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April 10th, 2018, 08:39 AM  #1 
Member Joined: May 2015 From: Australia Posts: 77 Thanks: 7  Not sure whether to use weak acid or base equation
I have attached a dropbox link to a clear image of the question (you dont need a dropbox account to view it): https://www.dropbox.com/s/g2brhpydfm...help1.PNG?dl=0 I have also attached a picture of the question, but i dont think it will be clear. I understand how to solve the question, BUT the only thing i'm stuck on is that I dont know how to figure out whether the weak acid or weak base equation should be used. In the image, all of the pink highlight is what I wrote so it might be incorrect. BUT all the other writing is the solution. Also, the green section on the bottom is what my teacher told us when we asked him how to figure out which equation to use. I'm really confused. So far, the only pattern i can see is that when the molecule has a weak base component, then we use the weak acid equation (vice versa). but i know that this is the incorrect way to approach this question. Any input would be much appreciated 
April 10th, 2018, 03:58 PM  #2 
Senior Member Joined: Jun 2015 From: England Posts: 891 Thanks: 269 
These two pages should help you here. Remember when looking in texts etc you are looking for pH calculations of hydrolysis of salts, not calculations on titrations, indicators or buffers. 
April 11th, 2018, 02:57 AM  #3 
Member Joined: May 2015 From: Australia Posts: 77 Thanks: 7 
for part d, i think they used the weak acid equation because: the species is weak base and the conjugate of this species is a weak acid. I say this because the green note at the bottom of the image says just that, but it was written in a way that i couldnt understand straight away. That's what i think, but I might be wrong in the way I explained it. 

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acid, base, equation, weak 
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