Contents
The concept of equilibrium constants is fundamental in Chemistry Topics as it quantitatively describes the extent of chemical reactions at equilibrium.
What are the Chemical Properties of Metals and Non-Metals?
Metals and non-metals show different chemical properties. Some of the important chemical properties of metals and non-metals are given below.
1. Reaction with Oxygen
(i) Metals react with oxygen to form metal oxides. Metal oxides are basic in nature.
Activity 2
Magnesium is a metal. We take a magnesium wire, hold it with a pair of tongs and heat it over a flame. Magnesium wire burns vigorously producing a bright white light to form an ash (which is magnesium oxide). We put this magnesium oxide ash in a boiling tube, add a little water in the boiling tube and shake it. We will find that magnesium oxide dissolves in water partially.
We now add some red litmus solution to the boiling tube and observe the change in colour. We will see that red litmus solution turns blue. This shows that magnesium oxide is basic in nature (because only basic substances turn red litmus to blue). From this activity we conclude that magnesium is a metal which forms a basic oxide (magnesium oxide) on burning in air. This basic magnesium oxide turns red litmus blue.
The chemical reactions involved in the above activity are given below:
(a) When magnesium burns in air, it combines with the oxygen of air to form magnesium oxide (which is a basic oxide) :
(b) Magnesium oxide dissolves partially in water to form magnesium hydroxide solution :
Magnesium hydroxide turns red litmus to blue showing that it is a base and that magnesium oxide is a basic oxide.
Similarly, sodium is a metal which forms a basic oxide, sodium oxide (Na2O). A solution of sodium oxide in water turns red litmus blue. Please note that when we want to react a metal with oxygen, we usually burn the metal in air. It is the oxygen present in air which combines with the metal on burning to form a metal oxide. We will now discuss the reaction of iron metal with oxygen of air which takes place in nature. We have studied the rusting of iron in Class VII. During the rusting of iron, iron metal combines slowly with the oxygen of air in the presence of water (moisture) to form a compound called ‘iron oxide’. This iron oxide is rust.
The reaction of iron metal with oxygen in the presence of water can be written as follows :
Activity 3
We will now describe an activity to show that iron oxide (or rust) is basic in nature. Take a spoonful of rust (from any rusted iron object) in a test-tube, add a little of water and shake it well. In this way, we will get a suspension of iron oxide in water. Test this suspension of iron oxide (or rust) with blue litmus paper and red litmus paper, one by one. We will find that the red litmus paper turns blue. This shows that iron oxide suspension is basic in nature (because only basic substances turn red litmus paper to blue). From this activity we conclude that iron metal forms a basic oxide (iron oxide) on reaction with oxygen of air. In other words, rust is basic in nature.
We will now describe the reaction of copper metal with moist air which takes place in nature. When a copper object is exposed to moist air for a long time, then copper reacts with water, carbon dioxide and oxygen present in moist air to form a green coating on the copper object. The green coating (or green material) is a mixture of copper hydroxide [Cu(OH)2] and copper carbonate (CuCO3) which is formed by the action of moist air on copper object. This reaction can be written as :
Thus, when a copper vessel is exposed to moist air for a long time, it acquires a green coating on its surface.
The mixture of copper hydroxide and copper carbonate which forms the green coating is commonly known
as ‘basic copper carbonate’ (because it is basic in nature). If we make a suspension of a little of green coating
(from a copper vessel) in water and test it with litmus papers, we will find that it turns red litmus paper to blue.
This shows that the green coating formed on a copper vessel (or any other copper object) is basic in nature.
The formation of green coating of basic copper carbonate on the surface of copper objects on exposure to
moist air is called corrosion of copper. While iron rusts, other metals corrode.
(ii) Non-metals react with oxygen to form non-metal oxides. Non-metal oxides are acidic in nature.
Thus, non-metals react with oxygen to form acidic oxides. The acidic non-metal oxides turn blue litmus to red. This property will become more clear from the following activity
Activity 4
Sulphur is a non-metal. We take a small amount of sulphur powder In a deflagrating spoon and heat it over a flame [Figure (a)]. As soon as sulphur starts burning with a blue flame, we introduce the deflagrating spoon in a gas jar and allow the sulphur to burn inside the gas jar [Figure (b)). Cover the gas jar with a lid to prevent the gas being formed from escaping. Sulphur burns in the air of gas jar to form a pungent smelling gas (sulphur dioxide) [Figure (c)). Remove the deflagrating spoon from the gas jar. We now put some water in the gas jar, cover it with a lid and shake It to dissolve sulphur dioxide gas. Add some blue litmus solution to the gas jar. We will see that the blue litmus solution turns red. This shows that sulphur dioxide gas is acidic in nature (because only acidic substances turn blue litmus to red). From this activity we conclude that sulphur is a non-metal which forms an acidic oxide (sulphur dioxide) on burning in air.
The chemical reactions involved in this activity are given below :
(i) When sulphur burns in air, it combines with the oxygen of air to form sulphur dioxide (which is an acidic oxide) :
(ii) Sulphur dioxide dissolves in water to form sulphurous acid solution :
This sulphurous acid turns blue litmus to red showing that it is an acid and that sulphur dioxide is acidic in nature. Similarly, carbon is a non-metal which forms an acidic oxide, carbon dioxide (CO2). A solution of carbon dioxide in water turns blue litmus red. From the above discussions we conclude that:
- Metals form metal oxides on burning in air. Metal oxides are basic in nature and turn red litmus to blue.
- Non-metals form non-metal oxides on burning in air. Non-metal oxides are acidic in nature and turn blue litmus to red.
This property of the nature of oxides can be used to identify whether a given element is a metal or a non-metal. This is because :
(a) If an element forms a basic oxide (which turns red litmus blue), then the element will be a metal.
(b) If an element forms an acidic oxide (which turns blue litmus red), then the element will be a nonmetal.
We have studied acids and bases in Class VII. We can now understand that metal oxides are basic in nature and form bases on dissolving in water. On the other hand, non-metal oxides are acidic and form acids on dissolving in water. Some of the bases and acids, and the metals and non-metals present in them (from whose oxides they are formed) are given on the next page :
Metals in Bases
Name of base | Name of metal |
1. Magnesium hydroxide | Magnesium |
2. Calcium hydroxide | Calcium |
3. Sodium hydroxide | Sodium |
4. Potassium hydroxide | Potassium |
Non-Metals in Basis
Name of acid | Name of non-metal |
1. Sulphurous acid | Sulphur |
2. Sulphuric acid | Sulphur |
3. Nitric acid | Nitrogen |
4. Carbonic acid | Carbon |
Please note that most of the non-metals form acidic oxides but there are some exceptions. This is because some of the non-metals form neutral oxides (which are neither acidic nor basic). For example, hydrogen is a non-metal which forms a neutral oxide H2O (which is commonly known as water).
2. Reaction with Water
(i) When a metal reacts with water, then a metal hydroxide and hydrogen gas are formed.
Metal + Water → Metal hydroxide + Hydrogen
The vigour (or intensity) of reaction of a metal with water depends on its chemical reactivity. Some metals react vigorously even with cold water, some metals react with hot water, some metals react with steam whereas some metals do not react even with steam. For example, sodium is a very reactive metal, therefore, sodium metal reacts violently even with cold water. Magnesium is a comparatively less reactive metal so it reacts slowly with cold water, it reacts rapidly only with hot boiling water or steam. The metals like zinc and iron are less reactive which react slowly even with steam. And the metals like copper, silver and gold are so unreactive that they do not react with water or even with steam. The reaction of sodium metal with water is described below. Sodium metal reacts violently (explosively) with cold water forming sodium hydroxide solution and hydrogen gas :
Thus, the gas liberated when sodium metal (or any other metal) reacts with water is hydrogen. The reaction of sodium metal with water can be studied as follows.
Activity 5
We cut a small piece of sodium metal carefully and dry it by using a filter paper. This piece of sodium metal is placed in water filled in a beaker. We will find that the piece of sodium metal starts moving in water making a hissing sound due to formation of bubbles of a gas and reacts with water causing little explosions. Soon the piece of sodium metal catches fire (see Figure). When the reaction stops, touch the beaker. We will feel the beaker to be somewhat hot. This is because heat is produced in this reaction. If we test the solution in the beaker with red and blue litmus papers one by one, we will find that it turns red litmus paper blue.
This shows that the solution formed by the reaction of sodium and water is basic in nature. These observations can be explained as follows : Sodium metal reacts with water to form sodium hydroxide and hydrogen gas. A lot of heat is also produced in this reaction. This heat burns the hydrogen gas as well as sodium metal. The burning of hydrogen gas causes little explosions. The formation of sodium hydroxide makes the solution basic. And this basic solution turns red litmus paper blue.
Sodium is a very reactive metal. It reacts with the moisture (water), oxygen and other gases present in air. So, if sodium metal is kept exposed to air, it will react with the various components of air and get spoiled. In order to prevent its reaction with the moisture and other gases of air, sodium metal is always stored under kerosene. Potassium metal is also highly reactive. So, potassium metal is also stored in kerosene.
(ii) Non-metals do not react with water.
Sulphur is a non-metal. Sulphur does not react with water. In fact, some of the reactive non-metals are kept under water to protect them from the action of air. For example, phosphorus is a very reactive non-metal element. If phosphorus is kept open in the air, it reacts with the oxygen of air and catches fire. So, in order to protect phosphorus from atmospheric air, it is stored in a bottle containing water.
3. Reaction with Acids
(i) Most of the metals react with dilute acids to form salts and hydrogen gas.
Metal + Acid → Salt + Hydrogen
Only the less reactive metals like copper, silver and gold do not react with dilute acids. The vigour of reaction of a metal with dilute acid depends on the chemical reactivity of the metal. Depending on their reactivity, some metals react violently (explosively) with dilute acids, some metals react rapidly with dilute acids, some metals react with dilute acids only on heating whereas some metals do not react with dilute acids at all. The reaction of magnesium metal with dilute hydrochloric acid is given below.
Magnesium metal reacts with dilute hydrochloric acid to form magnesium chloride and hydrogen gas. This reaction can be written as :
Aluminium, iron and zinc metals also react with dilute hydrochloric acid to form the corresponding metal chlorides and hydrogen gas. This hydrogen gas burns with a ‘pop’ sound when a lighted matchstick is brought near the mouth of test-tube (containing metal and dilute hydrochloric acid). The less reactive metals like copper, silver and gold do not react with dilute acids (like dilute hydrochloric acid or dilute sulphuric acid). Thus, copper, silver and gold do not produce hydrogen gas with dilute acids.
Activity 6
We will now describe a simple activity to show that when a metal reacts with a dilute acid, then hydrogerygas is produced. We take four test-tubes. Put a small piece of magnesium ribbon in the first test-tube, a piece of aluminium foil in the second test-tube, some iron filings in the third test-tube and a piece of uncovered copper wire in the fourth test-tube. Add 10 ml. of dilute hydrochloric acid in each test-tube and warm them gently. Test the gas produced in each test-tube by bringing a lighted matchstick (or burning matchstick) near the mouth of each test-tube.
- When we bring a lighted matchstick near the mouth of the first test-tube containing a piece of magnesium ribbon and dilute hydrochloric acid, the gas produced burns with a ‘pop’ sound, showing that it is hydrogen gas.
- When we bring a lighted matchstick near the mouth of the second test-tube containing a piece of aluminium foil and dilute hydrochloric acid, the gas burns with a ‘pop’ sound showing that it is hydrogen gas.
- When we bring a lighted matchstick near the mouth of the third test-tube containing iron filings and dilute hydrochloric acid, the gas burns with a ‘pop’ sound showing that it is hydrogen gas.
- When we bring a lighted matchstick near the mouth of the fourth test-tube containing a piece of copper wire and dilute hydrochloric acid, nothing happens showing that no hydrogen gas is produced in this case.
This activity shows that though magnesium, aluminium and iron metals react with dilute hydrochloric acid to produce hydrogen gas but copper metal does not react with dilute hydrochloric acid to form hydrogen gas. Dilute sulphuric acid reacts with these metals in a similar way.
Copper metal also does not react with dilute sulphuric acid to produce hydrogen gas. Copper metal, however, reacts with hot and concentrated sulphuric acid but no hydrogen gas is produced. We will study these reactions in higher classes.
The reactions of metals with acids have some important implications in our daily life. Certain foodstuffs like citrus fruit juices (say, orange juice), pickles, chutney and curd, etc., contain acids. When foodstuffs containing acids are kept in iron, aluminium or copper containers, the acids present in them react with the metal of the container slowly to form toxic salts (or poisonous salts). And these toxic salts can make us sick and damage our health. So, iron, aluminium and copper containers (or utensils) should not be used to store acidic foods like citrus fruit juices (such as orange juice), pickles, chutney and curd, etc. For example, we cannot store lemon pickle in an aluminium vessel. This is because the acid present in lemons will react with aluminium metal of vessel to form toxic salts which can make us sick and damage our health.
(ii) Non-metals do not react with dilute acids.
Non-metals do not react with dilute acids to form salts and hydrogen gas. For example, if we take some sulphur powder (or charcoal powder) in a test-tube and add dilute hydrochloric acid, then no reaction takes place even on heating. This shows that sulphur and carbon non-metals do not react with dilute acids and hence no hydrogen gas is produced. Some of the non-metals, however, react with hot and concentrated sulphuric acid and nitric acid but no hydrogen gas is produced in such cases. We will study these reactions in higher classes.
4. Reaction with Bases
(i) Some metals react with bases to form salts and hydrogen gas.
Metal + Base → Salt + Hydrogen
Aluminium is a metal and sodium hydroxide is a base. When aluminium is heated with sodium hydroxide solution, then sodium aluminate (salt) and hydrogen gas are formed :
Activity 7
We can demonstrate the formation of hydrogen gas in the reaction of aluminium metal with sodium hydroxide as follows: Take 5 mL of freshly prepared sodium hydroxide solution in a boiling tube. Drop a piece of aluminium foil in the sodium hydroxide solution and heat the boiling tube over a burner. Bring a lighted matchstick near the mouth of boiling tube. We will find that the gas produced burns with a ‘pop’ sound showing that it is hydrogen gas.
Zinc metal also reacts with sodium hydroxide solution to form hydrogen gas. Thus, aluminium and zinc are the two common metals which react with bases (like sodium hydroxide) to produce hydrogen gas. In general we can say that: Some metals react with sodium hydroxide to produce hydrogen gas. Please note that all the metals do not react with bases (like sodium hydroxide) to produce hydrogen gas.
(ii) Some non-metals react with bases (like sodium hydroxide) but no hydrogen gas is produced. The reactions of non-metals with bases are complex. We will study these reactions in higher classes.
Before we go further and study the displacement reactions of metals, we should know the reactivity series of metals. This is described below
Reactivity Series Of Metals.
Some metals are chemically very reactive whereas other metals are less reactive Reactivity Series of Metals or unreactive. On the basis of vigour of reactions of various metals with oxygen, water and acids, as well as the displacement reactions, the metals have been arranged in a group (or series) according to their chemical reactivities. The arrangement of metals in a vertical column in the order of decreasing reactivities is called the reactivity series of metals (or activity series of metals). In reactivity series, the most reactive metal is placed at the top whereas the least reactive metal is placed at the bottom. The reactivity series of some common metals is given alongside.
Please flote that potassium is the most reactive metal, so it has been placed at the top of the reactivity series. As we come down in the reactivity series, the chemical reactivity of metals decreases gradually. For example, sodium is less reactive than potassium ; calcium is less reactive than sodium ; magnesium is less reactive than calcium ; aluminium is less reactive than magnesium ; zinc is less reactive than aluminium ; iron is less reactive than zinc, copper is less reactive than iron and silver is less reactive than copper. Gold being the least reactive metal here has been placed at the bottom of the reactivity series. We should remember the reactivity series of metals because it will help us in understanding the displacement reactions of metals.
5. Displacement Reactions
(i) A more reactive metal displaces a less reactive metal from its salt solution. This means that when a more reactive metal is placed in the salt solution of a less reactive metal, then the more reactive metal displaces (pushes out) the less reactive metal from its salt solution. The more reactive metal becomes a part of the salt whereas the less reactive metal is set free. Let us take some examples to make this point more clear.
(a) Reaction of Iron Metal with Copper Sulphate Solution. When a strip of iron metal (or an iron nail) is placed in copper sulphate solution for some time, then the blue colour of copper sulphate solution fades and a red-brown coating of copper metal is deposited on the iron strip (or iron nail). This reaction can be written as :
In this case the solution turns greenish due to the formation of iron sulphate. We know that iron metal is more reactive than copper metal. So, in this reaction, a more reactive metal ‘iron’ is displacing a less reactive metal ‘copper’ from its salt solution, copper sulphate solution.
The products of this displacement reaction are ‘iron sulphate solution’ and ‘copper metal Please note that the blue colour of copper sulphate solution changes to greenish due to the formation of iron sulphate (which is green in colour). The copper metal produced in this displacement reaction forms a red-brown coating over the iron strip (or iron nail). In the above displacement reaction, iron metal displaces copper from copper sulphate solution. This displacement reaction takes place because iron is more reactive than copper. The displacement reaction between iron metal and copper sulphate solution can be performed as follows.
Activity 8
We take about 50 mL of water in a beaker and dissolve 5 grams of copper sulphate in it to obtain copper sulphate solution (which is blue in colour). Put a clean iron nail in copper sulphate solution in the beaker and keep the beaker undisturbed for some time. We will find that the blue colour of copper sulphate solution starts fading gradually. And the iron nail gets covered with a red-brown layer of copper metal. This change takes place because iron metal displaces copper metal from its compound copper sulphate. It is the copper metal set free from its compound which forms a red-brown layer on the surface of iron nail.
We will now discuss the reverse case in which a copper strip is placed in iron sulphate solution.
A less reactive metal cannot displace a more reactive metal from its salt solution. For example, if we place a strip of copper metal in iron sulphate solution for some time, then no displacement reaction takes place. That is :
This displacement reaction does not occur because copper metal is less reactive than iron metal. So, a less reactive metal copper’ cannot displace a more reactive metal ‘iron from its salt solution, iron sulphate solution. Thus, copper metal cannot displace iron from iron sulphate solution.
(b) Reaction of Zinc Metal with Copper Sulphate Solution. When a strip of zinc metal is placed in copper sulphate solution for some time, then the blue colour of copper sulphate solution fades gradually and red-brown copper metal is deposited on the zinc strip. This reaction can be written as :
We know that zinc metal is more reactive than copper metal. So, in this reaction, a more reactive metal ‘zinc’ is displacing a less reactive metal ‘copper’ from its salt solution, copper sulphate solution. The products of this displacement reaction are ‘zinc sulphate solution’ and ‘copper metal’. Please note that the blue colour of the copper sulphate solution gradually disappears due to the formation of colourless zinc sulphate solution. The copper metal which is formed in this displacement reaction deposits on the zinc strip in the form of a red-brown coating. In the above displacement reaction, zinc metal displaces copper metal from copper sulphate solution.
This displacement reaction between zinc and copper sulphate solution occurs because zinc is more reactive than copper. Let us now discuss the reverse case in which a copper strip is placed in zinc sulphate solution.
If we place a strip of copper metal in zinc sulphate solution, then no displacement reaction will take place. That is :
This displacement reaction does not take place because copper metal is less reactive than zinc metal. So, a less reactive metal copper’ cannot displace a more reactive metal ‘zinc’ from its salt solution, zinc sulphate solution. Thus, copper cannot displace zinc from zinc sulphate solution.
(c) Reaction of Zinc Metal with Iron Sulphate Solution. When a strip of zinc metal is placed in iron sulphate solution, then a displacement reaction takes place to form zinc sulphate solution and iron metal. This reaction can be written as:
In this reaction, zinc metal displaces iron metal from iron sulphate solution. This displacement reaction takes place because zinc is more reactive than iron. Let us now discuss the reverse case in which an iron nail is placed in zinc sulphate solution.
If we place an iron nail in zinc sulphate solution, then no displacement reaction takes place. That is :
This displacement reaction does not occur because iron metal is less reactive than zinc metal. So, a less reactive metal iron cannot displace a more reactive metal zinc from zinc sulphate solution.
Please note that magnesium metal is more reactive than zinc, iron and copper. So, magnesium metal can displace zinc, iron and copper metals from their salt solutions.
(ii) A more reactive non-metal displaces a less reactive non-metal from its salt solution. We will study these displacement reactions in higher classes.
Comparison Between the Chemical Properties of Metals and Non-Metals
We will now compare the important chemical properties of metals and non-metals in tabular form. Alongwith physical properties, the chemical properties can be used to distinguish between metals and non-metals.
Differences in Chemical Properties of Metals and Non-Metals
Metals | Non-Metals |
1. Metals form basic oxides. | 1. Non-metals form acidic oxides. |
2. Metals react with water (or steam) to produce hydrogen gas (except copper, silver and gold which do not react with water or steam). | 2. Non-metals do not react with water (or steam). |
3. Metals react with dilute acids to produce hydrogen gas (except copper, silver and gold which do not react with dilute acids). | 3. Non-metals do not react with dilute acids. |
We will now answer some questions based on the properties of metals and non-metals.
Example Problem 1.
An element reacts with oxygen to form an oxide. An aqueous solution of this oxide turns red litmus paper blue. Is the element a metal or a non-metal ? Give reason for your answer.
Answer:
We know that basic substances turn red litmus to blue. Since an aqueous solution of this oxide turns red litmus to blue, it means that the oxide is basic in nature. Now, basic oxides are formed by metal elements. So, the given element is a metal.
Example Problem 2.
Why is iron not deposited over a copper plate when the copper plate is dipped in iron sulphate solution ?
Answer:
Copper is less reactive than iron, so copper is not able to displace iron from iron sulphate solution to form free iron metal. Since no iron metal is formed, it is not deposited over copper plate.
Example Problem 3.
Consider the following displacement reactions :
On the basis of these two displacement reactions, find out which is the most reactive metal and which is the least reactive metal out of copper, iron and zinc.
Answer:
- In the first reaction, iron metal displaces copper metal from copper sulphate solution, therefore, iron is more reactive than copper.
- In the second reaction, zinc metal displaces iron metal from iron sulphate solution, so zinc is more reactive than iron.
Now, since zinc is more reactive than iron, and iron is more reactive than copper, therefore, in this case: zinc is the most reactive metal whereas copper is the least reactive metal.
Example Problem 4.
Saloni took a piece of burning charcoal and collected the gas evolved in a test-tube.
(a) How will she find the nature of the gas ?
(b) Write down word equations of all the reactions taking place in this process. (NCERT Book Question)
Answer:
Charcoal is a form of carbon (which is a non-metal). When carbon (charcoal) burns in air, it forms an acidic oxide called carbon dioxide (which is a gas).
(a) To find the nature of carbon dioxide gas, dissolve it in water. Test the aqueous solution of carbon dioxide gas with blue litmus paper and red litmus paper. The aqueous solution of carbon dioxide gas will turn blue litmus paper to red showing that carbon dioxide is acidic in nature.
(b) When carbon (or charcoal) burns in air, it combines with the oxygen of air to form carbon dioxide. The word equation for this reaction is :
Carbon dioxide dissolves in water to form carbonic acid (which turns blue litmus paper to red). The word equation for this reaction is :
Carbon dioxide + Water → Carbonic acid