ATAR Notes: Forum
HSC Stuff => HSC Science Stuff => HSC Subjects + Help => HSC Chemistry => Topic started by: RL989 on February 20, 2018, 06:22:53 pm
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Hi,
I need help with MC 8 from the 2014 paper (the acidic environment) attached below.
The answer is B, but I was stuck between B and D. (As the pH increases, does an acid become more or less ionised? And what does this mean?)
Thanks
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as the pH increases the ionization decreases. as pH decreases ionization increases. ionization or dissociation is basically how readily a molecule will split up into its separate ions. higher the ionization the more readily a molecule will split up. in acids the higher the ionization the more acidic the substance.
for example HCL + H2O = (H30+) +Cl-
in this reaction say around 99% of the HCL is converted into its separate ions of H30+ (hydronium ion as H+ cannot exist in solution by itself) and Cl- because it so readily dissociates is is a strong acid. it has very high ionisation.
hope this helped
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from the graph it is evident that as the temperature decreases, from right to left, you can see that the pH increases. As pH increases this means that less H+ ions are being dissociated and thus making the H+ concentration decrease. This leaves you with either B or D like you said. However, the terminology of ionising is interchangeable with dissociating, and as mentioned earlier as dissociation decreases, ionisation decreases. Thus the answer is B.
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Presumably, you already worked out why as pH decreases, the concentration of H+ increases.
Now, I feel like the easier way of thinking about it is that if the concentration of H+ increases, then the acid is really becoming more ionised. The reason this is the case is because of what "ionised" really means. To put it simply, it means to gain more ions.
Of course, H+ is literally an ion. So when you're increasing the concentration of H+, which is effectively speaking gaining more H+ (reason being in C=n/V, V stays constant), you're becoming more ionised.
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Thank you to everyone that replied! Really helped and I understand it now :)