Experiment 6.4
The Synthesis of Zinc Chloride

Purpose:
What happens when a metal is dissolved in an acid?

Caution:  always wear goggles when you work with acids.  Be careful not to spill any of the solution

Materials

Pegboard
lg. Clamp
5 zinc pieces
Graduated cylinder   
evaporating dish
Burner stand 

Balance
6M HCl (10 cm3)
water
Matches 
wood splint
goggles


Lg. Test tube
Beaker 
paper towels
burner 

:Procedure:

  1. Everyone will use the 10 cm3 of HCl.  Every group will use a different amount of zinc
  1. Mass an exact amount of zinc between .5g and 4 g.  Place the zinc in the test tube and add 10.0 cm3 of HCl.
  1. Place the test tube in a beaker of cool water. This will slow the reaction down.  At first the reaction will be vigorous.  However, to make sure the reaction is complete, allow the mixture to stand overnight. 


Next day

  1. pour the liquid form the test tube into an evaporating dish that you have already massed.  If there is still a piece of zinc that has not reacted, make sure that it stays in the test tube.
  1. Wash the test tube, and any remaining zinc with 5 cm3 of water.

  • Why should you add the washing water to the evaporating dish?

  1. Dry the left over zinc (from the test tube), and mass it.

  • How much of the metal reacted with the hydrochloric acid?

  1. Place the evaporating dish on the burner stand and heat it SLOWLY dry the solution.  Control the splattering by removing the burner when necessary.
  1. Continue heating until the solid appears to melt and a tiny pool of liquid forms in the bottom of the evaporating dish.
  1. Mass the dish and its contents when it cools.

  • What is the ratio of the mass of zinc reacted to the mass of zinc chloride formed?

  • Compare your results with those of your classmates.  Did an excess of either zinc or hydrochloric acid affect your results?

  • If the zinc chloride were not completely dry when massed, how would this affect your ratio?