Question

A student attempted to identify an unknown compound by the method used in the experiment. She found that when she heated the sample weighing 0.4862g, the mass barely changed, dropping to 0.4855g. When the product was converted to a chloride, the mass went up to 0.5247g. Is the sample a carbonate? What are the two compounds that might be the unknown?

Answer 1

Answer:

The sample is a carbonate.

The unknown samples are Na2CO3 and K2CO3.

Explanation:

Let's assume ,the sample is Na2CO3.

Na2CO3 produces 2 moles of NaCl via formation of Na2O

Number of moles of NaCO3= 0.48262g/106gmol= 4.586×10^-3mol

Mass of NaCl= 2(4.586×10^-3)×58.5=0.536g

Let's assume the sample is K2CO3

K2CO3 produces2 moles of KCl

Number of moles of K2CO3= 0.4862g/138.21gmol

Number of moles= 3.517×10^-3mol

Mass of KCl formed= 2(3.517×10^-3)×74.55=0.5246g

Answer 2

Na2CO3 + 2Cl- ⇒ 2NaCl + CO3^-2 

1 mole of Na2CO3 = 106 g 
2 moles of NaCl     = 2 x 58.4
                               = 116.8 g 
Na2CO3 would increase by 116.8 / 106 = 1.10 to form 2NaCl.
0.4862 g x 1.10 = 0.515 grams of NaCl.

K2CO3 + 2Cl- ⇒ 2KCl + CO3^-2 
1 mole of K2CO3 = 138.2 g 
2 moles of KCl = 149.1 

K2CO3 would increase by 149.1 /138.2 = 1.079 to form 2KCl

 0.4862 x 1.079 = 0.5246 g