Biology; Chemistry; Physics: Post your doubts here!

[Ahmedfj]

NEED HELP IN CHEMISTRY JUNE 2004 PAPER 1 MCQ # 12 ....

 

[ashiqbal]

the first one is D because all of these tissues respire. thats where the energy comes from.
the second is A i think cuz when if you add total number of seedlings in light, its 430. and in dark, 405 are cream-leaved so the remaining 25 may be lost due to experimental error. and also cuz all other options are larger then 25 =)

yes you are right

 

[Spidey21]

NEED HELP IN CHEMISTRY JUNE 2004 PAPER 1 MCQ # 12 ....

my guess..it would be D...

 

[Ahmedfj]

my guess..it would be D...

i want to know the logic behind the answer and also explain mcq 13 and 19 if u can please

 

[ashiqbal]

okay some mcqs i was stumped at:

3 In a titration between an acid (in the burette) a nd an alkali, you may need to re-use the same
titration flask.
Which is the best procedure for rinsing the flask?
A Rinse with distilled water and then with the alkali.
B Rinse with tap water and then with distilled water.
C Rinse with tap water and then with the acid.
D Rinse with the alkali.

40 Under certain conditions 1 mole of ethane reacts with 2 moles of chlorine in a substitution
reaction.
What is the formula of the organic product in this reaction?
(A) C2H5 Cl (B) C2H4 Cl2 (C) C2H2 Cl4 (D) CH2C l2

 

[Ahmedfj]

okay some mcqs i was stumped at:

3 In a titration between an acid (in the burette) a nd an alkali, you may need to re-use the same
titration flask.
Which is the best procedure for rinsing the flask?
A Rinse with distilled water and then with the alkali.
B Rinse with tap water and then with distilled water.
C Rinse with tap water and then with the acid.
D Rinse with the alkali.

40 Under certain conditions 1 mole of ethane reacts with 2 moles of chlorine in a substitution
reaction.
What is the formula of the organic product in this reaction?
(A) C2H5 Cl (B) C2H4 Cl2 (C) C2H2 Cl4 (D) CH2C l2

can u help me in june 2004 mcq number 12, 13, 19 and 24 ???

 

[khizer shahab]

okay some mcqs i was stumped at:

3 In a titration between an acid (in the burette) a nd an alkali, you may need to re-use the same
titration flask.
Which is the best procedure for rinsing the flask?
A Rinse with distilled water and then with the alkali.
B Rinse with tap water and then with distilled water.
C Rinse with tap water and then with the acid.
D Rinse with the alkali.

40 Under certain conditions 1 mole of ethane reacts with 2 moles of chlorine in a substitution
reaction.
What is the formula of the organic product in this reaction?
(A) C2H5 Cl (B) C2H4 Cl2 (C) C2H2 Cl4 (D) CH2C l2

first answer is (A) bcuz to re use first is to wash with distilled water than with the solution to be filled with.!!
and my guess for next is (C) bcuz this reaction is only possible when hydrogen is removed from carbon therefore four hydrogen would be removed for 4 chlorine so now the formula would be C2H2Cl4 (pls confirm it)

 

[khizer shahab]

i want to know the logic behind the answer and also explain mcq 13 and 19 if u can please

for q13 it would (C) bcuz


1mole --------------254g iodine
xmole---------------2.54g iodine

crossmultiply and u would get 0.01 moles and concentration is provided earlier therefore place in equation i.e C=N/V and get an answer of 0.04mol/dm3

for 19 my guess is (A) bcuz mg is higher in reactivity series therefore more would be reacted and so more the gas be, and while zn is below mg so less gas be produced,
and for there mixture the gas would be produced between the level of mg and zn.!!!!

 

[talalz]

okay some mcqs i was stumped at:

3 In a titration between an acid (in the burette) a nd an alkali, you may need to re-use the same
titration flask.
Which is the best procedure for rinsing the flask?
A Rinse with distilled water and then with the alkali.
B Rinse with tap water and then with distilled water.
C Rinse with tap water and then with the acid.
D Rinse with the alkali.

40 Under certain conditions 1 mole of ethane reacts with 2 moles of chlorine in a substitution
reaction.
What is the formula of the organic product in this reaction?
(A) C2H5 Cl (B) C2H4 Cl2 (C) C2H2 Cl4 (D) CH2C l2

In marking scheme the answer is B

 

[amna shah]

can anyone tell me in QUESTION 5 OF PHYSICS PAPER 2 SUMMER 05 ....... HOW DO YOU FIND OUT THE DIRECTION OF THE CURRENT ?
AS THEY HAVE NOT MENTIONED ANY ARROW OR SIGN ON THE BATTERY ... AND IN GENERAL TO FIND THE DIRECTION OF CURRENT IN A CIRCUIT/SOLENOID IF ITS NOT MENTIONED AS THEY CAN ASK YOU TO DETERMINE THE DIRECTION OF THE FIELD WHICH IS DEPENDANT ON THE DIRECTION OF CURRENT..

 

[ashiqbal]

first answer is (A) bcuz to re use first is to wash with distilled water than with the solution to be filled with.!!
and my guess for next is (C) bcuz this reaction is only possible when hydrogen is removed from carbon therefore four hydrogen would be removed for 4 chlorine so now the formula would be C2H2Cl4 (pls confirm it)

this is what i thought but for the first the answer in marking scheme is B and for the second the answer is B, although i have understood second question (alkane + chlorine --> chloro-alkane + HCl), i am still confused about the first one. why is it given in mark scheme as B ?

 

[Mayedah]

NEED HELP IN CHEMISTRY JUNE 2004 PAPER 1 MCQ # 12 ....

Mcq no 13 .firstcalculate moles if Iodine
2.54/254=0.01
Thn by the formula moles = concentration multiplied by volume ,divide 0.01 by 250 and to convert into dm cube,multiply answer by 1000 so the answer will be 0.04 mol/dm cube

Mcq no 19
Magnesium will have the fastest reaction with hcl bcuz it is higher in the reactivity series and more hydrogen bubbles will be produced and zinc is lower in the reactivity series thus it will produce least bubbles of hydrogen gas

Mcq no 24
This will also be done by the same formula
First take out moles of of hcl by multipying concentration by volume .
30 (multiply) 2= 60
Now as the reaction equation says tht 1 mol of hcl reacts with 1mol of naoh thn divide 60 by volume of naoh at highest point i.e 20 .the answer will be 3.

 

[stareaj]

Can someone pls explain me mcq 9 and 26 and 29 physics paper 1 oct nov 08 plsssssssssss

 

[Fallen316]

okay some mcqs i was stumped at:

3 In a titration between an acid (in the burette) a nd an alkali, you may need to re-use the same
titration flask.
Which is the best procedure for rinsing the flask?
A Rinse with distilled water and then with the alkali.
B Rinse with tap water and then with distilled water.
C Rinse with tap water and then with the acid.
D Rinse with the alkali.

40 Under certain conditions 1 mole of ethane reacts with 2 moles of chlorine in a substitution
reaction.
What is the formula of the organic product in this reaction?
(A) C2H5 Cl (B) C2H4 Cl2 (C) C2H2 Cl4 (D) CH2C l2

3. B
40.D

 

[ashiqbal]

3. B
40.D

why is it (B) in mcq 3?

 

[convent2012]

Can someone pls explain me mcq 9 and 26 and 29 physics paper 1 oct nov 08 plsssssssssss

29 ) A, because according to ohm's law , current and voltage are directly propotional so straight line graph .
9 ) A, because the increase in load is shared between two springs .

 

[multixamza01]

can anyone tell me in QUESTION 5 OF PHYSICS PAPER 2 SUMMER 05 ....... HOW DO YOU FIND OUT THE DIRECTION OF THE CURRENT ?
AS THEY HAVE NOT MENTIONED ANY ARROW OR SIGN ON THE BATTERY ... AND IN GENERAL TO FIND THE DIRECTION OF CURRENT IN A CIRCUIT/SOLENOID IF ITS NOT MENTIONED AS THEY CAN ASK YOU TO DETERMINE THE DIRECTION OF THE FIELD WHICH IS DEPENDANT ON THE DIRECTION OF CURRENT..

In O level we always take conventional current ( i.e from + to - ) .
So the current flows in a clockwise direction .
As for the magnetic field :

Use the right hand rule to find the North pole . It is at C . The magnetic field lines always originate and terminate at 90 degree to the surface and flow from north pole( C ) to south pole(A ) . So the needles will be pointing to the right at A and C and to the left at B.

 

[khizer shahab]

this is what i thought but for the first the answer in marking scheme is B and for the second the answer is B, although i have understood second question (alkane + chlorine --> chloro-alkane + HCl), i am still confused about the first one. why is it given in mark scheme as B ?

oh but why ??according to me..if we rinse it with tap water and then distilled water some of water would get remained in flask which would be affecting concentration of alkali.!! anyway would be consulting with my sir.

 

[convent2012]

i want help in 5090
s11 qp12 q7
s10 qp11 q4, q16, q24
w09 qp1 q16, q14, q9
s09 qp1 q5, q17, q19​

 

[ashiqbal]

oh but why ??according to me..if we rinse it with tap water and then distilled water some of water would get remained in flask which would be affecting concentration of alkali.!! anyway would be consulting with my sir.

k, make sure u inform me!