Solutions, Suspensions, and Colloids PDF

Solutions, Suspensions, Colloid. Chemistry SOLUTIONS A solution is a homogeneous mixture consisting of two or more components, one of which is usually a liquid. The major component of a solution is known as the solvent and the minor component is known as the solute. Some solutions may conta...

Solutions, Suspensions, Colloid. Chemistry SOLUTIONS A solution is a homogeneous mixture consisting of two or more components, one of which is usually a liquid. The major component of a solution is known as the solvent and the minor component is known as the solute. Some solutions may contain more than one solute, e.g. sea water. The solute and solvent can be gases, liquids or solids. When a gas or a solid dissolves in a liquid, the liquid is always the solvent, e.g. in a mixture of salt in water, salt is the solute and water is the solvent Solutions A saturated solution is one that contains as much solute as can be dissolved at a particular temperature in the presence of undissolved solute. Suspensions A suspension is a heterogeneous mixture containing minute particles which are visible to the naked eye. If left undisturbed, the particles in a suspension eventually settle. The components of a suspension can be separated by filtration.  Examples of Suspension Dust in air is a suspension of a solid in a gas. Powdered chalk in water is an example of a suspension of a solid in a liquid. Muddy water is another example of a solid suspended in a liquid. Colloids A colloid is a heterogeneous mixture containing particles that are intermediate in size between those of a solution and those of a suspension. The particles in a colloid cannot be seen even with a microscope, and if left undisturbed they do not settle. The properties of a colloid are intermediate between those of a solution and those of a suspension. Examples Colloids Smoke in air is a colloid of a solid in a gas, also known as a solid aerosol. Fog and aerosol sprays in air are colloids of a liquid dispersed in a gas, also known as liquid aerosols. Milk and mayonnaise are colloids of a liquid dispersed in a liquid, also known as emulsions. Solubility Solubility The solubility of a solute is an indication of how much of the solute can dissolve in a xed mass of solvent at a particular temperature. For example, we can nd the solubility of sodium chloride in water by determining how much sodium chloride can dissolve in 10 cm3 of water at a particular temperature. When no more solute can be dissolved in the solvent, the solution reaches saturation point and we say the solution is saturated If any more solute is added to the solvent, the solute will remain in solid form and will be mixed with the saturated solution. Solubility The solubility of a solute in water is usually measured as the mass of solute that will saturate 100 g of water. Each solute and solvent combination has a specific solubility at a given temperature. The solubility of a solute in a solvent is determined by the structure of the solute and solvent, and the temperature. The effect of temperature on Solubility For most solid solutes in water, solubility increases as temperature increases. This means that as the temperature increases, a greater mass of solute will saturate a xed mass of water. A solution which is saturated at one temperature will not be saturated at a higher temperature, and if a solution which is saturated at one temperature is cooled, crystals of the solute will form since less of the solute can dissolve at a lower temperature. The effect of temperature on Solubility The unit for solubility is g per 100 g water. However, it is not practical to weigh 100 g of water.In determining solubility of a solute in water in the laboratory, we make use of the fact that pure water has a density of 1 g cm−3 In other words,1 cm3 of water has a mass of 1 g, or 1 g of water has a volume of 1 cm3.This means that 100 g of water has a volume of 100 cm3, and it is easy to measure 100 cm3 of water in the laboratory.. The effect of temperature on Solubility When we plot solubility of a solute against temperature, we draw a graph Known as a solubility curve.The solubility curve for potassium chlorate(V), KClO3 is, (refer to Chemistry for CSEC by Anne Tindale,) The effect of temperature on Solubility Looking at the solubility curve, you can see that the solubility of potassium chlorate(V) increases with an increase in temperature. Solubility curves such as this can be used to obtain various useful pieces of information, for example: The solubility of a solid at any temperature within the range of the graph. Example What is the solubility of potassium chlorate(V) at 78 °C? Solubility of KClO3 at 78 °C 35 g per 100 g water. Example The temperature at which crystals would just start to form if an unsaturated solution containing a xed mass of solute is cooled to the point where it is just saturated. Example (CSEC for Chem pg. 23) At what temperature would crystals just begin to form if an unsaturated solution of potassium chlorate(V) containing 20 g of potassium chlorate(V) dissolved in 100 g of water is cooled from 80 °C? Temperature at which 20 g of KClO3 saturates 100 g of water 55 °C. ∴ temperature at which crystals just begin to form 55 °C Separating mixtures Mixtures are a type of matter where the components can be separated by physical means. The method by which a mixture can be separated into its component parts is determined by the physical properties of these parts, e.g. particle size, boiling point, solubility. METHODS USED TO SEPARATE MIXTURES Filtration Filtration is used to separate a mixture of a solid and a liquid where the solid does not dissolve in the liquid, i.e. it is used to separate the components of a suspension. Filtration makes use of lter paper to separate the solid from the liquid. The lter paper works like a sieve, keeping back the solid particles. The solid particles are too big to pass through the lter paper, whereas the liquid particles are small enough to pass through. The part of the mixture that stays behind in the filter paper is called the residue. The part of the mixture that passes through the filter paper is called the filtrate Filtration Imagine demonstration filtration Evaporation Evaporation is used to separate a solution of a solid dissolved in a liquid, but it only allows the solid to be collected. During evaporation,the solution is boiled allowing the liquid to vaporise into the air. The solute is left behind in the container. Evaporation is a fairly rapid process and if all the liquid evaporates, the solid remaining lacks any crystalline structure. The method is not suitable if the solid to be collected is decomposed by heat. Evaporation is useful to obtain the sodium chloride from a sodium chloride solution. Evaporation Crystallisation Crystallisation is used to separate a solution of a solid dissolved in a liquid, and it only allows the solid to be collected. Unlike evaporation, the solution is not boiled, itis left in a container at room temperature for the liquid to vaporise into the air. Crystallisation is a slow process and the solid remaining has a distinct crystalline structure. t is used if a hydrated solid containing water of crystallisation is required. Crystallisation is useful to obtain hydrated copper(II) sulfate crystals (CuSO4.5H2O) from a copper(II) sulfate solution. Crystallisation Simple distillation Simple distillation is also used to separate a solution of a solid dissolved in a liquid. It allows both the solid and the liquid to be collected. Simple distillation is an appropriate method of separation only if the liquid has a lower boiling point than the solid, i.e. the liquid becomes a vapour before the solid. One of the key components of the apparatus used in distillation is a Liebig condenser. Please refer to textbook 26 for detailed method. Simple distillation Fractional Distillation Fractional distillation is used to separate a mixture of two or more liquids which are miscible and have different boiling points that are close together. Miscible liquids are liquids that are able to mix. The apparatus used in fractional distillation is similar to that used in simple distillation. However, a fractionating column is attached between a round-bottomed ask and the Liebig condenser. Fractional distillation can be used to separate a solution of ethanol and water since the boiling point of ethanol is 78°C and that of water is 100°C. Fractional Distillation Separating Funnel A separating funnel is used to separate a mixture of liquids that are immiscible and have different densities. Immiscible liquids are liquids which are unable to mix. A separating funnel is a container that has a tap at bottom, allowing one liquid to be drained off before the other. It is usually conical in shape to reduce the amount of liquids lost at the interface of the two liquids. Oil and water are two liquids that are immiscible and they have different densities. If a mixture of oil and water is placed in a separating funnel,the oil with a lower density oats on the water which has a higher density. Separating Funnel Paper chromatography Paper chromatography is used to separate a mixture of dissolved substances which are coloured or can be coloured, and which will travel through a material, e.g. lter paper. The substances are separated based on: * how soluble they are in the solvent used * how strongly they are attracted to the paper. Inks and food colourings are mixtures of two or more dyes, which can be separated by paper chromatography. Paper Chromatography Graded Activity In groups of 5 or 7, conduct a research paper on the extraction of sugar cane from sucrose. Paper should include: Title Page Introduction Definition of sucrose, extraction and sugar cane The process by which sugar cane is extracted from sucrose. Diagrams as guides Reference for information Please note that you will be penalized for plagiarism and untidy work. Paper is due October 9, 2024.