Chemistry 20 Unit 3A Solutions FITB Notes. Topic A Classification of Solutions

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1 Chemistry 20 Unit 3A Solutions FITB Notes General Outcome: Topic A Classification of Solutions Matter is a substance with and A substance is a type of matter with one definite formula (elements, compounds) ex. O 2, He, NaF, Cu 2 O A is a combination of pure substances that can be separated by physical means ex. air (N 2, O 2, others), NaBr(aq), iodized salt mixtures are not uniform in composition, so the different parts are visible mixtures are uniform, so the different parts do not appear visible A is a homogeneous mixture, made of at least one solute substance dissolved in a solvent substance The is doing the dissolving, and is usually the substance present in the largest quantity (ex. mass, volume, etc.) ex. nitrogen (78%) in air, water in the ocean The is what is dissolved by the solvent ex. carbon dioxide in air, salts in the ocean Nearly any combination of is possible A solution is not restricted to a or dissolved in another liquid! You can have various combinations of solute and solvent phases: 1. in liquid ex. alcohol in water 2. in liquid ex. NaCl in water 3. in liquid ex. CO2 in carbonated pop 4. in ex. brass alloy is made of Cu and Zn 5. in ex. mercury amalgam fillings An solution is any solution in which water is the solvent Water is referred to as the solvent because it dissolves a lot of different solutes (due to its unique properties) Therefore, we will study aqueous Fact: % of the Earth s surface is water, % of animal tissue is water dissolve in water easily, which makes it easy to get poisoned or flush toxins out! 1

2 Topic B The Dissolving Process The process of dissolving one substance in another is a change There is absolutely no chemical! However, through the entire process: bonds are and energy is or Overall, the dissolving process is either or A solute may be molecular or ionic, with different forces involved with each: a molecular solute s separate molecules are held close together by weak forces (LD, DD, HB) an ionic solute s separate ions (+ and -) are held together by bonds When dissolving occurs, these bonds must and the solute must bond with solvent The 3 steps involved in dissolving an solute in water are: 1. bonds are broken between ions of solute thermic 2. forces are broken between molecules of water thermic 3. bonds form between of solute and molecules of water thermic The 3 steps involved in dissolving a solute in water are: 1. forces are broken between molecules of solute thermic 2. forces are broken between molecules of water thermic 3. bonds form between molecules of solute and water thermic The energy change in dissolving is equal to the total of the steps involved If energy is released than required, the overall dissolving process is exothermic (substance will dissolve on its own) If energy is released than is required, the overall dissolving process is endothermic (substance will not dissolve on its own and needs heat!) The degree to which solutes dissolve depends on the strength of attraction between: 1. particles 2. particles 3. particles and particles Particle are necessary for reactions Most reactions are very if the reactant particles are not dissolved in water Dissolving in allows the solute particles to separate, disperse and collide with other solute particles Dissolving allows chemical reactions to occur at a rate! Topic C Electrolytes vs. Non-Electrolytes are aqueous solutions that conduct electricity (ions present!) ex. all soluble ionic compounds, extremely polar molecular compounds (ex. acids) are aqueous solutions that do not conduct electricity (no ions present!) 2

3 ex. molecular compounds in solution If there are, it is an electrolyte! occurs when ionic compounds separate into ions in an aqueous solution Dissociation equations describe what happens to a when it is placed in water Dissociation is a change, since it involves dissolving (not a chemical change!) You can have 4 different situations: 1. Insoluble compounds ( ) dissolve significantly ( before and after states are identical!) use the table for the ionic compounds to confirm they do not dissolve, ex. AgCl(s) AgCl(s) most hydrocarbons do not usually dissolve, ex. C 25 H 52 (s) C 25 H 52 (s) 2. Soluble ionic compounds ( ) dissolve significantly to form ions in solution (going from to states) bonds are broken use a solubility table to confirm an ionic product s ( s or aq ) balance the number of formed ex. NaCl(s) Na + (aq) + Cl - (aq) 3. Soluble molecular compounds ( ) dissolve to form (not ions) in solution (from s, l or g to aq ) intermolecular forces ( ) are broken specific gases (, ) may dissolve hydrocarbons usually dissolve! ex. C 12 H 22 O 11 (s) C 12 H 22 O 11 (aq) 4. Acids ( ) they are molecular compounds, but polar enough to (they dissolve to form ions in solution) bonding of acids is midway between and (a continuum) balance the number of in solution ex. H 3 PO 4 (s) 3H + (aq) + PO 4 3- (aq) For the following, write balanced equations and identify each as electrolyte or non-electrolyte: potassium chloride carbon dioxide solid hydrogen nitrate aluminum sulphate sodium phosphate decahydrate gasoline barium sulphate Topic D Unsaturated, Saturated and Supersaturated Unsaturated An solution doesn t contain the maximum possible amount of dissolved solute at a given temperature (it still has room) 3

4 The equation for an unsaturated solution is the exact same one as that of an or (see topic C) It is drawn with a arrow, forming a solution (from its original state to ) Saturated A solution contains the maximum possible amount of dissolved solute at a given temperature (it is ) You know it is saturated because some of the solute remains at the bottom The overall of undissolved solute at the bottom remains unchanged When the maximum amount dissolves, it seems as if the dissolving process In reality, two things occur at the same time: 1. undissolved particles continue to become dissolved ( ) 2. dissolved particles crystallize ( ) A saturated solution is said to be in a state of Equilibrium occurs when dissolving and the reverse process, crystallization, take place at the same ex. KCl We use a arrow to indicate equilibrium in a saturated solution ex. CuSO 4 (s) Cu 2+ (aq) + SO 4 2- (aq) is Cu 2+ (aq) + SO 4 2- (aq) CuSO 4 (s) is CuSO 4 (s) Cu 2+ (aq) + SO 4 2- (aq) is the Supersaturated A supersaturated solution contains dissolved solute than its allows at a given temperature It is prepared by a solution as solute is being added, and then the solution The solubility of a solute in water is greater at a higher temperature The solute may precipitate out of solution if a crystal of the solute is added, turning the solution into a giant solid chunk! A supersaturated solution is drawn with a arrow, forming a solid ( aq to s ) The single arrow indicates that the solute has completely out of solution ex. Na + (aq) + CH 3 COO - (aq) NaCH 3 COO(s) Topic E Solubility Definition The of a solute is the amount of a solute that dissolves in a given quantity of solvent at a given temperature If a solution contains the amount of solute, it is considered saturated 4

5 ex. NaCl(s) has a solubility of 36 g/100ml at 20 C (a 100 ml saturated solution would contain g of NaCl) Solid solutes can be: 1) less than 0.1 g/100ml, although there is still a tiny bit of dissolving s 2) soluble between 0.1 g/100 ml and 1 g/100 ml s 3) soluble or soluble greater than 1 g/100 ml aq have dramatically lower densities than solids, but also dissolve in water For gases, the terms insoluble, slightly soluble and very soluble correspond to far solubilities (when compared with solids) ex. g/100 ml for O 2 (g) is considered a high solubility for a gas Temperature The of solids, liquids and gases are affected differently by temperature For, the particles are held together very tightly For, the particles are not held together tightly For, the particles have a lot of kinetic energy and must first be slowed down! Solid dissolving in water: at temperatures, the particles of the solute and solvent have more energy if enough heat is added, bonds between solid particles will be therefore, solubility increases as the temperature Liquid dissolving in water: higher temperatures do not have a effect on the bonds between liquid particles additional energy is needed, because it does not help! therefore, the of most liquids is not affected by temperature Gas dissolving in water: gas particles move quickly and have a great deal of energy (i.e. heat) particles must kinetic energy (slow down) by being cooled! therefore, the solubility of gases increases as the temperature The solubility for a substance is typically given as of solute dissolved in a of solution, at a specific temperature If more solution volume is required or is available, an equation may be used: ex. The solubility of carbon dioxide in water at 20 C is 0.17 g/100 ml. Determine how much more CO 2 can dissolve if the solution is chilled to 7 C, where solubility is 0.25 g/100 ml. Assume a total solution volume of 2.0 L. Pressure A change in pressure has very little effect on the solubility of or! The solubility of gases with increasing pressure This is because there are gas particles available to dissolve at higher pressures ex. a sealed pop can is under pressure to keep gases dissolved in the pop 5

6 Miscibility Miscibility is the ability of two substances to combine to form a mixture ex. ethanol and water are miscible Miscibility may apply to or Two substances that do not form a homogeneous mixture are ex. non-polar hydrocarbons and water Topic F Solution Concentration I Dilute vs. Concentrated is the amount of solute relative to the amount of solvent in a solution Dilute = solute, solvent (low solute concentration) Concentrated = solute, solvent (high solute concentration) In both cases, there is still solvent than solute present Percent by Mass The percent by mass (m/m) tells us how much of the total solution mass (solute + solvent) is just the mass of solute: Both masses must be in the same (both in g, mg, kg, etc.) ex. 1: An aqueous solution with a mass of 55.5 g contains 2.85 g of solute dissolved in it. What is the percent by mass of the solute in the solution? ex. 2: If 30 g of Zn(s) is dissolved in 170 g of Cu(s) to make the brass that is used for musical instruments, what is the % mass of the Zn(s) in the brass? ex. 3: A patient s blood sample contains 1.4% NaCl by mass. How much NaCl is present in a 50 g sample of blood? Parts Per Million = parts per million = parts per billion 6

7 ex. Carbon monoxide is deadly at 900 ppm. If there is 8.50 g of carbon monoxide in a room that contains 11.5 kg of air, what is the concentration of CO(g) in ppm? Is the level of carbon monoxide deadly? Molar Concentration (Molarity) Moles of a substance can be calculated: Molarity (molar concentration) moles of solute per litre of solvent (mol/l): Please remember to convert into L! ex. A sample of mol NaCl is dissolved to give L of solution. What is the molar concentration of this solution? ex. Calculate the concentration of 100 ml of a solution containing mol sulphuric acid. ex. Calculate the molar concentration of a 250 ml solution that has 3.2 g of NaCl dissolved in it. ex. Calculate the number of moles of Pb(NO3)2 needed to make 500 ml of a 1.25 mol/l solution. ex. How many litres of 4.22 mol/l solution would contain 3.69 mol of BaCl2? ex. Calculate the mass of the salt required to prepare 1.50 L of a mol/l solution of K3PO4. Topic G Molar Concentration of Ions 7

8 You will have to calculate the concentration of in solution Using your unsaturated dissociation equation (topic C), you can calculate the concentration of ions in solution using a Remember: anions are ions cations are ions The typical dissociation equation looks like this: Let s use an example: H 3 PO 4 (s) 3H + (aq) + PO 4 3- (aq) xa yb + zc We can use the Mole Ratio to calculate ion concentrations (x = 1): ex. Calculate the ion concentrations in a mol/l solution of KCl. ex. Calculate the ion concentrations in a mol/l solution of Al 2 (SO 4 ) 3. You may be asked to calculate the concentration of the solute as it is put in the water This may be done using one of the ion concentrations: ex. Calculate the concentration of dissolved Na 3 PO 4 10H 2 O(s) that gives a 0.30 mol/l concentration of Na + (aq) ions. 8

9 Topic H Solution Preparation A solution of known concentration is called a solution There are two ways to make a solution: 1) a standard solution with water, or 2) dissolve a mass of pure solute in a certain volume of water (make the solution from scratch) Dilution will be covered in the next topic Many chemical solutions must be prepared from a solute and distilled water You must learn how to write a procedure to prepare a solution of a: 1) particular 2) particular molar Using concentration and volume, of the solute needed must first be determined Then the procedure may be written in four steps, so that the solution may be made: 1) Measure out g (mass) of (solute). 2) Dissolve the solute in ml (half volume) of distilled water. 3) Transfer the solution to a ml (full volume) volumetric flask. 4) Bring the solution up to ml (full volume) and mix by inverting. ex. Describe how to prepare 100 ml of a mol/l solution of KMnO 4. Topic I Dilution I Not every solution is available in the correct concentration needed 9

10 You can make a concentrated solution out of a solution of known (standard) concentration by diluting (adding more water) Dilution decreases the concentration of a solution by adding more (water) The number of of solute stays constant! In dilution, concentration decreases and volume increases (MEMORIZE): ex. What volume of 1.0 mol/l NaCl solution does a chemist need to make 250 ml of a 0.20 mol/l NaCl solution? ex. What is the concentration of a 1.50 L solution if it is made by mixing 500 ml of 14.8 mol/l H 2 SO 4 (aq) with 1.00 L H 2 O? Topic J Net Ionic Equations Net ionic equations represent chemical, not dissociation equations! The process for writing a net ionic equation will be outlined in 3 steps The net ionic equation (in the last step) will not include any ions Spectator ions are present to ionic charges, and do not chemically react! There are three types of equations involved: 1. Equation this type of equation shows all reactants and products as if they dissociate in solution ex. Pb(NO 3 ) 2 (aq) + 2KI(aq) PbI 2 (s) + 2KNO 3 (aq) 2. (total) Ionic Equation this type of equation dissociates all (ionic or acid) compounds solids, liquids and gases ex. Pb 2+ (aq) + 2NO 3 - (aq) + 2K + (aq) + 2I - (aq) PbI 2 (s) + 2K + (aq) + 2NO 3 - (aq) 3. Ionic Equation this type of equation only shows the chemical species that ions are cancelled out the coefficients if needed ex. Pb 2+ (aq) + 2I - (aq) PbI 2 (s) ex. aluminum sulphate + sodium sulphide 10

11 ex. lead (II) nitrate + potassium iodide ex. barium hydroxide and aluminum nitrate Write the non-ionic, total ionic and net ionic reactions for the following: 1) A solution of silver nitrate is poured onto a piece of copper. 2) Carbon dioxide gas is bubbled into lithium hydroxide solution to form water and lithium carbonate. 3) Sodium and hydrochloric acid are mixed. 4) Cadmium metal is added to a solution of cobalt(iii) nitrate. 5) Fluorine gas added to a solution of sodium chloride. 11

12 Topic K Qualitative Analysis of Solutions Analysis process used to identify the of specific substances in a solution (number, quantity, how much, amount, etc.) ex. breathalyzer, testing drinking water Analysis process used to test for the of specific substances in a solution (appearance, yes/no, what it looks like, quality, etc.) ex. litmus paper, solution or flame colour Advanced techniques, like atomic-absorption spectroscopy (AAS) may identify They may be used along with chemical techniques like the following: 1. Ion Colour in Solution solutions of certain cations and anions have distinct (ex. Cu 2+, blue) 2. Flame Tests many metals produce a distinctive colour of when they are (ex. K +, violet) heat will thermally excite the in the ion or atom of the metal and move them to a higher energy level when the electrons return to their energy level, they visible light at a specific wavelength 3. Precipitation Reactions a precipitation reaction is a reaction in which a solid product is formed (the precipitate) you can add a solution to an unknown solution to see if a forms this can help you distinguish between ions in the unknown solution 4. Litmus Tests Red and blue litmus paper may be used to determine if a compound is acidic, basic or neutral If both types of paper are red, it is If both types of paper are blue, it is If both types stay the same, it is 5. Conductivity A conductivity meter uses an electric current to check for If a dissolved compound is an electrolyte (contains ), it will conduct electricity If a dissolved compound is a, it will conduct electricity! If it does not, it will not conduct! ex. You have a solution that contains either aluminum ions or barium ions. What solution could you add to the unknown solution to determine which of these two ions is present? 12

13 ex. A student has two unlabeled solutions to identify. One is NaNO 3 and the other is NaCl. Suggest an aqueous solution that may be used to identify each solution (not just one of them). 13