1. A student attempts to identify an unknown compound by the method used in this
ID: 892603 • Letter: 1
Question
1. A student attempts to identify an unknown compound by the method used in this experiment. She finds that when she heated a sample weighing 0.5015 g the mass went down appreciably, to 0.3432 g. When the product was converted to a chloride, the mass went up, to 0.3726 g.
a. Is the sample a carbonate? ____________ Give your reasoning.
b. What are the two compounds that might be in the unknown? ____________ and ____________
c. Write the chemical equation for the overall reaction that would occur when the original compound was converted to a chloride. If the compound is a hydrogen carbonate, use the sum of Reactions 1 and 2. If the sample is a carbonate, use Reaction 2.
Write the equation for a sodium salt and then for a potassium salt.
d. How many moles of the chloride salt would be produced from one mole of original compound? ____________
e. How many grams of the chloride salt would be produced from one molar mass of original compound? Molar masses: NaHCO3 ____________ g Na2CO3 ____________ g NaCl ____________ g KHCO3 ____________ g K2CO3 ____________ g KCl ____________ g If a sodium salt, ____________ g original compound ____________ g chloride If a potassium salt, ____________ g original compound ____________ g chloride
f. What is the theoretical value of Q, if she has an Na salt? ____________ if she has a K salt? ____________ g.
What was the observed value of Q? ____________
h. Which compound did she have as an unknown?
Explanation / Answer
multiple questions . pelase spit the rest of the question.
a) Yes, the sample seems to be a carbonate because on heating, carbonate gives off an oxide and C02 gas which leads to a reduction in the mass. However on conversion to chloride, the mass increases because chloride is bit heavier than the oxide.
b) The unknown compounds are oxide and chloride respectively.
c) The reactions are :
H2CO3 -(heat)--> H2O + CO2
Sodium
Na2CO3 (+heat) ---> Na2O + CO2
Na2O + HCl = HO + Na2Cl
Potassium
K2CO3 + high heat---> K2O + CO2
K2O + 2 HCl = H2O + 2 KCl
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