Chemistry: Post your doubts here!

[shazmina]

sorry View attachment 54693

Whats the ans?

 

[ashcull14]

CAN someone draw and explain?
the ans is D

 

[ashcull14]

Whats the ans?

D

 

[shazmina]

D

Yeah got it ... give me a mint ill explain

 

[shazmina]

sorry View attachment 54693

Free radical substitution reactions are initiated by the homolytic bond fission of the chlorine molecule .. And we know this.
keeping this in mind .. we can cross out Option A and B
So now i recommend you to draw both the isomers ie 1-Chloropropane and 2-Chloropropane
Now lets take 1-Chloropropane ..
You can see that the chlorine atom can be placed in three different orientation on the carbon number 1 and also you can see that there are 2 possibilities of obtaining 1-Chloropropane therefore altogether there will be 6 orientations for Chlorine atom in 1-Chloropropane
Similarly for 2-Chloropropane there will be only 2 orientation .. and hence when you find their ratio ie 6 : 2 you get it as 3 : 1

 

[The Sarcastic Retard]

Please explain them. Thanks.

Please explain them. Thanks.

34 is B bro...

Ohh typing Error :/
1 H2SO4 donated proton to HNO3 Hence H2SO4 is a acid its conjugate base will be HSO4-
2 HNO3 accpted a proton.. Hence its a base..

 

[Abdul Hanan]

ans is B how?

 

[ashcull14]

 

[ashcull14]

Free radical substitution reactions are initiated by the homolytic bond fission of the chlorine molecule .. And we know this.
keeping this in mind .. we can cross out Option A and B
So now i recommend you to draw both the isomers ie 1-Chloropropane and 2-Chloropropane
Now lets take 1-Chloropropane ..
You can see that the chlorine atom can be placed in three different orientation on the carbon number 1 and also you can see that there are 2 possibilities of obtaining 1-Chloropropane therefore altogether there will be 6 orientations for Chlorine atom in 1-Chloropropane
Similarly for 2-Chloropropane there will be only 2 orientation .. and hence when you find their ratio ie 6 : 2 you get it as 3 : 1

thnk u so mchhh.....tht ws quite helpful

 

[Studydayandnight]

Use of the Data Booklet is relevant to this question.

Ferrochrome is an alloy of iron and chromium. Ferrochrome can be dissolved in dilute sulfuric acid to produce a mixture of FeSO4 and Cr2(SO4)3. The FeSO4 reacts with K2Cr2O7 in acid solution according to the following equation.

14H+ + 6Fe2+ + Cr2O7 2– → 2Cr3+ + 6Fe3+ + 7H2O

When 1.00g of ferrochrome is dissolved in dilute sulfuric acid, and the resulting solution titrated, 13.1cm3 of 0.100moldm–3 K2Cr2O7 is required for complete reaction. What is the percentage by mass of Fe in the sample of ferrochrome?

A 1.22 B 4.39 C 12.2 D 43.9

How do we solve this??

Correct answer is D.

 

[Studydayandnight]

How is this B??

 

[mohhef3]

Aluminium carbide, Al 4C3, reacts readily with aqueous sodium hydroxide. The two products of the

reaction are NaAlO2 and a hydrocarbon. Water molecules are also involved as reactants.

What is the formula of the hydrocarbon?

A CH4
B C2H6
C C3H8
D C6H12
someone explain this plz the answer is A

 

[Falconwing]

View attachment 54699
ans is B how?

Plug in the numbers from the table, for B, there are 5 I atoms in the right side. The rest of the equation fits too, check it out using trial and error.

View attachment 54700

I suppose it is A. Balance the equations using trial and error. 1m of Butanoic acid completely combusts with 5m of O2.

Use of the Data Booklet is relevant to this question.

Ferrochrome is an alloy of iron and chromium. Ferrochrome can be dissolved in dilute sulfuric acid to produce a mixture of FeSO4 and Cr2(SO4)3. The FeSO4 reacts with K2Cr2O7 in acid solution according to the following equation.

14H+ + 6Fe2+ + Cr2O7 2– → 2Cr3+ + 6Fe3+ + 7H2O

When 1.00g of ferrochrome is dissolved in dilute sulfuric acid, and the resulting solution titrated, 13.1cm3 of 0.100moldm–3 K2Cr2O7 is required for complete reaction. What is the percentage by mass of Fe in the sample of ferrochrome?

A 1.22 B 4.39 C 12.2 D 43.9

How do we solve this??

Correct answer is D.

0.1 x 13.1/1000 = 1.31 x 10^-3. 1 mole reacts with 6 moles of iron, so 6 x 1.31 x 10^-3 = 7.86 x 10^-3. 1 / 7.86 x 10^-3 = 127.226 (molar mass of ferrochrome.)
55.8/127.226 x 100 = 43.9, 55.8 being the molar mass of iron.

 

[shazmina]

Use of the Data Booklet is relevant to this question.

Ferrochrome is an alloy of iron and chromium. Ferrochrome can be dissolved in dilute sulfuric acid to produce a mixture of FeSO4 and Cr2(SO4)3. The FeSO4 reacts with K2Cr2O7 in acid solution according to the following equation.

14H+ + 6Fe2+ + Cr2O7 2– → 2Cr3+ + 6Fe3+ + 7H2O

When 1.00g of ferrochrome is dissolved in dilute sulfuric acid, and the resulting solution titrated, 13.1cm3 of 0.100moldm–3 K2Cr2O7 is required for complete reaction. What is the percentage by mass of Fe in the sample of ferrochrome?

A 1.22 B 4.39 C 12.2 D 43.9

How do we solve this??

Correct answer is D.

First find the number of moles of K2Cr2O7
n = Vc
13.1*10^-3 *0.100 =1.31*10^-3 moles

As we know the mole ratio of Fe2+ to Cr2O7 2– we can cross multiply and find the number of moles of Fe2+ that have reacted with 1.31*10^-3 moles of Cr2O7 2–, which is equal to 7.86*10^-3 Moles
The Mr of Fe is 55.8g, so then multiply 7.86*10^-3 Moles of Fe2+ with it Mr to get the mass of iron that have reacted with K2Cr2O7 which is equal to 0.439

And then finally find the percentage by mass , 0.439/1*100 = 43.9%

Make sure you round off all the values to an appropriate significant figure when writing and remember to carry the Answers in your calculator for an accurate calculation

 

[Falconwing]

How is this B??

 

[qwertypoiu]

The Sarcastic Retard qwertypoiu I need help in this question ...

Here i have posted the link for the question paper and my doubt is in question no 21 ....
I have even posted the explanation for Q21 which was answered previously .... My doubt is I don't get what they are trying to say in the part where i have highlighted ... so can one of you clarify it to me further.. Thanks in advance

https://docs.google.com/viewer?a=v&...sLm9yZ3x0ZWFjaGVyc3xneDoxYmI0OTYwOWIyZDRmNWVj

If the compound was an alkane and had no rings or double bonds, number of H atoms present = 2n+2 = 2(20)+2 = 42

Now, every time there're 2H less, you'll either have a double bond or a ring. The question states that there's one aldehyde (C=O) and 1 ring structure which has 1 C=C so this accounts for 6 missing Hydrogens, thereby leaving you with 8 missing Hydrogens.

8/2 = 4 Hydrogens in the aliphatic side chain.

However, total C=C are 5 because you have to include the C=C from the cyclohexene + cis formation hence A

I will assume you have understood the parts you did not highlight. So there would have been 42 hydrogen atoms, if it were just a straight chain alkane. We wish for only 28 to be left.
6 hydrogen atoms are accounted for by the presence of aldehyde and ring structure. So 42-6 = 36 we'd expect now.
However we wish for 28. We need to eliminate 36-28= 8 more hydrogen atoms.
Every time a double bond is added to a saturated chain, 2 hydrogen atoms are gotten rid of.
Therefore, 8/2 = 4 double bonds required to satisfy our condition.

 

[Falconwing]

Aluminium carbide, Al 4C3, reacts readily with aqueous sodium hydroxide. The two products of the

reaction are NaAlO2 and a hydrocarbon. Water molecules are also involved as reactants.

What is the formula of the hydrocarbon?

A CH4
B C2H6
C C3H8
D C6H12
someone explain this plz the answer is A

Reaction => Al4C3 + 4NaOH + 4H2O --> 4NaAlO2 + 3CH4. You'll end up at this if you try to balance the equation.

 

[mohhef3]

Use of the Data Booklet is relevant to this question.

A sample of potassium oxide, K2O, is dissolved in 250cm3 of distilled water. 25.0cm3

solution is titrated against sulfuric acid of concentration 2.00moldm–3. 15.0 cm3 of this

acid is needed for complete neutralisation. of this sulfuric

Which mass of potassium oxide was originally dissolved in 250cm3 of distilled water?

A 2.83g
B 28.3g
C 47.1g
D 56.6g

 

[qwertypoiu]

Use of the Data Booklet is relevant to this question.

A sample of potassium oxide, K2O, is dissolved in 250cm3 of distilled water. 25.0cm3

solution is titrated against sulfuric acid of concentration 2.00moldm–3. 15.0 cm3 of this

acid is needed for complete neutralisation. of this sulfuric

Which mass of potassium oxide was originally dissolved in 250cm3 of distilled water?

A 2.83g
B 28.3g
C 47.1g
D 56.6g

K2O + H2SO4 ----> K2SO4 + H2O
Moles of acid = 15/1000*2 = 0.03mol
Moles of K2O in 25cm3 = 0.03mol, due to ratio.
Moles of K2O in 250cm3, = 0.03*10 = 0.3mol
Mass = (39.1*2+16)*0.3 = 28.26g

 

[mohhef3]

K2O + H2SO4 ----> K2SO4 + H2O
Moles of acid = 15/1000*2 = 0.03mol
Moles of K2O in 25cm3 = 0.03mol, due to ratio.
Moles of K2O in 250cm3, = 0.03*10 = 0.3mol
Mass = (39.1*2+16)*0.3 = 28.26g

oh i didnt multiply it by 10 he wanted it in the distilled solution.thx mate what r u studing?a levels or as