1 Solution X was added to a test tube containing aqueous potassium iodide and an organic solvent tetrachloromethane, CCl4. After shaking, a brown aqueous layer and a purple organic layer were obtained (brown aqueous layer is above the purple organic layer). X is likely to be
A potassium chloride
B potassium bromide
C potassium manganate(VII)
D potassium hydroxide
I wrote the answer as B but it's wrong. I am not sure of the reaction occurring in this case. Definitely not displacement reaction because both X and KI are potassium salts. Answer is C. Please help to explain why this is so.
2 Which statement about the elements in the Periodic Table is correct?
A The elements are arranged in increasing nucleon number
B Group VII elements form both ionic and covalent compounds
I chose A but answer is B. The other 2 choices are surely wrong so I did not bother to type them out... But A is true yea?
3 0.10 mole of sodium is reacted completely with water. The resulting aqueous solution formed is reacted with 1.5mol/dm3 of H2SO4 acid. What is the volume of H2SO4 acid required for the neutralisation?
A (0.10 X 1000) / 1.5cm3
B(1.5X1000)/0.10cm3
C (0.10X1000)/1.5cm3
D(0.10 X1000) / (2 X 1.5) cm3
I wrote out equation for the reaction between Na and H2O and realised the number of moles of NaOH is the same as that of Na at 0.10 mole.
The next reaction is 2NaOH + H2SO4 -> 2H2O + Na2SO4
Since we have 0.10 mole of NaOH, no. of moles of H2SO4 is 0.05mol.
Vol. of H2SO4 = 0.05 / 1.5
My ans: D. Actual ans: B
Where did I go wrong in the calculation? Thanks!
O level Pure Chemistry?
Originally posted by Babelfish:O level Pure Chemistry?
yea
ans is C cause manganate is purple =x
ps typo
colour... i guess... sorry i sec4 also =x
as for ur 2nd part
when they say arranged
they nvr say how ?
eg. accross period or down group. just say ARRANGE, can also be vertically what?
if they say across period then correct?
Na+ H20 -> NaOH +H2
u call this balanced? lol ?
Originally posted by yiha093:ans is C cause manganate is purple =x
ps typo
colour... i guess... sorry i sec4 also =x
as for ur 2nd part
when they say arranged
they nvr say how ?
eg. accross period or down group. just say ARRANGE, can also be vertically what?
if they say across period then correct?
Na+ H20 -> NaOH +H2
u call this balanced? lol ?
Hello yiha093
From what I see, your explanations are pretty invalid. Rewind back to the last question. If you look at anpanman's equations, you''ll realise that he did balance the equation. You balance yours and you write out the final reaction. It's exactly the same as what anpanman wrote. (I'll go try this question out now)
No offence, but your argument for the second part, well, isn't it vague? You can try turning to the chapter on periodity in the TB. If I'm not wrong they did say the elements are arranged according to increasing "proton"(so neutrons should also increase too) numbers. So your argument will mean that the TB's explanations have got problems because they did not tell you whether they are referring to the elements being arranged horizontally and vertically. Because it's natural for students to know that when they say arranged according to "increasing proton/neutrons/whatever there is", it means the horizontal consective arrangement.
So for question 2, I'd say there are grounds for debate on which option's the best one.
Not sure about question 1 though.
hello audi.
my bad ~
sorry anpanman =X
periodic table is arranged by increasing proton numbers, not nucleon number.
increase in protons is not the same as increasing nucleon number.
For Qn1, I- + I2 = brown solution. Then the I2 is soluble in org layer to form purple layer. So Solution X is oxidising, giving KMnO4 as ans
For Qn 2, regardless of the ambiguity, K has smaller atomic mass than Ar, pointing out that most isotopes of K have smaller nucleon number than that of Ar.
Halogens do form both ionic and covalent compounds such as NaCl and HF
Q3 is ambiguous. Is NaHSO4 or Na2SO4 formed?
Originally posted by Chemfreak022:For Qn1, I- + I2 = brown solution. Then the I2 is soluble in org layer to form purple layer. So Solution X is oxidising, giving KMnO4 as ans
For Qn 2, regardless of the ambiguity, K has smaller atomic mass than Ar, pointing out that most isotopes of K have smaller nucleon number than that of Ar.
Halogens do form both ionic and covalent compounds such as NaCl and HF
Q3 is ambiguous. Is NaHSO4 or Na2SO4 formed?
Still quite unsure about question 1.
I- + I2 = brown solution? (eh, what equation is that? ^_^)
Then again, nucleon number did increase along the periodic table...
thanks for the help everyone!
but i still insist purple= mag =X
I think I- + I2 gives (I3)-
Question 1, C is the only possible oxidising agent... KBr (or KCl) and KI are both reducing agent I guess so they won't react..
Question 2, most elements arranged in the table has a trend of increasing nucleon number, but there are some cases where an element has higher proton number but lower nucleon number, as in the case of potassium and argon...
Question 3, I think answer is wrong. I don't think we need 15000cm^3 of sulphuric acid to neutralise 0.10 mole of NaOH...
Regarding Qn 2,
If A and B appear to be right, then pick the option you know to be definitely right, which is B. For A to be proven wrong, you only need a single case to the contrary. TenSaru mentioned Ar to K, which is pretty good, but a very conclusive negative case is Te (Tellurium) to I. So is Th (Thorium) to Pa (Protactinium) in the Actinide series.