Which type of chemical reaction takes place when an iron nail is dipped in copper sulphate solution Why write a balanced chemical equation for this chemical reaction?

Iron is an el­e­ment of the eighth group of the fourth pe­ri­od in the Pe­ri­od­ic Ta­ble. It is a mal­leable sil­very met­al with good elec­tro­con­duc­tiv­i­ty and pro­nounced mag­net­ic prop­er­ties. In na­ture iron is main­ly en­coun­tered in an ox­i­dized state – for ex­am­ple brown iron ore Fe₂O₃·3H₂O, red iron ore Fe₂O₃ (hematite), pyrite FeS₂, mag­net­ic iron ore Fe₃O₄.

Ob­tain­ing iron and its re­ac­tion with sim­ple sub­stances

Metal­lic iron is ob­tained in in­dus­try by re­duc­ing it from iron ox­ide with car­bon monox­ide CO:

• Ob­tain­ing car­bon (IV) ox­ide from coal:

C + O₂ = CO₂;

• Ob­tain­ing car­bon II ox­ide (re­duc­er for ob­tain­ing iron):

CO₂ + C = 2CO;

• Re­duc­tion of iron from iron ox­ide:

Fe₂O₃ + 3CO = 2Fe + 3CO₂.

Iron can also be ob­tained di­rect­ly by re­duc­ing it with hy­dro­gen at a tem­per­a­ture of 1000 ᵒC (1832 ᵒF):

Fe₂O₃ + 3H₂ = 2Fe + 3H₂O.

Chem­i­cal­ly pure iron is ob­tained by elec­trol­y­sis of the so­lu­tion of its salt:

K(-): 1) 2H₂O + 2e = H₂ + 2OH⁻;

A(+): 2H₂O - 4e = O₂ + 4H⁺.

Sum­mar­i­ly:

Fe­S­O₄ + 2H₂O = Fe + H₂ + O₂ + H₂­SO₄.

With non-met­als, iron re­acts at high tem­per­a­tures:

• 3Fe + 2O₂ = Fe₃O₄ (a mix­ture of iron (II) and (III) ox­ides form);

• Fe + S = FeS;

• 2Fe + 3Br₂ = 2FeBr₃.

At a tem­per­a­ture of 700 ᵒC (1292 ᵒF), iron re­acts with ben­zol with the for­ma­tion of iron car­bide:

18Fe + C₆H₆ = 6Fe₃C + 3H₂.

At room tem­per­a­ture in air and in the pres­ence of mois­ture, iron cor­rodes (cor­ro­sion is the spon­ta­neous dis­in­te­gra­tion of met­al un­der the im­pact of the en­vi­ron­ment):

4Fe + 3O₂ + 6H₂O = 4Fe(OH)₃ (re­ac­tion takes place rather slow­ly in nor­mal con­di­tions).

When iron is fused with an al­ka­li in the pres­ence of ni­trate, fer­rates form on the cation of the al­ka­li:

Fe + 3NaNO₃ + 2NaOH = Na₂FeO₄ + 3NaNO₂ + H₂O.

Click here for ex­cit­ing ex­per­i­ments with iron.

Iron en­ters into a dis­place­ment re­ac­tion read­i­ly (re­ac­tions in which atoms or groups of atoms of the same ini­tial sub­stance re­place atoms or groups of atoms of an­oth­er ini­tial sub­stance – for ex­am­ple ac­cord­ing to the scheme АВ + С = АС + В). With di­lut­ed acids, iron re­acts with the for­ma­tion of iron (II) salt and hy­dro­gen:

Fe + 2HCl = Fe­Cl₂ + H₂.

Con­cen­trat­ed ni­tric acid (and con­cen­trat­ed cold sul­fu­ric acid) pas­si­vates iron, and this re­ac­tion does not take place. With con­cen­trat­ed hot sul­fu­ric acid and di­lut­ed ni­tric acid, acid re­acts as fol­lows:

• Fe + 6H₂­SO₄ = Fe₂(SO₄)₃ + 3SO₂ + 6H₂O (only with heat­ing);

• Fe + 4H­NO₃ = Fe(NO₃)₃ + NO + 2H₂O.

With salts, iron may also en­ter into a dis­place­ment re­ac­tion. Be­tween cop­per (II) sul­fate and metal­lic iron, the fol­low­ing re­ac­tion takes place (an ex­am­ple of a typ­i­cal dis­place­ment re­ac­tion be­tween in­or­gan­ic sub­stances):

Fe + Cu­SO₄ = Fe­S­O₄ + Cu (iron dis­places cop­per in the salt so­lu­tion; the iron dis­solves, turn­ing into so­lu­tion, and metal­lic cop­per of a red­dish col­or is re­leased).

The re­ac­tion does not take place in this way with all salts – dis­place­ment is only pos­si­ble if the dis­plac­ing met­al is more re­ac­tive than the dis­placed one. As iron is to the left of cop­per in the re­ac­tiv­i­ty se­ries (is re­ac­tiv­i­ty in the se­ries de­creas­es from left to right), we may say that iron is a more ac­tive met­al than cop­per. This is why it dis­places cop­per from cop­per salt so­lu­tion.

We may ob­serve some vis­ual ef­fects when car­ry­ing out this re­ac­tion. Cu­SO₄ (“cop­per sul­fate” or cop­per (II) sul­fate) is a salt with a bluish col­or. When a sil­very iron bar is put in a cop­per sul­fate so­lu­tion, the so­lu­tion slow­ly starts to change col­or – the bright blue col­or grad­u­al­ly turns green (the salt Fe­S­O₄ which forms in re­place­ment has a green col­or). Metal­lic cop­per of a red­dish col­or also starts to form around the dis­solv­ing iron bar. As the cop­per in this re­ac­tion has a rather loose struc­ture, it may sep­a­rate from the iron bar and pre­cip­i­tate.

The re­ac­tion be­tween cop­per sul­fate and iron is ox­i­da­tion-re­duc­tion: iron is ox­i­dized and cop­per is re­duced:

Fe + Cu­SO₄ = Fe­S­O₄ + Cu;

There are two pro­cess­es:

• Cu²⁺ + 2e = Cu⁰ (re­duc­tion process, Cu²⁺ is the ox­i­diz­er);

• Fe⁰ – 2e = Fe²⁺ (ox­i­da­tion process, Fe⁰ is the re­duc­er).

Oth­er ex­cit­ing ex­per­i­ments with cop­per

Metal­lic cop­per is of­ten used for the man­u­fac­ture of pipes, wires and pow­er ca­bles. Cop­per al­loys are also of­ten used in prac­tice – for ex­am­ple, bronze (cop­per and tin), brass (cop­per and zinc) and du­ra­lu­min (cop­per and alu­minum).

Iron has found an ap­pli­ca­tion in prac­ti­cal­ly all branch­es of in­dus­try – iron salts are used as cat­a­lysts in or­gan­ic syn­the­sis (for ex­am­ple Fe­Cl₃), to pu­ri­fy­ing wa­ter and man­u­fac­tur­er iron al­loys – for ex­am­ple cast iron and var­i­ous steels (both types of al­loys con­tain iron and car­bon in dif­fer­ent ra­tios).

To carry out the following reactions and classify them as Physical or Chemical changes.

• Burning of magnesium in air
• Sodium sulphate with barium chloride in the form of their solutions in water
• Iron nail with copper sulphate solution in water
• Zinc with dilute sulphuric acid
• Heating of copper sulphate

The Theory

In a chemical change, chemical reaction takes place and the substances undergo a change in their state.  During chemical reactions, one substance reacts with another to form a new substance. The chemical composition of the new substance is different from that of the reacting species.  Due to a chemical change, the chemical properties of matter also change. That means the product is entirely different from either of the reactants. Some chemical reactions may be either exothermic or endothermic in nature.

What are exothermic and endothermic reactions?

In endothermic reactions, a substance absorbs energy in the form of heat and undergoes a chemical reaction. An example is the heat energy absorbed during a chemical change involved in cooking, like baking a cake.

In exothermic reactions, heat energy is released. Explosion of fireworks is an example of exothermic chemical change. The explosion releases energy in the form of light.

Do you know what a photochemical reaction is?

Some chemical reactions do not take place in the dark, but take place only in the presence of sunlight or other radiations. Such reactions are called photochemical reactions. The most commonly known example is photosynthesis, in which plants convert carbon dioxide and water into sugars using energy from sunlight  and produce oxygen as a side product.

A chemical change changes the identity or property of a substance and may or may not be reversed.

Examples of Some Irreversible Chemical changes:

• Combustion (burning) of fuels:In combustion reaction, the fuel burns with an oxidizing agent such as oxygen or fluorine to form new products.
• Neutralization reaction:Neutralization reaction is a type of chemical reaction in which an acid and a base react to form salt and water. For example, sodium hydroxide reacts with hydrochloric acid to form sodium chloride and water. This reaction is highly exothermic, which means it releases heat in the form of energy.
• Rusting of iron:Rust is a chemical substance formed by the chemical action of moist air on iron. It is basically an oxidation reaction. The formula of rust is Fe2O3.xH2O.
• Ripening of fruit and cooking of eggs are also chemical changes.

There are also some chemical changes which are reversible in nature.

Examples:

• The thermal decomposition of ammonium chloride is a reversible chemical change. On heating above 340°C, it decomposes to form two gases such as ammonia and hydrogen chloride. On cooling, the reaction is reversed and solid ammonium chloride is formed.  

• The synthesis of ammonia from hydrogen and oxygen is a reversible reaction.

• The synthesis of hydrogen chloride from hydrogen and chlorine is also a reversible reaction.

Let us discuss about some simple chemical reactions.

Burning of Magnesium in Air

Magnesium is an alkaline earth metal with symbol Mg. It is a silvery white metal. Magnesium is a highly inflammable metal and it is easy to ignite its powdered form or thin strips. Magnesium burns in air by taking oxygen from air to form magnesium oxide and is basic in nature. 

Reaction between Sodium Sulphate and Barium Chloride

When barium chloride combines with sodium sulphate in the form of their aqueous solutions, a white precipitate of barium sulphate is formed which is insoluble in water. The reaction also creates sodium chloride, which remains dissolved in water and so cannot be seen. The precipitate of barium sulphate is insoluble in dil.HCl.

Here, the products formed are entirely different from the reactants in chemical composition and chemical properties. So this reaction is a chemical change.

Reaction of Iron Nails with Copper Sulphate Solution in Water

When an iron nail is dipped in copper sulphate solution, a brown coating of copper is formed on the surface of iron and the colour of copper sulphate solution changes from blue to light green. This reaction shows that iron is more reactive than copper as it displaces copper from its solution and iron passes into solution as Fe2+ ions and ferrous sulphate solution is formed.

This reaction is a single displacement reaction.

Reaction of Zinc with Dilute Sulphuric Acid

Zinc is more reactive than hydrogen and it displaces hydrogen from dilute acids. Zinc reacts with dilute sulphuric acid to form zinc sulphate and hydrogen gas is evolved. This is a single displacement reaction of a non-metal by a metal.

The products ZnSO4 and H2 (g) are entirely different in chemical composition and chemical properties from the reactants Zn and H2SO4. So, this reaction is a chemical change.

Heating of Copper Sulphate

Copper sulphate pentahydrate contain 5 moles of water per one mole of copper (II) sulphate. Its formula is written as CuSO4.5H2O. It can be converted into anhydrous copper sulphate when heated strongly. The blue colour of copper sulphate is due to water of hydration. When heated, it loses two water molecules at ~63°C followed by two more at ~109°C and the final water molecule at ~200°C and turns to white coloured anhydrous copper sulphate.

The above process can be reversed. When water is added to white coloured anhydrous copper sulphate, its colour changes to blue, indicating that the blue coloured copper sulphate pentahydrate is regenerated.  So, it is a reversible chemical change.

On further heating at ~650°C, the anhydrous copper sulphate decomposes to form copper oxide (CuO) and sulphur trioxide (SO3) and the reaction become irreversible.

Learning Outcomes

1. Students understand the term “Chemical reaction”.
2. Students visualize the different chemical reactions and understand the differences between physical changes and chemical changes.
3. Students perform different chemical reactions using the following:
   • Magnesium ribbon
   • Sodium sulphate and barium chloride
   • Iron nail and aqueous solution of copper sulphate
   • Zinc granules and dil. HCl
   • Hydrated copper sulphate
4. Students identify the products formed in each reaction & conclude that they are chemically different from that of reactants.
5. Based on the acquired skills, students should be able to perform a chemical reaction.

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Online Labs for Class IX makes use of animations, interactive simulators and practical content that gives experiments their due place in the area of Science and Technology, and promotes an experimental culture in the school system. The experiments covering various areas in chemical science such as: chemical reactions, study of chemical proprieties of matter, study of compounds and mixtures, etc.