Determine relative amount of NaHCO3 versus Na2CO3 in a sample

 

background [prelab assignment (25 points) due at the begining of lab]

This laboratory activity is based on investigation 7 in your AP chemistry lab manual. Unfotunately, it provides minimal background / support. Nonetheless, for the following prelab questions and this laboratory activity.

assume that heating a mixture of sodium bicarbonate and sodium carbonate would only affect the former compound and it is described by the following chemical equation:

2 NaHCO3(s)    →   CO2(g) + H2O(g) + Na2CO3(s)    [reaction 1]

1. A 4.622 g mixture of sodium bicarbonate and sodium carbonate was heated, where 3.189 g of the mixture remains. What is the % NaHCO3 ? and % Na2CO3 in the original mixture ? show your work.

2. A potential alternative reaction of heating NaHCO3 would be

2 NaHCO3   →   Na2O(s) + 2 CO2(g) + H2O(g)     [reaction 2]

Using a bunsen burner and a balance, describe how to differentiate between reaction 1 versus reaction 2 ? Provide calculations to support your method / analysis, where you assume to have a 10.0 g sample of sodium bicarbonate.

3. While the preceding statements assume that heat won't affect sodium carbonate, heat could affect sodium carbonate.

Na2CO3(s)   →    CO2(g) + Na2O(s)    [reaction 3]

Using a bunsen burner and a balance, describe how to support / refute such a possibility ?

purpose

as there is some ambiguity in the effect of heat on sodium carbonate and sodium bicarbonate, clarify the situation. that is, which reaction(s) ocurr: reaction 1 ? reaction 2 ? reaction 3 ?

determine the relative amount of sodium carbonate and sodium bicarbonate in a sample; expressed as % NaHCO3 & % Na2CO3 in the sample.

compare using the hot plate versus flame as a heat source

materials

~ 2 g sodium carbonate (alone)

~ 2 g sodium bicarbonate (alone)

~ 5 g mixture of sodium carbonate and sodium bicarbonate

hot plate, balance, watch glassm glass rod

methods / data analysis

student design

content of lab report [45 points]

experimental data

data analysis (refer to your experimental data)

which reaction(s) occur upon heating the sample: reaction 1 ? reaction 2 ? reaction 3 ? support your response by referring to your experimental data and / or any calculation

calculation to determine % sodium bicarbonate in your sample based on equation 1

statistical analysis & interpretation in regards to using a Bunsen burner versus hot plate as your heat source.

error analysis on your determination of % sodium bicarbonate and % sodium carbonte ? in the sample regarding ___; justify your response

effect of insufficient heating

effect of sample was contaminated by NaCl

effect of sample containing hydrated sodium carbonate (ref ) rather than anhydrous compound (hint: you'll need to know the definition of these terms)

potential error in your calculation of % NaHCO3 in the mixture (based on reaction 1); support your response using your experimental data

while the argumentation and documentation section in investigation 7 in the AP chemistry lab manual refers to "peer review", you won't be required to do this aspect of the lab, but you might do it if you attend UCLA. nonetheless, what is the purpose / value of peer review (wikipedia; ucb) ?