It consists of two or more elements or compounds combined in any ratio/proportion.
The following are the characteristics of mixtures:

• It might be homogeneous or heterogeneous.
• The component substances' characteristics are preserved.
• There is no formation of a new compound.
• Simple physical methods may be used to separate elements.
• It lacks a definite melting and boiling point.

An element is a material that cannot be broken down into two or simpler compounds by chemical processes such as applying heat, light, or electric energy. For instance, hydrogen is an element that cannot be broken down into two or simpler things. An Element is also described as: - A material composed of just one kind of atom. For example, copper metal is composed of just one kind of atom known as "copper atoms." There are 118 elements known so far, 94 of which exist naturally, while the other 24 are created artificially. Elements may take the form of solids, gases, or liquids.

A solution is a homogeneous combination of two components (or more substances). A homogenous mixture is the same throughout. Here are several examples of solutions: - Salt solutions, sugar solutions, air, soda water, and other similar substances. The following are the characteristics of solutions:

• A solution is a homogeneous combination of substances.
• A solution's particles are less than 1 nm (10-9 metres) in diameter. As a result, they are invisible to human sight.
• They do not scatter a light beam travelling through the solution due to their highly tiny particle size. As a result, the light path is not evident in a solution.
• The filtering technique cannot remove the solute particles from the mixture. If the solute particles do not settle when left undisturbed, indicating that the solution is stable.
• A true solution does not scatter light.

Important points to Remember

• A solution is made up of a solvent and a solute.
• The solvent is the component of the solution that dissolves the other component (typically the component present in the most significant proportion).
• The solute is the material that dissolves in a liquid to form a solution.

 

A specific chemical or physical change usually accompanies energy changes.

Physical changes

• Physical changes are those in which no new material is generated.
• The molecular makeup stays unchanged.
• The molecular composition of ice and water, for example, remains unchanged.
• The amount of energy necessary to bring about a physical change is the same as the energy required to reverse the change. There is no difference in energy.
• The modifications are reversible and only temporary. If the source of the alteration is eliminated, the response will be reversed. For example, water freezes to produce ice, and ice melts to form water. Physical change examples are sugar dissolution in water, Ice melting, and water freezing.

Chemical changes

• It is defined as a change in which the molecular composition is altered, and a new product is generated. A new product is being created.
• Chemical transformations are irreversible and everlasting. A chemical change cannot be reversed by adjusting or changing the experimental conditions.
• Energy shifts occur during chemical reactions. There is a difference in energy between breaking existing bonds in reactants and producing new bonds in products.
• Chemical change examples are wood or paper burning, camphor combustion, milk fermentation

Questions of class 9 science ch 2:

Question 1: Which separation procedures will you employ to separate the chemicals listed below?

(a) Tea leaves come from the beverage tea.

(b) Ammonium chloride is formed by the reaction of sodium chloride and ammonium chloride.

(c) Tiny metal pieces discovered in the engine oil of a car.

(d) Various colours obtained from flower petal extract were employed.

(e) Sodium chloride, which forms a solution in water

(f) Water-extracted oil.

(g) Butter made from curd

(h) Iron pins fashioned from sand.

(i) Wheat grains stripped of their husks.

(j) Suspended fine dirt particles in water.

Question 2: Write out the actions you would take to make tea. You may want to use the terms solution and solvent as well as the phrases solute and dissolve and the words soluble and insoluble.

Question 3. Pragya evaluated the solubility of three distinct compounds at various temperatures and recorded the findings, summarised in the table below (results are given in the following table, as grams of substance dissolved in 100 grams of water to form a saturated solution).

At 313 degrees Celsius, what mass of potassium nitrate would be required to generate a saturated solution in 50 grams of water, assuming that the solution was potassium nitrate?

A saturated solution of potassium chloride in water is prepared at 353 degrees Celsius by Pragya. The solution is left at room temperature for cooling. During the cooling process, what would she be able to observe? Explain. Calculate the solubility of each salt at 293 degrees Celsius. Is it possible to determine which salt has the greatest solubility at this temperature?

Question 4. Determine if the following substances are homogeneous or heterogeneous mixtures: Wood, soda water, dirt, vinegar, air, filtered tea.

Question 5. How would you determine if a colourless liquid that has been supplied to you is pure water?

Question 6. In the following mixes, choose the solutions that are the most appropriate.

Soil, seawater, air, coal, and soda water are all examples of natural resources.

Solutions of Class 9 Science Ch 2

Answer 1.

 (a) Filtration is the removal of contaminants from a solution

 (b) Sublimation.

 (c) Filtration is the removal of contaminants from a solution

 (d) Chromatography is a technique for separating various chemicals.

 (e) Evaporation  

 (f) Funnel for separating solids and liquids

 (g) Centrifugation is a technique for separating particles from liquids

 (h) Magnetism separation

 (i) Sedimentation and winnowing

 (j) Two ways of purification are decantation and filtering.

Answers 2.

1. To use as a solvent, heat a cup of water in a jar.
2. Incorporate a solute, such as sugar, into the mixture. It should be heated until all of the sugar has been dissolved.
3. You will be given a solution of water and sugar.
4. Sugar has a complete solubility in water.
5. Add half a teaspoon of tea leaves, which are insoluble in water, and mix well.
6. Bring the contents of the pan to a boil, then add the milk, which is also soluble in water, and bring it back to a rolling boil.
7. The tea should be filtered via a strainer; the tea in the cup represents the filtrate, and the tea leaves on the strainer represent the residue.

Answer 3.

(a) Mass of KNO3 required to generate a saturated solution of KNO3 in 100 grams of water at 313 K = 62 g Mass of KNO3 required to produce a saturated solution of KNO3 in 50 grams of water at 313 K = 62 g

It is possible to create crystals of potassium chloride by chilling a saturated solution of potassium chloride.

The solubility of each salt at 293 degrees Celsius is:

potassium nitrate = 32 g sodium chloride = 36 g potassium chloride = 35 g ammonium chloride = 37 g potassium nitrate = 32 g sodium chloride = 36 g potassium chloride = 35 g ammonium chloride = 37 g

The solubility of a salt increases as the temperature of the solution rises.

Answers 4.

Homogeneous ingredients include soda water, vinegar, and filtered tea.

Wood, air, and soil are all heterogeneous.

Answer 5.

By determining the boiling point of a colourless liquid that has been provided. If a liquid boils at 100 degrees Celsius at atmospheric pressure, it is considered to be pure water because pure substances have a fixed melting and boiling point.

Answer 6.

Seawater soda water and air are used as a solution.

 

Through these class 9 science ch2 solutions, we learned the meaning of the phrase "Is the matter around us pure?" Whenever a material is composed entirely of a single kind of molecule or particle, it is in its purest state. Pure substances, which are often incapable of being separated using basic physical processes, are typically classified as elements and compounds, except in rare cases.

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