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Thread: Hsc 2016 question help

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    Cadet cloud edwards's Avatar
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    Hsc 2016 question help

    I have trouble with the 2016 HSC CHEMISTRY questions 11 and 12.

    For Q11:
    I got answer A basing my rules on NUmber 1 being the element that starts first in the alphabet (i.e 1-bromo), then worked my way down to eventually getting (1-bromo-1-chloro-2,2,2 trifluorethane). HOWEVER, answer says it's D (2-bromo-2-chloro-1,1,1, trifluorethane). Why is this? Did i miss a fundamental rule of naming?

    Q12: I just don't know how the whole sequence of question works and serial dilutions work. I don't know if serial dilutions has to do with the question though =(

    Thanks
    PAPER: https://educationstandards.nsw.edu.a...6810f6-lHPDE.v

    ANSWERS: http://educationstandards.nsw.edu.au...e01834-lJl54sm
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    Cadet Sp3ctre's Avatar
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    Re: Hsc 2016 question help

    Q11: It is 2-bromo-2-chloro-1,1,1-trifluoroethane because you choose the name where the SUM is the LEAST. In this case, if you were to pick 1-bromo-1-chloro-2,2,2-trifluoroethane, the sum would be 1+1+2+2+2=8. If you choose D, it would be 2+2+1+1+1=7. Therefore, you would pick the latter.

    Q12: Work out the initial pH first
    pH = -log[H+] = -log(0.01) = 2

    To change pH to 4, you are essentially decreasing the concentration of H+ from HCl by 10^2 times. Therefore the answers can't be A or C. If you're decreasing [H+] by 10^2 times, you're increasing volume by 10^2 times, which is 100mL * 10^2 = 10000 mL. But you already have 100mL, therefore 10000mL-100mL gives you 9900mL. Therefore your answer is D.
    Last edited by Sp3ctre; 1 Aug 2017 at 9:09 PM. Reason: typo
    cloud edwards likes this.
    HSC 2017: English Adv - Maths Ext 1 - Maths Ext 2 - Chemistry - Physics
    ATAR Aim: 97.30

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