Baking soda is actually sodium bicarbonate.
To quantitatively capture the CO2, pass the gas evolved through sodium hydroxide and measure the mass difference after the reaction is complete. To qualitatively determine CO2, pass it through lime water (aqueous calcium hydroxide), which goes milky in the presence of CO2.
To quantitatively capture the water vapour, pass it through a tube filled with anhydrous copper(II) sulfate, and measure the mass difference. CuSO4 will also turn blue in the presence of water, making it a qualitative test as well.
The remaining powder is a source of the metal ion, but it is best to check flame tests on the original powder, to avoid sudden reactions. Dip a nichrome wire in concentrated HCl and hold it in a blue Bunsen flame until the flame colour no longer changes. Dip the wire in a sample of the powder and hold it in the flame again. An intense yellow colour indicates the presence of sodium.
