Physics, Chemistry and Biology: Post your doubts here!

[Nabeel.Ahmad]

THNX N SO WE HAVE TO LEARN THE AMOUNT OF HEAT REQUIRED AS IT IS NOT GIVEN IN THE QUESTION

Yes, only for common substances like Water/Ice.

 

[Iridescent]

Chemistry doubt
Each tablet contains the same number of moles of CaCO3 and MgCO3. One tablet
reacted with excess hydrochloric acid to produce 0.24 dm3 of carbon dioxide at r.t.p.
CaCO3 + 2HCl → CaCl2 + CO2 + H2O
MgCO3 + 2HCl → MgCl2 + CO2 + H2O
(i) Calculate how many moles of CaCO3 there are in one tablet.
number of moles CO2 = ..............
number of moles of CaCO3 and MgCO3 = ..............
number of moles of CaCO3 = ..............

(ii) Calculate the volume of hydrochloric acid, 1.0 mol /dm3, needed to react with one
tablet.
number of moles of CaCO3 and MgCO3 in one tablet = ..............
Use your answer to (c)(i).
number of moles of HCl needed to react with one tablet = ..............
volume of hydrochloric acid, 1.0 mol /dm3, needed to
react with one tablet

(i) 1 mole of any gas = 24 dm^3.
number of moles CO2 = 0.24/24 = 0.01 mol.
number of moles of CaCO3 and MgCO3 = (see the mole ratio in the equation. As the ratio of CO2 : CaCO3 is 1:1, the answer is 0.01 mol) 0.01 mol.
number of moles of CaCO3 = 0.01 mol.

(ii) number of moles of CaCO3 and MgCO3 in one tablet: 0.01 mol.
number of moles of HCl needed to react with one tablet: (see the mole ration in the equation. As the ratio of HCL : CaCO3 is 2:1, the answer is 0.02 mol) 0.02 mol.
volume of hydrochloric acid, 1.0 mol /dm3, needed to react with one tablet: Volume = no. of moles/ concentration i.e., 0.02/1 = 0.02 dm^3.

 

[Iridescent]

Thanx dude

Thanx alot

You're welcome!

 

[Amitesh]

Can you please help me out in this question- Physics CIE IGCSE w10 qp 61 question 3 part (c). I am getting the answer as 5.05 ohms but the correct answer is 10 ohms. Can you tell me how to go about this question

 

[Nabeel.Ahmad]

Can you please help me out in this question- Physics CIE IGCSE w10 qp 61 question 3 part (c). I am getting the answer as 5.05 ohms but the correct answer is 10 ohms. Can you tell me how to go about this question

Iridescent can help you.

 

[Iridescent]

Can you please help me out in this question- Physics CIE IGCSE w10 qp 61 question 3 part (c). I am getting the answer as 5.05 ohms but the correct answer is 10 ohms. Can you tell me how to go about this question

0.5*0.3 = 0.15A.
Total resistance = 2X.
T.R = 10.1 + X.
2X = 10.1 + X.
X = 10.1 ohms.

 

[Iridescent]

Physics Doubt
A radioactive substance has a half-life of 2 weeks. At the beginning of an investigation the
substance emits 3000 β-particles per minute.
How many β-particles will it emit per minute after 6 weeks?
A 0 B 375 C 500 D 1500

Half-life is the time taken for the activity of a sample of any radio-active isotope to decrease to half its original value.
As the half-life of this substance is two weeks, the count rate will be reduced to half the previous value every two weeks.

After 2 weeks, the count rate would be: 3000/2 = 1500 counts/minute.
After 4 weeks, the count rate would be: 1500/2 = 750 counts/minute.
After 6 weeks, the count rate would be: 750/2 = 375 counts/minute.

Thus, the answer is B.

 

[Iridescent]

Jazak Allah Khair

Wa iyyakum.

 

[Iridescent]

Physics Doubt

The air in the syringe is at a pressure of 2.0 × 105Pa. The piston is slowly moved into the
syringe, keeping the temperature constant, until the volume of the air is reduced from
80 cm3 to 25 cm3. Calculate the final pressure of the air.


pressure=

P1*V1 = P2*V2

2*10^5 * 80 = x * 25
x = 2 * 10^5 * 80/25
x=6.4*10^5.
pressure= 6.4*10^5.

 

[Iridescent]

thanx bro May God increase your knowledge and succeed you in your path.

You're welcome and thanks for the Dua'a.

 

[princess sofia]

aoa GUYZ HOW R WE GONNA DETERMINE THIS MCQ
the hydroxidesof allumminium,chromium and iron r insoluble. aqueous solutions of chlorine of these metals r tested with aqueous NAOH
which solutionsform a coloured precipitate?
A. CrCl3 and FeCl3
B.AlCl3 and FeCl3
C. AlCl3 and CrCl3
D. all

 

[Anirudh Agarwal]

what are oxidation states??? can anyone please explain???

 

[Counter Logic Gamer]

CHEMISTRY 0620/03



Paper 3

May/June 2006

aluminium oxide Al2O3

calcium oxide CaO

carbon dioxide CO2

carbon monoxide CO

magnesium oxide MgO

sulphur dioxide SO2





Which of the above oxides will react with hydrochloric acid but not with aqueous
sodium hydroxide?
[1]
(ii) Which of the above oxides will react with aqueous sodium hydroxide but not with
hydrochloric acid?
[1]
(iii) Which of the above oxides will react both with hydrochloric acid and with aqueous
sodium hydroxide?
[1]
(iv) Which of the above oxides will react neither with hydrochloric acid nor with
aqueous sodium hydroxide?
will u explain why??a BIG DOUBT!! ( P.S GIVE ME THE NOTES OF THIS TOPIC)

 

[Counter Logic Gamer]

CHEMISTRY 0620/03



Paper 3

May/June 2006

aluminium oxide Al2O3

calcium oxide CaO

carbon dioxide CO2

carbon monoxide CO

magnesium oxide MgO

sulphur dioxide SO2





Which of the above oxides will react with hydrochloric acid but not with aqueous
sodium hydroxide?
[1]
(ii) Which of the above oxides will react with aqueous sodium hydroxide but not with
hydrochloric acid?
[1]
(iii) Which of the above oxides will react both with hydrochloric acid and with aqueous
sodium hydroxide?
[1]
(iv) Which of the above oxides will react neither with hydrochloric acid nor with
aqueous sodium hydroxide?
BIG DOUBT!!! Pls gv me the notes of this topic!!!

 

[SREYAh]

hi dear.. can you send me some exams paper for Olevel plzzzzz..

 

[jackline]

https://docs.google.com/file/d/0B2kkRh7_BMZmNUVxZ2ZqeEdRZS1mcVN6NDA4UUZVUQ/edit?pli=1 question 2 answers

 

[Power_PC]

Hey Guys Oct/Nov 2013 session is about to start!..... nd im starting to freak out! Please give me helpfull tips for achieving A*-A in IGCSE Physics 0625 (Extended). And paper solving tips and tricks plus does anyone knows a good tutor/tuition for IGCSE Physics in Jubail, Saudi Arabia? May Allah make all the papers easier for us and we all score straight As in all subjects! Ameen.

 

[Iridescent]

Hey Guys Oct/Nov 2013 session is about to start!..... nd im starting to freak out! Please give me helpfull tips for achieving A*-A in IGCSE Physics 0625 (Extended). And paper solving tips and tricks plus does anyone knows a good tutor/tuition for IGCSE Physics in Jubail, Saudi Arabia? May Allah make all the papers easier for us and we all score straight As in all subjects! Ameen.

For Physics, solve as many past papers as you can. MCQs often come repeated so try to get 37-40 in P1. Try to solve at least 10 years of past papers and clear all your doubts. You will easily get an A*.
It's hard to find a good tutor in Jubail. I think Al-Hussan is the best school there. Try contacting their Physics teacher.
However, you will find many good tutors in Dammam, if you can easily go there.

 

[SREYAh]

https://docs.google.com/file/d/0B2kkRh7_BMZmNUVxZ2ZqeEdRZS1mcVN6NDA4UUZVUQ/edit?pli=1 question 2 answers

thank u soo much dear...:*

 

[SREYAh]

can anyone send me some notes on acid bases and salts (Olevel,extended) plzzz...
i badly need this...