A chemistry mcq question...

[balloonsandhighlighters]

22)why is it D? The examiner said, ''Zinc is not a very reactive metal and neither its carbonate nor its hydroxide is soluble in water"... but what does solubility have to do with reacting with acid? I don't get what the examiner said nor do i get why the answer is D... can you help please? Thanks a lot..
btw the paper is june 2008 !
26) i thought it would be B because if you write down the electronic confg., it would make sense that it forms a + charge... thanks!!!!!!

 

[Skynox]

View attachment 12186View attachment 12184 View attachment 12184
22)why is it D? The examiner said, ''Zinc is not a very reactive metal and neither its carbonate nor its hydroxide is soluble in water"... but what does solubility have to do with reacting with acid? I don't get what the examiner said nor do i get why the answer is D... can you help please? Thanks a lot..
btw the paper is june 2008 !
26) i thought it would be B because if you write down the electronic confg., it would make sense that it forms a + charge... thanks!!!!!!

For question 26,you should have a look at the periodic table..Element with proton number 35 is bromine so how come it is a postive charge?It's obvious that the answer is 37 which belongs to Rubidium in Group I
For 22,if you used Zinc hydroxide agains sulfuric acid that it is titration....Titration method is used for a strong group I alkali and a strong acid,probably..Plus,zinc hyrodxide is an insoluble base...
Titration used for a soluble base,alkali, and an acid.So that's the use of solubility here,

 

[balloonsandhighlighters]

For question 26,you should have a look at the periodic table..Element with proton number 35 is bromine so how come it is a postive charge?It's obvious that the answer is 37 which belongs to Rubidium in Group I
For 22,if you used Zinc hydroxide agains sulfuric acid that it is titration....Titration method is used for a strong group I alkali and a strong acid,probably..Plus,zinc hyrodxide is an insoluble base...
Titration used for a soluble base,alkali, and an acid.So that's the use of solubility here,

i undestand 26 now but not 22... what does titration have to do with the question, it doesn't mention it.... thanks for explaining though..! if you could explain 22 that would help a lot

 

[Skynox]

i undestand 26 now but not 22... what does titration have to do with the question, it doesn't mention it.... thanks for explaining though..! if you could explain 22 that would help a lot

Okay he asks about how to make a solution of zinc sulfate..
For this you may do the following:
-Adding zinc to dilute sulfuric acid.that way you will obtain zinc sulfate and hydrogen.
-Adding zinc oxide/hydroxide to dilute sulfuric acid that you obtain zinc sulfate and water.
-Adding zinc carbonate/hydrogen carbonate to diulute sulfur acid,that way you obtain zinc sulfate and carbon dioxide and water.
He needs to know wat state are these reagents added:
Either solid or aqueous..
Consider you chose that zinc hydroxide is aqueous,this is impossible since zinc hydroxide is an insoluble base so zinc hydroxide aqueous is not available..
For the bases,the only soluble bases are Group I hydroxide/carbonates , Ammonium hydroxide ammonium carbonate...
So for example zinc hydroxide is impossible to exist as aqueous since aqueous means in soultion or dissolved in water which is impossible..

 

[balloonsandhighlighters]

.

Okay he asks about how to make a solution of zinc sulfate..
For this you may do the following:
-Adding zinc to dilute sulfuric acid.that way you will obtain zinc sulfate and hydrogen.
-Adding zinc oxide/hydroxide to dilute sulfuric acid that you obtain zinc sulfate and water.
-Adding zinc carbonate/hydrogen carbonate to diulute sulfur acid,that way you obtain zinc sulfate and carbon dioxide and water.
He needs to know wat state are these reagents added:
Either solid or aqueous..
Consider you chose that zinc hydroxide is aqueous,this is impossible since zinc hydroxide is an insoluble base so zinc hydroxide aqueous is not available..
For the bases,the only soluble bases are Group I hydroxide/carbonates , Ammonium hydroxide ammonium carbonate...
So for example zinc hydroxide is impossible to exist as aqueous since aqueous means in soultion or dissolved in water which is impossible..

THANK YOU SO SO SO MUCH I LOVE YOU

 

[balloonsandhighlighters]

I know i'm annoying you now, but i just wanna ask a tiny question...
the examiner said , ''The insolubility of zinc hydroxide is in the syllabus – from the use of sodium
hydroxide in testing for aqueous zinc ions. '

I do not understand at all how we could get this fact ( that zinc hydroxide is insoluble) from the use of sodium hydroxide in testing blah blah blah.

but thats ok because i can just memorise it

problem is, is there anything else we're supposed to figure out from the qualitative analysis thing? Thanks a bunch and im truely thank ful for ur help!

 

[Skynox]

I know i'm annoying you now, but i just wanna ask a tiny question...
the examiner said , ''The insolubility of zinc hydroxide is in the syllabus – from the use of sodium
hydroxide in testing for aqueous zinc ions. '

I do not understand at all how we could get this fact ( that zinc hydroxide is insoluble) from the use of sodium hydroxide in testing blah blah blah.

but thats ok because i can just memorise it

problem is, is there anything else we're supposed to figure out from the qualitative analysis thing? Thanks a bunch and im truely thank ful for ur help!

Anytime and better know it from the insoluble bases..The only soluble bases are as mentioned above

 

[Rahma Abdelrahman]

For Q.22, when it is mentioned "excess", then the reagent should be in solid state.
For Q. 26, you have to look at the periodic table and find a group 1 metal with the correct proton no.

 

[Skynox]

For Q.22, when it is mentioned "excess", then the reagent should be in solid state.
For Q. 26, you have to look at the periodic table and find a group 1 metal with the correct proton no.

Acids can be in excess too...solids are not the only those who exist as excess..Even gases can be in excess...

 

[Rahma Abdelrahman]

But the Q. is only asking about the Zn compounds !

 

[Rahma Abdelrahman]

Acids can be in excess too...solids are not the only those who exist as excess..Even gases can be in excess...

But the Q. is only asking about Zn compounds!

 

[Rahma Abdelrahman]

Another question (Nov. 2010):

The answer in the ms is B, but I believe it should be A as temp. decreases in an endothermic reaction.

 

[TERMINATOR]

Another question (Nov. 2010):
View attachment 12299
The answer in the ms is B, but I believe it should be A as temp. decreases in an endothermic reaction.

I faced exactly the same problem while doing that question. So i use a method keeping in mind "evaporation is a cooling process" which is a fact-meaning temp. decreases during the process. So here, when steam is given off (evaporation), there is a temp. decrease. But they're doing sth opposite that is adding water, hence the temp. will increase. hope this method helps...

 

[Rahma Abdelrahman]

I faced exactly the same problem while doing that question. So i use a method keeping in mind "evaporation is a cooling process" which is a fact-meaning temp. decreases during the process. So here, when steam is given off (evaporation), there is a temp. decrease. But they're doing sth opposite that is adding water, hence the temp. will increase. hope this method helps...

Thanks, it really helps !
Another method: you need to supply heat to remove water from the crystals, hence an endothermic reaction. Verily, the reverse reaction is an exothermic one so temperature increases!