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Chemistry: Post your doubts here!

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nadeen64

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Does anyone have tips on how to study for chem p3??? My exam is on tuesday and idk how to prepare!!
 
Rizwan Javed

Rizwan Javed

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slisjunknown said:
Mj 15 P12, Q 12, 19, 29
can someone pls give me explainations to these?
Click to expand...

12. In this question, in the options all the compounds given are the group II compounds. So a general equation for all the decomposition reactions of Nitrates of Group II is:

2X(NO3)2 ----> 2XO + 4NO2 + O2

You are given, that 1.53g is lost, so the mass of XO formed is: 3 - 1.53 = 1.47g

1 mole of X(NO3)2 forms 1 moles of XO, find the moles of XO and X(NO3)2, put them equal and equate like this:
3/(X + 124) = 1.47/(X + 16)
solve it, you'll get
X = 87.76

From the periodic table, Strontium is the metal which has the Mr approximately equal to 87.76, so the answer is D.
 
Rizwan Javed

Rizwan Javed

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slisjunknown said:
Mj 15 P12, Q 12, 19, 29
can someone pls give me explainations to these?
Click to expand...
19. Divide the equation into half equations, the oxidation half and reduction half:

Oxidation half:
1/2Cl2 + 6OH- -------> ClO3 - + 3H2O + 5e

Reduction Half:
(1/2Cl2 + e ------> Cl- ) * 5

1/2Cl2 + 6OH- ------> ClO3 + 3H20 + 5e
5/2Cl2 + 5e -------> 5Cl-
------------------------------------------------------
3Cl2 + 6OH- -------------> 5Cl- + ClO3 + 3H20

So the answer is C.
 
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Rizwan Javed

Rizwan Javed

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slisjunknown said:
Mj 15 P12, Q 12, 19, 29
can someone pls give me explainations to these?
Click to expand...
29. Here you are asked about the RATE of formation of cloudiness. Here RATE depends on the strength of the bond between R-X (where X is the Halogen). R-I is weakest bond, so it will dissociate readily, and the rate of formation of cloudiness will be higher. R-Br is weaker than R-Cl but stronger than R-I, so the rate of formation of cloudiness when R-Br is present will be higher than R-Cl but lower than R-I. Same goes for R-Cl.

Hence the only option satisfying this is A.
 
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mistique_bee

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Rizwan Javed said:
29. Here you are asked about the RATE of formation of cloudiness. Here RATE depends on the strength of the bond between R-X (where X is the Halogen). R-I is weakest bond, so it will dissociate readily, and the rate of formation of cloudiness will be higher. R-Br is weaker than R-Cl but stronger than R-I, so the rate of formation of cloudiness when R-Br is present will be higher than R-Cl but lower than R-I. Same goes for R-Cl.

Hence the only option satisfying this is A.
Click to expand...
nerd :p
 
slisjunknown

slisjunknown

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Rizwan Javed said:
29. Here you are asked about the RATE of formation of cloudiness. Here RATE depends on the strength of the bond between R-X (where X is the Halogen). R-I is weakest bond, so it will dissociate readily, and the rate of formation of cloudiness will be higher. R-Br is weaker than R-Cl but stronger than R-I, so the rate of formation of cloudiness when R-Br is present will be higher than R-Cl but lower than R-I. Same goes for R-Cl.

Hence the only option satisfying this is A.
Click to expand...
:confused::confused:I think u misunderstood the paper; Mj 15 paper 1 variant 2( the answer to my question is C btw)
 
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