Solutions, Suspensions And Colloids | Is Matter Around us Pure?

2.2 What is a Solution? A solution is a homogeneous mixture of two or more substances. You come across various types of solutions in your daily life. Lemonade, soda water etc. are all examples of solutions. Usually we think of a solution as a liquid that contains either a solid, liquid or a gas dissolved in it. But, we can also have solid solutions (alloys) and gaseous solutions (air). In a solution there is homogeneity at the particle level. For example, lemonade tastes the same throughout. This shows that particles of sugar or salt are evenly distributed in the solution. Alloys: Alloys are homogeneous mixtures of metals and cannot be separated into their components by physical methods. But still, an alloy is considered as a mixture because it shows the properties of its constituents and can have variable composition. For example, brass is a mixture of approximately 30% zinc and 70% copper. A solution has a solvent and a solute as its components. The component of the solution that dissolves the other component in it (usually the component present in larger amount) is called the solvent. The component proportion of the solute and solvent can be varied. Depending upon the amount of solute present in a solution, it can be called a dilute, concentrated or a saturated solution. Dilute and concentrated are comparative terms. In activity 2.2, the solution obtained by group A is dilute as compared to that obtained by group B. of the solution that is dissolved in the solvent (usually present in lesser quantity) is called the solute. Examples: Activity 2.3 (i) A solution of sugar in water is a solid in liquid solution. In this solution, sugar is the solute and water is the solvent. Take approximately 50 mL of water each in two separate beakers. Add salt in one beaker and sugar or barium chloride in the second beaker (ii) A solution of iodine in alcohol known as 'tincture of iodine', has iodine (solid) as the solute and alcohol (liquid) as the solvent. with continuous stirring. When no more solute can be dissolved, heat the contents of the beaker. Start adding the solute again. (iii) Aerated drinks like soda water etc., are Is the amount of salt and sugar or barium chloride, that can be dissolved in water at a gas in liquid solutions. These contain carbon dioxide (gas) as solute and water (liquid) as solvent. (iv) Air is a mixture of gas in gas. Air is a homogeneous mixture of a number of gases. Its two main constituents are: oxygen (21%) and nitrogen (78%). The other gases are present in very small quantities. given temperature, the same? At any particular temperature, a solution that has dissolved as much solute as it is capable of dissolving, is said to be a saturated solution. In other words, when no more solute can be dissolved in a solution at a given temperature, it is called a saturated solution. The amount of the solute present in the saturated solution at this temperature is called its solubility. If the amount of solute contained in a solution is less than the saturation level, it is Properties of a solution A solution is a homogeneous mixture. The particles of a solution are smaller than 1 nm (10ºmetre) in diameter. So, they cannot be seen by naked eyes. Because of very small particle size, they do not scatter a beam of light passing through the solution. So, the path of light is not visible in a solution. The solute particles cannot be separated from the mixture by the process of filtration. The solute particles do not settle down when left undisturbed, that is, a solution is stable. called an unsaturated solution. What would happen if you were to take a saturated solution at a certain temperature and cool it slowly. We can infer from the above activity that different substances in a given solvent have different solubilities at the same temperature. The concentration of a solution is the amount of solute present in a given amount (mass or volume) of solution, or the amount of solute dissolved in a given mass or volume of solvent. Concentration of solution = Amount of solute/ 2.2.1 CONCENTRATION OF A SOLUTION In activity 2.2, we observed that groups A and B obtained different shades of solutions. So, Amount of solution Or we understand that in a solution the relative Amount of solute/Amount of solvent There are various ways of expressing the concentration of a solution, but here we will learn only two methods. (i) Mass by mass percentage of a solution The particles of a suspension can be seen by the naked eye. The particles of a suspension scatter a beam of light passing through it and make its path visible. The solute particles settle down when a suspension is left undisturbed, that is, a suspension is unstable. They can be separated from the mixture by the Mass of solute x100 %3D Mass of solution (ii) Mass by volume percentage of a solution Mass of solute x100 Volume of solution process of filtration. Example 2.1 A solution contains 40 g of common salt in 320 g of water. Calculate the concentration in terms of 2.2.3 WHAT IS A COLLOIDAL SOLUTION? The mixture obtained by group D in activity 2.2 is called a colloid or a colloidal solution. The particles of a colloid are uniformly spread throughout the solution. Due to the relatively smaller size of particles, as compared to that of a suspension, the mixture appears to be homogeneous. But actually, a colloidal solution is a heterogeneous mixture, for example, milk. mass by mass percentage of the solution. Solution: 40 g Mass of solute (salt) Mass of solvent (water) = 320 g We know, Mass of solution = Mass of solute + Mass of solvent Because of the small size of colloidal = 40 g + 320 g = 360 g particles, we cannot see them with naked eyes. But, these particles can easily scatter a beam of visible light as observed in activity 2.2. This scattering of a beam of light is called the Tyndall effect after the name of the Mass percentage of solution Mass of solute x100 Mass of solution scientist who discovered this effect. Tyndall effect can also be observed when a fine beam of light enters a room through a small hole. This happens due to the scattering of light by the particles of dust and smoke in 40 x100 =11.1% 360 2.2.2 What is a suspension? the air. Non-homogeneous systems, like those obtained by group C in activity 2.2, in which solids are dispersed in liquids, are called suspensions. A suspension is a heterogeneous mixture in which the solute particles do not dissolve but remain suspended throughout Path of - light Torch becomes visible the bulk of the medium. Particles of a suspension are visible to the naked eye. (a) (b) Properties of a Suspension Fig. 2.3: (a) Solution of copper sulphate does not show Tyndall effect, (b) mixture of water and milk shows Tyndall effect. Suspension is a heterogeneous mixture. Tyndall effect can be observed when sunlight passes through the canopy of a dense forest. In the forest, mist contains tiny droplets of water, which act as particles of colloid dispersed in air. They cannot be separated from the mixture by the process of filtration. But, a special technique of separation known as centrifugation (perform activity 2.5), can be used to separate the colloidal particles. The components of a colloidal solution are the dispersed phase and the dispersion medium. The solute-like component or the dispersed particles in a colloid form the dispersed phase, and the component in which the dispersed phase is suspended is known as the dispersing medium. Colloids are classified according to the state (solid, liquid or gas) of the dispersing medium and the dispersed phase. A few common examples are given in Table 2.1. From this table you can see that they are very common everyday life. Fig. 2.4: The Tyndall effect uestions Properties of a colloid A colloid is a heterogeneous mixture. The size of particles of a colloid is too small to be individually seen by naked 1. Differentiate between homogen- eous and heterogeneous mixtures with examples. 2. How are sol, solution and suspension different from each other? еyes. Colloids are big enough to scatter a beam of light passing through it and make its path visible. They do not settle down when left undisturbed, that is, a colloid is quite stable. 3. To make a saturated solution, 36 gof sodiumchloride is dissolved in 100 g of water at 293 K. Find its concentration at this temperature. More to know