Hardness of Water Quiz
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Questions and Answers

What is the primary cause of hard water?

  • Presence of sulfuric acid
  • High levels of carbon dioxide
  • Dissolved sodium ions
  • Dissolved calcium or magnesium ions (correct)

Which compound forms when soap is added to hard water?

  • Magnesium sulfate
  • Sodium hydrogen carbonate
  • Calcium stearate (correct)
  • Sodium sulfate

Which type of hardness can be removed by boiling water?

  • Permanent hardness
  • Both permanent and temporary hardness
  • Temporary hardness (correct)
  • Neither permanent nor temporary hardness

What is formed when calcium hydrogen carbonate is heated?

<p>Calcium carbonate, water, and carbon dioxide (A)</p> Signup and view all the answers

What is the main disadvantage of distillation as a method to remove hardness from water?

<p>It is too expensive for large scale use (D)</p> Signup and view all the answers

What is the role of washing soda in the context of hard water?

<p>It reacts with calcium ions to form insoluble calcium carbonate (B)</p> Signup and view all the answers

What type of resin is used in the ion-exchange method to soften water?

<p>Cation exchange resin (C)</p> Signup and view all the answers

What is the chemical formula for calcium sulfate, a contributor to permanent hardness?

<p>CaSO4 (A)</p> Signup and view all the answers

What is the purpose of rinsing the reagent bottle with deionised water?

<p>To remove any contaminants (B)</p> Signup and view all the answers

Which reagent is added to the sample to react in the redox process?

<p>Manganese(II) sulfate solution (C), Alkaline potassium iodide solution (D)</p> Signup and view all the answers

What is the indication that iodine has been released during the process?

<p>The solution becomes golden brown (D)</p> Signup and view all the answers

What is the total suspended solids concentration in p.p.m?

<p>1360 p.p.m (C)</p> Signup and view all the answers

What is the purpose of using starch indicator during titration?

<p>To signal the end point of titration (D)</p> Signup and view all the answers

How should the concentrated sulfuric acid be added to the bottle?

<p>By running it down the side of the bottle (B)</p> Signup and view all the answers

What does a high B.O.D indicate about the water quality?

<p>Low oxygen levels (C)</p> Signup and view all the answers

What should be calculated from the titration results?

<p>Dissolved oxygen in moles, grams, and p.p.m. (A)</p> Signup and view all the answers

Which method is used to measure the concentration of heavy metal ions in water?

<p>Atomic absorption spectrometry (AAS) (C)</p> Signup and view all the answers

What causes eutrophication in water bodies?

<p>Nitrates and phosphates from fertilizers and sewage (B)</p> Signup and view all the answers

What measurement technique is used to estimate the free iodine in the solution?

<p>Titration with thiosulfate solution (D)</p> Signup and view all the answers

What is the purpose of keeping one bottle in darkness during B.O.D testing?

<p>To stop photosynthesis from affecting the results (D)</p> Signup and view all the answers

What is essential to ensure during the inversion of the bottle filled with the sample?

<p>To ensure no air is trapped inside the bottle (C)</p> Signup and view all the answers

What does a low concentration of total dissolved solids indicate?

<p>Low levels of pollutants (C)</p> Signup and view all the answers

Which process is primarily used to remove heavy metal ions from water?

<p>Precipitation (D)</p> Signup and view all the answers

Why is monitoring oxygen levels in water essential for aquatic habitats?

<p>It ensures the survival of all aquatic plants and animals. (C)</p> Signup and view all the answers

What is the main aim of sewage treatment?

<p>To prevent waste from contaminating water systems (A)</p> Signup and view all the answers

Which process is involved in primary treatment of sewage?

<p>Mechanical removal of large solids (C)</p> Signup and view all the answers

What role do bacteria play in secondary sewage treatment?

<p>They decompose sewage using nutrients and oxygen (C)</p> Signup and view all the answers

What does tertiary treatment primarily remove from sewage?

<p>Phosphorous and nitrogen compounds (A)</p> Signup and view all the answers

What is the principle behind colorimetry?

<p>The absorbance of light is proportional to the concentration of a coloured solution (D)</p> Signup and view all the answers

Which method is used to detect heavy metals in water?

<p>Atomic Absorption Spectroscopy (D)</p> Signup and view all the answers

In the mandatory experiment, what is the purpose of adding ethanoic acid to the volumetric flasks?

<p>To adjust the pH for reaction with free chlorine (B)</p> Signup and view all the answers

What is the primary outcome expected from the addition of sludge removed during sewage treatment?

<p>To serve as nutrients for fertilizers or possible fuel (C)</p> Signup and view all the answers

What ions are exchanged by the cation-exchange resin when treating hard water?

<p>Ca^2+^ ions for Na^+^ ions (C)</p> Signup and view all the answers

What happens to the Na^+^ ions in the cation-exchange resin after repeated use?

<p>They are replaced and replenished with concentrated sodium chloride. (C)</p> Signup and view all the answers

Which ions are removed by the anion-exchange resin in a mixed-bed resin system?

<p>Negative ions only (C)</p> Signup and view all the answers

How is deionised water produced according to the content provided?

<p>By passing water through a mixed-bed resin of cation and anion exchange resins (D)</p> Signup and view all the answers

What characterizes distilled water compared to deionised water?

<p>It has all suspended and dissolved solids removed. (D)</p> Signup and view all the answers

What is a disadvantage of hard water?

<p>It blocks pipes and leaves scale on kettles. (B)</p> Signup and view all the answers

During the EDTA experiment for determining water hardness, what is necessary for rinsing the burette?

<p>Ethylenediaminetetraacetic acid solution (B)</p> Signup and view all the answers

In the cation exchange reaction represented as RH + Na+ RNa + H^+^, what does RH represent?

<p>Cation-exchange resin in its unreacted form (B)</p> Signup and view all the answers

What causes hard water and how does it waste soap?

<p>Presence of calcium hydrogencarbonate and it reacts with soap to form scum. (D)</p> Signup and view all the answers

How does the ion exchange process soften hard water?

<p>By replacing calcium and magnesium ions with hydrogen and hydroxyl ions. (A)</p> Signup and view all the answers

What is the effect of adding chlorine in excessive amounts to water?

<p>It can make the water taste of chlorine. (B)</p> Signup and view all the answers

What is the purpose of adding a fluorine-containing compound in water treatment?

<p>To prevent tooth decay. (B)</p> Signup and view all the answers

Why are heavy metal ions such as Hg^2+ or Pb^2+ a concern in water pollution?

<p>They pose serious health risks to humans and animals. (A)</p> Signup and view all the answers

Which instrumental technique is typically used to detect heavy metal ion concentrations in water?

<p>Atomic Absorption Spectroscopy (C)</p> Signup and view all the answers

What is a common test for chloride ions (Cl^--^) in water?

<p>Adding silver nitrate and dilute nitric acid. (C)</p> Signup and view all the answers

What is the biochemical oxygen demand (BOD) of a water sample?

<p>The oxygen consumed over 5 days under specific conditions. (D)</p> Signup and view all the answers

Flashcards

Hard Water

Water that doesn't easily form a lather with soap due to dissolved calcium (Ca²⁺) or magnesium (Mg²⁺) ions.

Temporary Hardness

Hardness in water that can be removed by boiling, caused by calcium hydrogencarbonate (Ca(HCO₃)₂) and magnesium hydrogencarbonate (Mg(HCO₃)₂).

Permanent Hardness

Hardness in water that cannot be removed by boiling, caused by calcium sulfate (CaSO₄) or magnesium sulfate (MgSO₄).

Temporary Hardness Removal Method

Boiling the water causes the calcium and magnesium hydrogen carbonate to decompose into their respective carbonates, and carbon dioxide which escapes into the air. This process removes the temporary hardness.

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Distillation

A method of removing water hardness by boiling water and collecting the steam. Impurities are left behind in the residue (salt).

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Washing Soda

A method for removing water hardness. Sodium carbonate (Na₂CO₃) reacts with Ca²⁺ ions to create insoluble calcium carbonate.

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Ion-Exchange Resin

A method of softening water by exchanging Ca²⁺ and Mg²⁺ ions for sodium (Na⁺) ions.

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Water Softening

Process of removing Ca²⁺ or Mg²⁺ ions from water to improve its interaction with soap.

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How does cation-exchange resin work?

The resin, represented as RNa, exchanges its sodium ions (Na+) for calcium ions (Ca2+) in the water. Each Ca2+ ion is replaced by two Na+ ions, resulting in softened water.

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Replenishing the resin

Once the resin loses all its sodium ions, it needs to be recharged. This is done by passing a concentrated sodium chloride (NaCl) solution through it, replacing the calcium and magnesium ions with sodium ions.

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Deionised water

Water that has all its dissolved ions (positive and negative) removed, but may still contain dissolved gases.

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How is deionised water produced?

Water is passed through a mixture of cation-exchange resin (removes positive ions) and anion-exchange resin (removes negative ions). This is called a mixed-bed resin.

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Difference: Deionised vs Distilled

Deionised water has all dissolved ions removed, while distilled water is the purest form, with all dissolved solids and gases removed.

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Hard water advantages

Hard water provides calcium for teeth and bones, has a nicer taste, and is useful for brewing and tanning leather.

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Total Suspended Solids (TSS)

The amount of solid material that is suspended in a water sample and can be filtered out using a standard filter paper.

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Total Dissolved Solids (TDS)

The total amount of dissolved material in a water sample, including salts, minerals, and organic compounds.

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Biochemical Oxygen Demand (BOD)

The amount of oxygen used by microorganisms in a water sample during a 5-day period at 20 degrees Celsius.

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Why is a BOD test important?

It's a crucial indicator of the health of an aquatic ecosystem. High BOD levels indicate high levels of organic pollution, which can lead to oxygen depletion and harm aquatic life.

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What causes eutrophication?

Excessive enrichment of water with nutrients like nitrates and phosphates, often from fertilizers and sewage.

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How does eutrophication harm aquatic life?

Algal blooms block sunlight, cutting off oxygen production by underwater plants. Decomposing algae further depletes oxygen, leading to fish kills.

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What are heavy metal ions?

Metal ions like lead (Pb²⁺) that are toxic to organisms even in small amounts. They can accumulate in water bodies.

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How are heavy metal ions removed?

A process called precipitation is used to remove them. This involves adding chemicals that react with the heavy metal ions to form solid precipitates that can then be removed.

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Primary sewage treatment

A mechanical process where large solids are removed by screening and some suspended solids are removed by settlement.

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Secondary sewage treatment

A biological process where bacteria decompose organic matter using nutrients from sewage and oxygen.

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Tertiary sewage treatment

A chemical process where phosphorus and nitrogen compounds are removed.

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Activated sludge process

The use of bacteria in secondary sewage treatment to decompose organic waste.

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What is AAS used for?

Atomic Absorption Spectroscopy (AAS) is used to measure the concentration of heavy metals in water samples.

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What is colorimetry used for?

Colorimetry is used to measure the concentration of colored substances in water samples.

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What is the principle of colorimetry?

The amount of light absorbed by a colored solution is proportional to the concentration of the solution.

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Eutrophication

The excessive growth of algae and other aquatic plants in a water body due to nutrient pollution.

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How does hard water waste soap?

Calcium and magnesium ions react with soap molecules, forming an insoluble precipitate called scum, which reduces the soap's ability to clean.

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Ion Exchange Softening

A method of removing calcium and magnesium ions from hard water by replacing them with sodium ions using a resin.

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Flocculating Agent

A chemical added to water treatment to clump together small particles, making them easier to remove.

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Chlorine's Role in Water Treatment

Chlorine is used to kill harmful pathogens (disease-causing organisms) in water.

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Excessive Chlorine: The Problem

Too much chlorine can give water an unpleasant taste and smell.

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Heavy Metal Pollution

Pollution of water by heavy metal ions, like mercury (Hg²⁺) and lead (Pb²⁺), which is dangerous to health.

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Dissolved Oxygen Measurement

A method to determine the amount of dissolved oxygen in water using a redox reaction involving manganese(II) sulfate, alkaline potassium iodide, and sodium thiosulfate.

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What is the purpose of adding concentrated sulfuric acid?

Concentrated sulfuric acid is added to dissolve the brown precipitate formed in the reaction and release free iodine, resulting in a golden brown solution.

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Why is the bottle inverted repeatedly?

Inverting the bottle repeatedly ensures the reaction between the chemicals and dissolved oxygen is complete, leading to the formation of the brown precipitate.

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Why is starch indicator used?

Starch indicator is used to detect the end point of the titration with sodium thiosulfate, indicating when all the free iodine has reacted.

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Sewage Treatment

The process of treating wastewater from towns and cities to remove contaminants and make it safe for discharge or reuse.

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How does the thiosulfate titration work?

Sodium thiosulfate solution is used to titrate the released iodine. The reaction consumes iodine until it is completely reacted, indicated by a color change.

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What does 'p.p.m.' refer to?

Parts per million (p.p.m.) is a unit used to express the concentration of dissolved oxygen in water samples.

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Why is it important to measure dissolved oxygen in water?

Dissolved oxygen is crucial for aquatic life, and its levels can indicate water quality. High levels are generally good, while low levels can signal pollution or other problems.

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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 dissolved Ca2+ or Mg2+ ions in the water
  • Soap reacts with calcium or magnesium ions in the water to form an insoluble compound (e.g., calcium stearate)
  • Hardness is categorized as temporary or permanent

Temporary Hardness

  • Temporary hardness can be removed by boiling the water
  • It is caused by dissolved calcium hydrogen carbonate (Ca(HCO3)2) and magnesium hydrogen carbonate (Mg(HCO3)2)
  • Boiling the water decomposes the carbonates into insoluble calcium carbonate (CaCO3) and magnesium carbonate (MgCO3), which precipitate out of the solution
  • This removes the hardness-causing ions

Permanent Hardness

  • Permanent hardness cannot be removed by boiling the water
  • It is caused by dissolved calcium sulfate (CaSO4) and magnesium sulfate (MgSO4)
  • Heating the water does not affect these salts; therefore, hardness remains even after boiling
  • These salts persist in the water even after boiling

Methods of Removing Hardness

  • Distillation: Boiled water, removing dissolved solids
  • Washing Soda: Reacts with Ca2+ ions to form insoluble calcium carbonate
  • Ion-exchange resin: Exchanges Ca2+ and Mg2+ ions for Na+ ions, which do not cause hardness. This is a cation exchange resin. This process needs to be replenished using Sodium Chloride
  • Deionised water: Uses a mixture of cation and anion exchange resins. Cation resin removes positive ions (e.g., Ca2+), and anion resin removes negative ions (e.g., sulfate). This results in pure water (deionised) containing only H+ and OH- ions, which combine to form water.

Advantages and Disadvantages of Hard Water

  • Advantages: Good for teeth and bones, better taste, good for brewing and tanning leather
  • Disadvantages: Blocks pipes, leaves scale in kettles, wastes soap, produces scum

Water Treatment

  • Screening: Removal of floating debris (e.g., branches, plastic bags).
  • Flocculation: Small suspended particles are coagulated, forming larger particles for better sedimentation. This is done through use of flocculating chemicals (e.g., aluminum sulfate).
  • Sedimentation: Water is passed into a tank to allow for maximum sedimentation. Larger particles settle to the bottom.
  • Filtration: Water passes through beds of sand to remove remaining particles.
  • Chlorination: Chlorine is added to sterilise water and kill harmful microorganisms.
  • Fluoridation: Fluoride added to prevent tooth decay.
  • pH adjustment: Adjustment of pH of the water to the optimum pH of 7.2. This is done by adding acids or bases as necessary.

Water Pollution

  • Water Pollution affects the amount of oxygen in water which leads to safety of aquatic life
  • BO.D. (Biochemical Oxygen Demand): The amount of dissolved oxygen consumed by biological activities in water over five days at 20°C. High BOD indicates low oxygen levels, which means a high level of microorganisms

Water Pollution- Eutrophication

  • Excessive enrichment of water with nutrients (e.g., nitrates and phosphates)
  • Causes excessive growth of algae and other plants, leading to oxygen depletion and harming aquatic life.

Heavy Metals in Water

  • Heavy metals (e.g., lead, mercury) can have serious consequences for organisms and affect human health
  • Atomic Absorption Spectroscopy (AAS) is used to detect heavy metals in water

Dissolved Oxygen

  • Dissolved oxygen in water due to plants
  • is necessary for aquatic life, thus requiring BOD tests

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Description

Test your knowledge on the hardness of water, including its types, causes, and methods for removal. This quiz covers both temporary and permanent hardness, focusing on the chemical processes involved. Understand the implications of hard water and how it affects everyday life.

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