Account for your observation in the experiment, such as the temperature, pH values, concentration, equilibrium constant and anything in particular.
Purpose: To investigate the way in which the temperature of an equilibrium mixture influences the position of the equilibrium.
H3PO4 (aq) [equilibrium arrow] H2PO4- (aq) + H+ (aq) ; exothermic reaction
1. Pour 1 M phosphoric acid into each of two semi-micro test-tubes, to a depth of about 3cm. Add two drops of methyl violet indicator to each test-tube.
2. Place one test-tube in ice-water. Carefully heat the other test-tube until the solution almost boils. Record the colour of the indicator in the heated and cooled test-tubes.
3. Note the acidity of each solution. Methyl violet indicator is yellow in solutions with a high concentration of H+ (aq). Its colour changes through green, blue to violet as the H+ (aq) concentration reduces.
1 Answer | Add Yours
It would be helpful to know what your observations were in this experiment. I shall address my answer as towards the equilibrium constant, which is a number dependent on the strength of the solution and its ability to dissociate and produce positive and negative solution ions. This experiment appears to use cold solution as a control, compared to solution heated to the boiling point, which would probably give a change in color to the methyl violet indicator. This change in color would indicate a rise in the amount of ions present and forming the phosphoric acid. There would be increased activity of dissociation and association, causing the methyl violet to change to its yellow color. The pH value would probably remain the same, as pH is dependent on the strength of the acid to begin with. Adding heat would increase the amount of dissociation, but the number of moles of phosphoric acid would remain the same, so the pH should remain the same.
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