Hsc 2016 question help (1 Viewer)

[cloud edwards]

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....-e76232cd-1d84-4d3e-92ce-ea41546810f6-lHPDE.v

ANSWERS: http://educationstandards.nsw.edu.a...-818e942f-37a4-4ee9-a5ec-e40c59e01834-lJl54sm

 

[Sp3ctre]

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.