Important Questions (1 mark): Matter in our Surroundings - Class 9

"For iron sulfide, two elements (sulfur and iron) are heated together so that they form the compound iron sulfide. Although iron sulfide contains both sulfur and iron, it is not a mixture: it is a pure substance. Both the sulfur and the iron have 'given up' their individual properties to become a compound.

Steam is water, which is a compound, the Hydrogen and Oxygen are chemically bonded. In a mixture they are not chemically bonded.

Brass is an alloy of copper and zinc, in proportions which can be varied to achieve varying mechanical and electrical properties. It is a substitutional alloy: atoms of the two constituents may replace each other within the same crystal structure. In contrast, bronze is an alloy of copper and tin.

Boiling of water is a physical change
Boiling of water produce water vapors. Chemically the water and water vapors composed of H₂O molecules. Here the change in physical state occurred. During this conversion The liquid is changed in to gas. On cooling these water vapors condensed into water. Hence it is a reversible reaction.

Mercury is the only metal that is a liquid at normal temperatures and pressure. Because of the behavior of the valence electrons, mercury has a low melting point, is a poor electrical and thermal conductor and doesn't form diatomic mercury molecules in the gas phase.

Blood is not a pure substance. Blood is made up of many different components like cells, salts, proteins, water, etc.

Ice and liquid water are the same substance. H₂O Though ice water is a mixture of both solid and liquid it is a pure substance, based on the molecular structure of its components .

True Solution is a homogeneous mixture of two or more substances in which substance dissolved (solute) in solvent has the particle size of less than 10-9 m or 1 nm. Simple solution of sugar in water is an example of true solution. Particles of true solution cannot be filtered through filter paper and are not visible to naked eye.

Compound is a thing that is composed of two or more separate elements; a mixture. A compound is always homogeneous (uniform). Compounds cannot be separated by physical means. Separating a compound requires a chemical reaction. The properties of a compound are usually different than the properties of the elements it contains.

A colloid is a heterogeneous mixture where the size of solute particles is intermediate between those in true solution and in suspensions.

They cannot be separated from the mixture by the process of filtration.

But they can be separated by a special technique called as Centrifugation.

Centrifugation method is used for separating suspended particles of substances from a liquid in which the mixture is rotated at high speed in a centrifuge.

Iron is one of the most common and cheapest of all metals and accounts for over 5 percent of the Earth's crust, making it fourth on the list of abundant elements. Iron combined with carbon makes steel. There is archaeological evidence that humans have used iron for thousands of years.

Tyndall effect is shown by colloidal solution. Here milk and starch solution are colloids therefore milk and starch solution will show Tyndall effect.

Particle size of true solution is very less due to which it don't scatter the light therefore path of beam of light is not visible through a true solution.

The processes proposed heretofore for the purification of ordinary camphor are of a physical or chemical kind: to the first belong the processes based on sublimation, on fractional condensation and on crystallization from aromatic solvents; to the second belong the processes using nitric acid as solvent for the impurities. Whilst the latter give no satisfactory results, those of a physical kind reach their aim, but only after costly and repeated operations.

Properties of Carbon Dioxide:
- Carbon dioxide is a chemical compound composed of one carbon atom and two oxygen atoms (CO2).
- It is a colorless and odorless gas at standard temperature and pressure.
- Carbon dioxide is denser than air and does not support combustion, making it a non-flammable gas.
- It is soluble in water, and when dissolved, it forms carbonic acid, which contributes to the acidity of water bodies.
- Carbon dioxide is a greenhouse gas, playing a significant role in global warming and climate change.
- It is produced through various natural processes such as respiration, volcanic eruptions, and decay of organic matter.
- Human activities, such as burning fossil fuels and deforestation, contribute to the increased levels of carbon dioxide in the atmosphere.
- Carbon dioxide is used in various industries, such as food and beverage production, fire extinguishers, and carbonated drinks.
- It is also used in greenhouse farming to enhance plant growth.
- In high concentrations, carbon dioxide can be harmful to humans, causing respiratory problems and asphyxiation.
Therefore, the properties of carbon dioxide are totally different from both carbon and oxygen.

Evaporation: A solid substance dissolved in a solvent can be separated by the process of evaporation. The dissolved substance is left as a solid residue after the solvent has evaporated. The solvent itself cannot be recovered by this method. Common salt is obtained from sea water by evaporation. Sea water. Trapped in shallow lakes called lagoons, is subjected to the heat of the sun. Water evaporation leaving behind salt as a solid. If any impurities are present in the dissolved solid, they would still be present after it’s recovered after its recovery by evaporation.

Crystallisation: When a hot, concentrated solution of a substance is allowed to cool slowly, crystals of pure solid are formed, while impurities remain dissolved in the solvent. This process is called Crystallisation. The crystals can be separated by filtration. An impure sample of compound, like copper sulphate or alum, can be purified by crystallization.

Unsaturated Solution: An unsaturated solution is one in which you can dissolve more quantity of solute at a given temperature.

The particle size of colloidal solution is intermediate between that of a true mixture and suspension i.e. between 1 - 1000nm. Colloidal particles are small enough and cannot be seen by naked eyes. These can be seen through a microscope. So, the correct answer is (c).

To separate a mixture of alcohol (ethanol) and water, you can use a process known as fractional distillation. This technique relies on the fact that the compounds in the mixture have different boiling points. Since ethanol boils at a lower temperature (78.5 degrees Celsius, or 173.3 degrees Fahrenheit) than water, the alcohol vaporizes while most of the water remains a liquid. A good distillation column will produce a mixture of 95 percent alcohol and 5 percent water. This ratio represents the most pure form of ethanol possible with distillation and is widely accepted as an industry standard.

The minimum temperature at which a solid melts to become a liquid at atmospheric pressure as its "Melting Point."

Correct Answer :- b

Explanation:- D-Fructose (levulose or fruit sugar) is the sweetest of all sugars. It is found in honey, corn syrup, and in the fruit and other parts of plants. It is much sweeter than sucrose (cane sugar).

Cattle diet varies from one period to another period. Generally the diet of cattle includes 15-10% of roughage and rest of them includes concentrate and other materials.

Emulsion is a colloidal solution of liquid in liquid.

The quality and taste of honey depends upon the flora, pasturage or orchards available for the nector and pollen collection. Pasturage/orchard flora of honey bees include a variety of flowering plants such as mango (aam), coconut (narial), almond (badam), tamarind (imli), ber, Berseem, litchi, cotton,shishame,apple,mahua,coriander,cashew,coffee,rubber plants,guava,sunflower,neem etc.