Transcript Reactivity of Metals - Windham School Department, Windham

Reactivity of Metals
Laboratory
Purpose
•To measure the relative reactivities
of selected metallic elements.
Background
• Elements have different uses depending
on their reactivity.
• Gold is commonly used in jewelry because
it is so resistant to chemical reactions.
• Sodium is not used in jewelry because it
explodes when it contacts water.
• Differences in chemical reactivity depends
on the relative ease with which elements
give up electrons.
Background, cont.
• You can measure relative reactivity of two
metals by placing a sample of one metal in
a solution of the ions of the other metal.
• If the solid metal sample is more reactive,
electrons will move from the metal into the
solution and the solid sample with become
ions and dissolve.
• Meanwhile, the less reactive ion sample
will take the electrons and form a solid.
Background, cont.
• This is an example of a redox reaction
because electrons are transferred from
one species to another.
• If the solid sample is less reactive than the
ionized metal solution, no reaction will
occur.
Your Mission
• To test the reactivities of a variety of metals with
different metal ions.
• To write chemical equations for each reaction
that occurs.
• To then use the results of your tests to construct
a scale of relative reactivities of the metals.
• To write electron configurations for each metal
and attempt to explain relative reactivity based
on electron configuration.
Materials needed per pair
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Goggles and aprons; gloves are recommended
Well plate
Dropper pipets
Forceps
Steel wool or sand paper (to polish any corroded solid metal
samples)
Chemicals
supplied
•Copper wire or mesh
•Zinc pellets or foil
•Magnesium ribbon
•2.5% lead(II) nitrate solution
•0.1% silver nitrate solution
•2.5% copper(II) nitrate solution
•2.5% magnesium nitrate solution
•2.5% zinc nitrate solution
•2.5% sodium nitrate solution
Caution!
•Be familiar with the hazards associated with
chemicals before handling them!
•Read bottles, refer to MSDS information, ask
questions.
Procedure
• Labs need to be written in the 3rd person, singular,
present tense, neutral gender.
• Instead of “add 5 drops of copper nitrate solution” write
“5 drops of copper nitrate solution is added”
• Instead of “we added the magnesium to the test tube”
write “magnesium is added to the test tube”
Procedure, cont.
• These are the metals you will be testing:
Lead, copper, silver, zinc, magnesium,
sodium
• Write a procedure to compare these metals,
using the chemicals that are provided, so
that you will have the data you need to put
the metals in order of increasing reactivity.
• Plan this before you begin working in the
lab.
Data and Observations
• Construct a table to record data and
observations.
• Here is a suggestion:
Tube Metal
ion
1
Pb2+
Metal
Cu
Observations
Calculations
• Write unbalanced net ionic equations for the
redox reactions that actually occur.
– Ex. K + Ca2+  K+ + Ca
• There are no real calculations, but you will need
to do some reasoning to put your elements in
order. Do this work in the calculations section.
Show your thinking.
• Write the electron configuration or orbital box
diagram for each metal and metal ion (Na, Na+,
Mg, Mg2+, Ag, Ag+, Cu, Cu2+, Zn, Zn2+, Pb, Pb2+)
Conclusions
• This should be statements that compare the
reactivities of each of the elements citing
laboratory data as evidence to support each
conclusion.
– Ex. Potassium is more reactive than Calcium. When
solid potassium and calcium ion were combined a
reaction occurred, as indicated by bubbling and heat.
When solid calcium was added to a potassium ion
solution, no reaction occurred.
Discussion
• Connect your lab observations to the atomic
structure, specifically referring to electron
configurations.
– Ex. Potassium has only one electron in its outermost
shell to lose to become stable while calcium has two
valence electrons. This explains why potassium reacts
more vigorously to lose its electron when compared to
calcium. When tin loses 2 electrons it has a full d
subshell. This gives it some stability, but not as much
as calcium, which is isoelectronic with a noble gas once
it loses 2 electrons. This explains why tin is not as
reactive as calcium.
Discussion, cont.
• Describe what you think would happen if
strips of lead were put into sodium chloride
solution. Describe what you think would
happen if strips of lead were put into silver
nitrate solution. Explain why using both lab
data and the concept of reactivity.
Error Analysis
• Specific sources of error are be discussed.
• There is no precision or accuracy to
calculate.