Post by 1dave on Mar 28, 2020 12:00:56 GMT -5
When a metal enters a solution of the salt of another metal, it may be more energetically feasible for the "new metal" to exist as an ion and the "old ionic metal" to exist as the element. Therefore the new metal will "displace" the ionic metal and the two will swap places.
BUT MOLECULES HAVE DIFFERENT REACTIVITY LEVELS THAN THEIR ELEMENTS!
en.wikipedia.org/wiki/Standard_electrode_potential_(data_page)
www.electrochemsci.org/papers/vol13/130605971.pdf
A metal can displace metal ions listed below it in the activity series, but not above. For example, zinc is more active than copper and is able to displace copper ions from solution
Zn(s)+Cu2+(aq)→Zn2+(aq)+Cu(s)(P3.1)
This is an Activity Series of some of the more common metals, listed in descending order of reactivity from highest to lowest. It is used to determine the products of single displacement reactions.
Metal A will replace another metal B in a solution only if A is higher in the series.
Metals . . . Metal Ion . . . Reactivity
NOTE: Oxygen and Silicon are the first and second most common element in earth's crust.
K . . . K+ . . . reacts with water . . . 7th most common element in earth's crust.
Na . . . Na+ . . . reacts with water . . . 6th most common element in earth's crust.
Li . . . Li+ . . . reacts with water
Ba . . . Ba2+ . . . reacts with water
Sr . . . Sr2+ . . . reacts with water
Ca . . . Ca2+ . . . reacts with water . . . 5th most common element in earth's crust.
Mg . . . Mg2+ . . . reacts with acids . . . 8th most common element in earth's crust.
Al . . . Al3+ . . . reacts with acids . . . 3rd most common element in earth's crust.
Mn . . . Mn2+ . . . reacts with acids
Zn . . . Zn2+ . . . reacts with acids
Cr . . . Cr2+ . . . reacts with acids
Fe . . . Fe2+ . . . reacts with acids . . . 4th most common element in earth's crust.
Cd . . . Cd2+ . . . reacts with acids
Co . . . Co2+ . . . reacts with acids
Ni . . . Ni2+ . . . reacts with acids
Sn . . . Sn2+ . . . reacts with acids
Pb . . . Pb2+ . . . reacts with acids
<H2 . . . H+ . . . included for comparison>
Sb . . . Sb2+ . . . highly unreactive
Bi . . . Bi2+ . . . highly unreactive
Cu . . . Cu2+ . . . highly unreactive
Hg . . . Hg2+ . . . highly unreactive
Ag . . . Ag+ . . . highly unreactive
Au . . . Au3+ . . . highly unreactive
Pt . . . Pt+ . . . highly unreactive
The reactivity of metals is due to the difference in stability of their electron configurations as atoms and as ions. As they are all metals they will form positive ions when they react.
Metals that require the loss of only one electron to form stable ions are more reactive than similar metals which require the loss of more than one electron. Group 1A metals are the most reactive for that reason.
Metals with a greater total number of electrons tend to be more reactive as their outermost electrons (the ones which will be lost) exist further from the positive nucleus and therefore they are held less strongly.
It is important to distinguish between the displacement of hydrogen from an acid and hydrogen from water.
Those metals that can displace H+ ions from acids are easily recognized by their position above H in the activity series. The boundary between the metals that react with water and those that don't is harder to spot. For example, calcium is quite reactive with water, whereas magnesium does not react with cold water but does displace hydrogen from steam. A more sophisticated calculation involving electrode potentials is required to make accurate predictions in this area.
Sodium is highly active and is able to displace hydrogen from water:
2Na(s)+2H2O(l)→2NaOH(aq)+H2(g)
Less active metals like iron or zinc cannot displace hydrogen from water but do readily react with acids:
Zn(s)+H2SO4(aq)→ZnSO4(aq)+H2(g)
Silver cannot displace copper ions from solution.
Potassium has a single outer shell electron to lose to obtain a stable "Noble gas" electron configuration; the precious metals which exist in the d-block cannot form structures which are much more stable than their elemental state with the loss of just a few electrons.
BUT MOLECULES HAVE DIFFERENT REACTIVITY LEVELS THAN THEIR ELEMENTS!
en.wikipedia.org/wiki/Standard_electrode_potential_(data_page)
www.electrochemsci.org/papers/vol13/130605971.pdf
pyrite oxidation takes place at potentials of -0.28 V (SHE) at pH 9.2 and 0 V at pH 4.6, considerably lower than previously assumed. - May 10, 2018
A metal can displace metal ions listed below it in the activity series, but not above. For example, zinc is more active than copper and is able to displace copper ions from solution
Zn(s)+Cu2+(aq)→Zn2+(aq)+Cu(s)(P3.1)
This is an Activity Series of some of the more common metals, listed in descending order of reactivity from highest to lowest. It is used to determine the products of single displacement reactions.
Metal A will replace another metal B in a solution only if A is higher in the series.
Metals . . . Metal Ion . . . Reactivity
NOTE: Oxygen and Silicon are the first and second most common element in earth's crust.
K . . . K+ . . . reacts with water . . . 7th most common element in earth's crust.
Na . . . Na+ . . . reacts with water . . . 6th most common element in earth's crust.
Li . . . Li+ . . . reacts with water
Ba . . . Ba2+ . . . reacts with water
Sr . . . Sr2+ . . . reacts with water
Ca . . . Ca2+ . . . reacts with water . . . 5th most common element in earth's crust.
Mg . . . Mg2+ . . . reacts with acids . . . 8th most common element in earth's crust.
Al . . . Al3+ . . . reacts with acids . . . 3rd most common element in earth's crust.
Mn . . . Mn2+ . . . reacts with acids
Zn . . . Zn2+ . . . reacts with acids
Cr . . . Cr2+ . . . reacts with acids
Fe . . . Fe2+ . . . reacts with acids . . . 4th most common element in earth's crust.
Cd . . . Cd2+ . . . reacts with acids
Co . . . Co2+ . . . reacts with acids
Ni . . . Ni2+ . . . reacts with acids
Sn . . . Sn2+ . . . reacts with acids
Pb . . . Pb2+ . . . reacts with acids
<H2 . . . H+ . . . included for comparison>
Sb . . . Sb2+ . . . highly unreactive
Bi . . . Bi2+ . . . highly unreactive
Cu . . . Cu2+ . . . highly unreactive
Hg . . . Hg2+ . . . highly unreactive
Ag . . . Ag+ . . . highly unreactive
Au . . . Au3+ . . . highly unreactive
Pt . . . Pt+ . . . highly unreactive
The reactivity of metals is due to the difference in stability of their electron configurations as atoms and as ions. As they are all metals they will form positive ions when they react.
Metals that require the loss of only one electron to form stable ions are more reactive than similar metals which require the loss of more than one electron. Group 1A metals are the most reactive for that reason.
Metals with a greater total number of electrons tend to be more reactive as their outermost electrons (the ones which will be lost) exist further from the positive nucleus and therefore they are held less strongly.
It is important to distinguish between the displacement of hydrogen from an acid and hydrogen from water.
Those metals that can displace H+ ions from acids are easily recognized by their position above H in the activity series. The boundary between the metals that react with water and those that don't is harder to spot. For example, calcium is quite reactive with water, whereas magnesium does not react with cold water but does displace hydrogen from steam. A more sophisticated calculation involving electrode potentials is required to make accurate predictions in this area.
Sodium is highly active and is able to displace hydrogen from water:
2Na(s)+2H2O(l)→2NaOH(aq)+H2(g)
Less active metals like iron or zinc cannot displace hydrogen from water but do readily react with acids:
Zn(s)+H2SO4(aq)→ZnSO4(aq)+H2(g)
Silver cannot displace copper ions from solution.
Potassium has a single outer shell electron to lose to obtain a stable "Noble gas" electron configuration; the precious metals which exist in the d-block cannot form structures which are much more stable than their elemental state with the loss of just a few electrons.