Biology; Chemistry; Physics: Post your doubts here!

[usama321]

thanks both

 

[usama321]

http://papers.xtremepapers.com/CIE/...al O Level/Chemistry (5070)/5070_w04_qp_1.pdf

mcq 40. Answer is B. What is the explanation? Anyone pls?

 

[Saad Mughal]

http://papers.xtremepapers.com/CIE/Cambridge International O Level/Chemistry (5070)/5070_w04_qp_1.pdf

mcq 40. Answer is B. What is the explanation? Anyone pls?

Margarine is an alkane (saturated compound). Vegetable oil is an alkene (unsaturated compound).
When an alkene is hydrogenated it forms an alkane. Hence, the answer is B.
Also, options A and D are horribly incorrect, bromine gas is not colored but decolorized by alkenes and alkenes have double bonds b/w carbon atoms not carbon AND hydrogen atoms. C is incorrect because Alkenes plus steam = ALCOHOLS and not alkanes (solid margarine).
Hope you get it.

 

[usama321]

Margarine is an alkane (saturated compound). Vegetable oil is an alkene (unsaturated compound).
When an alkene is hydrogenated it forms an alkane. Hence, the answer is B........................ B is incorrect because
Hope you get it.

heheheheheeh. thanks by the way, i got what you are trying to say. You meant c the second time

 

[Saad Mughal]

heheheheheeh. thanks by the way, i got what you are trying to say. You meant c the second time

Oh yeah, obviously. Apologies for the error.

 

[Mustafa Malik]

transition elements are mostly catalysts. So, from the list, C is a transition element. By the way, for 21, the answer seems to be D, for alkali metals do not have very high melting points, and C can't be the answer as it states poor conductivity.

The answer for 20 is C. The oxide of the element X is a catalyst. We know that most catalysts are from the transition metals, so among the 4 options, either D or C are transition elements, A is argon and B is magnesium. C is Manganese and is the answer since Lead (D) oxide and dioxide are good oxidizing agents rather than catalysts.
For 21, the answer is D, Sodium has a low melting point AND density.

Thanx got it... yeah its D, oopsie

 

[sadiaali]

Please anyone do for me...
A student carries out a single experiment to determine the speed of reaction between calcium
carbonate and an excess of hydrochloric acid.
Which of the following does not change during the course of the reaction?
(a) concentration of the hydrochloric acid solution
(b) mass of calcium carbonate
(c) volume of carbon dioxide evolved
(d) volume of the hydrochloric acid solution

 

[asma tareen]

Please anyone do for me...
A student carries out a single experiment to determine the speed of reaction between calcium
carbonate and an excess of hydrochloric acid.
Which of the following does not change during the course of the reaction?
(a) concentration of the hydrochloric acid solution
(b) mass of calcium carbonate
(c) volume of carbon dioxide evolved
(d) volume of the hydrochloric acid solution

i think d

 

[falcon678]

Please anyone do for me...
A student carries out a single experiment to determine the speed of reaction between calcium
carbonate and an excess of hydrochloric acid.
Which of the following does not change during the course of the reaction?
(a) concentration of the hydrochloric acid solution
(b) mass of calcium carbonate
(c) volume of carbon dioxide evolved
(d) volume of the hydrochloric acid solution

thnkin same as well...most probably D...
cuz conc of HCl is gona be effected as it reacts...mass of CaCO3 is gona get reduced....Volume of CO2 evovld ....so it wld b volume of solution? not sure thou......

 

[sadiaali]

thnkin same as well...most probably D...
cuz conc of HCl is gona be effected as it reacts...mass of CaCO3 is gona get reduced....Volume of CO2 evovld ....so it wld b volume of solution? not sure thou......

Ans is D..Thank you

 

[falcon678]

Ans is D..Thank you

 

[Suchal Riaz]

Please anyone do for me...
A student carries out a single experiment to determine the speed of reaction between calcium
carbonate and an excess of hydrochloric acid.
Which of the following does not change during the course of the reaction?
(a) concentration of the hydrochloric acid solution
(b) mass of calcium carbonate
(c) volume of carbon dioxide evolved
(d) volume of the hydrochloric acid solution

answer is D because the volume of HCL solution wont change although the mass of calcium carbonate will change but not of solution. concentration of HCL will change however.

 

[HDIWAN]

Please anyone do for me...
A student carries out a single experiment to determine the speed of reaction between calcium
carbonate and an excess of hydrochloric acid.
Which of the following does not change during the course of the reaction?
(a) concentration of the hydrochloric acid solution
(b) mass of calcium carbonate
(c) volume of carbon dioxide evolved
(d) volume of the hydrochloric acid solution

yeh konsay year ka question hai??

 

[thementor]

http://papers.xtremepapers.com/CIE/Cambridge International O Level/Physics (5054)/5054_s11_qp_22.pdf
Q9 a(i)
The first two sections of the graph were easy.....What is confusing me is the third section: "He opens his parachute at t=20s and decelerates until t=25s.......
In books it has been shown that a curved line is drawn after the parachute is opened until terminal velocity is reached.....However according when I checked the past papers answers, a straight line with a (-ve) gradient is drawn.....why is this...?

 

[TheStallion-Reborn]

C and D will be vigorous reactions, we can't react them safely.
B is not possible (for forming KCl), the reason being that Sulphate ions are more stable and reactive than Chloride ions hence the Potassium ion prefers to be with the Sulphate ion rather than the less stable chloride ion therefore the reaction is not feasible.

y cant v simply say tht potasium sulphate and sodium chloride are both basic??

 

[Saad Mughal]

y cant v simply say tht potasium sulphate and sodium chloride are both basic??

Basic? I don't get you.
If it was NaSO4 + KCl, then the reaction would have happened, double displacement, KSO4 and NaCl would have formed. They are both salts, the more reactive element will displace the less reactive element.

 

[ijlalm]

Koi BAAP ka DADA hai to explain this MCQ..
Energy, Work and Power MCQ 50

http://books.google.com.pk/books?id...=gbs_selected_pages&cad=3#v=onepage&q&f=false

 

[usama321]

y cant v simply say tht potasium sulphate and sodium chloride are both basic??

NaCl basic? it is a salt

 

[Saad Mughal]

Koi BAAP ka DADA hai to explain this MCQ..
Energy, Work and Power MCQ 50

http://books.google.com.pk/books?id...=gbs_selected_pages&cad=3#v=onepage&q&f=false

Yeah yeah, we know. It's difficult. I can't even guess an answer.

 

[ijlalm]

I think we use the formulae W=F*d, then use the value of W in the formulae K.E=1/2mv2 to find the speed maybe..