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Questions and Answers
What ion does a cation-exchange resin primarily exchange for positive ions in water?
What ion does a cation-exchange resin primarily exchange for positive ions in water?
Deionised water is produced by passing water through a device that only contains cation exchange resin.
Deionised water is produced by passing water through a device that only contains cation exchange resin.
False
What happens to the Na^+ ions in the cation-exchange resin after prolonged use?
What happens to the Na^+ ions in the cation-exchange resin after prolonged use?
They are replaced and the resin needs to be replenished.
What causes temporary hardness in water?
What causes temporary hardness in water?
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The process of producing deionised water combines cation-exchange resin and __________ resin.
The process of producing deionised water combines cation-exchange resin and __________ resin.
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Match the type of water with its characteristic:
Match the type of water with its characteristic:
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Permanent hardness can be removed by boiling the water.
Permanent hardness can be removed by boiling the water.
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Which of the following ions is not exchanged by the cation-exchange resin?
Which of the following ions is not exchanged by the cation-exchange resin?
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What is formed when soap is added to hard water?
What is formed when soap is added to hard water?
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Hard water has advantages and disadvantages, including providing calcium for teeth and bones.
Hard water has advantages and disadvantages, including providing calcium for teeth and bones.
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Temporary hardness is caused by Ca(HCO3)2 and Mg(HCO3)2, which are known as ________.
Temporary hardness is caused by Ca(HCO3)2 and Mg(HCO3)2, which are known as ________.
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What is the role of ethylenediaminetetraacetic acid (EDTA) in the experiment to determine water hardness?
What is the role of ethylenediaminetetraacetic acid (EDTA) in the experiment to determine water hardness?
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Match the following substances with their effects on water hardness:
Match the following substances with their effects on water hardness:
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Which method of removing water hardness involves boiling?
Which method of removing water hardness involves boiling?
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Ion-exchange resins can replace calcium and magnesium ions with sodium ions.
Ion-exchange resins can replace calcium and magnesium ions with sodium ions.
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What is the role of washing soda in softening hard water?
What is the role of washing soda in softening hard water?
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What is the primary purpose of adding fluorine compounds to water?
What is the primary purpose of adding fluorine compounds to water?
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Fluoridation of water is optional in Ireland.
Fluoridation of water is optional in Ireland.
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What happens if excess chlorine is added to water?
What happens if excess chlorine is added to water?
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The optimum pH for water is _____
The optimum pH for water is _____
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Match the following chemicals with their purpose:
Match the following chemicals with their purpose:
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What problem is associated with excess Sodium carbonate in water?
What problem is associated with excess Sodium carbonate in water?
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What is the total suspended solids if the mass of dry filter paper increased by 0.68 g after filtering a water sample?
What is the total suspended solids if the mass of dry filter paper increased by 0.68 g after filtering a water sample?
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To determine total dissolved solids, you must _____ the filtered water sample.
To determine total dissolved solids, you must _____ the filtered water sample.
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What is the approximate concentration of total suspended solids in water in ppm?
What is the approximate concentration of total suspended solids in water in ppm?
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Eutrophication is caused only by a decrease in plant nutrients in the water.
Eutrophication is caused only by a decrease in plant nutrients in the water.
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What is B.O.D. defined as?
What is B.O.D. defined as?
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The process used to measure heavy metal ions in water is called __________.
The process used to measure heavy metal ions in water is called __________.
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Match the following terms with their definitions:
Match the following terms with their definitions:
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Which method is used to prevent photosynthesis during B.O.D. testing?
Which method is used to prevent photosynthesis during B.O.D. testing?
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Lead ions (Pb²⁺) can have serious consequences for organisms if they accumulate in water.
Lead ions (Pb²⁺) can have serious consequences for organisms if they accumulate in water.
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What causes an increase in the growth of algae and other plants in water?
What causes an increase in the growth of algae and other plants in water?
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What color indicates the end point of the titration when using EDTA with hard water?
What color indicates the end point of the titration when using EDTA with hard water?
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The mole ratio of EDTA to calcium ions is 1:2.
The mole ratio of EDTA to calcium ions is 1:2.
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What is the total hardness of the water sample in ppm?
What is the total hardness of the water sample in ppm?
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The flocculating agent used in water treatment is __________.
The flocculating agent used in water treatment is __________.
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Match the following water treatment processes with their description.
Match the following water treatment processes with their description.
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How much solid indicator is added to the conical flask during the titration?
How much solid indicator is added to the conical flask during the titration?
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The sedimentation process typically removes 50% of the particles from the water.
The sedimentation process typically removes 50% of the particles from the water.
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What is the purpose of chlorination in water treatment?
What is the purpose of chlorination in water treatment?
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What is the main purpose of adding manganese(II) sulfate and alkaline potassium iodide to the water sample?
What is the main purpose of adding manganese(II) sulfate and alkaline potassium iodide to the water sample?
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The free iodine must be estimated using a potassium iodide solution.
The free iodine must be estimated using a potassium iodide solution.
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What color does the iodine solution turn when the excess iodide has been consumed during the titration?
What color does the iodine solution turn when the excess iodide has been consumed during the titration?
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The _____ is used to measure the concentration of dissolved oxygen in water samples.
The _____ is used to measure the concentration of dissolved oxygen in water samples.
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Which step follows the addition of concentrated sulfuric acid to dissolve the precipitate?
Which step follows the addition of concentrated sulfuric acid to dissolve the precipitate?
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Match the following steps in the procedure with their outcomes:
Match the following steps in the procedure with their outcomes:
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What concentration of thiosulfate solution is used during the titration?
What concentration of thiosulfate solution is used during the titration?
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Sewage treatment refers to the material delivered to _____ treatment plants.
Sewage treatment refers to the material delivered to _____ treatment plants.
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Study Notes
Hardness of Water
- Hard water is water that does not easily form a lather with soap. Hardness is caused by Ca²⁺ or Mg²⁺ ions dissolved in the water.
- Common soap ingredient is sodium stearate (C₁₇H₃₅COONa). In hard water, calcium or magnesium ions react with stearate ions to form insoluble calcium stearate, which floats on the water.
- Temporary hardness is hardness that can be removed by boiling the water.
- Source of temporary hardness is calcium hydrogencarbonate (Ca(HCO₃)₂) and magnesium hydrogencarbonate (Mg(HCO₃)₂).
- Boiling converts these to calcium carbonate (CaCO₃), which precipitates out of solution, and releases carbon dioxide (CO₂) and water (H₂O).
- Permanent hardness is hardness that cannot be removed by boiling the water.
- Caused by the presence of calcium sulfate (CaSO₄) or magnesium sulfate (MgSO₄) in the water.
- Heating does not precipitate these ions, so the hardness is not removed
Methods of Removing Hardness
- Distillation: Boiled water, removing all dissolved solids. Expensive
- Using Washing Soda: Washing soda (Na₂CO₃•10H₂O) reacts with Ca²⁺ ions to form calcium carbonate, which is insoluble.
-
Ion-exchange Resin: Exchanges Ca²⁺ and Mg²⁺ for Na⁺ ions.
- The resin is a cation exchange resin because it exchanges positive ions.
- Eventually, the resin needs replenishment with a concentrated sodium chloride solution to restore the Na+ ions.
-
Producing Deionised Water: Using a mixture of cation and anion exchange resins (mixed-bed resin) to remove all positive and negative ions, respectively.
- Cation resin exchanges Na⁺ for H⁺ ions.
- Anion resin exchanges Cl⁻ for OH⁻ ions.
- The H⁺ and OH⁻ ions combine to form water (H₂O).
- Distilled Water: The purest form of water, as all dissolved solids, including gases, are removed.
Advantages and Disadvantages of Hard Water
- Advantages: Provides calcium for teeth and bones, better taste, good for brewing and tanning.
- Disadvantages: Blocks pipes, leaves scale, wastes soap, produces scum
Mandatory Experiment: Determining Total Hardness
- Procedure involves using EDTA solution and an indicator to determine the total hardness in a water sample.
Water Treatment
- Screening: Removes floating debris.
- Flocculation: Coagulates small suspended particles for better sedimentation.
- Sedimentation: Allows larger particles to settle by gravity.
- Filtration: Removes remaining particles using sand filters.
- Chlorination: Sterilizes the water by killing harmful microorganisms.
- Fluoridation: Prevents tooth decay.
- pH Adjustment: Adjusts the pH level to the optimal level (7.2).
Water Pollution Overview
- Biochemical Oxygen Demand (BOD): Defined as the amount of dissolved oxygen consumed by biological action in a water sample kept at 20°C in the dark for five days.
- Eutrophication: Excessive enrichment of water with nutrients, leading to excessive growth of algae or plants—caused by fertilizers and sewage.
Pollution Caused by Heavy Metals
- Heavy metal ions like lead (Pb²⁺) can have serious consequences if they build up in water bodies.
- Atomic absorption spectrometry (AAS) can measure heavy metal concentration in water.
- Precipitation can remove certain metal ions from water.
Mandatory Experiment: Measuring Dissolved Oxygen
- Procedure involves rinsing a 250 cm³ bottle, filling it with water sample (avoiding air bubbles), adding manganese(II) sulfate, alkaline potassium iodide solution, stoppering (allowing overflow), inverting to allow precipitate to settle, adding sulfuric acid to dissolve precipitate, and then repeating the inversion till precipitate is dissolved.
- free iodine can be calculated using thiosulfate titration.
Sewage Treatment
- Primary Treatment: Removes large solids by screening and settlement.
- Secondary Treatment: Uses biological oxidation to reduce dissolved and organic matter. Activated sludge process.
- Tertiary Treatment: Removes phosphorous and nitrogen to prevent eutrophication.
Instrumental Methods of Water Analysis
- pH Analysis: Uses pH sensors.
- Atomic Absorption Spectroscopy (AAS): Used to detect heavy metals in water.
Mandatory Experiment: Estimating Free Chlorine
- Uses 5% ethanoic acid and potassium iodide solution for the procedure to estimate free chlorine in swimming pool water using either a comparator or a colorimeter , plotting a graph of absorbance versus concentration of chlorine to find the result.
Exam Questions/Summary
- Hard water is caused by calcium/magnesium hydrogen carbonate.
- Hard water causes scum when soap is used—this is due to the reaction of the Ca2+ and Mg2+ ions with soap.
- Water can be softened by ion exhange to remove positive ions.
- Flocculating agents are used to remove fine suspended particles.
- Chlorine is used to kill harmful microorganisms in water.
- Fluorine helps prevent tooth decay.
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Description
Explore the concepts of water hardness, including the causes of hard water and the differences between temporary and permanent hardness. Learn about various methods to remove hardness from water, including boiling and distillation. Test your understanding through this engaging quiz.
