Ashaq Hussain Bhat
Teacher school education
Department
Jammu And Kashmir
9thChemistry Lesson No 2
Is Matter Around Us Pure(part 1st)
Pure substance
Pure matter is that which is made up of only one kind of particle. These particles can be atoms ions or molecules for example the element sulphur is made up of only one type of particle called Sulphur atom. Therefore, sulphur is a pure substance.
Similarly, water is made up of only one type of particles called water molecule. Therefore, Water is a pure substance. Virtually all elements such as hydrogen, oxygen, nitrogen, chlorine, Bromine, iodine, carbon, sulphur, copper, gold, mercury, silicon etc. and the compounds like water (H2O), carbon dioxide (CO2), common salt (NaCl), sugar, copper sulphate, sodium chloride, Hydrogen chloride, naphthalene, etc. All are pure substances.
Types of pure substances
One the bases of chemical composition pure substances can be classified in to two category
(I) Elements
(II)Compounds
ELEMENTS.
The word element was introduced for the first time by Lavoisier, a French chemist. According to him, An element is the simplest or basic form of a pure substance which cannot be broken into anything simpler than it by physical or chemical methods. The definition of an element has been modified. It may now be defined as:
The pure substance which is made up of one kind of atoms only
The common examples of elements are hydrogen, carbon, oxygen, nitrogen, sulphur, copper, silver, gold etc. Till date there are nearly 118 elements known.
Types of Elements.
Elements are further classified into three types on the basis of their physical state and properties. These are metals, non-metals and metalloids.
• Metals:-
Nearly 70 elements belong to a particular class known as metals. In the metals, the atoms are very closely packed together and have special types of bonds known as metallic bonds. Because of very tight or close packing, the metals are quite hard.
The important characteristics of the metals are listed.
(1) All Metals are solids at room temperature (Except Mercury)
(2) The surface of metals shines. They usually have silver-brown or golden-yellow surfaces. This property is known as lustre or glitter.
(3.) Metals are good conductors of heat and electricity.
( 4.) Metals are usually hard.(except few)
(5. )Metals are ductile or adaptable in nature. This means that they can be beaten to make very thin sheets eg , thin aluminium and silver foil is used to wrap a variety of food. Or for the decoration of sweets
6. Metals are malleable in nature. This means that they can be drawn in to thin wires .
7. Metals are sonorous, that means when we bend or beater them , they make a crashing sound or metallic sound.
8. Metals usually have more melting and boiling points.
Non-metals,
As the name suggests, they are antagonistic to metals, which means they have sufficient properties different from metals. Their numbers are relatively small. They are only about fourteen to fifteen In numbers till date listed
1. Non-metals are either gases or solids at room temperature.
2. Non-metals have different colours. Their surfaces are usually dull.
3. Non-metals are mostly poor conductors of heat and electricity.
4. Most non-metals are very soft and have a lower density than metals.
5. Non-metals are Malleable and ductile in nature.
6. Non-metals are not So much sonorous
7. Compared to metals, non-metals have very low melting and boiling points.
Metalloids
Some elements have characteristic of both metals and non-metals. These are actually borderline elements and are known as metalloids. Some common examples of Metalloids are: arsenic, antimony, bismuth...
Physical change.
These are changes that involve only physical features ,In this change only substances change, but no new substance is formed, In physical change substances do not Change their identities but only change some of their physical characteristics, like shape and size. Physical changes are temporary and, therefore can be easily reversed, such as melting of ice and , freezing of water is a well-known example of physical change. In the same way water boils to form steam and the vapours of steam becomes water(liquid) on condensation
Preparing solution, breaking of glass tumbler, forming of clouds, pulling of rubber band , tearing of Paper, etc. are some examples of physical transformation. Or physical change.
Chemical Change.
The changes in which new substances are formed are called chemicals Changes. In a chemical change, the original substances lose their identity and are transformed into the New substances. New substances can not be converted back into real substances by any Physical action. Physical changes are permanent and are irreversible, such as burning of magnesium Ribbon, burning a piece of paper, rusting of iron, digesting of food, making yogurt, frying of Eggs are some examples of chemical changes...
Mixture.
A Mixture is a substance that are in close contact with each other . The constituents of mixtures are mixed together in a fixed proportion. The components of the mixture can be separated by simple mechanical means.
Examples: -
1. Air is a mixture of nitrogen, oxygen, carbon dioxide, water vapor (moisture) and a small amount. Other substances.
2. Gunpowder is a mixture of nitrate (potassium nitrate), sulphur and coal.
Features of the mixture: -
1. A mixture can be homogeneous or heterogeneous.
2. The components of the mixture can be separated by physical methods such as filtration, evaporation, sublimation, magnetic separation, etc.
3. In the preparation of a mixture, energy is usually neither given out nor absorbed.
4. The composition of a mixture is not fixed.
5. Mixture has no special melting and boiling point, etc.
6. In the genesis of a mixture, no chemical reaction. Takes place
Types of mixtures: -
( i) Heterogeneous Mixture : - A Mixture in which its various components are not evenly mixed is called an Heterogeneous Mixture. In a Heterogeneous Mixture the ingredients can be easily identified either with or without the aid of the sophisticated eye . For example, in a mixture of sulphur, carbon, nitrate and sand, each Ingredients can be seen under the magnifying glass. Or by naked eye Also, the composition of the mixture is not Same, ie, somewhere there may be more sulphur and somewhere there may be more sand or nitrite or carbon.
( ii)Homogenous Mixture or(Smooth mixture)
A mixture is said to be homogeneous mixture if all the components of the mixture are completely mixed together and are indistinguishable from one another. Sugar solution, alcohol and water solution, air and alloys are all examples of Homogenous mixture
Compound
A compound is defined as a pure substance made up of two or more than two different elements chemically combined in a fixed proportion by mass e.g. water, carbon dioxide, common salt, marble or CaCO3, methane, silica (SiO2), ammonia etc.
Characteristics of Compound: -
- 1. A Compound cannot be separated into its components by mechanical or physical means.
- 2. The properties of a Compound differ completely from its constituent elements.
- 3. When a Compound is formed, energy is usually produced or absorbed (in the form of heat or light). During chemical reactions.
- 4. In a Compound, the constituent elements are present in a certain proportion by weight.
- 5. A Mixture has a fixed melting point, a fixed boiling point, and so on.
- 6. A Mixture is a homogeneous substance, In all its features and structure.
Differentiate Between Mixture And Compound
Mixture.
3. The ingredients of a mixture can be easily Separate from physical methods such as filtration, evaporation, distillation, sublimation, extraction with solvents, magnet, etc
7. A mixture can be uniform or non uniform
8. Energy (in the form of heat or light) is neither absorbed nor evolved during the formation of a Compound
COMPOUND
1. Elements react together to form a new substance called Compound
2. As a result of chemical change compound is farmed
3. The constituents can be separated from each other by chemical method or by electro chemical reactions
4. The properties of a mixture are completely different from its components.
5. The composition of a mixture is always. fixed, Mass is present in a fixed proportion. Therefore, a mixture has a definite formula.
6. The melting and boiling points of a compound is fixed.
7. A Compound is a homogeneous substance.
8. Energy ( in the form of heat or light). Is absorbed or evolved during the formation of a. Compound.
Solution
A solution is defined as a homogeneous mixture of two or more chemically non-reactive substances. Composition may vary within limits.
Solvent
The liquid in which a substance is dissolved is called a solvent. A solvent is thus dissolving agent In a true solution, i.e., in a completely homogeneous solution, the solvent is called the medium of dispersion. Solvent is always present in a higher quantity.
Salute
A substance that dissolves in a solvent to form a solution is called a solute . Solute Particles in a real solution are called dispersed particles. Solute is always present in small quantities. eg in a sugar solution sugar is solute and water is solvent
Aqueous Solution
The solution formed by dissolving a substance in water is called aqueous solution. For example, the Solutions of sodium chloride, ammonium chloride and copper sulphate in water are all aqueous solutions.
Non Aqueous solution
There are some substances which can form solutions by dissolving in liquids other than water such as alcohol, acetone, carbon tetrachloride and carbon disulphide. Such solutions are called nonaqueous solutions
True Solution
The solution, in which solute particles disappears in the inter molecular or inter atomic spaces of solvent, such solution is called as true or real solution .
PROPERTIES OF SOLUTIONS.
1. A solution is clear and transparent. For example, a solution of sodium chloride in water is clear and transparent.
2. The solute in a solution does not settle down even after the solution is kept undisturbed for some time.
3. In a solution, the solute particles cannot be distinguished from the solvent particles or molecules even under a microscope. In a true solution, the particles of the solute disappear into the space between the solvent molecules.
4. A solution is homogeneous, i.e., the composition of a solution is the same throughout.
5. The components of a solution cannot be separated by filtration.
6. The diameter of the solute particles in a solution is of the order of 10-8 cm.
Types of solutions;
The solution can be divided into two types depending on the amount of solute dissolved
1. Unsaturated solution: - Unsaturated solution is one in which more solute can be dissolved without. Increase in temperature. For example, a solution of sugar in water which can dissolve more sugar at a given temperature is An unsaturated solution
2. Saturated solution: - There is a limit to the amount of solute which can be dissolved in a certain amount of Solvents at a certain temperature. A solution containing the maximum possible amount of solute Dissolved at a given temperature is called a saturated solution.
3. Super Saturated Solution: - Sometimes it is possible to prepare a solution with quantity of solute more than the required This type of solution is called supersaturated Solution
4. A supersaturated solution can be made by slowly cooling a saturated solution at a given temperature. Prepared at a high temperature. Super-saturated solutions are very volatile. Because they quickly crystallized by Addition even 0.1 gram of more solute
Concentration of the Solution.
The concentration of a solution is expressed as the amount of the solute present in a given amount of the solvent or solution. It is normally expressed as mass percent or as volume percent.
• Mass Percent:-
Mass percent of a solution may be defined as, the number of parts by mass of one component (solute or solvent) per 100 parts by mass of the solution.
If A and B are the two components of a binary solution, Mass present of A = WA ×100/WA+WB
Where WA is the weight of solute
and WB mass of
solvent.
• Volume Percent:-
Volume percent of solution may be defined as the number of parts by volume of one component (solute or solvent) per 100 parts by volume of the solution.
Mathematically, Volume percent of
A = VA ×100/VA + VB
Volume percent of B = VB ×100/VA + VB
Mass percentage is use to express those solutions where solvent and solute are expressed in Kg’s or grams. In volume percentage both are expressed in litters..
Suspension
A suspension is a heterogeneous mixture in which the solute particles do not dissolve but remain suspended throughout the bulk of the medium. The solute particles of a suspension are so large in size (more than 10-5 cm) that they are visible to the naked eye and cannot pass through a filter paper. Some common examples of suspension are, Chalk water mixture, muddy water, milk of magnesia, sand particles suspended in water and flour in water
PROPERTIES OF SUSPENSIONS:-
1. A suspension is a heterogeneous mixture.
2. The particles in a suspension are large enough to be visible either by the unaided eye or under an ordinary microscope.
3. The particles in a suspension are too large to remain in suspension for a long period. If a suspension is allowed to stand, the suspended particles settle down at the bottom.
4. The particles in a suspension can be separated from the liquid by filtration.
5. In a suspension, the size (diameter) of the particles is of the order of 10-5 cm or larger.
Colloid
Colloids are contrasting compounds in which the particle size is Between 10-7cm (actual solution size = 1nm) and 10-5Cm (size of course suspension = 100nm). The size of the solution particles in colloids is larger than the actual solution but smaller than that Of a suspension. Colloids particles may look similar to us, but they are actually found Varied Or different on observation through a high power microscope. Some examples of colloids are , soap solution, milk, ink, blood etc.
Is Ghee and Air pure substance
A pure substance means a single substance (or substances) that cannot be separated into another type of substance by any physical action. Thus, ghee or oil is not a pure substance as it is mixed with many other substances.
Similarly, air is not a pure substance because many gases like oxygen, nitrogen, carbon dioxide, water, Vapours etc. are present in it..
click on the link below for 2nd blog
https://jkgovtschoolnotes.blogspot.com/2022/01/9th-class-chemistry-is-matter-around-us.html
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