Lab 4: determining the empirical formula for zinc chloride

objective

To synthesize a compound containing zinc and chlorine; to determine the empirical formula of the compound; to dry a solid to constant mass

safety

Hydrochloric acid is corrosive and can cause burns. The hydrogen gas that is produced in the reaction is flammable. Handle hot beakers with crucible tongs.

chemical formula

displays the composition of a substance

empirical formula

the simplest whole number ratio of each type of atom in an ionic or molecular compound

molecular formula

gives the actual number of each type of atom in a molecule of a compound

deliquescent

substances absorb enough moisture from the air to dissolve in it

hygroscopic

substances absorb moisture from the air

drying to constant mass

heating, cooling, and massing the substance until 2 consecutive masses agree within a specified range

procedure

• zinc chloride is synthesized with a displacement reaction between zinc and excess HCl

• reaction forms aqueous solution of zinc chloride with flammable hydrogen gas byproduct

• Heat the solution to evaporate liquid, leaving a white solid

• zinc chloride is difficult to dry bc it is hygroscopic

• dry to constant mass within ±0.02 g

empirical formula of zinc chloride

ZnCl₂