Chemistry: Post your doubts here!

Xaptor16

Xaptor16

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33) Valence shell electron pair repulsion theory should be used to answer this question. Which species are trigonal planar?
1 BH3
2 CH3+
3 PH3
the answer is B (1 and 2 only are correct)
can someone please explain how to use the Valence shell electron pair repulsion theory to answer this? i don't get it! :(
Solids W, X, Y and Z are compounds of two different Group II metals. Some of their applications are described below.
Compound W is used as a refractory lining material in kilns.
Compound X is used as a building material. It can also be heated in a kiln to form compound Y. When Y is hydrated, it forms compound Z which is used agriculturally to treat soils. Which statements about these compounds are correct?
1 More acid is neutralized by 1 g of W than by 1 g of X.
2 The metallic element in W reacts with water more quickly than the metallic element in Y.
3 Adding Z to a soil decreases the pH of the soil.
the answer is D (1 only is correct)
and here too please, i get that W is probably MgO, X is probably CaCO3, Y may be CaO and Z most likely Ca(OH)2. i know that 2 and 3 are wrong, but please explain why 1 is correct, thanks in advance!
 
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Metanoia

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Xaptor16 said:
33) Valence shell electron pair repulsion theory should be used to answer this question. Which species are trigonal planar?
1 BH3
2 CH3+
3 PH3
the answer is B (1 and 2 only are correct)
can someone please explain how to use the Valence shell electron pair repulsion theory to answer this? i don't get it! :(
Solids W, X, Y and Z are compounds of two different Group II metals. Some of their applications are described below.
Compound W is used as a refractory lining material in kilns.
Compound X is used as a building material. It can also be heated in a kiln to form compound Y. When Y is hydrated, it forms compound Z which is used agriculturally to treat soils. Which statements about these compounds are correct?
1 More acid is neutralized by 1 g of W than by 1 g of X.
2 The metallic element in W reacts with water more quickly than the metallic element in Y.
3 Adding Z to a soil decreases the pH of the soil.
the answer is D (1 only is correct)
and here too please, i get that W is probably MgO, X is probably CaCO3, Y may be CaO and Z most likely Ca(OH)2. i know that 2 and 3 are wrong, but please explain why 1 is correct, thanks in advance!
Click to expand...

VSEPR in simple terms states hat LP-LP repulsion> BP-LP repulsion > BP-BP repulsion.
And such repulsion will to an extent, determine molecular shapes.
All you have to do is follow the usual method of figuring out the number of lone pairs and bond pairs in a molecule to determine the shape.

1. 3 BP, 0 LP
2. 3 BP , 0 LP
3. 3 BP, 1 LP (trigonal pyramidal)


1g of MgO = 1/40 moles of MgO
1g of CaCO3 = 1/100 moles of CaCO3

Using HCl as example
MgO + 2HCl --> MgCl2 + H2O (HCl neutralised = 1/20 mol)
CaCO3 + 2HCl --> CaCl2 + CO2 + H2O (HCl neutralised = 1/50 mol)
 
Xaptor16

Xaptor16

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Metanoia said:
VSEPR in simple terms states hat LP-LP repulsion> BP-LP repulsion > BP-BP repulsion.
And such repulsion will to an extent, determine molecular shapes.
All you have to do is follow the usual method of figuring out the number of lone pairs and bond pairs in a molecule to determine the shape.

1. 3 BP, 0 LP
2. 3 BP , 0 LP
3. 3 BP, 1 LP (trigonal pyramidal)


1g of MgO = 1/40 moles of MgO
1g of CaCO3 = 1/100 moles of CaCO3

Using HCl as example
MgO + 2HCl --> MgCl2 + H2O (HCl neutralised = 1/20 mol)
CaCO3 + 2HCl --> CaCl2 + CO2 + H2O (HCl neutralised = 1/50 mol)
Click to expand...
Thank you so much! really helped me! :) :)
 
qwertypoiu

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Q4:
assume partial pressure of CO is x. Then partial pressure of H2O must also be x. Therefore:
Kp = (x*x)/(10,000*10,000) = 0.288
x^2 = 2880000000
x = 53665.63146 = 5.37kPa = A.
Q5:
The answer is B. Adding 0.1 moldm-3 of H2O2 makes the solution more dilute, and thus the intial reaction rate of Y was slower. However, adding more H2O2 caused more oxygen to be given out overall at the end of the reaction, as the graph shows.
Q9:
C3H7OH + 4.5O2 --> 3CO2 + 4H2O
0.1 mole of acid was burned. 0.45 mole of oxygen must have been used up therefore. Volume = 0.45*24 = 10.8 dm3. 0.3 mole of CO2 was relaesed as well. 0.3*24 = 7.2dm3
12dm3 of oxygen existed initially, 10.8 of it was consumed, so 12-10.8=1.2dm3 left, plus 7.2 of co2 = 8.4dm3. Therefore B.

Sorry gtg too many to answer :)
 
qwertypoiu

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Farhad221 said:
Asslamoalaikum
I need help with this question
Click to expand...
Answer is D. Only student Y is correct. All the carbon atoms bonded in the ring have tetrahedral structure, and are sp3 hybridised. this is because every carbon is attached to four groups. So like when you draw optical isomers, in fact, every carbon with 4 substituents have a 3 dimensional tetrahedral structure. Therefore, they cannot be on the same plane. As for cis-trans, this is obvious, whenever a C=C double bond exists, a cis-trans isomerism is possible (not always but usually.)


EDIT: Sorry, answer is B actually. The compound is prevented from having a cis-trans isomer, because of the ring.
 
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princess Anu

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image.jpg is this lab preparation for chlorine correct? But haven't we studied Nacl with H2so4 makes HCL and not Cl2?:/
 
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shazmina

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qwertypoiu said:
Answer is D. Only student Y is correct. All the carbon atoms bonded in the ring have tetrahedral structure, and are sp3 hybridised. this is because every carbon is attached to four groups. So like when you draw optical isomers, in fact, every carbon with 4 substituents have a 3 dimensional tetrahedral structure. Therefore, they cannot be on the same plane. As for cis-trans, this is obvious, whenever a C=C double bond exists, a cis-trans isomerism is possible (not always but usually.)
Click to expand...
The answer is B for that questions .. sorry maybe u might haven't noticed it ... :/
 
Metanoia

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qwertypoiu said:
Answer is D. Only student Y is correct. All the carbon atoms bonded in the ring have tetrahedral structure, and are sp3 hybridised. this is because every carbon is attached to four groups. So like when you draw optical isomers, in fact, every carbon with 4 substituents have a 3 dimensional tetrahedral structure. Therefore, they cannot be on the same plane. As for cis-trans, this is obvious, whenever a C=C double bond exists, a cis-trans isomerism is possible (not always but usually.)
Click to expand...

The part on the cis-trans is incorrect. We are talking of cycloalkenes, for ring structures less than 8 carbons, we will not expect to see the trans isomer due to the strain on the bonds.

shazmina said:
The answer is B for that questions .. sorry maybe u might haven't noticed it ... :/
Click to expand...
 
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