سؤال قراءة ستيب محلول — المفردات في السياق (تدريب 6093)

(1) Many mixtures contain useful substances mixed with unwanted material. In order to obtain these useful substance s, chemists often have to separate them from the impurities. Chemists have developed many different methods of separation. Filtering (2) When a cup of tea is poured through a tea strainer, this is a filtering process. Filtration is a common separation technique used in chemistry laboratories throughout the world. It is used when a solid needs to be separated from a liquid. For example For example, sand can be separated from a mixture with water by filtering through filter paper. The filter paper contains holes that are large enough to allow the molecules of water through but not the sand particles. The sand gets trapped in the filter paper and the water passes through it. Decanting (3) Vegetables do not dissolve in water. When you have boiled some vegetables, it is easy to separate them from the water by pouring it off. This process is called decanting. This technique is used quite often to separate an insoluble solid (a solid that doesn’t dissolve) from a liquid. Centrifuging (4) Another way to separate a solid from a liquid is to use a centrifuge. It is usually used when the solid particles are so small that they spread out throughout the liquid and remain mixed. They do not settle to the bottom of the container, as heavier particles would do, under the force of gravity. The technique of centrifuging involves the liquid being spun round very fast in a centrifuge so that the solid gets flung to the bottom of the tube What does the writer think about the process of separating mixtures?