Separating Mixtures Chapter 6.4 PDF

6.4 Separating Mixtures Does your family LEARNING TIP have a “junk drawer” Before reading this somewhere, maybe in section, “walk” through it, looking...

6.4 Separating Mixtures Does your family LEARNING TIP have a “junk drawer” Before reading this somewhere, maybe in section, “walk” through it, looking at the headings. the kitchen or near What ways of separating the door (Figure 1)? mixtures do you think you Have you ever tried will learn about? to sort out all the items that have collected in the drawer? In everyday life, there are many situations in which people want to separate the parts of a Figure 1 mixture. For example, How could the boy separate the items in the drawer? you do not want to drink water that contains algae or fish, or dissolved chemicals from factories. You prefer to have these removed from the water before it is pumped to your home. Harmful or toxic substances from factories must be removed from any waste products before the waste products can be released into the environment. Depending on the mixture involved, separating the parts can be easy or difficult. In this section, you will learn about some ways to separate different types of mixtures. Picking Apart You would probably separate the mixture in a junk drawer by simply taking out the different items—tools, elastic bands, scrap paper, and so on. You would use observable properties, such as shape and colour, to separate the mixture. If the pieces in a mixture are smaller, you might have to use a magnifier and forceps. Picking apart works when you can easily see the different pieces (Figure 2). It only works Figure 2 well for small quantities of mixtures. It is too time-consuming to use Picking apart a mixture for large quantities. 148 Unit B Chemistry NEL Filtering You can remove solid pieces of matter from a liquid or gas by passing the mixture through a device that allows smaller particles to pass through but holds back larger particles. This is called filtering (Figure 3). Drinking water is an example of a mixture that is filtered. The water passes through a filter, which allows the liquid through but holds back larger particles. The liquid that passes through is called the filtrate and the solid material that is held back by the filter is called the residue. There are many other examples of filtration. Air is filtered in car Figure 3 engines and factory smokestacks. Window screens act as filters to Filtering a mixture keep flies and mosquitoes out of homes. Workers who use spray paint wear facemasks so that they do not breathe in droplets of paint. Tea bags keep tea leaves out of tea, and coffee filters keep coffee grounds out of coffee. Even very small pieces of substances can be removed from mixtures by filtration if the holes in the filter are small enough. Thus, filters can be used to separate solids from mechanical mixtures or suspensions. Filters cannot be used, however, to separate parts of solutions. Using Density Density can also be used to separate mixtures. If the substances in a mechanical mixture have different densities, one substance may float and another may settle to the bottom (Figure 4). For example, density can be used to separate a mixture of sand and wood chips. Figure 4 If water is added to the mixture, the wood chips float and the sand Using density to separate sinks, making the mixture easy to separate. a mixture Using Magnetism Magnetism can be used to separate a mechanical mixture if one of the substances in the mixture is attracted to a magnet (Figure 5). This works well for a mixture of iron filings in sand. iron filings and sand Figure 5 Using magnetism to separate a mixture NEL 6.4 Separating Mixtures 149  Dissolving You can sometimes dissolve one of the substances in a mixture. When a substance dissolves, it mixes completely with another substance. For example, if you add water to a mixture of sand and salt, the salt dissolves. This makes the undissolved sand easier to separate out of the mixture by filtering (Figure 6). salt and sand Evaporating You can also evaporate part of a solution to get a substance dissolved Figure 6 in it (Figure 7). For example, you can evaporate the water from a cup Dissolving one of the substances in a mixture of tea. The solid that remains is the tea. Sometimes, the solid that remains crystallizes. For example, when the water evaporates from a salt-water solution, the salt crystallizes. CHECK YOUR UNDERSTANDING salt-water solution 1. Describe the method you would use to separate each mixture in Figure 8. Figure 7 Evaporating one of the substances a) marbles and b) sand and c) oil and d) salt and in a mixture foam balls water water pepper e) wood chips and f) sand and g) sugar and h) aluminum nails pieces of brick pebbles water and iron nails Figure 8 2. List several different filters in your home and school. What is the purpose of each filter? 150 Unit B Chemistry NEL