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Everything to Know about Water [Free JAMB Tutorial on Chemistry]

This Chemistry Tutorial will focus on WATER. This topic has been explained to ensure you understand it very well. At the end of the tutorial, you’ll be able to download it for FREE. Please share this page with your friends who may need it.

Water is a chemical substance with the chemical formula H2O, meaning it consists of two hydrogen atoms covalently bonded to one oxygen atom.

It is one of the most essential and abundant compounds on Earth, playing a crucial role in various biological and physical processes.

Water as a product of the combustion of hydrogen and its composition by volume.

Before we proceed, let’s explain what combustion means in simple terms.

Combustion is like a special kind of dance between two partners: a fuel and something that loves to help it burn, usually oxygen.

Imagine you have a birthday candle. When you light the candle with a match, you’re starting a tiny combustion dance. The wax from the candle is the fuel, and the oxygen in the air is its dance partner. They mix together, and when they do, they create heat and light, and you see a flame!

So, combustion is a process where something (like the wax in a candle or hydrogen gas) reacts with oxygen, and they release energy in the form of heat and light.

Combustion of Hydrogen

When hydrogen undergoes combustion, it reacts with oxygen to produce water.

Think of hydrogen as a little adventurer, and when it teams up with oxygen, they go on a thrilling journey. This journey is called combustion. The special thing about this adventure is that they create something new when they come together.

In the world of chemistry, when hydrogen and oxygen combine, they make water.

The chemical equation for this adventure is:

2H2​(g) + O2​(g) → 2H2​O(l)

This equation indicates that two molecules of diatomic hydrogen (H2​) react with one molecule of diatomic oxygen (O2​) to form two molecules of water (H2​O).

The adventure starts with gases (hydrogen and oxygen) and ends with liquid water.

Composition by Volume

Now, let’s talk about the volume of these gases. Imagine you have two balloons of hydrogen and one balloon of oxygen.

When they decide to go on their adventure, they mix and create two balloons of water vapor.

So, it’s like saying, “For every two balloons of hydrogen, there’s one balloon of oxygen, and together they make two balloons of water vapor.”

In science terms, we express this as 2 volumes of hydrogen plus 1 volume of oxygen equals 2 volumes of water vapor. It’s like a rule they follow during their adventure.

Expressed as: 2 volumes of H2​(g)+1 volume of O2​(g) → 2 volumes of H2​O(g)

Think of it like mixing ingredients for a recipe. If you have two cups of flour and one cup of sugar, the recipe might say you get two cups of cake. Here, hydrogen and oxygen mix in a 2:1 ratio to make water vapor.

So, when hydrogen and oxygen decide to have their chemistry adventure, they end up making water, and we can understand their journey by talking about volumes, like balloons filling up with their special creation! 🎈💧

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Hard water is water that contains a relatively high concentration of dissolved minerals, mainly calcium and magnesium ions. These minerals are picked up by the water as it percolates through mineral deposits in the ground, such as limestone and chalk. The degree of hardness is often expressed in terms of calcium carbonate equivalents (CaCO3).

In simple terms, imagine you have a friend named Harry. Harry is a bit tough and strong. Just like Harry, hard water is water that contains a lot of minerals, especially calcium and magnesium. These minerals make the water a bit tough or hard. You usually find hard water in areas where there are a lot of rocks or underground minerals. When you drink hard water, it’s safe, but it might not taste as fresh, and it can leave some funny-looking spots when it dries.

There is a temporary and permanent hardness of water.

Temporary Hardness: Temporary hardness of water is caused by the presence of bicarbonate ions (HCO3-) and carbonate ions (CO32-) in water, mainly due to the dissolution of calcium and magnesium carbonates.

This type of hardness can be easily removed or reduced by boiling the water.

When water is heated, these ions react to form insoluble carbonate salts, which precipitate out of the water.

The equation for the reaction is:

Ca(HCO3​)2(aq)​ → CaCO3​(s) + CO2​(g) + H2​O(l)

The resulting calcium carbonate (CaCO3) is the white, chalky substance often seen as a scale or deposits in kettles.

Permanent Hardness: Permanent hardness is caused by the presence of sulfate ions (SO42-), chloride ions (Cl), and sometimes nitrate ions (NO3-) of calcium and magnesium in water.

Unlike temporary hardness, permanent hardness cannot be removed by boiling. It requires a different approach for softening.

Methods of Softening Hard Water:

  1. Boiling:
    • Boiling is effective for reducing temporary hardness by causing the precipitation of calcium carbonate. However, it may not be practical for large-scale water softening due to energy costs and the formation of scale in the water-heating equipment.
  2. Lime-Soda Ash Softening:
    • In this method, calcium hydroxide (lime) and sodium carbonate (soda ash) are added to water. The calcium and magnesium ions react with the hydroxide and carbonate ions to form precipitates, which can then be removed.
      The equations for these reactions are:
      Ca(HCO3​)2(aq)​+Ca(OH)2(aq) ​→ 2CaCO3​(s)+2H2​O(l)
  3. Ion Exchange Softening:
    • This is a common method that uses ion exchange resins. The resin beads are charged with sodium ions, and as hard water passes through the resin, the calcium and magnesium ions in the water are exchanged with sodium ions on the resin, effectively softening the water. Periodically, the resin needs to be regenerated by flushing it with a solution of sodium chloride (salt).
  4. Reverse Osmosis:
    • Reverse osmosis is a filtration process that removes ions, molecules, and larger particles from water. It is effective at reducing both temporary and permanent hardness, producing softened water.
  5. Chelation Softening:
    • Chelating agents, such as EDTA (ethylenediaminetetraacetic acid), can be added to water to form stable, water-soluble complexes with calcium and magnesium ions, preventing them from causing hardness.

The choice of water softening method depends on factors such as the level of hardness, the specific ions present, and the scale of application (domestic or industrial). Each method has its advantages and disadvantages, and the most suitable one is selected based on the particular needs and constraints of the situation.

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Soft Water: Soft water, on the other hand, contains low concentrations of calcium and magnesium ions. It may naturally occur in areas with certain types of rock formations or can be created through water treatment processes.

In simple terms, soft water is your other friend, Sally. Sally is soft and gentle. Soft water is like Sally – it doesn’t have many minerals. It’s the opposite of hard water. Soft water is often better for washing because it makes soap lather up more easily. So, when you take a bath or wash your hands with soft water, it feels smoother and the soap works better.

  1. Causes:
    • Soft water generally has low levels of calcium and magnesium ions. It may naturally occur in areas with soft rock formations, such as granite.
  2. Effects:
    • Soap and detergents lather more easily in soft water, making it more efficient for cleaning.
    • Soft water helps prevent the buildup of limescale in pipes and appliances, extending their lifespan.
  3. Testing and Treatment:
    • Water hardness testing can confirm the softness of water. Water softeners are devices that can artificially soften water by exchanging calcium and magnesium ions with sodium ions.

Treatment of water for town supply

The treatment of water for town supply involves a series of processes designed to ensure that the water provided to the community is safe, clean, and meets established quality standards. The specific treatment steps can vary depending on the source of water (surface water, groundwater, or a combination) and the specific contaminants present. Here is a general overview of the typical processes involved in treating water for town supply:

  1. Water Intake:
    • Water is sourced from lakes, rivers, reservoirs, or wells, depending on the local geography and availability of water resources.
  2. Screening:
    • Large debris, such as sticks, leaves, and other physical impurities, is removed through screening processes. Screens or barriers prevent these larger particles from entering the water treatment system.
  3. Coagulation and Flocculation:
    • Chemicals like aluminum sulfate (alum) are added to the water to create tiny, sticky particles called floc. These floc particles attract and bind with impurities, forming larger particles that are easier to remove.
  4. Sedimentation:
    • The water is allowed to sit undisturbed in large settling basins. During this time, the heavy floc particles settle to the bottom, forming sediment. This clarified water is then moved to the next stage.
  5. Filtration:
    • The water passes through layers of sand, gravel, and sometimes activated carbon to remove smaller particles and remaining impurities. Filtration helps ensure that the water is clear and free of solid contaminants.
  6. Disinfection:
    • To kill or inactivate harmful microorganisms (such as bacteria, viruses, and parasites), a disinfectant is added. Common disinfectants include chlorine, chloramine, or ultraviolet (UV) light. This step is crucial for preventing waterborne diseases.
  7. pH Adjustment:
    • The pH of the water may be adjusted using chemicals like lime or soda ash to ensure it falls within a safe and acceptable range. Proper pH helps maintain the effectiveness of disinfection and prevents corrosion of pipes.
  8. Stabilization:
    • Some treatment plants add chemicals to stabilize the water and prevent corrosion of distribution pipes. This is particularly important in areas with older infrastructure.
  9. Fluoridation (Optional):
    • Fluoride may be added to drinking water in some locations to help prevent tooth decay. The addition of fluoride is typically done in controlled amounts to achieve optimal dental health without causing harm.
  10. Storage and Distribution:
    • The treated water is stored in reservoirs before being distributed to homes and businesses through a network of pipes. The distribution system is carefully monitored to maintain water quality during transport.
  11. Water Quality Testing:
    • Regular testing is conducted at various stages of the treatment process and throughout the distribution system to ensure that the water meets regulatory standards for safety and quality.

These steps collectively make up a comprehensive water treatment process that provides clean and safe drinking water to communities. The goal is to address both physical and chemical impurities, as well as microbial contaminants, to deliver water that is fit for consumption and other domestic uses.

That’s all we’ll cover in this tutorial.

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Practice Questions

1: What type of water hardness can be reduced by boiling?
A) Temporary hardness
B) Permanent hardness
C) Both
D) None

2: If you have 3 volumes of hydrogen gas, how many volumes of oxygen gas are required for complete combustion?
A) 0.5 volumes
B) 1 volume
C) 1.5 volumes
D) 2 volumes

3: Which process contributes to water softening through ion exchange?
A) Filtration
B) Coagulation
C) Reverse osmosis
D) Distillation

4: Which chemical element has a higher electronegativity, contributing to water’s polarity?

A) Hydrogen
B) Oxygen
C) Sodium
D) Chlorine

5: In the combustion of hydrogen, if 5 volumes of hydrogen react, how many volumes of oxygen gas are needed?
A) 1 volume
B) 2 volumes
C) 2.5 volumes
D) 3 volumes

6: Which type of water hardness is associated with the presence of bicarbonate ions?
A) Temporary hardness
B) Permanent hardness
C) Both
D) Neither

7: What is the primary role of coagulation in water treatment?
A) Removing dissolved gases
B) Forming floc particles
C) Adjusting pH
D) Disinfection

8: Why is the density of water highest at 4 degrees Celsius?
A) Water molecules repel each other
B) Hexagonal arrangement of water molecules
C) Increase in molecular motion
D) Decrease in molecular attraction

9: Which method of water softening involves the addition of lime and soda ash?
A) Reverse osmosis
B) Ion exchange
C) Lime-soda ash softening
D) Distillation

10: How does water’s high specific heat capacity contribute to its role as a temperature regulator?
A) By facilitating ion exchange
B) By preventing freezing
C) By absorbing and releasing heat
D) By increasing molecular motion

11: In the molecular structure of water, what causes the bent shape with a 104.5-degree angle?
A) Lone pairs of electrons
B) Hydrogen bonding
C) Linear arrangement
D) Tetrahedral arrangement

12: What is the primary purpose of disinfection in water treatment?
A) Removing dissolved gases
B) Neutralizing acidity
C) Killing microorganisms
D) Adjusting pH

13: Which type of water hardness is not affected by boiling?
A) Temporary hardness
B) Permanent hardness
C) Both
D) Neither

14: How does the presence of hard water affect the formation of lather with soap?
A) Enhances lather formation
B) Reduces lather formation
C) Has no effect
D) Turns lather yellow

15: In the composition by volume of water vapor formed during the combustion of hydrogen, what is the ratio of volumes between hydrogen and oxygen?
A) 1:1
B) 1:2
C) 2:1
D) 2:2

Answers and Explanations

Make sure you actually try answering these questions yourself.

1. (A) Temporary hardness
Explanation: Boiling removes temporary hardness by causing the precipitation of calcium carbonate.

2. (C) 1.5 volumes
Explanation: The balanced equation (2H2​+O2​→2H2​O) indicates a 2:1 ratio of hydrogen to oxygen.

3: (A) Filtration
Explanation: Ion exchange occurs during the filtration process in water softening using ion exchange resins.

4. (B) Oxygen
Explanation: Oxygen has a higher electronegativity, leading to water’s polarity.

5. (C) 2.5 volumes
Explanation: The balanced equation requires one volume of oxygen for every two volumes of hydrogen.

6: (A) Temporary hardness
Explanation: Bicarbonate ions are associated with temporary hardness.

7: (B) Forming floc particles
Explanation: Coagulation involves creating floc particles that aid in the removal of impurities.

8. (B) Hexagonal arrangement of water molecules
Explanation: At 4 degrees Celsius, water molecules form a hexagonal arrangement, resulting in maximum density.

9: (C) Lime-soda ash softening
Explanation: Lime and soda ash are added to precipitate calcium and magnesium ions.

10. (C) By absorbing and releasing heat
Explanation: Water’s high specific heat capacity allows it to absorb and release large amounts of heat.

11: (A) Lone pairs of electrons
Explanation: Lone pairs of electrons on oxygen cause repulsion, resulting in a bent shape.

12: (C) Killing microorganisms
Explanation: Disinfection is done to eliminate harmful microorganisms.

13: B) Permanent hardness
Explanation: Permanent hardness is caused by non-carbonate ions and is not removed by boiling.

14: B) Reduces lather formation
Explanation: Hard water forms insoluble precipitates with soap, reducing its effectiveness.

15: (C) 2:1
Explanation: The balanced chemical equation (2H2 ​+ O2 ​→ 2H2​O) indicates a 2:1 ratio of hydrogen to oxygen.

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