Chemistry : The Periodic Table

anpanman SG

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!

Babelfish SG

O level Pure Chemistry?

anpanman SG

O level Pure Chemistry?

yea

yiha093 SG

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 ?

Audi SG

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.

yiha093 SG

hello audi.

my bad ~

sorry anpanman =X

SexyChin SG

periodic table is arranged by increasing proton numbers, not nucleon number.

increase in protons is not the same as increasing nucleon number.

Chemfreak022 SG

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?

anpanman SG

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!

yiha093 SG

but i still insist purple= mag =X

TenSaru SG

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...

quirK SG

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.