Questions like these trip me up too much. Any tips and advice in how to approach these questions (1 Viewer)

[Dane Red]

I'm having a mod 6 assessment task coming up and i noticed that these types of questions tend to trip me too often due to their use of dilutions as a result i struggle in answering these types of questions. Any tips?

 

[gamja]

Tips to solve STEP 1:
1. make n/c/v table - we have lots of info for KHP acid (volume, mass/100mL, MM) so organising this makes stuff easier.
2. Learn the conversion between m/100mL and n/V (molar concentration).
i.e. recall that with n=m/MM, we can make m the subject so

m=nMM.



I memorise the simple formula

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[gamja]

For step 2-4, to get better (esp with the dilution part you struggle with) make a good method and spam it with prac q before exam. My method:

1. write the equation (I find this a good first method for basically all practise questions as it's like a rote step I apply to all questions which gives me confidence/comfort in exam situation) - hint: citric acid is c6h8o7 - triprotic - so naoh needs a 3 in front of it

2. THE DILUTION - if we are getting a volume of 75mL to dilute to 250mL, we are reducing the concentration by a factor of 10/3 [hint the number of moles stays the same]

3. THE HARD STEP
using step 1, extract the concentration of naoh. multiply that to volume to get the moles(naoh). Use the chemical equation to get conc(diluted) of citric acid, and then multiply by 10/3 to get undiluted concentration answer!!