Chemistry Exam Questions (Preliminary) (1 Viewer)

[wiliaamnguuyen]

I'm doing a practice exam and I'm unsure of my solutions, would anyone care to provide their solutions?
16. A student analysed a sample of Bondi beach sand and found it contained 5.2%, 11.3% sodium chloride with the balance being silicon dioxide. Calculate the mass of silicon dioxide in a 135g sample of beach sand.
For this question, I did
Silicon dioxide: 11.3% x 135 = 15.255g
n(SiO2) = 15.255 / 28.09 + 2(16)
= 0.25 moles (2dp.)
Is this correct or no?

17. 2NaCl (l) -> 2Na(l) + Cl2(g)
In this reaction, electrolysis of molten ionic compound, sodium chloride, give sodium metal and chlorine gas.
How can I describe this reaction?
Can I say, sodium ions loses electrons and chloride ions gain electrons? Or sodium and chloride ions both lose/gain electrons? I'm a little confused of this question.

18. Assess the role of technologies in making new metals available for human use.
For this question, am I suppose to write what I think, my judgement is prior to the role of techonologies in making new metals available for human use? If so, what are some dot points that'd assist me in answering this question?
I know the availability of new metals such as bronze back in the early ages caused nations to manufacture weapons to take over neighbouring nations and all. Is there anything else?

 

[wiliaamnguuyen]

19 (last question): A mixture of 100mL carbon dioxide (CO) and 100mL oxygen is sparked to cause reaction (to form carbon dioxide). 2CO(g) + O2(g) - 2.CO2 (g)

Calculate the change in volume resulting from the reaction. (All volumes are measured at constant temperature and pressure).
n(O2) = V/MV
= 0.1L / 22.71L
= 0.0044 moles.
n(O2) : n(CO2)
1:2
therefore n(CO2) = 0.0088 moles
n(CO2) = V/MV
0.0088 = V / 22.71
V = 0.199L
= 199mL

Change in volume: 199 - 100
= 99mL.
Is this correct?

 

[wiliaamnguuyen]

20. The mass of this gaseous compound filled a 1.35L flask to a pressure of 100kPa at 298K was 3.31g. Calculate the molecular weight of the compound.
n = 1.35 / 24.79
= 0.054 moles
n = m/M
M= 3.31g /0.054
M= 61.3g