Physics, Chemistry and Biology: Post your doubts here!

[saadiee]

How to do final preparation for Biology papers (1&2) to get an A*??

 

[saadiee]

What is natural selection??

 

[My Name]

What is natural selection??

Read from here:
http://biology-igcse.weebly.com/selection.html

 

[sj0007]

chemistry problem
A question came to draw two straight intersecting lines
You guys are having any idea how to do that

I don't know which question u r talking abt but it is mostly like this......

 

[Mr.Physics]

I don't know which question u r talking abt but it is mostly like this......

View attachment 53339

Does calcium make a precipitate in ammonia solution (NH4) ?? In marks scheme it is written that faint ppt but in my book it is written that it doesn't make any ppt .

 

[mujtabamajeed]

describe star formation

 

[Saad the Paki]

Does calcium make a precipitate in ammonia solution (NH4) ?? In marks scheme it is written that faint ppt but in my book it is written that it doesn't make any ppt .

both are acceptable... It depends on the volume / concentration etc etc..
But usually theres no ppt
(Not a 100% sure tho)

 

[My Name]

both are acceptable... It depends on the volume / concentration etc etc..
But usually theres no ppt
(Not a 100% sure tho)

Does calcium make a precipitate in ammonia solution (NH4) ?? In marks scheme it is written that faint ppt but in my book it is written that it doesn't make any ppt .

Taken from syllabus 2015

 

[skyangel]

what are imp chap of bio that mostly come in exams paper 3

 

[DANISH182]

The answer should always be according to the marks mentioned. Anyway, this is how it goes...
There are three diagrams in the question.The retort stand to fix the beaker of water,the balance to measure the amount of water and thermometer to measure the temperature.

By using the balance has same of both the fuels so that you're test is fair.
First measure the initial temperature of the water using a thermometer.
Fix the beaker of water in the retort stand and place the fuel under it.
Then burn the fuel and record the temperature of water.
Repeate the experiment with the other fuel and the fuel that gives the greatest rise in temperature( for a period of time) produces more energy.
(In other words it would be a better fuel.)

Take a look at the mark scheme to make sure all points have been covered.If you wish to add a diagram you can draw like this(pic below...just that the test tube would be a beaker of water) and write the steps.
View attachment 53317
Hope that helps

how to fix a beaker at a retord?

 

[DANISH182]

Who is doing chemistry paper 62 on Tuesday or before?

ME

 

[DANISH182]

HEY HOW DO WE KNOW WHEN THE POINT OF CRYSTALLISATION IS REAHCED?

 

[NOneed2speedd]

HEY HOW DO WE KNOW WHEN THE POINT OF CRYSTALLISATION IS REAHCED?

Dip a cold glass rod and if crystals are formed at the tip of the glass rod.. it has reached crystallisation point

 

[DANISH182]

Dip a cold glass rod and if crystals are formed at the tip of the glass rod.. it has reached crystallisation point

THNX FOR UR HELP

 

[DANISH182]

HOW TO DO THIS QUESTION B(II),C(II) AND D(II)

 

[DANISH182]

NO ANSWER TILL NOW\

 

[sfhn_128]

NO ANSWER TILL NOW\

which year is it??

 

[DANISH182]

which year is it??

OCT NOV 2014

 

[The_Boss]

HOW TO DO THIS QUESTION B(II),C(II) AND D(II)View attachment 53358

Bii- Carbonate have enough Activation Energy so not required.
Cii- When crystallizing at later stage the acid will concentrate in the crystals of salt to produce an impure composition.
Dii- Turns Anhydrous and gives off steam.

 

[DANISH182]

Bii- Carbonate have enough Activation Energy so not required.
Cii- When crystallizing at later stage the acid will concentrate in the crystals of salt to produce an impure composition.
Dii- Turns Anhydrous and gives off steam.

SHOULDN'T WE WRITE DEHYDRATE FOR THE LAST ONE