion willen sin innaffected, b Since, one of the seaclemk had an abnormally hogh Labsorbance, causing its concentration to be high Thessefoss, as frer 6q,--- a {fe Seat For [Fexy [sent If Fey.concentration is increased by 2 times hekea changed - [Fe Senty se [Felge sca] That is Keg' < keq is less than the orging concentration]

3. d. As tingan pents in s ette causes scattering ttle loght therefore eless absolhance of liophile taille take places, Dcausing flat sloper contentia- stion calculated will be lles than abrafen but Xe change in equilibrium constenkaloill take Tefllace or semain': cumalbected by this technique Paror 494 Xalerie aad (HXOSL acts as oxidizing agent therefore, there will be dess F ions in the solution or more amount of F ions Hence, the absorbance heading ter Been Solution will be too low 6. Sence, the concentratuin o tation is lors, there- fole as oper eq... 0 ° ve Keq = [FeSCN²7 [Fe3+] [san] Equilibrium denstant for the grecestion coll be higher ! If uge. put smaller walue of Elly in Equation Therefore, changed Keqor Key will be buore han_keq.