- Substance- The substance is called pure when all of its constituent particles are of one kind and exhibit the same and definite set of properties throughout its bulk.
- Element - Element is a pure substance that cannot be broken down into a simpler substance by the physical and chemical processes. It is made up of one kind of atoms. Ex - Na, Ca, etc.
- Types of elements - Four types of elements are :
(i) Metals- Na,Ca
(ii) Nonmetal - C, N
(iii) Metalloids- B, Si and
(iv) Noble gases - He, Ne. - Mixture- A mixture is composed of two or more substances whose particles are in contact but not chemically combined and have not lost their individual properties. Ex. A mixture of sugar and water, salt and water, etc.
- Types of the mixture. There are two types of mixtures. Homogeneous mixture and Heterogeneous mixture.
- Compound - Compound is a pure substance composed of two or more elements combined chemically in a fixed proportion by mass. The properties of a compound are different from the properties of its constituent elements.
- Solution - A homogeneous mixture of two or more substances chemically non-reacting whose composition can be varied within certain limits called a solution.
- Properties of a solution-
(i) The particles of a solution are smaller than 1 nm (10-9 meters) in diameter. They cannot be seen by naked eyes.
(ii) It is a homogeneous mixture.
(iii) They do not scatter a beam of light passing through the solution. So, the path of light is not visible in a solution.
(iv) The solute particles cannot be separated from the mixture by the process of filtration. The solute particles do not settle down when left undisturbed. - Solvent - The substance of the solution that dissolves the other component is called the solvent.
- Solute - The substance of the solution that is dissolved in the solvent is called the solute.
- Unsaturated solution - An unsaturated solution is a solution that contains less solute at a given temperature as much solute as it can hold in a given mass of solvent.
- Solubility - The solubility of the substance is the mass of the substance in grams that dissolve in 100 gm of solvent or solution.
- Alloys - Alloys are homogeneous mixtures of two or more elements, made by combining two or more metallic elements to give greater strength or resistance to corrosion. The elements could be two metals, or a metal and a non-metal.
- Brass – Mixture of two elements Copper (70%) and zinc (30%) is called brass.
- Crystallization - Crystallization is a process by which the crystals of a substance are obtained from a hot saturated solution by cooling. In this process, liquid solution converted into a solid crystalline state.
- Metalloids - Metalloids are monatomic elements that show the properties of both metals and nonmetals. Ex - Arsenic, antimony, germanium, etc.
- Homogeneous mixture - A mixture that has the same composition and properties
throughout its mass is called a homogeneous mixture. Ex.- sugar solution.
- Heterogeneous mixture - A mixture that has different compositions and properties in different parts of their mass is called a heterogeneous mixture. Ex.- sand and salt.
- Colloidal solution - A colloidal solution is a heterogeneous mixture in which the size of the particle lies between 1mm (10-9 m) and 1000mm (10-6 m).
- Properties colloidal solution - Colloidal solution is fairly stable. Particles of this solution cannot be separated by filtration.
- Tyndall effect - When a beam of light is passed through a glass of milk in a dark, a path of the beam is observed. This phenomenon is called the Tyndall effect, it is due to the scattering of light by the particles of colloidal solution.
- Sublimation - In the mixture of salt and ammonium chloride, ammonium chloride is a sublime substance. On heating the mixture, ammonium chloride sublime and separate from the mixture and sodium chloride left in the container.
- Solubility - The amount of solute present in the saturated solution at a given temperature is called its solubility. Therefore solubility of a solute in a particular solvent at a fixed temperature is the equivalent of the maximum number of grams of the solute necessary to saturate 100 g of that solvent at that temperature.
- Factors on which solubility depends -
(i) Temperature- The solubility of solids in water increases with the rise in temperature and solubility of gases in water decreases with rising temperatures.
(ii) Size of the solute particles - Smaller the size of the particles, greater the solubility of that solute. (smaller size of the particles, greater it's total surface area exposed to the solvent).
(iii) Stirring - This helps to increase the rate of formation of a solution. - Physical change - A physical change is the process, which changes the shape, size, physical state, but not it's chemical composition.
Ex- When ice is heated, it changes into water and then changes into water vapour, but there is no change in chemical properties.
Ex- When ice is heated, it changes into water and then changes into water vapour, but there is no change in chemical properties. - Chemical change - A chemical change is a permanent change in which a new
substance is formed with different compositions and chemical properties.
Example - When iron is kept in moist air, it slowly changes into a brown substance called rust with different composition and chemical properties.
Example - When iron is kept in moist air, it slowly changes into a brown substance called rust with different composition and chemical properties. - The interconversion of states is a physical change - The interconversion of states is a physical change because these changes occur without a change in the chemical properties of the substance and in the composition. Although ice, water, and water vapour all are different in a state like solid, liquid, and gas, they are chemically the same.
- Suspension - It is a heterogeneous mixture in which the solute particles do not dissolve and remain suspended throughout the liquid.
- Properties of suspension:
i. Suspensions are a heterogeneous mixture.
ii. The particles of its greater than 1000 mm.
iii. Suspension neither passes through animal membranes nor through filter paper.
iv. Suspension particles may scatter light passing through it. - Centrifugation - Centrifugation is the method of separating solid particles from a solution according to their size, shape, and density.
- Uses of centrifugation-
i. In washing machines to squeeze out water from the wet cloths.
ii. For separating cream from milk.
iii. In diagnostic laboratories for testing blood/urine. - Chromatography - Chromatography a technique for the separation of a mixture by passing it in solution or suspension through a medium in which the components move at different rates.
- Principle of chromatography - It is based on the difference in the rate of adsorption of different substances on the surface of a solid medium. It occurs in two phases, one is the stationary phase and the other is the moving phase.
- Applications of chromatography - i. Chromatography is used in industrial processes to purify chemicals
ii. Forensic Testing: This can take the form of crime scene testing (the analysis of blood or cloth samples) and iii. Drug testing. - Crystallization - It is a Separation technique. The process of cooling a concentrated hot solution of a substance to obtain crystals is called crystallization. The process of crystallization is used for obtaining a pure substance from the impure substance.
- Uses of crystallization process -
i. The salt we get from seawater has many impurities in it. The crystallization method is used to remove these impurities.
ii. To get sugar crystal from the sugar solution. - Reasons for being better than simple evaporation: The process of evaporation gives residue which may contain impurities. When there is a requirement to obtain solid without impurity, the crystallization method is preferred.
In some cases e.g. sugar crystal cannot be obtained by simple evaporation technique because sugar gets charred on heating to dryness. In such cases, the crystallisation technique is applied. - Distillation - Distillation is a process of heating a liquid into vapour and then cooling the vapour to get back liquid. Distillation is a widely used method for separating the component substances from a liquid mixture by selective evaporation and condensation.
- Fractional distillation - Fractional distillation is the process of
separating two miscible liquids into fractions differing in boiling
point (and hence chemical composition) by means of distillation, the
distillate is collected in fractions boiling at
different temperature.
- Saturated solution:
(i)A saturated solution is a solution that contains solute at a particular temperature as much solute as it can hold in a given mass of solvent
(ii) No more solute can be dissolved in a saturated solution at this temperature. - Unsaturated solution: An unsaturated solution is a solution that contains less solute at a given temperature as much solute as it can hold in a given mass of solvent.
- The concentration of the solution - The concentration of a solution is the amount of solute present in a given amount of solution or the amount of solute dissolved in a given mass or volume of solvent.
The concentration of solution = Amount of solute/ Amount of solution
Or Amount of solute/Amount of solvent.
Or Mass by the mass percentage of a solution = (Mass of solute / Mass of solution) ×100
Or Mass by volume percentage of a solution = (Mass of solute/volume of solution) ×100. - Dispersed phase and dispersed medium in the colloidal solution -
The components of a colloidal solution are the dispersed phase and the dispersion medium. The solute-like component of the dispersed particles in a colloid form the dispersed phase, and the component in which the dispersed phase is suspended is known as the dispersing medium. - Obtaining of coloured component (dye) from blue-black ink - Evaporation can be used to obtain coloured component which is volatile, from its solution. Keep a watch glass on the mouth of the beaker which is half-filled with water. Put a few drops of ink on the watch glass. Now start heating the beaker. We should not heat the ink directly. We will see that evaporation is taking place from the watch glass. Continue heating as the evaporation goes on and stop heating when we do not see any further change on the watch glass.
Now we will observe that the water gets evaporated from the watch glass and residue is left in the watch glass which is the coloured component that is a dye. In this way, evaporation can be used to obtain volatile components from its solution. - Separation of cream from milk - Milk is a mixture that contains different amounts of fat. In this mixture, particles are very small and pass through a filter paper. So filtration technique cannot be used for separation. Such mixtures are separated by the centrifugation process. In this process, denser particles of milk are forced to the bottom and the lighter particle cream stays at the top when spun rapidly.
- Application of centrifugation-
(i) Used in dairies and home to separate butter from cream.
(ii) Used in washing machines to squeeze out water from wet clothes.
(iii) Used in diagnostic laboratories for blood and urine tests. - Principle of separation of immiscible liquids-
The principle of separation of immiscible
liquids separates out in different layers depending on their
different densities.
To separate kerosene oil from water using a separating funnel.
Pour the mixture of kerosene oil and water in a separating funnel.
Let it stand undisturbed for some time so that separate layers of oil and water are formed.
Open the stopcock of the separating funnel and pour out the lower layer of water carefully.
Close the stopcock of the separating funnel as the oil reaches the stop-cock.
In this way, we can separate two immiscible liquids. - Chromatography - Chromatography is a technique used for the separation of those solutes that dissolve in the same solvent. This technique was first used for the separation of colours, so this name was given.
- Applications of chromatography :
To separate:
(i) Colours in a dye
(ii) Pigments from natural colours
(iii) Drugs from the blood. - Obtaining of different gases from the air - Air is a homogeneous mixture and we can be obtained different gases by fractional distillation. The flow diagram shows the steps of the process.
Step 1: First we compress air and cool by increasing pressure and decreasing temperature. Air converted into liquid air.
Step 2: Now allow the liquid air to worm up slowly in a fractional distillation column.
Gases get separated at a different height.
In this way, we can obtain different gases from the air. - Physical and chemical changes
A physical change is a process, which changes the shape, size, physical state, but not it's the chemical composition.
A chemical change is a permanent change in which a new substance is formed with different compositions and chemical properties.
When a candle burns both physical and chemical changes take place.
The melting of wax and vapourization of melted wax is a physical change. The burning of wax is a chemical change in which new substance carbon dioxide and water vapour formed. - Properties of metals:
(i) They have a luster
(ii) They conduct heat and electricity.
(iii) They are ductile and can be drawn into wires.
(iv) They are malleable and can be hammered into thin sheets.
(v) They are sonorous, make a ringing sound when hit.
Examples of metals are gold, silver, copper, iron, sodium, potassium, etc. Mercury is the only metal that is liquid at room temperature. - Properties of nonmetals:
(i) They are not lustrous.
(ii) They are poor conductors of heat and electricity.
(iii) They are not ductile.
(iv) They display a variety of colours.
(v) They are not sonorous or malleable. - Obtaining pure copper sulfate from an impure sample - We can obtain pure copper sulphate from an impure sample by the crystallization process.
Take approximately 5 g some impure sample of copper sulfate in a china dish. Dissolve it in a minimum amount of water and filter the impurities out. Evaporate water from the copper sulfate solution so as to get a saturated solution then cover the solution with a filter paper and leave it undisturbed at room temperature to cool slowly for a day. After some days we will obtain the crystals of copper sulfate in the china dish. This process is called crystallization,
Take approximately 5 g some impure sample of copper sulfate in a china dish. Dissolve it in a minimum amount of water and filter the impurities out. Evaporate water from the copper sulfate solution so as to get a saturated solution then cover the solution with a filter paper and leave it undisturbed at room temperature to cool slowly for a day. After some days we will obtain the crystals of copper sulfate in the china dish. This process is called crystallization, - Differences between compound and mixture.
Mixtures
Compounds
1. Elements or compounds just mix together to form a mixture and no the new compound is formed.
1. Elements react to form new compounds.
2. A mixture has a variable composition.
.2. The composition of each new substance is always fixed.
3. A mixture shows the properties of the constituent substances.
3. The new substance has totally different properties.
4. The constituents can be separated by physical methods.
4. The constituents can be separated only by chemical methods.
5. The mixture may be homogenous or heterogeneous.
5. The compound is a pure substance.
- The concentration of the solution - The concentration of a solution is the amount of solute present in a given amount (mass or volume) of the solution, or the amount of solute dissolved in a given mass or volume of solvent.
The concentration of solution = Amount of solute/ Amount of solution Or Amount of solute/Amount of solvent. - Two expressions of the concentration of a solution - Two expressions of the concentration of a solution are:
(i) Mass by the mass percentage of a solution
= ( Mass of solute × 100)/Mass of solution
(ii) Mass by volume percentage of a solution
= (Mass of solute ×100 )/Volume of solution.
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