Before we move on, We have… Representing the video clips available
Lesson Outline <ul><li>distinguish among solute, solvent and solution </li></ul><ul><li>show an awareness of the importance of factors that affect the solubility and rate of dissolving of substances in homes and industries </li></ul><ul><li>show an understanding that indicators are substances that change colour when an acid or alkali is added to them </li></ul><ul><li>deduce the nature of solutions and suspensions by simple laboratory tests </li></ul><ul><li>investigate the factors affecting the solubility and rate of dissolving of substances </li></ul>
<ul><li>investigate the effect of a variety of acidic, alkaline and neutral solutions on Universal Indicator paper and natural indicators </li></ul><ul><li>investigate the effect on Universal Indicator paper when acidic and alkaline solutions are mixed </li></ul><ul><li>investigate the properties of acidic and alkaline solutions </li></ul><ul><li>show an appreciation of scientific attitudes (accuracy) in investigations on solubility and pH </li></ul>
8.1 Solutions A solution contains both solute and solvent. solute substance that the solute dissolves in <ul><li>Generally, there are three types of solutions: </li></ul><ul><li>Dilute solution – contains small amount of solute dissolved in large amount of solvent </li></ul><ul><li>Concentrated solution – contains large amount of solute dissolved in small amount of solvent </li></ul><ul><li>Saturated solution – contains maximum amount of dissolved solute in a given amount of solvent at a given temperature </li></ul>substance that dissolves solvent = = + solution = mixture in which its components are evenly mixed
When a substance dissolves in a solvent, it is soluble in that solvent. Water is known as the universal solvent as many substances can dissolve in it. Aqueous solution is thus a solution which has water as the solvent. Nature of solutions When a solution is formed, solute particles are evenly and completely mixed with the solvent particles. evenly mixed Can solutions be separated by physical methods? solvent solute Alcoholic drinks
Homogeneous (solution) = physical (e.g. colour) and chemical properties are the same in every part The solute does not settle to the bottom or float to the top when the iodine in alcohol solution is left to stand Light passes through the solution when light is shone through it. Reason : The tiny solute particles are too small to block any light passing through the solution. Filtration cannot be used to separate solutes from its solvent. Reason : The tiny solute particles can pass through the filter paper.
8.2 Suspensions A suspension = mixture containing insoluble solid particles suspended in a liquid A suspension can also consist of liquid droplets or fine solids in a gas Some example of suspensions chalk dust and water calamine lotion hazy environment medicine Nature of suspensions When a suspension is formed, solute particles remain as large visible insoluble solid particles
Heterogeneous (suspension) = physical (e.g. colour) and chemical properties are different in every part The insoluble particles will settle to the bottom or float to the top when the suspension is left to stand Light cannot pass through the suspension when light is shone through it Reason : large insoluble particles are large enough to prevent light passing through the suspension Filtration can be used to separate solute from its solvent and the residue collected is the solute Reason : The insoluble particles are too large to pass through the filter paper
8.3 Factors Affecting the Solubility of Substances Solubility = maximum amount of a solute which can dissolve in 100 g of solvent at a fixed temperature For example: 200 g of salt in 100 g of water at 30 °C <ul><li>Factors affecting the solubility of a solute in a solvent: </li></ul><ul><li>nature of the solute </li></ul><ul><li>nature of the solvent </li></ul><ul><li>temperature of the solution </li></ul>Solubility of solids and liquids when temperature Solubility of gases when temperature
8.4 Factors Affecting the Rate of Dissolving of Substances Rate of dissolving = time taken for solute to completely dissolve when it is added to a fixed amount of solvent <ul><li>Factors affecting the rate of dissolving a solute in a given volume of solvent: </li></ul><ul><li>surface area of the solute </li></ul><ul><li>temperature of the solution </li></ul><ul><li>rate of stirring </li></ul>Faster rate of dissolving 85 °C 15 °C Faster rate of dissolving
Applications at Home and in the Industry Many substances that we use are in the form of solutes, solvents and solutions. Hence, it is important to know about factors affecting the solubility and rate of dissolving of substances At home : washing machine uses hot water and rotating drum to increase the solubility and rate of dissolving of detergent in water In fizzy drinks industry : Temperature of water, Solubility and rate of dissolving extracts BUT, Temperature of water, Solubility and rate of dissolving of carbon dioxide gas So how do we increase the solubility and rate of dissolving of the extracts and gas at the same time?
8.5 Acids and Alkalis acid alkali Acids and alkalis are two common types of aqueous solutions we use every day. Acids Acids can be found all around us: Citrus fruits Contains: Citric acid Tea Contains: Tannic acid Stomach secretions Contains: Hydrochloric acid
General Properties of Acidic Solutions <ul><li>Acids are generally corrosive – they can burn our skin and react with many materials </li></ul><ul><li>All acids have sour taste </li></ul><ul><li>Acids turn blue litmus paper red </li></ul><ul><li>Dilute acids react with reactive metals to produce hydrogen gas </li></ul><ul><li>Aqueous solutions of acids are good electrical conductors </li></ul>Test for hydrogen gas: a ‘pop’ sound is heard when a burning splint comes into contact with the hydrogen gas Sodium + dilute hydrochloric acid sodium chloride + hydrogen (metal) (acid) (salt) (gas) Word equation: Go to Video 8.1
Test of carbon dioxide: Clear limewater will turn chalky when carbon dioxide passes through it (white precipitate formed) <ul><li>Dilute acids react with carbonates to produce carbon dioxide gas </li></ul>calcium carbonate + dilute nitric acid calcium nitrate + carbon dioxide + water (carbonate) (acid) (salt) (gas) Alkalis Alkalis can also be found all around us: Household cleaners Contains: Ammonia solution Soap Contains: sodium hydroxide Go to Video 8.2
General Properties of Alkaline Solutions <ul><li>Alkalis are generally corrosive – they can burn our skin and can cause bleaching </li></ul><ul><li>All alkalis taste bitter and feel soapy </li></ul><ul><li>Alkalis turn red litmus paper blue </li></ul><ul><li>Alkalis are good electrical conductors </li></ul><ul><li>Alkalis react with acid to form salts can water only </li></ul>Potassium hydroxide + nitric acid potassium nitrate + water (alkali) (acid) (salt) Go to Video 8.3
8.6 Indicators To determine how acidic or alkaline a solution is, we use a suitable indicator (e.g. litmus paper, Universal Indicator) Acidity increases Alkalinity increases Indicator = substance which changes colour according to whether the solution is acidic, alkaline or neutral Universal Indicator <ul><li>mixture of several types of indicators </li></ul><ul><li>shows a variety of colours according to the different degrees of acidity or alkalinity of the solution </li></ul><ul><li>comes with a colour chart for comparing the colour shown on it (representing degree of acidity or alkalinity) with colour chart </li></ul>Compare the colour changes of the different indicators Go to Video 8.4
A particular slide catching your eye?
Clipping is a handy way to collect important slides you want to go back to later.