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Moles question

hi, can someone help me out with this question please?
EEAA0EA9-0011-4C44-B3FE-D7F7579D26B5.jpg.jpeg

I’ve made a start but not sure how to ascertain how much CO2 and H2O is within that mass. I was thinking of some sort of a ratio but not sure. Thanks in advance
Reply 1
Hi I am not 100% sure if this is right but this is what I think
so the decomposition of 2NaHCO3 -> Na2CO3 + H2O + CO2
so if I let the number of moles of Na2CO3 produced as x, then the equation will be
2xNaHCO3 -> xNa2CO3 + xH2O + xCO2
so xCO2 + xH2O = 10-8.708
62x = 1.292
x = 0.02084 moles
so mass of NaHCO3 = 2x0.02084x(23+1+12+16x3) = 3.501g
% of NaHCO3 = 3.501/10 x 100% = 35%
% of Na2CO3 = 1-35% = 65%
Reply 2
Original post by subbhy
hi, can someone help me out with this question please?
EEAA0EA9-0011-4C44-B3FE-D7F7579D26B5.jpg.jpeg

I’ve made a start but not sure how to ascertain how much CO2 and H2O is within that mass. I was thinking of some sort of a ratio but not sure. Thanks in advance


Step 1 - Find the unknown mass

10g-8.708g=1.292 this is the mass of CO2 and H2O collectively

Step 2 Find the moles

Moles = mass/mr
1.292/62=0.0208387…. we are dividing by 62 as it’s the mr of CO2 and H2O combined, we can do this as they are a equal molar ratio and we have a combined mass

Step 3 Molar ratio


Molar ratio is 2:1 in equation 2 for NaHCO3 to the H2O + CO2

0.0208387x2=0.041677…

Step 4- Find the mass of NaHCO3

Mass = moles x mr
Mass =84 x 0.041677
Mass=3.51g

Mass of NaHCO3 = 3.51

Step 5 find the mass of NaCO3

Mass of NaCO3 = 10 - 3.51 = 6.49 subtract from combined total of NaCO3 and NaHCO3 at the beginning

Answer:

Mass of NaHCO3 = 3.51g
Mass of NaCO3 = 6.49


Hope this helps!
Reply 3
Original post by Eunice Mak
Hi I am not 100% sure if this is right but this is what I think
so the decomposition of 2NaHCO3 -> Na2CO3 + H2O + CO2
so if I let the number of moles of Na2CO3 produced as x, then the equation will be
2xNaHCO3 -> xNa2CO3 + xH2O + xCO2
so xCO2 + xH2O = 10-8.708
62x = 1.292
x = 0.02084 moles
so mass of NaHCO3 = 2x0.02084x(23+1+12+16x3) = 3.501g
% of NaHCO3 = 3.501/10 x 100% = 35%
% of Na2CO3 = 1-35% = 65%


Thank you for your help, this is correct!
Reply 4
Original post by Maths_Duck
Step 1 - Find the unknown mass

10g-8.708g=1.292 this is the mass of CO2 and H2O collectively

Step 2 Find the moles

Moles = mass/mr
1.292/62=0.0208387…. we are dividing by 62 as it’s the mr of CO2 and H2O combined, we can do this as they are a equal molar ratio and we have a combined mass

Step 3 Molar ratio


Molar ratio is 2:1 in equation 2 for NaHCO3 to the H2O + CO2

0.0208387x2=0.041677…

Step 4- Find the mass of NaHCO3

Mass = moles x mr
Mass =84 x 0.041677
Mass=3.51g

Mass of NaHCO3 = 3.51

Step 5 find the mass of NaCO3

Mass of NaCO3 = 10 - 3.51 = 6.49 subtract from combined total of NaCO3 and NaHCO3 at the beginning

Answer:

Mass of NaHCO3 = 3.51g
Mass of NaCO3 = 6.49


Hope this helps!


Thanks very much! I was unsure about if I could do Step 2 or not

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