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why A? (1 Viewer)
- Thread starter kkk579
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kkk579
hello
bump
kkk579
hello
bump
Sodium hydroxide acts as a base in solution. So imagine, when the indicator is in a basic solution, the protons/H+ in H2Z are going to be 'attracted' to the base, creating that ionisation seen in the question. Or consider it in terms of Le Chatelier's principle - if we add more basic solution to the 1st equation, it will shift towards the RHS with acidic H3O+ to counteract this. Same thing happens then in the 2nd equation, so the equilibrium is eventually shifted towards the blue colour in basic solution.
Same idea applies to HCl, just the equilibrium is shifting to the left in both equations. The more acid we add, the more the equation shifts to the left to counteract this/the more acid is used up. So, you end up with the red solution.
Finally, sodium acetate is only slightly basic (compared to NaOH, which has a much higher pH at the same concentration). This means that the equilibrium shifts to the right, but not as much as with NaOH. So, you kind of end up in between yellow and blue -> green.
A big part of this question is just kind of knowing how acidic/basic different solutions are relative to each other. E.g., we know that HCl is more acidic than ammonium chloride, hence the answer can't be B.
Same idea applies to HCl, just the equilibrium is shifting to the left in both equations. The more acid we add, the more the equation shifts to the left to counteract this/the more acid is used up. So, you end up with the red solution.
Finally, sodium acetate is only slightly basic (compared to NaOH, which has a much higher pH at the same concentration). This means that the equilibrium shifts to the right, but not as much as with NaOH. So, you kind of end up in between yellow and blue -> green.
A big part of this question is just kind of knowing how acidic/basic different solutions are relative to each other. E.g., we know that HCl is more acidic than ammonium chloride, hence the answer can't be B.
kkk579
hello
Yeah i get this, but then what would happen? Do the 2 colours merge or something? Or is it like a progression, where it first turns red to yellow then yellow to blue? I was unsure as to how the equations actually work together
Eagle Mum
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The two statements in your question aren’t mutually exclusive. The change in colour is a progression, but it is also true that in the solution, red reflects a state when the indicator is ‘all’ in the form of H2Z and yellow is when it is all in the form of HZ-, whereas orange is when half of the indicator is in the form of H2Z and the other half is in the form of HZ-, so it is also a state of mixture of yellow and red indicator species. Similarly, yellow reflects a state when the indicator is all in the form of HZ- and blue is when it is all in the form of Z2-, and green is when half of the indicator is in the form of HZ- and the other half is in the form Z2-.