1. A student attempts to identify an unknown compound by the method used in this

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 0.5032 g the mass barely changed, dropping to 0.2663 g. When the product was converted to a chloride, the mass went up, to 0.3747 g.

a. Is the sample a carbonate? Yes

b. What are the two compounds that might be in the unknown? KHCO3 and NaHCO3?

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? _____ 1?

e. How many grams of the chloride salt would be produced from one molar mass of original compound? Molar masses: NaHCO3 84.008 g Na2CO3 105.99 g NaCl58.44 g KHCO3 100.118 g K2CO3 138.21 g KCl 74.55 g

If a sodium salt, ____________ g original compound ____________ g chloride 58.44 g; 35.5g

If a potassium salt, ____________ g original compound ____________ g chloride 74.6g; 35.5g

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?

The answers I think I know are bolded...please help and let me know if it's right. Try to show me steps for F-H I am unsure how to do it.

Explanation / Answer

(a) The sample is a crabonate compound. As, upon heating, essentially CO2 will be released andtotal mass of the sample would get reduce. Example rxn CaCO3 --> CaO + CO2

However the conversion of product to chloride results in increase in the mass as chlorine is heavier than the oxide.

(b) Unknow compounds can be NaHCO3 and KHCO3, Na2CO3 also.

(C) Reactions

Heating

2NaHCO3 ---> Na2CO3 + H2O + CO2

Na2CO3 + HCl --> 2NaCl + H2O + CO2

Simialar equations can be written for KHCO3.

Na2CO3 +heat ---> Na2O + CO2

Na2O + HCl = HO + Na2Cl

Potassium

K2CO3 + heat---> K2O + CO2

K2O + 2 HCl = H2O + 2 KCl

(d) If it is bidrocarbonate, 1 moles of chloride will generate.

If it is carbonate, 2 moles of chloride will gernerate

(e)

1 mol NaHCO3 weigh 84.008 g will produce 1 mol of NaCl which weigh around 58.5 g

1 mol Na2CO3 weigh 105.99 g will produce 2 mol of NaCl which weigh 117 g

1 mol KHCO3 weigh 100.118 g will produce 1 mol of KCl which weigh 74.5 g

1 mol K2CO3 weigh 138 g will produce 2 mol of KCl which weigh 149 g ((increase in the mass)

0.5032 g NaHCO3 can form 0.3504 g NaCl

0.5032 g Na2CO3 can form 0.5555 g NaCl

0.5032 g KHCO3 can form 0.3749 g KCl

0.5032 g K2CO3 can form 0.5430 g KCl

(f)

Q is 0.5555 g if she has Na salt

Q is 0.5430 g if she has K salt

g. The observed value of Q is: 0.5430 g

h. The compound she has is K2CO3

This is long question. Please split the probelm.

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