Unit 3B Chemistry :) How was the exams? Comment here :P

[cardude456]

yh..............???

 

[qstar.inc]

Mine
2P+3I2 -2PI3
...do u think its correct?

I wrote the same.

 

[qstar.inc]

it was caco3 calcium carbonate

Ca(CO3)2 isn't it?​

 

[qstar.inc]

i messed up in the last questn... btw what were ur answers to the calculations?

me too... messed up there

 

[qstar.inc]

in calculating the energy of the reaction were we supposed to use 50 or 55?

i used 55

 

[-Edge-]

The paper sucked!
What was the mass in the specific heat capacity? 50 or 55?
And the enthalpy change?

 

[qstar.inc]

The paper sucked!
What was the mass in question 2...the specific heat capacity? 50 or 55?
And the enthalpy change?

i used 55 but not sure abt it.

 

[cardude456]

i used 50

 

[-Edge-]

i used 55 but not sure abt it.

I used 55 too.

 

[blossom edward]

srsly.....it was 55...dont tell me....till now i got approximately alll right answers...but...noooooooooooooooooooooo....plz say its 5o..plz..plz.plz!! :/

 

[alex]

50 is the correct value to use
the mass of zinc is not used in the calculation of the heat energy b/c its heat capacity is very small.

 

[nadee_W]

i think it should be 50 because 50cm3 is multiplied by the density of water-1g/cm3 (density=mass/volume so mass=density*volume)...and Zn does not have a similar density as water coz its a solid..

 

[blossom edward]

50 is the correct value to use
the mass of zinc is not used in the calculation of the heat energy b/c its heat capacity is very small.

haaaan...u serious...plz let it be 50...ooo.ALLAH....
INSHALLAH the curves will be low INSHALLAH!!

 

[alex]

in calculating the energy of the reaction were we supposed to use 50 or 55?

50

Some questions I remember:

1) Why do you add the Iodine in small quantities?
2)Why use anhydrous calcium sulphate?
3) What is the 9th step?
4) Why is this question not suitable for large-scale manufacturing? (last question)

oh also
Why observations would you see when you add NaI to ---- don't rem?

1)the reaction is highly exothermic
2)because it is a drying agent
3)i dont remember
4)- low atom economy (only 33% of the products is the desired one)
-economic reasons since there is going to be a lot of storage for by-products


5) add AgNO3, then the precipitate is yellow and insoluble in excess NH3

Hey guys wat did ya write for improving d accuracy of the experiment using stop watch?

- weight about 5 grams of zinc using a balance and 50 cm3 of CuSO4 using a pipette
-keep measuring the temperature for about 3 minutes stirring the mixture
-then add zinc at 3.5 minutes and keep recording the temperature for about 5-10 minutes after the addition of the solid every 1 minute
-draw a cooling curve (temperature against time) and extrapolate the lines and find the maximum temperature @ 3.5 minutes (when you added zinc).
-max T- initial T= dT

The formula of red phosphorus is P4 (i think) so i wrote:
P4 + 6I2 ==> 4PI3 but i ain't sure.


This is what i wrote. I don't know if what is said is correct :/

 

[Missyyy]

The formula of red phosphorus is P4 (i think) so i wrote:
P4 + 6I2 ==> 4PI3 but i ain't sure.


This is what i wrote. I don't know if what is said is correct :/

I wrote the same! Hope its correct

 

[jtbteddy]

Yes, the first one said that sulfate was absent, therefore, you had to say that there was no ppt. I messed up on the last question too Pretty hard paper. I expected graphs to come up sincce they come up every year, and they're quite easy, but they didn't
One more thing, for the diagram of distillation, I don't know why, but I put the thermometer in a test tube. It was in the correct place, but I just put it in a test tube, I don't know why, how many marks do you reckon I'd get out of 3?

I checked mark schemes of previous years for that diagram, the marks are for:
"Round-bottomed/pear-shaped flask (and
contents) and heat/mantle/water bath (1)
Still-head with stoppered thermometer
opposite opening to condenser (1)
Condenser with water flowing up(1)
Collection of product from an unsealed
apparatus either as shown or from a delivery
tube into a flask/beaker or straight from the
condenser into flask/beaker. (1)"

I did all the above perfect, except I put the thermometer in a test tube How much would I get for it?

 

[qstar.inc]

I wrote the same! Hope its correct

its the correct one: 2 P + 3 I2 = 2 PI3
check here: http://www.webqc.org/balance.php?reaction=P%2BI2%3DPI3

 

[qstar.inc]

can anyone tell specifically about the question about stop clock???

 

[jtbteddy]

can anyone tell specifically about the question about stop clock???

alex replied to that already,

- weight about 5 grams of zinc using a balance and 50 cm3 of CuSO4 using a pipette
-keep measuring the temperature for about 3 minutes stirring the mixture
-then add zinc at 3.5 minutes and keep recording the temperature for about 5-10 minutes after the addition of the solid every 1 minute
-draw a cooling curve (temperature against time) and extrapolate the lines and find the maximum temperature @ 3.5 minutes (when you added zinc).
-max T- initial T= dT

 

[qwerty123123]

its obviously 50g coz its the mass of the solution, the solid doesn't matter. For how do you know if iodine is still present, I put pink colour because iodine is pink in alcoholic solvent right?