Question

2. (10 pts) Using the information below and the table provided, estimate the pH of a TM solution of sodium bisulfate (NaHSO4). • When phenolpthalein is added to 1 M NaHSO4 the resulting solution is colorless. . When thymol blue is added to 1 M NaHSO4 the resulting solution is yellow. • When methyl violet is added to 1 M NaHSO4 the resulting solution is violet. Indicator Solution Methyl Violet Thymol Blue pH range in which the color changes 0.5 - 2.0 1.2 - 2.8 8.2 - 9.1 3.1 -4.4 6.0 - 7.6 8.0 - 9.8 Color Change of indicator Yellow to Violet Red to Yellow Yellow to Blue Red to Yellow Yellow to Blue Colorless to Red Methyl Orange Bromothymol Blue Phenolphthalein

Answer 1

2)

• If phenolphthalein is colorless, it means the pH is below 8.0
• If thymol blue is yellow, it means the pH is above 2.8 and below 8.2. Since phenolphthaleine was colorless, the range would be between 2.8 and 8.0
• If methyl violet is violent, the pH is above 2.0, but we know it actually has to be above 2.8, because of the yellow thymol blue.

Overall, we can say that the pH is between 2.8 and 8.0.

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Equilibrium. The equilibrium constant for the given system is:

$K=\frac{[N_{2}O_{4}]}{[NO_{2}]^{2}}$

As can be seen in the graph, when the system is in equilibrium (when the concentrations become constant in their values), the concentration of NO₂ is higher than the concentration of N₂O₄. Taking a look at the equilibrium constant, this means that the denominator is bigger than the numerator, which means that the value of K will be smaller than 1. The right answer is then c.