The process of adding alum to water to hasten sedimentation is called 'loading'. Why has this name been given to the process? When alum is added to water, it dissolves in water and makes the suspended impurities heavier making them settle down quickly. Therefore, the addition of alum is known as loading. What is the difference between homogeneous and heterogeneous mixtures? Give an example of each mixture.
Homogeneous mixture Heterogeneous mixture The components of the mixture are uniformly distributed in the mixture. The components of a mixture are not uniformly distributed in the mixture. Example: Salt dissolved in water is a homogeneous mixture. Example: Iron filings mixed in sand is a heterogeneous mixture. Following are the properties of mixtures: The constituents of a mixture may be present in any ratio.
The constituents of a mixture retain their individual properties The molecules of the constituents do not change. For example, when iron and sulphur are mixed together, their properties do not change. Constituents of a mixture can be separated easily. For example, stones in rice can be separated easily by visual observation. It is necessary to separate a mixture into its constituents for the following situations: Removing undesirable constituents: For example, it is desirable to remove small stones in rice, or separating tea leaves from tea.
To obtain useful substances: Butter is obtained by churning curds. In the same way, crude oil can be separated into various oils such as petrol, kerosene, diesel etc. Draw a labelled diagram to show the arrangement used to filter a mixture of a liquid and an insoluble solid. The arrangement used to filter a mixture of a liquid from an insoluble solid is shown below:. Diagram of apparatus used to distil out pure waterfrom a solution. To separate a mixture of grass, pebbles and sand, the first step is to pass the mixture through a fine filter.
Sand will pass through the filter leaving grass and the pebbles on the filter. Then, we can winnow the grass and the pebbles since, they have different weights to separate them from each other. Oil and water can be separated using a separation funnel. The experimental set up is shown in the figure: The mixture of oil and water is poured into the separating funnel and allowed to stand for some time.
The oil accumulates at the top of the funnel and water near the bottom as shown in the figure. If the stop cock at the bottom is opened, water flows out of the funnel and can be collected in a beaker. If the stop cock is closed when the oil reaches the level of the stop cock, we will have oil in the funnel and water in the beaker. Water is considered an important solvent because: Water can dissolve a large number of substances that are important for life.
Waste products are also dissolved in water before they can be excreted from the body. Most of the chemical reactions occurring in the body take place in the presence of water.
Gases such as oxygen and carbon dioxide are soluble in water. This makes aquatic life possible. Yes, water can dissolve liquids such as alcohol or milk. It can also dissolve gases such as oxygen, nitrogen etc. Salt is soluble in water but chalk is not. So, if you add salt to water it will dissolve and form a clear liquid.
However, chalk will not dissolve in water and the chalk dust remains in the water. Think and write how you will separate a mixture of water, sand, salt and iron filings.
You may have to use a method not given in the chapter to separate sand and iron filings. To separate the constituents of the mixture we can use the following steps: The first step is to pass the mixture through a filter paper. This will separate out a mixture of sand and iron filings from the salt solution. Now, pass a magnet over the mixture of sand and iron filings. The iron filings will be attracted to the magnet. Finally, evaporate the salt solution and collect the vapours.
Condense the vapour to get water, while salt will be left behind. A mixture of salt and sugar is prepared by grinding them together. Do the molecules of the salt and sugar undergo any change? No, the molecules of salt and sugar remain as they are even when salt and sugar are crushed to make a mixture. A saturated solution of sugar in water is prepared. Will the solution continue to be saturated?
Give reasons. If a solution is saturated, it means that more solid will not dissolve in the solution at that temperature. If the temperature is lowered, then the solubility of sugar will be reduced even further and the solution will continue to remain saturated. Sea water has salt dissolved in it.
You know that pure water can be obtained from sea water by distillation. However, this method is not used to get drinking water from sea water.
What do you think is teh reason? Sea water has salt dissolved in it and pure water can be obtained by distillation. However, the energy required to heat large quantities of sea water to make this process widely applicable is too expensive. Also, the condensers required are very expensive if they are to be sized large enough to distill vast quantities of sea water.
As a result, distillation is not used to get drinking water from sea water. Page No Question 1: Most of the substances we see around us are a pure elements. Answer: d mixtures Most of the substances we see around us are mixtures of different elements and compounds. Question 2: A solution of salt in water is a a compound. Answer: b homogeneous mixture When salt is dissolved in water, the salt is distributed uniformly in the solution. Question 3: The property used in separating a mixture of two solids by winnowing is a difference in colour.
Answer: c difference in weight Winnowing is used to separate two solids of different weights, such as wheat and chaff. Balasubramanian R, Perumal SV, Vijayaraghavan K Equilibrium isotherm studies for the multi-component adsorption of lead, zinc, and cadmium onto Indonesian peat. Ind Eng Chem Res 48 4 — Fuel — Ecotoxicol Environ Saf — J Environ Sci Health A 52 2 — Chapman HD Cation-exchange capacity. Part 1. Agronomy monograph 9.
ASA, Madison, pp — Clay Clay Miner 59 2 — Duquette M, Hendershot W Contribution of exchangeable aluminun to cation exchange capacity at low pH. Can J Soil Sci 67 1 — Apure uptake. Int J Environ Sci Technol 3 3 — Proceedings of the 14 th International Congress. Soil science, Kyoto, Japan. Commun Soil Sci Plant Anal — Gaboriaud F, Ehrhardt J Effects of different crystal faces on the surface charge of colloidal goethite alpha-FeOOH particles: an experimental and modeling study.
Geochim Cosmochim Acta 67 5 — Soil Sci Soc Am J 40 4 — Clean Soil Air Water 40 4 — Chin J Chem 25 60 — Orient J Chem 30 3 — Kosmulski M Surface charging and points of zero charge. Book Google Scholar. Kosmulski M The pH-dependent surface charging and points of zero charge. J Colloid Interface Sci 1 :1— J Colloid Interface Sci — Bol Soc Esp de Ceram V 49 2 — J Colloid Interface Sci 1 — Ceylon J Sci — Ind Eng Chem Res 50 17 — Water Res 36 6 — Soil Sci Soc Am J 53 4 — PLoS One 9 10 :e Using appropriate scientific language and ideas to explain, evaluate and communicate their findings.
Asking their own questions about scientific phenomena. Learning outcomes Children will: Observe that some materials will dissolve in liquid to form a solution, and describe how to recover a substance from a solution.
Use knowledge of solids, liquids, and gases to decide how mixtures might be separated, including through filtering, sieving, and evaporating. Concepts supported Children will learn: That their knowledge of separating techniques can be used to solve real-life problems.
Suggested activity use This activity provides a good open-ended problem solving context for children to use their knowledge of separating mixtures to solve the incident described. Practical considerations This activity also provides an excellent assessment opportunity. Level years years. Use Practical experiments Download. Related articles. Ideas How to solve a murder TZ Combine chemical analysis and practical activities to crack a crime and engage younger students.
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