Question

2NaHCO3 ------> Na2CO3 + H20 + CO2

I have an impure mixture of NaHCO₃ blended with NaCl. A 1.158 g sample of the mixture decomposes with heat, liberating gaseous products, and forming a final residue with a mass of 1.081 g.   Answer the following.

18. Calculate the total mass lost in the form of water and carbon dioxide.

19. Calculate the number of moles of each gas, CO₂ and H₂O, that must have been lost as a result. (Hint: they have the same coefficient and can be treated as one compound with a combined molar mass.)

20. Calculate the number of grams of sodium hydrogen carbonate that must have reacted away.

21. Calculate the percent by mass of sodium hydrogen carbonate in the original sample.

22. According to the lab text, what problem may result if you melt the mixture at an early stage in the reaction? If this were to happen, how should this throw off your calculated result for % NaHCO₃ in the mixture?

Answer 1

2NaHCO3 ------> Na2CO3 + H20 + CO2

I have an impure mixture of NaHCO3 blended with NaCl. A 1.158 g sample of the mixture decomposes with heat, liberating gaseous products, and forming a final residue with a mass of 1.081 g.   Answer the following.

18. Calculate the total mass lost in the form of water and carbon dioxide.

1.158 g of NaHCO3

mass of gases = mass of sample initially - mass of leftover = 1.158 - 1.081 = 0.077 g of gases

19. Calculate the number of moles of each gas, CO2 and H2O, that must have been lost as a result. (Hint: they have the same coefficient and can be treated as one compound with a combined molar mass.)

mol of each:

mass of water + mass of CO2 = 0.077

mol of water*MW of water + mol of CO2 * MW of CO2 = 0.077

substitute

mol of water*18 + mol of CO2 * 44 = 0.077

mol of water= mol of CO2

(18+44)x = 0.077

x = 0.077/(18+44)

x = 0.001241 mol of each species

20. Calculate the number of grams of sodium hydrogen carbonate that must have reacted away.

mass of NaHCO3 reacted

ratio is:

1 mol of NaHCO3 --> 1 mol of water

0.001241 mol of water --> 0.001241 mol of NaHCO3

mass of NaHCO3 = mol*MW = 0.001241 *84.007 = 0.104252 g

21. Calculate the percent by mass of sodium hydrogen carbonate in the original sample.

%mass of NaHCO3 = mass of NaHCO3 / mass of sample * 100%

%mass of NaHCO3 = 0.104252 / 1.158 * 100%

%mas s= 9.00 %

22. According to the lab text, what problem may result if you melt the mixture at an early stage in the reaction? If this were to happen, how should this throw off your calculated result for % NaHCO3 in the mixture?

if you fail to dry the NaHCO3 into Na2CO3... then expect a higher yield

since Na2CO3 in sample will have H2O and CO2