Solutions Unit 4 Chemistry Notes PDF

Water and Its Properties Most compounds with molecular masses similar to that of water (methane, for example) are gases at room temperature. Their molecules are small, with relatively few electrons, so their intermolecular forces are weak. Not much energy is required to overcome the forces and allow...

Water and Its Properties Most compounds with molecular masses similar to that of water (methane, for example) are gases at room temperature. Their molecules are small, with relatively few electrons, so their intermolecular forces are weak. Not much energy is required to overcome the forces and allow the molecules to move independently. The fact that water is a liquid at ambient temperatures suggests that its intermolecular forces are unusually strong. Recall that for a compound to exist as a liquid or solid, its intermolecular forces must be strong enough to “stick” the molecules together. The strength or “stickiness” of this attraction increases as the size or polarity of the molecules increases. A methane molecule, for example, consists of a central carbon atom bonded to 4 hydrogen atoms. Since the electronegativity difference between carbon and hydrogen is small, each carbon-to-hydrogen bond is slightly polar. However, the symmetrical arrangement of these bonds around the central carbon atom makes the methane molecule non-polar. In Chapter 3, you learned that the only type of intermolecular attraction between non-polar molecules is the London dispersion force. Since this is the weakest of all intermolecular attractions, small non-polar molecules such as methane are gases at room temperature Hydrogen chloride is a molecular compound consisting of a hydrogen atom cova- lently bonded to a chlorine atom. Since chlorine has a greater electronegativity than hydrogen, the chlorine atom attracts the bonding electron pair more strongly. The result is a polar covalent bond and a polar molecule. Recall that the intermolecular attractions between the molecules of a polar compound such as hydrogen chloride are both London dispersion forces and dipole–dipole forces. In Chapter 3, you also learned that the H−O bond in the water molecule is highly polar. The water molecule is highly polar because of these polar bonds and their asymmetrical arrangement. Hydrogen bonds form between the hydrogen atom of one water molecule and the oxygen atom of a nearby molecule. Hydrogen bonding is a special type of dipole–dipole intermolecular force. Although water molecules also experience London dispersion forces, it is the hydrogen bonding that provides the additional “stickiness” to hold water molecules together as a liquid, up to almost 100 °C The Significance of Hydrogen Bonding Hydrogen bonding accounts for many of the unique physical properties of water. These properties are very significant for life on Earth Property Physical or biological significance high melting and boiling points permits water to exist as a liquid at room temperature keeps body fluids liquid over a large range of temperatures expansion when cooling from 4 °C to 0 °C causes ice to float causes water to freeze from the top down, allowing life to continue below it high surface tension pulls water into round droplets allows small insects to “walk on water” ability to exchange thermal energy with little change in temperature enables water to absorb a great deal of thermal energy for a small increase in temperature and to release a great deal of energy for a small decrease in temperature has a moderating effect on temperature changes in organisms and the environment (Figure 1) inability to mix with non-polar compounds enables organisms to retain water because of a waterproof coating (e.g., wax on leaves) allows organisms to store non-polar substances (e.g., fats, oils) A solution is a homogeneous mixture of two or more substances. It is a homogeneous mixture because there is only one phase and the components are uniformly mixed, giving a uniform appearance. (“Phase” means “visible part.”) As a result, samples taken from two different locations in the solution have exactly the same composition. That is why the first few millilitres of clear apple juice taste just as sweet as the last. Solutions can be solids, liquids, or gases. Liquid and gaseous solutions are trans- parent because the entities they contain are too small to block light as it passes through. Solutions may be coloured or colourless depending on the substances they contain. Let’s consider a specific solution: the glucose solution used for intravenous (IV) drips. Glucose (sometimes called dextrose) is a form of sugar. To prepare this solution, a specific mass of glucose, C6H12O6, is first dissolved in water. After the glucose and water are thoroughly mixed, the grains of glucose are no longer visible (Figure 2). At the molecular level, the molecules within each grain have separated and are dispersed evenly throughout the flask. Each molecule is in direct contact with water molecules. Since the mass of these molecules is so small, they will never settle to the bottom of the flask. The diameter of these molecules is also extremely small (in the order of 1029 m), so light can pass directly through the mixture. The result is a clear homogeneous mixture: a solu- tion. This liquid looks just like pure water, but it is different at the molecular level. Homogeneous and Heterogeneous Mixtures Solutions are homogeneous mixtures because they are uniform and have only one phase. A heterogeneous mixture has two or more phases. Oil and vinegar is an example of a heterogeneous mixture. Even though they are both liquids, oil and vinegar (which is mostly water) separate into two distinct layers or phases. Other mixtures, such as blood and milk, at first appear to be homogeneous, but a closer look reveals that they are not. If you looked at a blood sample under the microscope you would see that it is made up of many different cells suspended in a liquid (Figure 3). Its composition is hardly uniform. Blood is a heterogeneous mixture. In fact, all liquid and gaseous mixtures that are translucent (semi-transparent) or opaque (not transparent) are heterogeneous mixtures. Air is an example of a mixture that, depending on its composition, can be either homogeneous or heterogeneous. Dry, clean air is a homogeneous mixture or solution of mostly nitrogen, oxygen, argon, and carbon dioxide. Air is transparent because the gas entities it contains are too small to interfere with the passage of light. The difference in entity size can sometimes be used to distinguish solutions from other mixtures that appear to be homogeneous. The air in your classroom may also appear to be homogeneous. However, when light from a projector passes through it, tiny suspended dust particles in the air deflect the light, making the path of the light beam visible. This is proof that the classroom air is actually a heterogeneous mixture. The same effect can also be seen in liquids (Figure 4). We can use this evidence to distinguish true solutions from mixtures that appear to be solutions. Components of a solution: concentration: the ratio of the quantity of solute to the quantity of solution or solvent; usually quantity of solute per unit volume of solution concentrated solution: a solution with a relatively large quantity of solute dissolved per unit volume of solution dilute solution: a solution with a relatively small quantity of solute dissolved per unit volume of solution Aqueous Solutions The most familiar types of solutions are aqueous solutions. An aqueous solution con- tains water as the solvent. (“Aqua” is the Latin word for water.) Most of the solutions used in your investigations are aqueous solutions, as are many common consumer products: pop, vinegar, and clear shampoo, for example. All aqueous solutions are transparent. They can be coloured or colourless. Since they are so common and have such important applications, much of this unit will focus on aqueous solutions New attempt: Lesson 8.1: - Water has unique characteristics that make it essential for life, such as its ability to exist as a liquid at room temperature due to strong intermolecular forces (hydrogen bonding). - The contrasting physical state of water compared to other similar molecular compounds (like methane) demonstrates the strength of its intermolecular forces. - Hydrogen bonding leads to important physical properties of water, including high boiling and melting points, surface tension, thermal energy retention, and non-mixing with non-polar compounds. - The water cycle plays a crucial role in purifying water, cycling it through evaporation, condensation, and other natural processes. - The global water crisis is driven by factors such as population growth, pollution, and increased demand for fresh water, particularly in developing regions. - The United Nations recognizes access to clean water as a basic human right, highlighting the need for global action to ensure potable water access for all. Lesson 8.2: - Lead exposure is harmful, especially to children, as it impairs nervous system development. - A solution is defined as a homogeneous mixture of two or more substances, existing in one phase with uniform composition. - Solutions can be solid, liquid, or gas, and can be transparent or colored, depending on their components. - For example, a glucose solution for IV drips is a homogeneous mixture of glucose dissolved in water, where glucose acts as the solute and water as the solvent. - Solutions are different from heterogeneous mixtures, which contain visibly distinct phases, like oil and vinegar. - Aqueous solutions contain water as the solvent and are common in daily life (e.g., soft drinks, vinegar). - Concentration refers to the amount of solute in a given volume of solution; solutions can be categorized as concentrated or dilute. - Alloys are solutions of metals, and amalgams are specific alloys that include mercury.  - The discussion of solutions encompasses various examples, properties, and the significance of understanding mixtures in both environmental and health contexts. Lesson 8.3: - Researchers studied Arctic Fulmars and found toxic chemicals in their excrement, suggesting pollution is entering the Arctic food chain. - High concentrations of pollutants like mercury, PCBs, and DDT were found in carnivores like seals and polar bears, indicating a fat-soluble nature of these toxins. - Dissolving process at the molecular level is explained through the dissociation of sodium chloride in water, showing how ionic bonds are broken by polar solvent interactions. - Ionic compounds dissolve in polar solvents due to strong water-ion attractions overcoming solute attractions. - Molecular compounds like ethanol are miscible in water due to hydrogen bonding, while non-polar compounds like oil are immiscible. - The concept "like dissolves like" explains solubility based on polarity; polar solvents dissolve polar solutes and non-polar solvents dissolve non-polar solutes. - Surfactants help mix oil and water by reducing surface tension and allowing interaction between non-polar and polar substances. Lesson 8.4: Dispersant Usage - Large volumes of chemical dispersants were deployed to prevent oil from forming a slick at the surface. - Dispersants work similarly to detergents, breaking down oil into smaller droplets for easier decomposition by microorganisms. - Controversy of Dispersants - Critics argue dispersants move the problem from the surface to the ocean floor, affecting bottom-dwelling organisms. - Dispersants utilized in unprecedented quantities and under extreme pressure depths, raising questions about their effectiveness and impact. - Future Considerations - Increasing offshore drilling in Canada and potential exploration near the Arctic raise concerns about oil spill response. - Engineering teams tasked to evaluate the lessons learned from Gulf spill dispersant use for future Canadian policy. - Research Questions for Evaluation How do dispersants function? Will oil break down similarly in Canadian waters? Evidence of adverse effects on ecosystems? Challenges for offshore drilling in Canada? Decision-Making on Dispersant Use Need to assess appropriateness and readiness of dispersants for Canadian waters. Explore alternative oil spill responses if dispersants are deemed unsuitable. Action Plan Investigate the current status of oil and gas exploration in Canadian waters and governmental positions on it. Opportunity for public engagement through letters to Members of Parliament regarding views on dispersant use and oil exploration. Lesson 8.5: Carbonation in Drinks: Carbon dioxide is added to beverages under pressure, creating fizz. When the cap is removed, pressure release allows gas to escape, causing the drink to go flat. Solubility Concept: Solubility is the maximum amount of solute that dissolves in a solvent at a specific temperature, typically expressed in grams of solute per 100 grams of water. Saturation Degrees: Saturated Solution: Contains the maximum solute at a given temperature; additional solute added does not dissolve. Unsaturated Solution: Less than the maximum solute; additional solute will dissolve. Supersaturated Solution: Contains more solute than equilibrium allows; often unstable, where solute can crystallize out upon disturbance. Solubility Curve: A graph showing how solubility changes with temperature. Points on the curve indicate saturation, below indicate unsaturation, and above indicate supersaturation. Solubility Trends: Solubility of solids usually increases with temperature. Solubility of gases generally decreases with increased temperature. Gas solubility increases with higher pressure. Environmental Impacts: Oxygen solubility impacts aquatic life; warm water holds less oxygen, stressing fish. Thermal pollution (e.g., from industrial discharges) can reduce dissolved oxygen levels in water, harming aquatic ecosystems. Decompression Sickness: Scuba divers risk gas bubbles forming in blood if ascending too quickly from depths, due to decreased pressure allowing dissolved gases to come out of solution. Practical Applications: Tests for saturation can be performed by adding more solute and observing if it dissolves. The solubility of compounds varies; knowledge of these properties is vital for many scientific and industrial applications. Experimental Investigation: A procedure to create and observe a supersaturated solution using sodium thiosulfate pentahydrate can demonstrate these principles in action. Lesson 8.6: Hazards of Jumper Cables: Jumpstarting a dead car battery can be dangerous due to the production of hydrogen gas, which is flammable and can cause explosions if ignited by a spark. Conventional Car Batteries: Composed of lead plates in concentrated sulfuric acid, hydrogen gas is produced, which can accumulate in poorly ventilated areas. Chemical Burns: Concentrated sulfuric acid can cause painful burns; diluted forms used in laboratories are less hazardous. Concentration Definition: Refers to the quantity of solute per unit volume of solution. Concentrated Solution: Contains a large amount of dissolved solute. Dilute Solution: Contains a small amount of dissolved solute. Amount Concentration: The term used to express solution concentration in moles per liter (mol/L), previously known as molarity. IUPAC Guidelines: Prefers the term "amount concentration" for clarity in terminology. Formula: c = n/V, where c = amount concentration, n = moles of solute, V = liters of solution. Stock Solutions: Concentrated solutions intended for dilution before use in experiments. Dilution Process: Requires careful addition of acid to water to prevent dangerous reactions and splattering due to thermal energy. Safety Reminder: Always add acid to water, not the reverse. Calculating Concentration and Mass: Use formula c = n/V to find concentration or rearrange to find moles or mass of the solute based on given data. Sample calculations showed how to find amount concentration and mass required for specific volumes and concentrations. Standard Solution: A solution with a precise, known concentration, typically prepared using volumetric flasks for accuracy. Practical Skills: Describes methodical steps for preparing solutions and orders of operations, highlighting importance of measurements and conversions. Safety in Storage: Standard solutions should be stored in sealed containers to prevent contamination and concentration changes. Potential Exam Questions: Covering key concepts like concentration definitions, acid dilution methods, calculations related to concentrations, and why standard solutions are precisely measured. Lesson 8.7: Concentrated Products: Concentrated forms of cleaners or fruit juices are often diluted before use, making them economical and environmentally friendly due to reduced packaging and shipping costs. Dilution Process: Dilution involves adding solvent (usually water) to a concentrated solution to decrease its concentration. For example, diluting orange juice concentrate involves mixing it with three cans of water. Dilution Factors: The concentration of a solution decreases based on the volume increase. For instance, diluting 1.0 L of 12 mol/L hydrochloric acid to 4.0 L results in a final concentration of 3.0 mol/L, effectively reducing the concentration by a factor of 4. Volumetric Glassware: Precise measurement tools like volumetric pipettes and graduated pipettes are crucial for making accurate dilutions. Volumetric pipettes deliver fixed volumes, while graduated pipettes allow for a range of volumes. Dilution Calculations: To determine final concentrations, the formula used is based on the principle that the number of moles of solute remains constant after dilution: c_c * V_c = c_d * V_d Where: c_c = concentration of the concentrated solution V_c = volume of the concentrated solution c_d = concentration of the diluted solution V_d = volume of the diluted solution Sample Calculation: Example problem shows how to find the concentration after diluting 250 mL of 16.0 mol/L nitric acid to 4.5 L, resulting in 0.89 mol/L final concentration. Practice Problems: The summary includes several practice problems to reinforce the dilution calculation concept, with provided answers for self-checking. Applications: The use of dilutions has practical applications at home (e.g., cleaning products) and in laboratories where precise concentrations are required. Environmental Considerations: Transporting concentrated chemicals is more environmentally friendly as it reduces the volume/weight transported, but poses risks if not managed properl Lesson 8.8: Hydrogen Peroxide in Hair Kits: Used to lighten hair color through a process called "lifting." The extent of color lift depends on the concentration of hydrogen peroxide and duration of contact with hair. Higher concentrations (e.g., 30 volume) lift color faster but may cause more damage. Concentration Expressions: Common methods include: Volume/Volume (% V/V): Indicates the volume of solute in a total volume of solution. Example: 50% isopropyl alcohol means 50 mL of alcohol in 100 mL solution. Weight/Volume (% W/V): Indicates mass of solute in a specified volume of solution. Example: 6% W/V hydrogen peroxide means 6 g of hydrogen peroxide in 100 mL of solution. Weight/Weight (% W/W): Indicates mass of solute per mass of solution. Example: 5% W/W benzoyl peroxide means 5 g in 100 g of the mixture. Calculating Concentrations: Formulas used for calculations include: % V/V = (Volume solute / Volume solution) * 100% % W/V = (Mass solute / Volume solution) * 100% % W/W = (Mass solute / Mass solution) * 100% Example Problems: Illustrate calculating concentrations using the above formulas and solving dilution problems. Very Low Concentrations: Expressed in parts per million (ppm), parts per billion (ppb), and parts per trillion (ppt). Example: 1 ppm is 1 g of solute in 1,000,000 g of solution and often used for small contaminant concentrations. General Units in Concentrations: % V/V: liquid-liquid mixtures. % W/V: solid-liquid mixtures. % W/W: mixtures of solids or liquid-solid mixtures. ppm: small concentrations in various applications. BPA Controversy: Research needed on its sources, health risks, and effects of toxic designations. Points for consideration include impact on manufacturers and viable alternatives. Summary of Practical Applications: Importance of standardized concentration expressions in industry and various consum Lesson 9.2: Types of Water Contaminants: Physical Contaminants: Include debris and suspended particles that cloud water and can interfere with disinfection. Biological Contaminants: Bacteria, viruses, and protozoa, often introduced through waste, posing health risks like E. coli contamination from sewage or agricultural runoff. Chemical Contaminants: Water-soluble substances from industrial and agricultural sources, including heavy metals and organic solvents, that pose various health concerns. Water Quality Standards: Health Canada sets guidelines for acceptable contaminant levels in drinking water, with provincial and territorial governments implementing testing programs to ensure compliance. Water Treatment Process: Involves several steps designed to remove contaminants and make water potable, including collection, treatment, disinfection, and sometimes softening to reduce mineral content. Water Softness: Hard water contains high levels of calcium and magnesium, leading to issues like soap scum and clogged appliances; residential water softeners often use ion-exchange resins to remove hardness. Health and Economic Benefits: Improvement in water quality and sanitation can lead to significant health benefits and economic returns, enhancing productivity and education. Lesson 9.3: Chemical Analysis Types: Qualitative Analysis: Identifies specific substances (e.g., using color change). Quantitative Analysis: Measures concentration of substances (e.g., X-ray diffraction). Precipitation Reactions: Certain ions can be detected using differences in solubility (e.g., lead ions form yellow PbI2 precipitate). Identifying Cations: Example of analysis workflow demonstrates steps to identify lead and barium ions through specific reagent additions: Add KI to check for lead ions (yellow precipitate). Filter out lead precipitate, then test filtrate for barium. Flame Tests: An alternative method for identifying cations through characteristic flame colors; limitations exist in mixtures. Spectroscopy: An advanced method to analyze light emissions for qualitative and quantitative data. Applications extend to environmental monitoring and astrophysics. Summary of Key Concepts: Health risks can be mitigated by identifying and minimizing exposure to harmful substances. Use of solubility tables enhances qualitative analysis efficiency. Correct procedure order is essential in chemical testing to avoid false positives. Technological advancements facilitate deeper scientific understanding and broader applications.