Evidences of rx

• Changes:

– Color

– Temperature

– PS: production of gas, ppt– PS: production of gas, ppt

– pH

– smell

• Fire

Replacement reaction

• A + BC � AC + B (A and B are metals)

• “Single replacement”

• What to look for Element + compound on each

side of equation

Reaction # 1

Replacement

• Zn(s) + HCl(aq) �

• 6M HCl in test tube (~ ½ full, measure)

• ~ 1 t Zn in balloon (tare balloon, weigh)• ~ 1 t Zn in balloon (tare balloon, weigh)

• Complete and balance equation, what is in the balloon at the end of the reaction? PS? – relate to stoichiometry

• What evidences that a reaction occurred?

• What is LR, ER??

Zn(s) + 2HCl(aq) � ZnCl2(aq) + H2(g)

Replacement Reaction # 2

• Zn(s) + CuSO4(s) �

• ¼ test tube copper sulfate (or copper chloride)

• Add Zinc

• Note changes, balance equation• Note changes, balance equation

Replacement Reaction # 2

• Zn(s) + CuSO4(s) � Cu(s) + ZnSO4(aq)

• If there is a limited amount of copper sulfate,

the solution will become colorless as all the

copper ions are converted to copper metal

• The Zinc ions produced are colorless

• Zinc is considered more active than copper

• Zinc “replaces” copper in the compound

– Later when we look at redox reactions

– Electrons move from Zinc (making it a soluble Zinc – Electrons move from Zinc (making it a soluble Zinc

ion) to copper (making it an insoluble metal)

– The sulfate ions are called “spectator ions” – they

do not play a part in the reaction

Reaction # 3

Replacement

• Fe(s) + CuSO4(aq) �

• Steel wool in test tube, add copper sulfate to ½ the level of the steel wool – observe– observe

• Make observations, complete balanced equation

Fe(s) + CuSO4(aq) � FeSO4(aq) + Cu(s)

Steel wool on the left,, “copper wool” on the right

Note original blue color of copper sulfate solution

In left hand solutionIn left hand solution

On the right all the copper ions have “plated out”

as copper metal, the blue color of the solution is

gone!

Reaction #4

Replacement Reaction

• Cu(s) + ZnSO4(aq) �

• ¼ test tube or beaker of ZnSO4 add copper

turningsturnings

• Observe

• Copper does not push Zinc out of a compound

spontaneously

– You can “push” this reaction in the reverse by

“pushing “ an electrical current through it!!“pushing “ an electrical current through it!!

Do all possible replacement reactions

occur?

• Activity series “what can replace what”

• Metals and H:

…….

Activity Series for MetalsCan be used to predict the outcome of replacement reactions

• Listed Most Active to Least Active

• Li K Ba Ca Na Mg--- Al Mn Zn Cr Fe Co Ni Sn PbHCu Ag Hg Pt Au

• Any element on the list can replace from a compound elements to its right

• Everything to the left of H can push H out of an acid• Everything to the left of H can push H out of an acid

• Everything to the left of the “---” can push H out of water

• Elements to the right of H do not react with acids by replacing H (copper has a redox reaction with concentrated nitric acid, but does not react with other acids)