Background.. Questions... Experiment 13 The Determination of Ko, for FeSCN2 Intr
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Background.. Questions...Experiment 13 The Determination of Ko, for FeSCN2 Introduction t solution that are equalbrium reactions, that is, they do not go are many reactions that take place in both the forward and reverse reaction are occurring and both reactants and to completion present. such as ammonia reacting with water, and the formation of "comalex jans in which a metal ioo one or more negative lons. A reaction involving the formation al a complex ion which occurs whnuh of iron(IlI) constant determined products are Examples of this type of reaction include weak acids such as acetic acid water, weak bases are combined with solutions of the negative thiocyanate ion will be studied and the Concepts ·Chemical equilibrium . Equilibrium constant Complex-ion reaction Colorimetry Background Chemical reactions are driven to completion by two forces: a decrease in energy (exothermic reaction), or an increase in entropy. If both an energy decrease and an entropy increase oour in the forward reaction, the reaction will go to completion. An example of this type of reaction is the burning of ethane. The reaction is exothermic and has an increase in entropy, and it goes to completion However, when an energy decrease drives a reaction in one direction and an entropy increase drives it in the reverse direction, equilibrium will result. The reaction wil not go to completion, but will reach a point where both reactants and products are present in a fuxed ratio of concentration. The reaction will continue at the same rate in both forward and reverse directions, and the concentrations of products and reactants will stay constant These ideas can be expressed mathematically in the form of the equilbrium constant Consider the following general equation for a reversible chemical reaction Equation The equilibriurm constant , for this general reaction is given by Equation 2, where the square brackets refer to the molar concentrations of the reactants and products at equilbrium CHDr AMBP Equation 2 The equilibrium constant gets its name from the fact that for any reversible chemical reaction, the value of R, is a constant at a particular temperature. The concentrations of reactants and products at equillbrium vary, depending on the initial amounts of materials present. The special ratio of reactants and products described by s alwagys the came as long ai the system has reached equiltbrium and the tamperature does not change. The The reverisible chemical reaction of iron/in ions (Pe) with thiocyanate lons (SCN-) provides a convenient oK cah be calculated if the concentrations of reactants and products at equilibrium are known. example for determining the equilibrium constant of a reaction As shown in Equation 3,P and SCions combine to form a special type of combined or "compler ion having the formula PeSCN Equation 3 Pale yellou Coloriess Blood-red Laboratory Experiments for AP Chemistry 165
Explanation / Answer
1.The equilibrium constant is the relationship between the concentration of products and reactants, on the same conditions this value should be constant for your experiments, if you change the temperature of the experiment the equilibrium constant may change
2. the equilibrium constant gives you an idea of which compounds are favored, if the K equilibrium is higher than 1 it means that there are more products than reactants, if it is lower than 1 then there are more reactants than products, if it is 1 it means that products and reactants are in the same proportion
3. A spectrophotometer is an instrument that measures the transmittance or absorbance at a particular wavelenght of light through a sample, standard solutions are prepared by measuring know ammounts of reactants and getting the concentration and the absorbance of these, with this information you can create a calibration curve
4. Different color is more appropiate because solution color is determined by the wavelength of light being absorbed, the color you see is complementary to the other color, the color for FeSCN+2 is red/brown color. The documents do not specifiy which color of light you used, for this particular experiment is common to use a blue color.
5. The spectrophotomer is precise to 3 figures, the volumetric material is precise to 2 figures so these ones are more imprecise.
6. some experiments that are colored or change color over time
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