Chemistry MCQ thread...

[histephenson007]

this seems to be an easy question but im not getting the answer.
Use of the Data Booklet is relevant to this question.
When a sports medal with a total surface area of 150 cm2 was evenly coated with silver, using
electrolysis, its mass increased by 0.216 g.
How many atoms of silver were deposited per cm2 on the surface of the medal?
A 8.0 × 10^18
B 1.8 × 10^19
C 1.2 × 10^21
D 4.1 × 10^22

its C,

m= 0.216 .. Mr= 108
n= 0.216/108 = 0.002 moles

number of atoms (avogadro's constant = 6.02 x 10^23 )= 0.002 x 6.02 x 10^23 = 1.204 x 10^21 = 1.2 x 10^21
correct me if i m wrong

The question asked u to find how many atoms of silver were deposited per cm2, so you're answer was incomplete

 

[xHazeMx]

oh didnt give attention to this part

 

[Saturation]

http://www.xtremepapers.me/CIE/Internat ... 4_qp_1.pdf

Question 12, Why is the answer B!? Why can't it be C?

 

[xHazeMx]

at higher temperatures, the curve shortens and moves to the right side. Hence, it's B

 

[Zishi]

http://www.xtremepapers.me/CIE/International%20A%20And%20AS%20Level/9701%20-%20Chemistry/9701_w04_qp_1.pdf

Question 12, Why is the answer B!? Why can't it be C?

C shows that at very high temperatures, there's same number of molecules with very high energy as room temperature. That's why it is wrong.

 

[Zishi]

zishi, can u explain number 3 more, i dont get it

The energy of diamond is more than that of graphite. And energy of combustion products, CO2 and H2O is less than both diamond and graphite. Keeping(Imagining) in mind the energy profile diagram, which will have larger enthalpy change of combustion?

 

[sakibfaiyaz]

http://www.xtremepapers.me/CIE/International%20A%20And%20AS%20Level/9701%20-%20Chemistry/9701_w04_qp_1.pdf

Question 12, Why is the answer B!? Why can't it be C?

C shows that at very high temperatures, there's same number of molecules with very high energy as room temperature. That's why it is wrong.

but Zishi why cant it be D?...the peak would be lower and to the right of the original curve. With an increase of just 10 degrees, there is a significant shift to the right. So shouldn't the shift at 500 degrees be much more to the right(as in D)?
:S

 

[ideggkr]

Can anyone explain this please?

I don't usually find MCQ hard, but I somehow don't know what's going on in this question. Thanks

* My fault! I tried to attach bmp file and didn't realise i was rejected lol

So please answer?

 

[Zishi]

http://www.xtremepapers.me/CIE/International%20A%20And%20AS%20Level/9701%20-%20Chemistry/9701_w04_qp_1.pdf

Question 12, Why is the answer B!? Why can't it be C?

C shows that at very high temperatures, there's same number of molecules with very high energy as room temperature. That's why it is wrong.

but Zishi why cant it be D?...the peak would be lower and to the right of the original curve. With an increase of just 10 degrees, there is a significant shift to the right. So shouldn't the shift at 500 degrees be much more to the right(as in D)?
:S

What makes you think that B doesn't show a significant increase? In my opinion B shows a very significant increase while keeping the area under the curve same. Option D decreases the area.

 

[Zishi]

Can anyone explain this please?

I don't usually find MCQ hard, but I somehow don't know what's going on in this question. Thanks

Which MCQ are you talking about?

 

[sakibfaiyaz]

@zishi: yes I get it now ...in D, area is decreased!

 

[xHazeMx]

what is the answer for this queston ? explain ur choice

 

[Zishi]

what is the answer for this queston ? explain ur choice

C. Number of molecules = moles x avogadro's constant

Numbr of molecules = 3x10^ -21 times 6 x10^23 = 1800

 

[xHazeMx]

what is the answer for this queston ? explain ur choice

D. Number of molecules = moles x avogadro's constant

Numbr of molecules = 3x10^ -21 times 6 x10^23 = 1800

u mean C

 

[Zishi]

what is the answer for this queston ? explain ur choice

D. Number of molecules = moles x avogadro's constant

Numbr of molecules = 3x10^ -21 times 6 x10^23 = 1800

u mean C

Oops sorry, yes I mean C.

 

[xHazeMx]

how about this one? explain ur choice

 

[MHHaider707]

how about this one? explain ur choice

Is it C??

 

[MHHaider707]

No its C!!!

Final answer

 

[kakarocks]

It's c . suppose pv=nrt so v = nrt/p so p1 v1 = p2 v2 so p1 nrt/p1 = p2 nrt/p2 and no of moles = mass / mr so 2/1 = m/2 so 4g of duetrium would give the same pressure at the same volume . so 2g would give 1/2 p and 1g of hydrogen would give 1/2 p so overall it become p !

 

[Zishi]

See the attachment.