Chemistry MCQ thread...

[abdullah181994]

26 An alcohol with molecular formula CnH2n+1OH has a chiral carbon atom but does not react with
MnO4 / H+.
What is the least number of carbon atoms such an alcohol could possess?
A 5 B 6 C 7 D 8

please answer this question

 

[xHazeMx]

someone show the calculations for this question

I reckon that it's C. Tell me if I'm correct, then I'll post the solution.

thats correct. explanation ?

 

[xHazeMx]

26 An alcohol with molecular formula CnH2n+1OH has a chiral carbon atom but does not react with
MnO4 / H+.
What is the least number of carbon atoms such an alcohol could possess?
A 5 B 6 C 7 D 8

please answer this quuestion

its C

 

[abdullah181994]

26 An alcohol with molecular formula CnH2n+1OH has a chiral carbon atom but does not react with
MnO4 / H+.
What is the least number of carbon atoms such an alcohol could possess?
A 5 B 6 C 7 D 8

please answer this quuestion

its C

please explian also

 

[histephenson007]

I don't think any calculations are involved in this question.,

First of all, we know that it doesn't react with MnO4/H+ (which is an oxidant)...which shows that the alcohol is tertiary.

so we get the basic layout..... (CH3)3 C-OH
But, the molecule has to have a chiral centre... so we just add up a few methyls on the CH3 branches to achieve a Chiral centre (the C which is bonded to the OH group)

 

[xHazeMx]

please explian also

it is a tertiary alcohol because it doesnt react with kmno4. so we need chiral centres around C ( one bond is with OH ) so we need a compound of 1 C atom and a compound of 2 C atoms and a compound of 3 C atoms bonded to the middle C atom to make different groups which makes a total of 7 C atoms

 

[Zishi]

someone show the calculations for this question

I reckon that it's C. Tell me if I'm correct, then I'll post the solution.

thats correct. explanation ?

If you've done Hess's law, then there should be no problems. But anyways. . .


Route 1 = Route 2

-286 = delta H_r + (-283) + (-44)

This gives the answer.

 

[histephenson007]

Q.

When a mineral was heated in a Bunsen flame to constant mass, a colourless gas that turned limewater mily was evolved. The remaining solid was cooled and then added to aqueous hydrochloric acid. Vigorous effervescence was seen.

What was the mineral?
A. aragonite, CaCO3
B. artinite, MgCO3.Mg(OH)2.3H2O
C. barytocalcite, BaCO3.CaCO3
D. dolomite, CaCO3.MgCO3

 

[xHazeMx]

Q.

When a mineral was heated in a Bunsen flame to constant mass, a colourless gas that turned limewater mily was evolved. The remaining solid was cooled and then added to aqueous hydrochloric acid. Vigorous effervescence was seen.

What was the mineral?
A. aragonite, CaCO3
B. artinite, MgCO3.Mg(OH)2.3H2O
C. barytocalcite, BaCO3.CaCO3
D. dolomite, CaCO3.MgCO3

its C

 

[abdullah181994]

Q.

When a mineral was heated in a Bunsen flame to constant mass, a colourless gas that turned limewater mily was evolved. The remaining solid was cooled and then added to aqueous hydrochloric acid. Vigorous effervescence was seen.

What was the mineral?
A. aragonite, CaCO3
B. artinite, MgCO3.Mg(OH)2.3H2O
C. barytocalcite, BaCO3.CaCO3
D. dolomite, CaCO3.MgCO3

I think its A

 

[Dickinson]

why it is not D !!

Because ethanoic acid doesn't compltely with water

 

[histephenson007]

Which one is it C or A?? plz explain

 

[hassam]

YA ITS c...baco3 has high thermal stability so will not decompose initialyy.....later on will react with acid

 

[hassam]

 

[hassam]

35 Use of the Data Booklet is relevant to this question.
Which statements about Na+, Mg2+ and Al3+ ions are correct?
1 NaCl has no covalent character as Na+ is an ion with low charge density.
2 Al3+ forms Al(H2O)6
3+ readily but not Na+.
3 Al3+ has the most exothermic enthalpy change of hydration.
guyx waitng for ur ansers to chek ur preparation

 

[Zishi]

B

 

[xHazeMx]

35 Use of the Data Booklet is relevant to this question.
Which statements about Na+, Mg2+ and Al3+ ions are correct?
1 NaCl has no covalent character as Na+ is an ion with low charge density.
2 Al3+ forms Al(H2O)6
3+ readily but not Na+.
3 Al3+ has the most exothermic enthalpy change of hydration.
guyx waitng for ur ansers to chek ur preparation

A?

 

[Zishi]

35 Use of the Data Booklet is relevant to this question.
Which statements about Na+, Mg2+ and Al3+ ions are correct?
1 NaCl has no covalent character as Na+ is an ion with low charge density.
2 Al3+ forms Al(H2O)6
3+ readily but not Na+.
3 Al3+ has the most exothermic enthalpy change of hydration.
guyx waitng for ur ansers to chek ur preparation

Though enthalpy change of hydration isn't in syllabus(we just have to know its definition), but I'll go with A.

 

[hassam]

A dibromoalkane CH3CH2CHBrCHBrCH2CH3 was treated with excess alcoholic
potassium hydroxide. The main product would be
A CH3CH2CH(OH)CH(OH)CH2CH3
B CH3CH2CH2O-K+
C CH3CH=CH-CH=CHCH3
D CH3CH2CH=CHCH2CH3

 

[xHazeMx]

A dibromoalkane CH3CH2CHBrCHBrCH2CH3 was treated with excess alcoholic
potassium hydroxide. The main product would be
A CH3CH2CH(OH)CH(OH)CH2CH3
B CH3CH2CH2O-K+
C CH3CH=CH-CH=CHCH3
D CH3CH2CH=CHCH2CH3

A