HOw would you predict the colour change or changes in number of states for the following:
To a solution of 5 drops of 0.3 M K2CrO4 ans 2 drops of 0.3M NaOH add a drop at a time 0.1 M Ba(NO3)2 until a change is noticed.
Given:
BaCrO4(s) ---> Ba2+ + CrO42-
2CrO42-+2H+ --->Cr2O7 2- + H2O
To predict the color change or changes in the number of states in the given reaction, we need to analyze the reactants and products involved and their respective colors.
First, let's look at the reactants:
1. K2CrO4 (potassium chromate solution): This compound is typically yellow in color.
2. NaOH (sodium hydroxide solution): Sodium hydroxide is a clear, colorless liquid.
Based on the reactants alone, the solution would have a yellow color due to the presence of potassium chromate (K2CrO4).
Next, let's consider the addition of Ba(NO3)2 (barium nitrate solution) drop by drop. The reaction between Ba(NO3)2 and K2CrO4 leads to the formation of a precipitate, BaCrO4 (barium chromate). The balanced chemical equation is as follows:
K2CrO4(aq) + Ba(NO3)2(aq) → BaCrO4(s) + 2KNO3(aq)
BaCrO4 is a yellowish solid, so as more Ba(NO3)2 is added drop by drop, the yellow color would become more intense.
However, the formation of BaCrO4 is not the only step in the reaction. The second part of the given reaction involves the conversion of chromate ions (CrO42-) to dichromate ions (Cr2O7 2-). This occurs in the presence of an acid, which in this case can be assumed to be the H+ ions from the NaOH solution.
The balanced equation for the second reaction is as follows:
2CrO42-(aq) + 2H+(aq) → Cr2O7 2-(aq) + H2O(l)
When the BaCrO4 precipitates, it removes CrO42- ions from the solution, which drives the equilibrium of the second reaction to the right, resulting in the formation of more dichromate ions (Cr2O7 2-). The color of the solution would change from yellow to orange due to the presence of Cr2O7 2- ions, which exhibit an orange color.
To summarize, the color change during the reaction can be expected to progress from yellow (due to K2CrO4) to a more intense yellow (due to BaCrO4 precipitation) and finally to orange (due to the formation of Cr2O7 2- ions).
It is important to note that the exact number of drops required to notice the color changes cannot be determined without further information about the volumes involved and the specific concentrations of the solutions used. Conducting the experiment in a controlled laboratory setting would be necessary to obtain precise results.