Science Question Answer (2 Marks)

If a saturated solution is heated to a higher temperature, then it becomes unsaturated. If a saturated solution is cooled to a lower temperature, then some of its dissolved solute will separate out in the form of solid crystals.

1. Solute: The substance which is dissolved in a liquid to make a solution is called as solute.
2. Solvent: The liquid in which solute is dissolved is known as solvent.

1. Homogeneous mixtures: Those mixtures in which the substance are completely mixed together and are indistinguishable from one another, are called homogeneous mixtures.

Example: Sugar solution, copper sulphate solution.

2. Heterogeneous mixtures: Those mixtures in which the substances remain separate and one substance is spread throughout the other substance as small particles, droplets or bubbles, are called heterogeneous mixtures.

Example: Starch solution, soap solution.

A suspension is a heterogeneous mixture in which the small particles of a solid are spread throughout a liquid without dissolving in it.
Example: Muddy-water, Milk of magnesia.

A true solution can be distinguished from a colloidal solution by experimenting Tyndall effect. A true solution does not scatter a beam of light passing through it but a colloidal solution scatters a beam of light passing through it.

A solution is a homogeneous mixture of two or more substances.
Example: Salt solution, metal alloys.

A solution is a homogeneous mixture of two or more substances whereas a colloid is a kind of solution in which the size of solute particles is intermediate between those in true solutions and those in suspensions.

When sea water is a mixture of dissolved salts and water only, it is homogeneous solution. And if sea water contains suspended impurities like decayed plants or animal material, etc. then it is called heterogeneous solution.

Brass is a mixture because:

1. It shows the properties of its constituents, copper and zinc.
2. It has a variable composition.

Sugar is soluble in water whereas sand is insoluble in water. The difference in their solubility is used to separate them. The mixture of sand and sugar is dissolved in water, then it is filtered with the help of filter paper. Sand remains as residue on the filter paper while sugar solution is obtained as filtrate. The filtrate is then evaporated to get crystals of sugar.

• Chemical change: Coal burning in air, making of cake.
• Physical change: A glass bottle breaking, wool beging knitted into a sweater.

• Homogeneous mixtures: Soda water, air, vinegar, alcohol and water mixture, sugar and water mixture, Copper sulphate solution.
• Heterogeneous mixture: Wood, petrol and water mixture, chalk and water mixture.

Salt is soluble in water whereas sand is insoluble in water. The difference in their solubility is used to separate them. The mixture of sand and salt is dissolved in water, then it is filtered with the help of filter paper. Sand remains as residue on the filter paper while salt solution is obtained as filtrate . The filtrate is then evaporated to get crystals of salt.

The maximum amount of a solute which can be dissolved in 100g of a solvent at a specified temperature is known as the solubility of that solute in that solvent. The solubility of solids in liquids is directly proportional to temperature whereas the solubility of gases in liquids is inversly proportional to temperature.

• Two solid elements at room temp.– Iron and copper.
• Two liquid elements at room temp.– Mercury and bromine.
• Two gaseous elements at room temp.– Hydrogen and oxygen.

Starch solution and milk will show Tyndall effect. This is because in a milk solution and starch solution (colloidal solutions) the size of solute particles is big enough to scatter the light passing through it.

Evaporate both the liquids separately. A pure compound will evaporate completely, leaving no residue whereas solution will not be evaporated completely, i.e. some residue will be left behind.

In industries, the impurity of iron present in several substances is removed by the use of magnets. Iron objects stick to the magnet leaving behind other objects.

• Solutions: Brine.
• Suspensions: Chalk water mixture, milk of magnesia, Muddy river water.
• Colloids: Milk, blood, ink, shaving cream, smoke in air, soda water.

Water is a compound because:

1. Water cannot be separated into its constituents, hydrogen and oxygen by physical methods.
2. Heat and light are given out when water is prepared by burning hydrogen in oxygen.

A compound is a substance made up of two or more elements chemically combined in a fixed proportion by mass. NaCl cannot be separated into its constituents by physical process and the properties of NaCl is completely different from that of Na and Cl, so NaCl is a compound and not a mixture.

Mixture of camphor and sand is heated. Camphor sublimes on heating leaving behind sand and can be recovered in the form of sublimate by cooling its vapours.

• True Solutions: Salt solution and sugar solution.
• Colloidal Solution: Starch solution, Ink, Blood.

A colloid is a kind of solution in which the size of solute particles is intermediate between those in true solutions and those in suspensions.
Example: Soap solution, milk.

Soap solution will scatter light because in true solution i.e. sugar solution, the solute particles are so small that they cannot scatter light rays while in soap solution particles are big enough to scatter light.

1. Water and kerosene mixture can be separated by using a separating funnel because these are immiscible liquids and they have different densities.
2. Water and acetone mixture cannot be separated by by using a separating funnel because these are miscible liquids.

1. Formation of curd from milk: Chemical change.
2. Condensation of steam: Physical change.
3. Growth of plant: Chemical change.
4. Breaking of a glass tumbler: Physical change.

A mixture is a substance which consists of two or more elements or compounds not chemically combined together. As energy is neither evolved nor absorbed during the formation of sugar solution and a sugar solution shows properties of both sugar and water so sugar solution is a mixture not a compound.

The given solution is taken in a beaker. Then, a strong beam of light is allowed to fall on the solution from one side of the beaker in a dark room. If the beam of light is visible in the solution, then it is a colloidal solution.

Mixtures are generally heterogeneous in which there is a boundary separation between different substituents. Solutions are homogeneous mixtures in which no separation is visible between different materials.

The change in which no new substance is formed is called a physical change.
Example: Melting of candle wax, mixing of iron filings and sand.

1. Burning of magnesium wire: Chemical change.
2. Freezing of water: Physical change.
3. Rusting of iron: Chemical change.
4. Glowing of electric bulb: Physical change.

A colloid is a kind of solution in which the size of solute particles is intermediate between those in true solutions and those in suspensions whereas a suspension is a heterogeneous mixture in which the small particles of a solid are spread throughout a liquid without dissolving in it.

Mixtures: A mixture is a substance which consists of two or more elements or compounds not chemically combined together.
Examples: Air, gun powder.

The particles of a suspension cannot pass through a filter paper whereas particles of colloids can easily pass through filter paper. Colloidal solutions are quite stable whereas suspensions are very unstable.

The change in which new substance is formed is called a chemical change.
Example: Burning of candle wax, burning of wood.

• Elements: Gold, Diamond, Graphite.
• Compounds: Common salt, Sea water, Marble.
• Mixtures: Brass, Sand, Petroleum, Chalk, Air.

The solubility of solids in liquids increases on increasing the temperature and decreases on decreasing the temperature.

As energy is neither evolved nor absorbed during the formation of salt solution and a salt solution shows properties of both salt and water so salt solution is a mixture not a compound.

Both the given solutions will be kept stationary in different beakers for some time. The beaker in which the dissolved particles settle down after some time is a suspension and another one is a solution.

• Physical change: Melting of candle wax, mixing of iron filings and sand, breaking a piece of chalk, cutting a piece of paper.
• Chemical change: Burning of candle wax, burning of wood, burning of piece of paper.

All the elements can be divided into following three groups:

• Metals: Iron and copper.
• Non-metals: Carbon and sulphur.
• Metalloids: Boron and silicon.

• Similarity: In both the cases, the mixture can be separated into their constituents by physical methods.
• Difference: No separation is visible in the mixture of sugar and water whereas separation is visible in mixture of sand and sand.

• Metals: Mercury, Sodium.
• Non-metals: Diamond, Sulphur, Iodine, Carbon, Boron.
• Metalloids: Silicon, Germanium.

Dissolution of a solid in liquid form a homogenous mixture called solution. Solution is clear in nature as the solid particles (solute) in a solution are very small and get completely dissolved in the liquid (solvent).

Two types of pure substances:

1. Pure substance made up of same kind of atoms.

Example: Sulphur.

2. Pure substance made up of same kind of molecules.

Example: Water.

Mixture of iodine and common salt is heated. Iodine sublimes on heating leaving behind common salt and can be recovered in the form of sublimate by cooling its vapours.

Hydrogen and oxygen cannot be split up into two or more simpler substances by applying heat, light or electric energy. Whereas, water can be split up into hydrogen and oxygen by applying electric energy, so it is not an element.

1. Malleability: Metals show this property but non-metals don’t.
2. Ductility: Metals show this property but non-metals don’t.
3. Electrical conductivity: Metals are good conductors of electricity whereas non-metals are bad conductors except graphite.