CHEM PAPER 3 DOUBT... PLEEEZ HELP

[Violettamee]

How do u solve the 2nd two questions here :-

btw they ARE from iGCSE papers ... 1993 M/J

(click on the attachemnt below ... it has the mark scheme too ) :-

 

[gary221]

d first ques-
to caculate no. of moles 4 a gas, the formula is moles = volume(in dm3)/24
so moles of CO2 = 120/24 = 5 moles

for d second one in the equation, we can see that to produce 1 mole of CO2 2 moles of NaHCO3 is needed
so value for y is 2

for the third one it is said tht one mole of either carbonate produces one mol of CO2
5 moles of CO2 were made and 2 moles of NaHCO3 were present
so x = (5-2) = 3moles

hope u got it!!

 

[Violettamee]

d first ques-
to caculate no. of moles 4 a gas, the formula is moles = volume(in dm3)/24
so moles of CO2 = 120/24 = 5 moles

for d second one in the equation, we can see that to produce 1 mole of CO2 2 moles of NaHCO3 is needed
so value for y is 2

for the third one it is said tht one mole of either carbonate produces one mol of CO2
5 moles of CO2 were made and 2 moles of NaHCO3 were present
so x = (5-2) = 3moles

hope u got it!!

i dont understand why u subtract 5-2 to get 3 :////
why subtract ????????

 

[gary221]

d first ques-
to caculate no. of moles 4 a gas, the formula is moles = volume(in dm3)/24
so moles of CO2 = 120/24 = 5 moles

for d second one in the equation, we can see that to produce 1 mole of CO2 2 moles of NaHCO3 is needed
so value for y is 2

for the third one it is said tht one mole of either carbonate produces one mol of CO2
5 moles of CO2 were made and 2 moles of NaHCO3 were present
so x = (5-2) = 3moles

hope u got it!!

i dont understand why u subtract 5-2 to get 3 :////
why subtract ????????

1 mole of either CO3 will give u 1 mole of CO2
so u hve 5 moles of CO2
thus no of moles of total CO3 = 5
see u alredy hve 2 moles of NaHCO3
terefore moles of NaCO3 = 5-2 = 3
hope u got it!!

 

[Violettamee]

d first ques-
to caculate no. of moles 4 a gas, the formula is moles = volume(in dm3)/24
so moles of CO2 = 120/24 = 5 moles

for d second one in the equation, we can see that to produce 1 mole of CO2 2 moles of NaHCO3 is needed
so value for y is 2

for the third one it is said tht one mole of either carbonate produces one mol of CO2
5 moles of CO2 were made and 2 moles of NaHCO3 were present
so x = (5-2) = 3moles

hope u got it!!

i dont understand why u subtract 5-2 to get 3 :////
why subtract ????????

1 mole of either CO3 will give u 1 mole of CO2
so u hve 5 moles of CO2
thus no of moles of total CO3 = 5
see u alredy hve 2 moles of NaHCO3
terefore moles of NaCO3 = 5-2 = 3
hope u got it!!

ohh ok ... thnx dude !!!! :Yahoo!: :Yahoo!: :Yahoo!: