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Activity Series

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In the long form of periodic table all the known elements are arranged in increasing order of their atomic number. There are 7 periods (horizontal rows) and 18 groups (vertical column) with two series of fourteen elements in entire periodic table.


The left part of periodic table is rich in metallic elements while all non-metals are placed at the right side of periodic table. There is a line of elements which have intermediate characters and known as metalloids.


All the elements show different chemical and physical properties as well as different reactivity towards various reagents.

Activity Series Definition

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The reactivity of all elements; metals, non-metals and metalloids is different. In fact, two metals are differed in their reactivity towards various reagents. The reactivity of elements; metals and non-metals can assign with the help of activity series. Now the question comes in mind that what is activity series?

"It is a predictable series of elements either metals or non-metals on the basis of the product formation in replacement reactions."
Let’s understand the relationship between activity series and reactivity of elements. When we placed a metal rod (metal in elemental form) in a solution of any other metal compound, if it is feasible for metal to exist as an ion and the ionic metal from solution to exist as the element, the elemental metal will displace the ionic metal.

For example; when we place zinc rod in copper sulphate, copper will deposited on the zinc rod as zinc is more reactive compare to cooper can replace it from its on solution. On the contrary, silver cannot show same reaction with the copper as it is less reactive compare to copper.

Activity Series of Elements

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  1. All the elements are arranged in decreasing order of their reactivity, i.e. as we move from the top to bottom in the series, the reactivity of elements decreases.
  2. The elements places above in the series are more reactive compare to the elements place below in the series.
  3. Remember the more reactive element can replace the less reactive element in the series.
  4. As the distance between elements increases in the series, they react more vigorously compare to those elements which are placed at small distance in the activity series.
  5. Remember that the metals with low electro negativity (less than 1.4) are most reactive metals and have the low reduction potential (less than -1.6).
  6. Such type of metals can easily react with water to form hydrogen and good reducing agent but they are not very good oxidizing agents. Therefore their ions cannot reduce to metal in their aqueous solution.
  7. The top most elements of the activity series reacts rapidly with air and ignite to form oxides.
  8. The reaction of flame with sand makes the flame smoother and shows no reaction.
  9. The elements with medium electro positivity like aluminum do not react rapidly with air and form a tarnish layer of oxide with the atmospheric oxygen.
  10. Like aluminum surface covers with the layer of aluminum oxide which prevent the further oxidation of metal surface.
  11. Some of metals like iron react with atmospheric oxygen and water to form rust that are oxides of iron and the phenomenon is known as corrosion.
  12. Here the metal surface acts as an anode and some points on the surface acts as a cathode.
  13. At cathode oxygen is reduced to hydroxyl ion while at anode iron gets oxidized to Fe2+ ion.
  14. The Nobel metals which are placed at the bottom of activity series are less reactive and do not corrode easily like mercury, platinum etc. That is the reason; they are widely used in coinage and jewellery.
  15. Some of the metallic oxides like mercury oxide are less stable and decompose at high temperature.

Solved Example

Question: Identify the more reactive metal in the reaction of solid aluminum metal with aqueous solution of silver nitrate.
Solution:
The aqueous solution of silver nitrate reacts with solid aluminum to form aluminum nitrate solution and deposit silver, therefore aluminum is more reactive compare to silver.

Activity Series of Metals

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The activity series starts from lithium and till sodium, they are more reactive metals and can easily react with water to release hydrogen gas and form metal hydroxides. Like the reaction of lithium with water to form lithium hydroxide and release hydrogen gas.

Next metal is magnesium after sodium is also a reactive metal but less than sodium. It reacts with hot water or steam to form metal oxide and released hydrogen gas. All the metal oxides cannot reduce easily to metal with the use of hydrogen gas as reducing agent.

After magnesium, next metal is iron which is a transition metal and can easily replace hydrogen from inorganic acids like hydrochloric acid, or sulfuric acid. There are total five metals; Mg, Al, Mn, Zn and Fe.

Mn + 2H2O $\rightarrow$ Mn(OH)2 + H2

After iron, next five metals till lead show similar reactivity and their oxides form hydrogen, carbon, and carbon monoxide after reduction. Remember, metals till copper can oxidizes by oxygen to form oxides. The metals placed at the bottom from mercury to gold least reactive metals and often found in native state.

They usually react at high temperature and can only form oxides by indirect manner. The reactivity series is useful for the prediction of products of chemical reactions and also help in the extraction of metals in their metallurgical process.
  • The reactivity series of metals can also determined with the help of free energy change during transfers electrons in a Redox reaction.
  • The reactivity series of metals show the reactivity of metals towards hydrogen-ion sources like acid solution or water. In such reactions, the metals are oxidized and release hydrogen gas.
  • Let’s discuss about the relation between the standard reduction potential of a metal cation with their order in the reactivity series.
  • The metals with the positive value of standard reduction potential make the metal more difficult to oxidize, and such metals are placed at the bottom of the activity series.

Solved Example

Question: What will happen when we drop a piece of copper metal in a jar filled with water?
Solution:
There will be no reaction as copper is placed low position in the activity series and quit less reactive, therefore, it cannot displace the hydrogen from water to release hydrogen gas.

Activity Series Chart

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The activity series chart of metals can use to show the reactivity of metals. Let’s take few examples of the reactions. The reaction of the metal like magnesium or zinc releases hydrogen gas and form the metal compounds in acidic medium. If both metals react in acidic medium solution, the magnesium metal can replace the zinc ions from the solution but reverse reaction is not possible.

It proves that Mg is more reactive compare to zinc, but both metals are more reactive compare to hydrogen. Therefore, copper places at lowers point compare to zinc. The order of reactivity can be written as Mg > Zn > H. As the gap between metals increases the reaction between both elements becomes vigorous in nature.

Hydrogen includes in activity series in for comparison of reactivity with other metals. The top most metals are more reactive compare to lower metals or the strong reducing agents place at the top of reactivity series. After iron, the next metal is nickel which can also displace the hydrogen gas from hydrogen ion solution.

Ni(s) + 2H+(aq) $\rightarrow$ Ni2+(aq) + H2(g)

Nickel, tin and lead have same reactivity and show similar kinds of reactions. Below hydrogen, copper, silver, platinum and gold are least reactive and cannot react with other reagents. The reactivity of metals can assign with the help of reactivity series.

In some of the cases it’s difficult to assign the reactivity like copper can't release hydrogen gas from acids, but it cannot react with nitric and sulfuric acid as they can react as oxidizing agents. The metals with low ionization potential and low electron-negativity are more reactive compare to other metals and easily show the displacement reactions.
  1. The electro negativity of electropositive metals like alkali and alkaline earth metals lies between 1.4 and 1.9 with the reduction potential value of 0.0 to -1.6 V.
  2. Some of the metals with less electro positivity have the electro negativity in between 1.9 to 2.54.
  3. Such metals cannot oxidize in acidic solution and good oxidizing agents.
  4. In fact, these metals can oxidize hydrogen and produce hydrogen ion in solution.
  5. The top most metals are highly reactive and readily react with water to form hydroxides and hydrogen gas as these metals are able to displace the hydrogen from water to form hydrogen gas.
For example, potassium forms potassium hydroxide with hydrogen gas. On the other hand, less reactive metals like zinc cannot give reaction with water only but release hydrogen gas with inorganic acids like sulfuric acid.

Element/Metals
Number of electrons transfer during Redox rection
Reactivity Series
K
1
Highly reactive metal, easily reacts with water to form hydroxide and hydrogen gas, ignite in oxygen to oxide
Na
1
Li
1
Ba
2
Sr
2
Ca
2
Mg
2
Medium reactivity, can react with acids to form metallic compounds
Al
3
Mn
2
Zn
2
Cr
2
Fe
2
Cd
2
Co
2

Activity Series of Non-Metals

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Like metals; we can also arrange non-metals in the reactivity series. Non-metals are generally electron-negative in nature and tend to accept electrons to form anions in Redox reactions.

Due to this they are strong oxidizing agents while metals are good reducing agents. Like activity series of metals, in the non-metal activity series the most reactive non-metal places at the top while least reactive appear on the bottom.

Solved Example

Question: Predict the product of fluorine gas with the aqueous solution of aluminium chloride.
Solution:
The reaction of fluorine with an aqueous solution of aluminum chloride results the formation of aluminum fluoride with chlorine gas as fluorine is a strong oxidizing agent compare to chlorine.

Activity Series of Halogens

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  1. Halogens are placed in the group-17 of the periodic table which second last group of table.
  2. All the halogens are non-metals and highly electronegative elements because of seven electrons in their valence shell.
  3. Due to seven electrons, they lack of only one electron for getting octet configuration.
  4. As we move top to bottom in the group from fluorine to iodine, the electro negativity of elements decreases because of increase in atomic radius.
  5. The activity series of halogens starts from fluorine which is strongest oxidizing agent.
  6. The oxidizing power decreases from fluorine to iodine due to less electro negativity of iodine.
  7. If we compare the oxidizing power of halogens with sulfur and phosphorus, the oxidizing power of phosphorus is least, and sulfur comes after iodine.
  8. Let’s compare the reactivity of halogens with the example of reaction of halogens with halogen solution.
  9. The reaction of chlorine gas with bromine ion solution results the formation of bromine and chloride ion in solution.
  10. The same reaction can be observe with the reaction of chlorine gas with iodide solution which forms iodine in solid state and release chloride ion in solution.
  11. If we add bromine solution in solution of chloride ion, there will be no reaction because chlorine cannot replace bromine from the solution. Same reaction can observe with iodine solution.

Solved Examples

Question 1: Write the balanced reaction of liquid bromine solution with solid potassium iodide.
Solution:
 
The balanced equation is
Br2 (l) + 2KI(s) $\rightarrow$ 2KBr(s) + I2 (s)

 

Question 2: Iodine crystals with a solution of sodium chloride and platinum wire in a solution of FeCl3 do not show any reaction. Why?
Solution:
 
The reason of no reaction of iodine with sodium chloride is least reactivity of iodine in the activity series of halogens. Second reaction cannot occur due to non-reactivity of platinum metal which is placed below hydrogen in the activity series and known as Noble element.
 

Activity Series Problems

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Let’s recall the concept of the activity series with the help of some problems related to activity series. We will discuss some of the reactions in which a metal (in elemental state) reacts with ion of any species.

Let’s discuss what will occur during the reactions. The reaction of solid manganese with aqueous solution nickel chloride involves the reaction between elemental manganese with nickel ions. Since in the reactivity series, the manganese metal places above nickel, it will act as reducing agent and oxidize to Mn2+ ions.

On the contrary, nickel ion will reduce to elemental nickel and the reaction can be written as follow;

Mn(s) + Ni2+(aq) $\rightarrow$ Mn2+(aq) + Ni(s)

Let’s take an example of a single displacement reaction.

The reaction between copper with aqueous solution chromium acetate forms no products as copper placed at very low in the activity series. The reaction of elemental chromium with aqueous solution of nickel sulphate results the formation of chromium (III) ions with elemental nickel.

2Cr(s) + 3Ni2+(aq) $\rightarrow$ 2Cr+3 + 3Ni(s)

The reaction of platinum with aqueous solution hydrogen bromide show no reaction as platinum is placed at the bottom of the activity series and will not react with hydrogen ions of hydrogen bromide.

The reaction of hydrogen gas with copper (II) chloride solution replaces copper ions forms the solution and form elemental copper.

H2(g) + Cu2+ $\rightarrow$ 2H+(aq) + Cu(s)

Remember metals with high reactivity compare to hydrogen are placed above hydrogen in series while less reactive metals are placed below it.