Question on both SS and chem

last SG · 2009-11-01T13:14:41+00:00

acidity is measured by the concentration of H+ or OH- in the solution so the concentration of an acid or alkali will affect acidity.SS idk, too long din take...

ItchyArmpit SG

another question.

A student says that the perfume does not diffuse but is carried around by the air currents. What can you do to check?

edit: nvm i know le.. for those curious, it is to drop a few drops of liquid bromine in a gas jar. The bromine evaporates to fill the gas jar with reddish-brown vapour. Place another gas jar full of air above the gas jar filled with bromine vapour. Remove the lid that is separating the two gas jar, u will see the reddish-brown vapour filling up the whole 2 gas jar even though it is denser than air.

(disclaimer: i saw this answer in my textbook)

ItchyArmpit SG

another chem question.

when a reaction occurs, and the temperature decreases, is it an endothermic or exothermic reaction?

my answer is endothermic, because take in heat energy.. correct?

darkhour SG

temperature of what decreases?if temperature of surrounding decreases, yes its endothermic, if temperature of solution decreases then different liao...

yiha093 SG

temperature of what decreases?if temperature of surrounding decreases, yes its endothermic, if temperature of solution decreases then different liao...

but technically it is not possible to measure the tmep of 'reacting particles'

u can only measure temp of soln and surrounding ( both are same)

i dun understand wth u talking about 1b)

its freaking vague.

ItchyArmpit SG

the temperature will affect the surrounding too... so it is about the same.. so i guess it is endothermic right?

1b) the question is actually asking why we do not let the water enter from the top of the condenser and leave from the bottom of the condenser?

ItchyArmpit SG

dkcx SG

ok thanks!

urmm another question...

1. In distillation
a) where does the water enter and leave the condenser?
b) why do we not let it flow int he opposite direction?

2.

a)Where is the bulb of the thermometer placed?

b) what temperature does it show?

please see if my answer is correct or wrong... and for 1b) i totally dont know.

1a) Water enter from the bottom of the condender and leave from the top of the condenser. (is it right to say bottom and top of condender? it feels wierd to say that)

1b) i totally dont know

2a) The bulb of the thermometer is placed above the solution being distillated and near the entrance of the condenser.

2b) It shows the temperature of the boiliing point of the substance in the mixture which has the lowest boiling point, followed by the next higher boiling point and continue to the highest boiling point of the substance in the mixture.

i feel that all my answers sounds wierd. please give me ur model answer, and please elaborate and explain more on 1b). thanks!

1a) Should be fine to say that

1b) If you let the water in from the top, it will not fill the condensor fully before the water leaves from the bottom. This will not enable adequate cooling as little water will actually reach the entire middle tube which needs to be cooled for condensation to occur.

2a) Yes you have to place the bulb of the thermometer near the entrance to the condensor as you are measuing the temperature of the gas entering the condenser.

b) I would write a simpler answer along the lines of it will show the boiling point temperature of each fraction in the mixture depending on how many marks this question is worth.

ItchyArmpit SG

temperature of what decreases?if temperature of surrounding decreases, yes its endothermic, if temperature of solution decreases then different liao...

in what way is it different? isnt it that the surrounding becomes cold because the energy is taken in by the solution?

dkcx SG

Yes its endo

ItchyArmpit SG

1a) Should be fine to say that

2a) Yes you have to place the bulb of the thermometer near the entrance to the condensor as you are measuing the temperature of the gas entering the condenser.

b) I would write a simpler answer along the lines of it will show the boiling point temperature of each fraction in the mixture depending on how many marks this question is worth.

wow.. i somehow really find ur answer dam useful... i understood the minute u said it! thanks!!

dkcx SG

wow.. i somehow really find ur answer dam useful... i understood the minute u said it! thanks!!

no prob :)

ItchyArmpit SG

ok i suddenly thought of this so called conception doubt i have for a long time..

here it goes

i have learnt that oxides of metal are basic oxides, they dissolve in water to react with acids.

oxide of non-metals are acidic oxides, they dissolve in water to react with alkaline.

does that mean that ALL metal oxide are soluble? which are not?
does that mean that ALL non-metal oxide are soluble too? which are not?

also, in solubility table, we learn that ALL carbonates are insoluble EXCEPT sodium, potassium and ammonium. we also learn that ALL hydroxides are insoluble EXCEPT sodium, potassium, ammonium, and calcium(slightly)

then i came across this thing b4.. because of my lousy teacher teaching (i am not blaming, it is the truth) i do not know anything now and is very doubtful of the solubility table.

she said that lithium hydroxide are soluble, because lithium is the same group as sodium and potassium, and therefore has the same characteristics. therefore lithium hydroxide is soluble.

she also said that lithium hydroxide and lithium oxide is about the same thing, therefore they are soluble. then next day, i put lithium oxide is soluble, she said no, i rebutt by saying that all metal oxide are soluble and dissolve in water to react with acid.

she said that solubility table nv say lithium hydroxide is soluble, therefore not soluble.. lithium hydroxide and lithium oxide is about the same.. therefore lithium oxide is NOT soluble.

now, i got many questions from all these.

1) is lithium hydroxide soluble in water?
2) is lithium oxide about the same as lithium hydroxide?
3) if all metal oxides are basic, does that mean all metal hydroxide is basic?
4a) does the grouping in periodic table affect the solubility of compounds?
4b) if lithium hydroxide is soluble, then why solubility table do not have lithium hydroxide being soluble?

(for question 4, example, since potassium hydroxide is soluble, and alkaline, does that also means that Rubidium or lithium hydroxide is also soluble and alkaline?)

5) so is ALL non-metal oxides soluble and is acidic?
6) is ALL metal oxides soluble and basic?

please please please clear my doubts.. i think i have a very serious conception mistake here. thanks a lot for helping!

ItchyArmpit SG

ok guess i am being lazy.. now i found the answer to a few of my questions being asked.

1) yes lithium hydroxide is soluble in water and forms alkalis (react with water to form alkali and hydrogen gas)

2) i do not know. (btw, if they are about the same, in what way they are same, and what are the difference?)

3) i also do not know

4) i think i had asked a bit vague... i shall rephrase, lets not use group I metals. for example, lead chloride is insoluble. does that also mean lead bromide, lead iodide, lead halogens are insoluble? same goes for silver...

5) i dunno
6) i dunno

qdtimes2 SG

I may be wrong too though.

5)All metal oxides all basic and not all of them are soluble in water except for the common metals, Sodium and Potassium. However, they all dissolve in acid.

6)All non-metal oxides are acidic but not all of them are soluble in water too. E.g. Silicon dioxide, sand.

3) Metal hydroxides are basic but are called alkalis because they dissolve in water.

The solubility of salts seem to decrease as the reactivity of the metal ion in it decreases too. My teacher said something about the size of the metal ions but I'm not convinced..

ItchyArmpit SG

ic thanks a lot!

now another question.

metal oxide are metal oxide... but when dissolve in water, wat are the ions?

metal ions, H+, OH- but since it is metal oxide and NOT metal hydroxide, the ions O2- <---- is there such thing?

or issit that the metal oxide dissolve in water to from metal hydroxide and then the ions become H+ metal ions and OH-

qdtimes2 SG

the metal oxide dissolve in water to from metal hydroxide and then the ions become H+ metal ions and OH-

dkcx SG

ok i suddenly thought of this so called conception doubt i have for a long time..

2) Li2O is a base, LiOH is an alkali, thats the only slight difference as 1 is solid 1 is aq.

3) All basic oxides form basic hydroxides. However do not that not all metal oxides are basic.

4) The trend should be similar. However do note that insoluble is a relative term and almost all salts might be soluble to a very very small degree and the series gor eg F to I will vary very slightly in their solubility but nothing too major generally to change the general pattern.

5,6) Not all metal and non metal oxides are soluble in water but most acidic and basic oxides are. Neutral oxides and amphoteric oxides are mostly insoluble.

To qdtimes2: SiO2 is a neutral oxide not acidic.

dkcx SG

Basic oxides (not all metal oxides) that dissolves in water will all form their respective hydroxides.

For O's level, O2- does not exist.

ItchyArmpit SG

wow.. i really got mixed up there...

but luckily u guys helped.. thanks a lot really!

dkcx SG

wow.. i really got mixed up there...

but luckily u guys helped.. thanks a lot really!

Remember that u all study 4 types of oxides and not just acidic and basic. Do not mix up the 4 different kind of oxides and their respective properties.

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