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7. Set up a filtration apparatus and filter each mixture separately. Is there any residue left on the filter paper? 8. Based on your observations, do you think these are the same types of mixtures or are they different? These are indeed different types of mixtures. How? Let us explore further! 5.2 Solutions Grade 8 CuriosityYou have learnt that solutions are homogeneous mixtures. You have also Chapter 9learnt that solutions are prepared when a solute (the substance that gets dissolved) is mixed with a solvent (the substance that dissolves the solute). In the mixture of sugar and water, sugar is the solute, and water is the solvent. In what proportion are a solute and a solvent present in a solution? Can these be expressed quantitatively? 5.2.1 Concentration of a solution Grade 6 You have learnt how Oral Rehydration Solution (ORS) is prepared. We add Chapter 6specified amounts of salt and sugar to a fixed amount of water to prepare ORS. If we change the amount of salt or sugar added to the same volume of water, or change the volume of water for the specified amounts of salt and sugar, we will get a solution of salt and sugar in water, but that will Note not be ORS. In other words, we cannot freely add any amount of salt and Not all sugary sugar to a fixed amount of water to make ORS. drinks prepared Let us take another example. When farmers spray pesticides on their at home or sold crops, they must mix the right amount of pesticide with a fixed amount of in the market water to prepare a solution. If they do not do so, what is likely to happen? are ORS. Too little pesticide may not protect crops, while too much can damage crops, soil and the environment. Can you think of other such examples? Meet a Scientist The right proportion is always essential when preparing a Dilip solution. Mahalanabis, an Indian The amount of solute dissolved in a given amount of paediatrician, solvent or solution is termed as the concentration of the first solution. developed Understandingconcentrationisessentialnotonlyinscience and laboratories but also in everyday life, whether in medicine, implemented the treatment agriculture, food, cosmetics, or even while making a simple for dehydration caused by diseases, such as cup of tea! diarrhoea and cholera. He formulated the ORS that has 5.2.2 How do we express concentration? revolutionised rehydration Let us now explore the different ways to express the therapy. It has saved millions concentration of a solution, and understand where and why of lives after the World each method is more suitable. Health Organization (WHO) Collect some commercial packaged products (Fig. 5.4) and popularised it worldwide. note down the information given for each item. 74 Exploration|Grade 9