A candle flame produces easily seen specks of soot near the edges of the flame, especially when the candle is moved. A plece of glass held over a candle flame will become coated with soot, which is the result of the incomplete combustion of candle wax. Elemental
analysis of a compound extracted from a sample of this soot give these results: 7.74% and 92.26% C by mass. Calculate the
empirical formula of the compound.

"you start with 15.67 g mgco3-xh2o, when heated and all the water is removed, you are left with 7.58 g mgco3 only.

therefore, you had 15.67 - 7.58 = 8.09g h2o  

moles of each :

7.58g mgco3 = ? moles = 7.58g / 83.4g/mole = 0.09moles  

8 09g h2o = ? moles = 8.09g / 18g/mole = 0.44moles  

molar ratio between the two by dividing both numbers by the smallest number :

0.09 / 0.09 = 1  

0.44 / 0.09 = 4.8  

mgco3-5h2o"

if you mean hydrogen and oxygen then water is the product

your answer is a. the enthalpy of formation for a pure element in its standard state is always positive.

c. electrical charges of ionic bonds.