Samacheer Class 6 Science - Matter Around Us

Matter is defined as anything that has mass and occupies space or volume. Matter exists in three main states: solid, liquid, and gas. In the solid state, matter has a fixed shape and fixed volume with particles tightly packed together. In the liquid state, matter has a fixed volume but no fixed shape, taking the shape of its container. In the gaseous state, matter has neither fixed shape nor fixed volume, and its particles are widely spread apart. All physical objects and substances around us are made of matter.

Before cooking, husk or fine dust particles in rice are separated by winnowing, not sedimentation. Winnowing is a process in which the mixture is exposed to wind or air current. The lighter impurities like husk and dust particles are blown away by the wind due to their lower density, while the heavier rice grains fall straight down and are collected. This method is effective because it takes advantage of the difference in weight between the rice grains and the lighter impurities. Alternatively, sedimentation can be used where the rice and impurities are placed in water, and the heavier rice grains sink to the bottom while lighter particles may float or remain suspended.

We separate mixtures because a mixture is an impure substance that contains particles of two or more different substances mixed together. By separating mixtures, we can obtain the pure components of the mixture, which can then be used for specific purposes. Separation of mixtures is important in many practical applications, such as obtaining pure drinking water from salt water through distillation, separating different components of crude oil through fractional distillation, and removing impurities from food items before cooking. Separation also helps us to identify and study the individual components of a mixture and to use them for various industrial, domestic, and scientific purposes.

An example of a mixture is 22 carat gold. This is a mixture composed of gold and copper, or gold and cadmium. This is a good example of a mixture because it contains two or more different substances that are physically combined but not chemically bonded. The gold and copper (or cadmium) retain their individual properties and can theoretically be separated by physical means such as melting and selective dissolution. The reason 22 carat gold is a mixture rather than a pure substance is that it contains approximately 92 percent gold and about 8 percent other metals like copper or cadmium, which are added to increase the hardness and durability of the gold for jewelry making.

Sedimentation is a separation process in which a mixture containing a liquid and insoluble solid particles is allowed to stand undisturbed for some time. During this process, the heavier solid particles gradually settle down and accumulate at the bottom of the container due to gravity, while the lighter liquid remains above. This settling down or deposition of heavy solids in the mixture is called sedimentation. The process relies on the difference in density between the solid particles and the liquid. After sedimentation is complete, the clear liquid can be separated from the settled solids by carefully pouring off the liquid, a process called decantation. Sedimentation is commonly used in everyday applications, such as washing rice before cooking, where dust and lighter impurities settle while heavier rice grains sink to the bottom.

Yes, a rubber ball can be called a solid. A solid is defined as a substance that has a definite shape and a definite volume or size. Although the rubber ball changes its shape when we press or squeeze it, this change is only temporary. Once we stop applying the external force, the rubber ball returns to its original shape. This property of returning to the original shape after the removal of external force is called elasticity. Therefore, despite its ability to change shape under pressure, a rubber ball still qualifies as a solid because it has a fixed volume and a definite shape under normal conditions.

The picture shows the sieving method of separation. Sieving is used to separate solid particles of different sizes from a mixture. In this method, a sieve or strainer with small holes is used. Particles smaller than the holes pass through the sieve and fall below, while larger particles are retained on the sieve. Common examples of sieving include separating bran from flour during grain processing and separating sand from gravel. This method is simple, quick, and effective for separating dry mixtures where the components have different particle sizes.

Food adulteration is the process of mixing harmful, unwanted, or inferior substances with pure foodstuffs that we buy in the market. These adulterants are added to increase the quantity of food, reduce its cost, or improve its appearance, but they are often injurious to health. Common examples of food adulteration include adding water to milk, mixing cheap oils with expensive oils, adding artificial colors or preservatives, or mixing stones or dirt with grains. Food adulteration is a serious problem that affects public health and is illegal in most countries. Consumers should be aware of adulterated food and purchase from trusted sources to ensure they consume pure and safe food.

To separate the mixture of chalk powder, mustard oil, water, and coins, multiple separation methods must be used in sequence. First, hand-picking can be used to remove the coins since they are large and easily visible. Next, sieving can be used to separate the chalk powder from the remaining mixture. Then, decantation or filtration can be used to separate the water from the mustard oil, as they are immiscible liquids with different densities. Finally, evaporation can be used to separate any remaining components if needed. The flow chart would show: mixture → hand-picking (remove coins) → sieving (separate chalk powder) → decantation or filtration (separate water and mustard oil) → individual components separated.

The groundnuts should be separated from urad-dhal using the hand-picking method. This method is suitable because groundnuts and urad-dhal have significant differences in their size and appearance. Groundnuts are much larger than urad-dhal seeds, making them easily distinguishable by sight. In the hand-picking method, the mixture is spread on a flat surface and the larger groundnuts are manually picked out one by one and separated from the smaller urad-dhal. This method is simple, does not require any special equipment, and is very effective for separating components of different sizes. Hand-picking is commonly used in households and in food processing to remove unwanted materials or to separate different types of grains and legumes based on their size and appearance.