Solutions - Hardness - Cl - N - F PDF

SOLUTIONS ESE-142P LECTURE 6 Molarity – 1 molar solution (1 M) contains 1 gram molecular weight of chemical per liter of solution. A mole is one gram molecular weight of a substance  The Number of moles of solute EXAMPLE 1: 1. Prepare a 1M NaCl solution Solution: a. Find the Molecular We...

SOLUTIONS ESE-142P LECTURE 6 Molarity – 1 molar solution (1 M) contains 1 gram molecular weight of chemical per liter of solution. A mole is one gram molecular weight of a substance  The Number of moles of solute EXAMPLE 1: 1. Prepare a 1M NaCl solution Solution: a. Find the Molecular Weight (MW) of NaCl: Na = 23 Cl = 35.44 Thus, the MW of NaCl is 23+35.44=58.44 g/mol 2. Measure the amount of NaCl required for a 1M solution: A 1M solution means you need 1 mole of NaCl in 1 liter of solution. = so you weigh, 58.44 grams of NaCl and dissolve it in enough water to make the final volume 1 liter. EXAMPLE 2: 2. Prepare a 2M HCl solution a. Molecular Weight of HCl: H = 1.0 g/mol, Cl = 35.5 g/mol. Therefore, the molecular weight of HCl is 1.0+35.5=36.5 g/mol b. 2 Moles of HCl: Since 1 mole of HCl weighs 36.5 grams, 2M would weigh: 2×36.5 g= 72.9 g c. Preparation of 2M HCl Solution: To make a 2M HCl solution, you need to weigh 72.9 grams of HCl and then dissolve it in enough water to make 1 liter of total solution. Molality – is a concentration measure based on the weight-to-weight relationship rather than a weight-to- volume relationship like molarity.  is the number of moles of solute dissolved in 1000 grams (1 kilogram) of solvent (e.g., water). Example: A 1m solution consists of 1 mole of a substance (e.g., NaCl) dissolved in 1000 grams of water (not 1 liter, since this refers to weight, not volume). Normal solution – refers to the concentration of a solution based on the equivalent weight of a substance dissolved in 1 liter of solution.  A 1 N solution contains one gram-equivalent weight of particular acid, base or salt per liter of water. To prepare 1 liter of normal solution of acid or base:  Amount of compound to furnish ion to yield 1.008 g of H+ or 17.007 g of OH-  Enough distilled water to make 1 liter  Normality of solution is its relation to normal solution, N  Half-normal solution is 0.5 N or N/2 Example Prepare N/50 Solution:  N/50 means the normality is 1/50th of 1N, or 0.02N.  In this case, we want to prepare a solution that has a concentration of 0.02N, or 2% of the strength of a 1N NaOH solution. Calculation:  To prepare an N/50 (0.02N) solution of NaOH:  We need 0.02 equivalents of NaOH per liter of water.  Since 1 equivalent of NaOH weighs 40 grams, we calculate the weight for 0.02N as: 0.02×40=0.8 grams  Therefore, 0.8 grams of NaOH is required to prepare 1 liter of a 0.02N NaOH solution. Preparation of 1N Solution: Determine the equivalent weight of the substance (e.g., acid, base).  For HCl, the equivalent weight is the same as its molecular weight (since it releases 1 mole of H⁺), i.e., 36.5 g/mol.  For NaOH, the equivalent weight is also the same as its molecular weight (since it releases 1 mole of OH⁻), i.e., 40 g/mol Normality and Neutralization Normality (N) is used to express the equivalency in chemical reactions, especially in acid-base neutralizations.  For example, 1N NaOH (sodium hydroxide) will exactly neutralize 1N H₂SO₄ (sulfuric acid) because the number of equivalents of the acid and base are equal in the reaction  The valence of sodium (Na⁺) is +1, and sulfate (SO₄²⁻) is -2. This is important in determining how much of each is needed for neutralization. Key Formula: The formula used to calculate normality during a reaction is: Problem: If 40 ml of 0.02 N NaOH is equivalent to 30 ml of CaCO , 3 what is the normality of the CaCO solution?3 Given: 40 mL of 0.02N NaOH is used 30 mL of CaCO₃ (Calcium Carbonate) solution is equivalent to the NaOH Normality of the CaCO₃ solution ? Using the formula: This calculation shows that 40 mL of 0.02N NaOH solution can neutralize 30 mL of CaCO₃ solution, and the normality of the CaCO₃ solution is 0.027N. This means that for every liter of the CaCO₃ solution, it contains enough equivalents to react with 0.027 moles of H⁺ ions Standard Solution a solution whose strength or reacting value per unit volume is known. Facilities needed for conducting volumetric analysis: 1. Equipment to measure the sample accurately, e.g. analytical balance, volumetric glassware such as pipet 2. Standard solution 3. Indicator to show stoichiometric end point 4. Calibrated burret to measure volume of standard solution Standard solutions are solutions where the concentrations are equivalent, meaning that 1 mL of reagent A will react exactly with 1 mL of reagent B. In acid-base reactions, the equivalency is based on the exchange of H⁺ (hydrogen ions) and OH⁻ (hydroxyl ions). EXAMPLE: 1 gram of hydrogen ion (H⁺) (equivalent to 1.008 grams) reacts with 1 gram ionic weight or 17.007 grams of hydroxyl ion (OH⁻), forming water: This reaction shows the fundamental principle of neutralization in acid-base chemistry, where hydrogen ions combine with hydroxyl ions to form water. Using Normality for Concentration Determination: When determining the concentration of a specific compound or ion in a solution, a solution of known normality is used because it allows precise measurements of how much reactant is needed to neutralize or react with the substance in question. Example 1: Determining Acidity Using NaOH: 0.02N NaOH is often used to measure the acidity of water, commonly expressed in terms of CaCO₃ (calcium carbonate). The NaOH neutralizes the acid in the water, allowing the acidity level to be calculated. Example 2: Determining Alkalinity Using H₂SO₄: To measure alkalinity, an acid of known normality, such as 0.02N H₂SO₄ (sulfuric acid), is used. The acid neutralizes the alkaline substances in the water, and the concentration of alkalinity can then be calculated. Example 3: Determining CO₂ in Water: When measuring carbon dioxide (CO₂) in water, which exists as H₂CO₃ (carbonic acid), a volumetric analysis method is employed using an acid-base reaction. To express the result in mg/L of CO₂ (with a molecular weight of 44), an alkaline solution with N/44 normality or 0.0227N is used. This normality corresponds to the specific amount of alkaline solution required to neutralize the carbonic acid and determine the CO₂ concentration. Stock Solution of convenient strength are prepared to formulate standard solutions of different normality.  Prepared by dissolving pure chemicals in distilled water.  1 liter stock solution of 1 N NaOH, 1 g NaOH should be dissolved in 1 liter of distilled water Indicators  Indicators serve as signal the reaching of the completed reaction  Types of indicators: electrometric, acid-base, precipitation, adsorption, oxidation – reduction Titrimetry  is the precise measurement of the concentration of ion in a solution.  It depends on carrying a chemical reaction to completion.  Titration involves adding measured amounts of a reagent by means of a burette to a measured volume of a sample.  End point – is completion of reaction; indictors show a change in color as a result of presence of a new ion. Acid-base reaction: change in pH – measured electrically or colorimetrically Electrochemically – use of device to measure current, voltage or resistance. Precipitation method: formation of precipitates, e.g. potassium dichromate K2CrO4 forms a Precipitate with silver chloride AgCl; this is used as indicator of presence of chloride Oxidation-reduction methods: adsorption indicators and those that change with oxidation reduction potential ALKALINITY. ACIDITY. pH ESE-142P LECTURE 7 Alkalinity Titration is performed in two steps using two indicators and an acid of specified normality on a single sample. Standard solution – 0.02 N H2SO4 1st end point: using 0.5% phenolphthalein indicator, changes color of sample from pink to colorless to the color of sample with an equal volume of distilled water containing same amount of phenolphthalein. 2nd end point: using 0.05% methyl orange indicator, changes color of sample from yellow topinkish orange. This image explains the alkalinity in water and how it is measured through titration with 0.02N H₂SO₄ (sulfuric acid), using two different pH indicators: phenolphthalein and methyl orange. Alkalinity in water is typically a result of three forms of ions: hydroxide (OH⁻), carbonate (CO₃²⁻), and bicarbonate (HCO₃⁻). 1. Phenolphthalein Alkalinity (pH Endpoint 8.3): Phenolphthalein alkalinity measures hydroxide (OH⁻) and carbonate (CO₃²⁻) ions. Titration with 0.02N H₂SO₄ is carried out until the pH drops to 8.3, which is the endpoint for phenolphthalein. At this point: Hydroxide ions (OH⁻) are completely neutralized. Half of the carbonate ions (½ CO₃²⁻) are converted to bicarbonate (HCO₃⁻). This is known as the caustic alkalinity (from OH⁻) and part of the carbonate alkalinity. 2. Methyl Orange Alkalinity (pH Endpoint 4.6): The methyl orange indicator is used to measure the total alkalinity, including bicarbonate (HCO₃⁻). The titration continues after phenolphthalein until the pH drops to 4.6, which is the endpoint for methyl orange. At this point, all carbonate ions (CO₃²⁻) are converted to bicarbonate. The bicarbonate (HCO₃⁻) is fully neutralized by sulfuric acid. This is the total alkalinity, including contributions from both carbonate and bicarbonate ions. ACIDITY HARDNESS WATERSOFTENING ESE-142P LECTURE 7 HARDNESS TOTAL HARDNESS = CHLORINATION ESE-142P LECTURE 7 Properties of Element Chlorine At ordinary temperature, chemical element chlorine is a poisonous, corrosive, greenish- yellow gas that has a sharp, suffocating odor and is 2 ½ times heavier than air. It is very irritating to the mucous lining of the lungs, and its inhalation in large quantities may be fatal. The gas is moderately soluble in water: 2.26 vol of water in 1 vol of water at 20oC. The gas condenses to aliquid at a temperature of –34.5oC at a pressure of one atmosphere, and freezes to a solid at –101.6oC. Chlorine is easily liquefied under pressure and is stored as a liquid in steel cylinders. When chlorine is to be dispensed as a gas, supplying thermal energy to vaporize the compressed liquid is necessary. CHLORIDES NITROGEN ESE-142P LECTURE 7  All life requires nitrogen-compounds, e.g., proteins and nucleic acids.  Air, which is 78% nitrogen gas (N2), is the major reservoir of nitrogen.  But most organisms cannot use nitrogen in this form.  Atmosphere is the reservoir of nitrogen gas  During lightning, nitrogen is oxidized to N2O5 and its union with water forms HNO3  Nitrates fertilize green plants to form proteins  Nitrogen gas is converted to protein by nitrogen “fixing” bacteria  Ammonia in soil is used by plants to further produce proteins  Humans and animals eat plants to get proteins  In the body, proteins are used for growth and repair of muscle tissues.  Proteins are released in the waste products (urine and feces) and in dead bodies  Heterotrophic anaerobic bacteria convert protein to ammonia  Non-digestible matter become part of humus  Nitrosomonas are nitrite-forming bacteria  Nitrobacter are nitrate-forming bacteria  Under anaerobic condition, nitrates and nitrites are reduced to ammonia by denitrifying bacteria  Subsequent reduction produces nitrogen gas, which cause sludge to float or buoy FLOURIDES ESE-142P LECTURE 7 Fluoride occurs naturally in most water supplies and may be added in larger concentrations above natural background in order to promote dental health. High levels of fluoride are known to cause health problems Fluoride concentrations in municipal water supplies were measured using an ion- selective electrode. Fluoride was detected in 23 of the 25 samples collected. All sites reported concentration well below EPA’s standard of 4 ppm and the WHO’s standard of 1.5 ppm METHOD OF REMOVAL FROM WATER 1. Distillation Capable of removing just about except volatile compounds from water. 2. Reverse Osmosis It relies on pressure and semi-permeable membrane to remove contaminants from water. RO can remove between 90% and 95% of fluoride depending on the efficiency of the system. 3. Activated Alumin Fluoride is strongly attracted to activated alumina (aluminium ocide0 which has a large surface area with a huge array of tunnel like pores. This is the most commonly used fluoride removal media today. When used properly it can remove up to 98% of the fluoride in water while also removing arsenic 4. BC-Carbon has been used for centuries to remove naturally occurring fluoride from water. It works similarly to the way bones in the human body attract fluoride. When use alone, BC Carbon can remove up to 90% of the fluoride in the water. Bone char works best at a slightly acidic pH and may not work as well with hard water.