Question

A sample of air is slowly passed through aqueous Sodium hydroxide and then over heater copper.

Which gases are removed by this process?
a) Carbon dioxide and water vapour
b) Carbon dioxide and oxygen
c) Nitrogen and oxygen
d) Nitrogen and water vapour

Answer 1

Question number2

The equation explains the colour change that occurs when aqeous potassium dichromate(6), what happens to the oxidation state of the chromium and the pH of the reaction mixture?

Oxidation State of chromium pH of the mixture
a) decrease decrease
b) decrease increase
c) stays the same decreases
d) stays the same increases

Answer 2

the equation

\[K _{2}Cr_{2}O_{7} + 2KOH \rightarrow 2K_{2}CrO_{4} + H_{2}O\]
potassium potassium chromate(6)
dichromate(6) yellow
orange

Answer 3

For first question.
slowly passed through aqueous Sodium hydroxide => it should be acidic gas => CO2
then over heater copper. => copper + air = copper oxide => O2
So the answer is B

Answer 4

ON of Cr2O7^2- = +6
ON of CrO4 ^2- = +6
=> ON = unchanged

Since OH^-1 ions are consumed in the reaction, the solution becomes less alkaline => pH decreases

So the answer is C

Answer 5

Bro this was a MCQ question for my semester exam, and i wrote the same answers as u did, bt ended up with bth wrng...

Answer 6

K2Cr2O7 (oxidising agent) oxidises itself and causes the reduction of other substance ( oxidises= oxidation number increase) by the definition cant we say oxidation state increases?

Answer 7

But there is no redox reaction there.... The ON doesn't change!!!

Answer 8

but the colour changes, does it mean that it has been oxidised?

Answer 9

Nope, it's simply because the substances present are different!!!

Answer 10

so why did the colour change?

Answer 11

and why did i get it wrong..i put C as my answer and got it wrng

Answer 12

dichromate ion is orange in colour
chromate ion is yellow in colour
you can say there is a chemical conversion. But it's not a redox!!!

Answer 13

Is that all given in your question ?

Answer 14

yeah
can u explain this?
ince OH^-1 ions are consumed in the reaction, the solution becomes less alkaline => pH decreases

Answer 15

pH value is depends on the concentration of the H+ and OH- ion
As OH- is used in the reaction, its concentration decreases. Hence, the solution becomes less alkaline

Answer 16

why is it used and even f it is used (KOH is added in excess) it cn replace the lost IONS and why doesnt the pH increase

Answer 17

you haven't mentioned in the question that it is in excess nor KOH would be added continuously...

Answer 18

Okai bro...now i get it...so why s OH- used? and how?

Answer 19

bro this is a part of the question?
as a result of adding an excess of aqueous potassium hydroxide to aqueous potassium dichromate (6), what hapens to the oxidation state of the chromium and the pH of the reaction mixture

Answer 20

in the equation , KOH is one of the reactants, if the reaction takes place, of course it would be consumed :S

Answer 21

hm ok but KOH is added in excess...thts in the question

Answer 22

and my answer was D actually and got it wrng

Answer 23

even so, the pH would not increase lol, it would only decrease because OH is consumed
BTW, my answer is C, not D , judge my answer again, I still can't believe my answer is wrong :P

Answer 24

hehe, okai then thats the answer fine ( i just mixed this with neutralisation reaction ) so thts why i got it as pH increased. anyway thnks bro...u r a genius ur answers wnt be wrng :P

Answer 25

I'm not a genius and I always get wrong in chem :S

Answer 26

bro i have another question can u just tell me how to work this out?

Answer 27

Silver ions react with chloride ions
\[Ag ^{+}(aq) + Cl^{-}(aq)\rightarrow AgCl (s)\]

It is found that 5cm^3 of a 0.1 mol/dm^3 solution of the chloride metal x needs 10 cm^3 of 0.1 mol/dm^3 of silver nitrate for the complete reaction

what is the formula of the chloride?
\[XCl_{4}\]
\[XCl_{2}\]
\[XCl\]
\[X_{2}Cl\]

Answer 28

no. of mole of metal chloride = 5/100 *0.1= 0.005 mole
No. of mole of silver nitrate= 10/100 * 0.1 = 0.01 mole
From the equation ,
no. of Cl ion used = 0.01mol
Therefore there are 0.01/0.005 = 2 Cl- ions in each metal chloride
the formula = XCl2

Answer 29

From the equation , no. of Cl ion used = 0.01mol ?

Answer 30

Ag + Cl -> AgCl
no of mole of Cl = no of mole of Ag = 0.01 (used in the reaction)

Answer 31

Ag+(aq) + Cl-(aq) -> AgCl(s)

Answer 32

why dont we take metal chloride? 0.005

Answer 33

i just concentrate on the Cl- in that case
No. of mole of Cl- used / no. of mole of metal chloride used = no of Cl- in each metal chloride

Answer 34

if u dont mind can u explain it a bit further, cuz i did it in another way and gt the answer

Answer 35

Like MgCl2 + 2AgNO3 -> Mg(NO3)2 + 2AgCl
no of mole of Ag = 0.01
no of mole of MgCl2 = 1/2 *no of mole of Ag = 0.005
Hmmm.. it's really difficult for me to explain :S

Answer 36

okai its alright..thnks i thnk i get it...are u a guy or a girl?

Answer 37

girl !

Answer 38

LOL, i was calling u a "bro" from the beginning...dint u hve the mind to corrct me?

Answer 39

ppl said they use 'man' to call sb... I guess it's similar ... I've thought of correcting you.. but ..anyway...

Answer 40

so what are you doing (exams and stuff)?

Answer 41

Hmm???

Answer 42

u r doing any exams? which grde are u in?

Answer 43

Yup exams, i assume it's grade 12 as you would call, the grade before uni.

Answer 44

oh alright...is it igcse?

Answer 45

Nope, it's called DSE here

Answer 46

so after exams engineering eh?

Answer 47

engineering is tough... I don't know :S

Answer 48

hm nothing is easy, if u thnk it as hard u will never do it:)

Answer 49

Hmm.. engineering doesn't seem to be a good subject for ordinary girl like me :P

Answer 50

haha...so what r u planning to do then? i guess u have the potential to work for it..cz u seem to clear my doubts which i thnk is sumthng great :) my advice is tht u go for it..

Answer 51

Chemistry.... It's not my cup of tea :P
No exact planning at the moment. It's something after the exam :) Though, I've ranked my uni choices

Answer 52

oh...something great to hear....LOL..btw u all r awarded with scholarships? or do u all pay for the whole course?

Answer 53

@CAllisto u there??????????????????

Answer 54

Don't understand... Sorry :S