Chemistry: Post your doubts here!

[The Sarcastic Retard]

http://onlineexamhelp.com/wp-content/uploads/2014/08/9701_s14_qp_11.pdf
Question 3.......Help please!!!!!!!! The Ans is D
My doubt is why cant the answer be C????

Why u think C to be correct choice?

 

[qwertypoiu]

Thanks.

 

[The Sarcastic Retard]

View attachment 54871

View attachment 54872

Thanks.

 

[Tasneem_m98]

Please help! O/N 2005 p1 question 12

One mole of magnesium, aluminium, and sulphur are each completely burnt in an excess of oxygen gas. Which graph shows the moles of oxygen used in each case?
Answer is D but when i worked the equations out, I got
Mg + 1/2 O2 -> MgO
Al + 3/4 O2 -> 1/2 Al2O3
S + O2 -> SO2

And i noticed that there is a difference of 0.25 between each so i assumed it's a direct proportion hence my answer was A ( a lineat graph). However the answer is D. Please help!

 

[qwertypoiu]

Lol thank you
I've found answers now for those interested:
Calcium flame = brick red
Strontium flame = scarlet red
Barium flame = apple green.

And 2,4-DNPH makes a precipitate without the need of warming,
Whereas Tollen's and Fehling's solution require warming of mixture for results.

 

[manya]

(65 x 3 + 63 x 7) / 10 you divide by the total abundance, not 100

In your working, you should have wrongly used 100 as the dominator rather than 10.

oh okay thankyou so much

 

[princess Anu]

HNO3= Oxidising agent ( O.A)
Nh3= Reducing agent ( R.A)
NO2 =Oxidising agent
NO & SO2 =R.A
H2S= R.A

^ are these correct?

& Cl2 is a better oxidising agent than H2so4 , right?

 

[nehaoscar]

Please help! O/N 2005 p1 question 12

One mole of magnesium, aluminium, and sulphur are each completely burnt in an excess of oxygen gas. Which graph shows the moles of oxygen used in each case?
Answer is D but when i worked the equations out, I got
Mg + 1/2 O2 -> MgO
Al + 3/4 O2 -> 1/2 Al2O3
S + O2 -> SO2

And i noticed that there is a difference of 0.25 between each so i assumed it's a direct proportion hence my answer was A ( a lineat graph). However the answer is D. Please help!

I thought the same! But apparently you're meant to consider SO3 formed and not SO2

 

[shazmina]

In your working, you should have wrongly used 100 as the dominator rather than 10.

(65 x 3 + 63 x 7) / 10 you divide by the total abundance, not 100

Usually we use 100 as the Abundance right? then why in this case we have to use 10? Can you pls clarify it further

 

[shazmina]

Why u think C to be correct choice?

As its also having 2 as its value and only sign difference
How do we know that this process will be Endothermic?

 

[shazmina]

http://onlineexamhelp.com/wp-content/uploads/2014/08/9701_s14_qp_13.pdf
Question 24, help please..... The Ans is B
Why is the ans isnt C?

 

[manya]

Usually we use 100 as the Abundance right? then why in this case we have to use 10? Can you pls clarify it further

no shazmina its the addition of 3+7 as the denominator also we use 100 when npercentages are given

 

[shazmina]

no shazmina its the addition of 3+7 as the denominator also we use 100 when npercentages are given

Ohkayyyyyyyyyyy

 

[qwertypoiu]

http://onlineexamhelp.com/wp-content/uploads/2014/08/9701_s14_qp_13.pdf
Question 24, help please..... The Ans is B
Why is the ans isnt C?

Amount of heat produced = 80 * 1000 * 4.18 = 334000J
Based on energy per mole information given, you can find the number of moles of each fuel.
For methane, it's 334000/890000 = 0.375, and for methanol it comes to 0.468
Obviously, since there is lesser moles of methane, it will produce less carbon dioxide.

 

[shazmina]

Amount of heat produced = 80 * 1000 * 4.18 = 334000J
Based on energy per mole information given, you can find the number of moles of each fuel.
For methane, it's 334000/890000 = 0.375, and for methanol it comes to 0.468
Obviously, since there is lesser moles of methane, it will produce less carbon dioxide.

Thank you so much

 

[awesomaholic101]

Can you explain these:
40 Fats and grease that build up on pans used in cooking are esters. Pans which are dirty from fats
or grease may be cleaned by heating them with a reagent that will react with the ester group.
What may be used to clean such pans by this reaction?
1 vinegar - aqueous ethanoic acid, CH3CO2H
2 alcohol - ethanol, C2H5OH
3 baking powder - sodium hydrogencarbonate, NaHCO3

U still want explanation? I slept just 10 mins before u've asked ...

 

[asadalam]

U still want explanation? I slept just 10 mins before u've asked ...

Naa.chemistry bhaar nai jaey

 

[Wkhan860]

Guyx does SiCl4 produce a precipitate upon dissolving in water?

 

[awesomaholic101]

Guyx does SiCl4 produce a precipitate upon dissolving in water?

yes, it reacts with water to give SiO2 - off white ppt.

 

[awesomaholic101]

Naa.chemistry bhaar nai jaey

hw was the paper?