If the equivalence point of a reaction is between the pH range of colour change for the indicator in use, does the change in colour happening at the maximum or minimum pH within that range or at the equivalence point? E.g. phenolphtalein has a pH range of colour change of around 8.3 to 10.0; if the equivalence point of the reaction is 9.1, will you observe the colour change from colourless to red-pink at about a pH of 8.3 or 9.1?
Sorry for the late reply!
The colour change of the indicator occurs somewhat gradually within its range. An indicator doesn't change instantly at a precise pH, but rather changes over a pH interval. For your example, phenolphtalein will begin turning slightly pink at a pH of 8.3 and will become darker as you reach pH of 10 If you want to read more about this you can do so
here hi!
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Did I do q2 correctly? I'm also not sure what the difference between q2 and q3 is.
thanks
For question 2, the c value you are using is 4.18J/g/K, meaning your mass should be expressing in grams, however it seems you might have expressed your mass in kg. Also note that you are calculating the temperature change of the final (100ml) solution, as such the mass in your energy calculation should be 100g (since 1ml of water = 1g of water).
When you are calculating the change in temperature you don't need to be converting it to kelvin as the change in degrees celcius is equal to the change in kelvin. If you do want to convert to kelvin, then you need to be adding 273 to both the initial and the final temperatures (to convert both into kelvin) as shown here for example:
you cannot just add 273 to the final change as you have done, you must convert both the initial and final temps before finding the change in temperature. Note that if you simplify the above equation as such:
which shows that when calculating the change in temperature, you do not need to convert anything into kelvin
Hopefully by taking on these tips you can fix up your answers for question 2
Question 3 is a similar question, however is not quite the same thing. Question 2 asks you to calculate the change in energy of the total reaction, however question 3 wants you to calculate the change in energy for just 1 mol of reaction. For reaction A this would be calculating the energy change for 1 mol of HCl to react with 1M of NaOH.
Hopefully this helps