Physics, Chemistry and Biology: Post your doubts here!

[black widow]

Assalamualaikum!!!
do any1 of you have an easy way of remembering the tests for gases in chemistry????

whenever u study chemistry, do revise the tests again and again and soon u will memorize them
here is a file containing all the tests included in the O Level syllabus

 

[black widow]

Acid Bases and Salts help please. :/

https://www.khanacademy.org/science/chemistry/acids-and-bases
this is really amazing
it is comprehensive and the lecture is conveyed accurately and i assure u, it will make greater sense to u than explaining it all here by typing

 

[♣♠ MagneD ♣♠]

Try yahoo answers where you will get variety of answer... !!!!

 

[♣♠ MagneD ♣♠]

Acids, Bases and Salts

Acids and Bases

Acid � A substance which ionizes to form H+ (H+ is a product).

Examples

HNO3(aq) � H+(aq) + NO3-(aq)

HCl(aq) � H+(aq) + Cl-(aq)

Base � A substance that accepts (reacts with) H+.

Examples

OH-(aq) + H+(aq) � H2O(l)

NH3(aq) + H+(aq) � NH4+(aq)

Note that to obtain hydroxide ions (OH-) we start with an ionic compound that dissolves in water to form hydroxide ions, such as the alkali metal
hydroxides, LiOH, NaOH, KOH, RbOH, etc.

Since both acids and bases dissolve in water to form ions, they are both electrolytes. However, most acids and bases do not completely dissociate to form ions, those that do are called strong acids or strong bases.

• Strong acid/base � Completely ionizes in solution
• Strong acid/base � Strong electrolyte
• Weak acid/base � Partially ionizes in solution
• Weak acid/base � Weak electrolyte

The list of strong acids and bases is given in your book in table 4.1 and below. You will be expected to memorize this list.

Strong Acids
Perchloric acid

HClO4

Chloric acid

HClO3

Hydrochloric acid

HCl

Hydrobromic acid

HBr

Hydroiodic acid

HI

Nitric acid

HNO3

Sulfuric acid

H2SO4

Strong Bases
Group 1A metal hydroxides

LiOH, NaOH, KOH, RbOH, CsOH

Heavy group 2A metal hydroxides

Ca(OH)2, Sr(OH)2, Ba(OH)2

Unless told otherwise we will assume that all other acids and bases are weak.

How can I recognize an acid?

We expect an acid when hydrogen combines with either a non-metal or a polyatomic anion.

Examples

H2S, H3PO4, HF, HCl, HClO, HC2H3O2 etc.

How can I recognize a base?

At the moment we will only concern ourselves with two types of bases:

• ionic compounds where hydroxide is the anion
• ammonia (NH3)

Examples

KOH, LiOH, NH3, Ca(OH)2, NH4OH, etc.

Neutralization Reactions and Salts

Neutralization Reaction � A reaction between an acid and a base.

If the base is a metal hydroxide then one of the products is water while the other product is a salt.

Example

HNO3(aq) � H+(aq) + NO3-(aq)

NaOH(aq) � OH-(aq) + Na+(aq)

When we combine HCl and NaOH solutions the H+ and OH- ions combine to form water and a salt solution:

HNO3(aq) + NaOH(aq) � H2O(l) + NaNO3(aq)

(acid) + (base) � (water) + (salt)

Salt � Any ionic compound whose anion comes from an acid and whose cation comes from a base.

 

[♣♠ MagneD ♣♠]

SOURCE: FROM NET BUT READ EVERYTHING AND POSTED...!!!

 

[AmmarI]

asslamualikum..

do any1 of u have a method of remembering test for remebering anions and cations !!! pls reply soon........

 

[black widow]

asslamualikum..

do any1 of u have a method of remembering test for remebering anions and cations !!! pls reply soon........

well try to revise them as much as possible
i will advise u to go through the list of cations, and arrange them in terms of their ppt formed and whether the ppt is soluble
for example, u can sort out using Cu+2, Fe+2, and Fe+3, as they all form a coloured ppt other than a white ppt
then u can sort out the remaining with their white ppt

do the same for anions,
u will notice that SO4-2, Cl-, Br-, and I-, all have a similar test with dilute nitric acid.
so whenever u revise chemistry, do pay a look at it

 

[ahmed butt]

i dont know how to study igcse bio,phy,chm in an organized way . i am feeling hopeless and i have igcse exam after 2 months.

 

[funky brat]

i dont know how to study igcse bio,phy,chm in an organized way . i am feeling hopeless and i have igcse exam after 2 months.

Utilise this month fully in reading the books. Two months are more than enough for the past papers. Do not skip anything. Do each topic thoroughly with complete understanding.

 

[ahmed butt]

Utilise this month fully in reading the books. Two months are more than enough for the past papers. Do not skip anything. Do each topic thoroughly with complete understanding.

10Q for advice

 

[ahmed butt]

can i get A* if i will read textbook this month ,next 2 month i will do pastpapper.

 

[♣♠ MagneD ♣♠]

can i get A* if i will read textbook this month ,next 2 month i will do pastpapper.

why not buddy..!! same plan here...!!

 

[ahmed butt]

there are to many topic to be read,i dont know how i will make a timetable.i dont know how many hours to study.

 

[♣♠ MagneD ♣♠]

there are to many topic to be read,i dont know how i will make a timetable.i dont know how many hours to study.

can u finish 4 chapter a day with all end of chapter questions..?? this is only the way...!!!

 

[black widow]

there are to many topic to be read,i dont know how i will make a timetable.i dont know how many hours to study.

well due to the scarcity of time, u are required to multi-study. like study 4 chapters from one sub and 4 chapters of another sub in one day
of u could study 8 chapters overall in one day.
do take breaks in between and keep studying until u dont finish the required goal u have set for the day

 

[funky brat]

well due to the scarcity of time, u are required to multi-study. like study 4 chapters from one sub and 4 chapters of another sub in one day
of u could study 8 chapters overall in one day.
do take breaks in between and keep studying until u dont finish the required goal u have set for the day

I think it's better to do the eight chapters from the same book each day and finish each subject this way otherwise you'll be confused.

 

[funky brat]

can i get A* if i will read textbook this month ,next 2 month i will do pastpapper.

I'll be doing the same and hoping for A*s.

 

[black widow]

I think it's better to do the eight chapters from the same book each day and finish each subject this way otherwise you'll be confused.

but the first one according to me is better, cuz in this age of extreme irate and easily boredom-stricken people, it wont bore the people of studying the same sub for a long period of time, by changing studied subs, one's mind can change

 

[Haidy_Ef]

Asslam Alliakom,
Please I would like to ask why the mark scheme the Question one (b) was answered as well judged best fit line
While it better to draw it as curve

So when do I draw a curve and when do I draw a line

 

[ahmed butt]

Asslam Alliakom,
Please I would like to ask why the mark scheme the Question one (b) was answered as well judged best fit line
While it better to draw it as curve

So when do I draw a curve and when do I draw a line

if only one or two points are not in line so it is best line fit . the curve part is only when there are many points are not in line.