Displacement Reactions-Spongy
Tin
Submitted by: Fidel Villarreal and Octavio Garcia, Institute Technol6gico de Monterrey, Monterrey S. I., Mexico Checked by: H. Ann Schnartz, Rucknell University, Lewishurg, Pennsylvania
PREPARATION
REMARKS
Provide two 600-ml heakers, stirring rod, and granular zinc (40 mesh). Prepare a 10% solution of tin(I1) chloride and 6 M hydrorhloric acid.
Hydrogen and tin are formed by the following reactions: Zn + 2HC1- H* + ZnCh Zn + SnCb Sn + ZnC4
DEMONSTRATION
Pour 200 ml of SnCL into the heaker and add 40 ml of 6 M HCI. Stir the solntion. Cover the bottom of the heaker with 2 to 3 g of granular zinc. After a few seconds spongy tin riws to the surface of the liquid.
Electrode Potentials with a Vacuum Tube Voltmeter
-
Hydrogen huhhles prevent the tin from settling to the hottom of the heaker. The sponge can he removed from the heaker in one piece with a glass st,irring rod. The experiment may he repeated ten times or more using the original solution. Concentrated hydrochloric acid and a few crystals of tin(I1) chloride may be added t o the original solution if more sponges are desired.
( Athm Ld I
I
S~tb?nzltcr/b?j: Louis Garhic, Regis College, Denver, Colorado Checked by: J. R. Brandou, hfichigan State University, East Lansing PREPARATION Prepare 1 X 1/2-in. shect or heavy foil samples of
the metals Zn, Cu, Pb, Ag, and Sn and clean with steel wool. Prepare 1 M solution of soluhle sahs of earh metal and K a S 0 3 (e.g., CuSOa, Ph(SOJ)z, SnCI:, ZnS04, AgSOJ. Cut an ll-cm filter paper as s h o ~ m in the figure and lay it on a 6-in. square glass plate. Connect a vacuum tube voltmeter to 110-v ac and set t,o 1.5-v dc range. DEMONSTRATION
Place 2 drops of 1 M CuSOa solution in one of the areas on t,he filter paper and lay t,he piece of copper on t,he moist,ened paper. Repeat t,he procedure for ZnSOn and Zn, SnClz and Sn, aod PhN03 and Ph (or AgN03and Ag) in the remaining sections. Add a drop or two of KaSOs to the central area to act as a salt bridge h e h e e n the met,al-metal ion sect,ions. Check the potentials between pairs of the metals with the vacuum tube voltmeter and record t,he readings. Concentration cells may he demonst,rated hy coinparing the voltage produced when one of t,he metals is in contact wit,h a solution of it,s salt at a ronrentration considerably different. from 1 M .
REMARKS
At the start of t,he experiment two samples of the same metal should he used in contact with the same solution of t,he metal salt, t,o show that no potential difference is indicated by t,he voltmeter. The NaN03 solut,ion ran he effect,ively used as an extremely dilute metal ion solution for concentration cell demonstrations. Comparisons hetween calculated and observed voltages are given in the t,able: Observed Cslrulxtrd
Zn-Sn
Zn-Cu
Sn-Cu
Pb-Cu
0.56 0.82
1.1
0.56 0.48
0.53
1.1
Journal of Chemirol Eduiolion
0.46
.
September 1961
