# Chemistry: Post your doubts here!

#### abcde

Here's an MCQ:
Gaseous particle X has a proton number n and a charge of +1.
Gaseous particle Y has a proton number (n+1) and is isoelectronic with (has the same number of electrons as) X.
Which statement correctly describes X and Y?
1. X has a large radius than Y.
2. X requires more energy than Y when another electron is removed from each particle.
3. X releases more energy than Y when an electron is added to each particle.

The correct answer is that '1 only is correct'. The logic given by our teacher was that atomic radii decrease across a period and since X precedes Y, 1 is correct.
I somehow remain unconvinced.

#### ismailmz

I NEED THIS PAPERS MARK SCHEME 9701_s02_qp_1. And can some one help me out wid these MCQS in this paper Q2,Q6,Q9,Q10. Please explain the answer even. Tanx in advance.

#### Nibz

XPRS Moderator
abcde said:
The logic given by our teacher was that atomic radii decrease across a period and since X precedes Y, 1 is correct.
I somehow remain unconvinced.
Yes, that's true.

Here's another explanation:
X has a charge of +1, and proton number n. Then its electron number = n - 1. Correct?
Since Y has one more proton, there must be one more electron as well. But the question says that the two are isoelectronic, i.e, no extra electron allowed. This means that the extra electron has been lost. With another electron lost, Y has a charge of +2.
As nucleur charge increases, the atomic radius decreases. Y has a greater nucleur charge hence smaller radius.

Vague, but I hope this somehow ' convinces ' you.

#### OakMoon!

abcde said:
The correct answer is that '1 only is correct'. The logic given by our teacher was that atomic radii decrease across a period and since X precedes Y, 1 is correct.
I somehow remain unconvinced.

Not exactly the correct logic for this situation. First of all we are not comparing atomic radii. It can be seen that either one of these is an ion or both of them are ions, otherwise, it's not possible for atoms to have an increased proton number and yet have the same number of electrons.
The reason why the radii of X is greater than Y is because Y has one more proton, so the net nuclear charge on the outer shell electrons will be greater than that in X and so in Y, due to greater attraction the outer shell will be pulled closer and reduce it's radius as compared to X.
SECONDLY, the reason why the condition ISOELECTRONIC is given is to tell you that X and Y have the same number of Shells. With the loss of elctron in Y or a gain of electron in X the shell number will always be the same, so the radius can be compared easily.

#### jason234

need help guys...

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#### libra94

Re: A-2 CHEMISTRY DOUBT!

#### OakMoon!

You could have posted the problem on this topic instead of posting the link. Secondly, learn to wait.

Coming the problem, we know that D is an aldehyde and E is a ketone. Just recall your concepts, is there anyway to convert aldehyde into a ketone? Not that any I have heard of, atleast none using a KMnO4 solution. But if there is a double bond present it can be broken down into a ketone and the second part which was a aldehyde can be oxidised into the carboxylic acid which is F. D is not independent of E and F. And to produce E and F, you need a double bond on D, so you can't have D as a cyclic compound.

Hope you get it.

#### niassu

guys plz I need help with that graph
the rate which I get is wrong

seems nobody is able to do it

#### RGBM211

Oct/Nov 2002 Q6 a)
Is it Elimination reaction ?

#### Gémeaux

Cud anyone explain this one?
"Use of the Data Booklet is relevant to this question.
Hard water contains calcium ions and hydrogencarbonate ions arising from dissolved calcium hydrogencarbonate, Ca(HCO3)2.
How many electrons are present in the hydrogencarbonate anions?
A. 30
B. 31
C. 32
D. 33 "
(9701/01/O/N/08) q.4

#### OakMoon!

H+, CO2 and O²- combine to make the hydrogencarbonate ion. 0+6+8+8+10=32

#### Mustehssun Iqbal

started AS..help needed
Q- Use ur knowledge of chemistry to suggest a method of removing the iron oxide coating from the sand grains that might be applied on an industrial scale.Justify ur answer. (3)

So sand grains are silicon(IV)oxide...ummm ...So are we goin to titrate them ? :unknown:
Assalamu alaikum,
You can use a magnet and run that magnet through the mixture of iron oxide coating and sand grains.The iron oxide coating can come out/separate and cling to the magnet.Iron oxide coating and sand grains can be separated like this.
Plus,titration is used to measure the quantities of chemicals required in a reaction.It's not mainly a separating technique,as far as I remember.
Apologies if my answer is wrong,which I hope is not wrong.
peace

#### omg

n07 p4 q5 part b!!!!!!!
wont it b 1.52-(-.68) ??? pls help :/

#### lonelyperson

Can anybody find me a summarized notes of chemistry of (AS LEVEL ) portion.