For a rate law experiment (Kinetics Of The Bromination Of Acetone), there are th

Question

For a rate law experiment (Kinetics Of The Bromination Of Acetone), there are three variables. Three solutions will be made. For each variable, two will be held constant while one variable will be tested at different concentrations.
Question 1: does it matter or should I regardless keep the volume the same for the variables (at constant concentration) for consistency?
Ex: Run 1: 3 ml 0.5 M Of A. 3ml 0.7 M Of B. 4 ml 0.4 M Of C Run 2: 3 ml 0.5 M Of A. 3ml 0.7 M Of B. 4 ml 0.7 M Of C Run 3: 3 ml 0.5 M Of A. 3ml 0.7 M Of B. 4 ml 0.9 M Of C
Question 2: when changing the concentration of one of the variables, using c1v1=c2v2 I will start out with a known concentration as c1, the amount used as v1, If I dilute 3ml of C1 with 1 ml of deionised water (keeping total volume at 4ml)- in this case from run 1 above C1 = 0.4 M, V1 = 3 ml, V2 = 4ml So C2 = 0.3M ?

For a rate law experiment (Kinetics Of The Bromination Of Acetone), there are three variables. Three solutions will be made. For each variable, two will be held constant while one variable will be tested at different concentrations.
Question 1: does it matter or should I regardless keep the volume the same for the variables (at constant concentration) for consistency?
Ex: Run 1: 3 ml 0.5 M Of A. 3ml 0.7 M Of B. 4 ml 0.4 M Of C Run 2: 3 ml 0.5 M Of A. 3ml 0.7 M Of B. 4 ml 0.7 M Of C Run 3: 3 ml 0.5 M Of A. 3ml 0.7 M Of B. 4 ml 0.9 M Of C
Question 2: when changing the concentration of one of the variables, using c1v1=c2v2 I will start out with a known concentration as c1, the amount used as v1, If I dilute 3ml of C1 with 1 ml of deionised water (keeping total volume at 4ml)- in this case from run 1 above C1 = 0.4 M, V1 = 3 ml, V2 = 4ml So C2 = 0.3M ?


Question 1: does it matter or should I regardless keep the volume the same for the variables (at constant concentration) for consistency?
Ex: Run 1: 3 ml 0.5 M Of A. 3ml 0.7 M Of B. 4 ml 0.4 M Of C Run 2: 3 ml 0.5 M Of A. 3ml 0.7 M Of B. 4 ml 0.7 M Of C Run 3: 3 ml 0.5 M Of A. 3ml 0.7 M Of B. 4 ml 0.9 M Of C
Question 2: when changing the concentration of one of the variables, using c1v1=c2v2 I will start out with a known concentration as c1, the amount used as v1, If I dilute 3ml of C1 with 1 ml of deionised water (keeping total volume at 4ml)- in this case from run 1 above C1 = 0.4 M, V1 = 3 ml, V2 = 4ml So C2 = 0.3M ?

Explanation / Answer

1) The number of moles of a species is given as

number of moles = (volume of the species in L)*(concentration of the species in mol/L or molarity of the species)

Now, different species react with each other in a fixed stoichiometric proportion of moles, i.e, the ratio of the numbers of moles of the reactants is a simple ratio.

Keeping the volume constant while varying the concentration of the species is a good way to alter the number of moles of the species taking part in the reaction. Another way to change the number of moles is to keep the concentration of the species constant and vary the volume of the species. In either case, we need to keep either the volume or the concentration of the starting material same. If both are varied, the calculations are unnecessarily complicated.

It is not mandatory that the volume or the concentration of the species is held constant, since we can anyway calculate the number of moles of the species using the formula above. However, in order to reduce calculations, it is common practice to keep either the volume or the starting concentration constant.

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