A student attempted to identify an unknown compound by the method used in this e

Question

A student attempted to identify an unknown compound by the method used in this experiment. she found that when she heated a sample weighing 0.4826 g, the mass barely changed, dropping to 0.4855 g. when the product was converted to a chloride, the mass went up, to 0.5247 g.

Is this a carbonate? if so why or why not?

What might the two unknown compounds be?

Explanation / Answer

Good question, Andrew! Not a carbonate. When a substance is heated, you can have dehydration- X(OH)2 -----> XO + H2O We know how much mass belongs to XO and how much belongs to H2O. We also know the molecular weight of H2O and can calculate the number of moles of H2O. The number of moles of XO is equal to moles H2O. So, know moles of XO we can back calculate molecular weight and the contribution from element X. Total mass: .5015 g Mass of XO: .3432 Mass H2O: .1583 Moles H2O= .1583/18= 0.00879 = moles of XO= 0.00879 MW of XO= 0.3432/.00879= 39.044 (round to 39) Oxygen contributes 16 to the molecular weight; element X contributes 23. As it happens, Sodium (Na) has

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