IAA ACADEMY – Lesson 4: Solution, Colloidal Solution and Suspension

How Things Mix: Solutions, Colloids, and Suspensions

Welcome back, class! In our previous lessons, we’ve explored the states of matter and the basic forms like elements, compounds, and mixtures. Today, we’re going to dive deeper into mixtures, specifically how different types of mixtures behave when one substance is spread out in another.

Imagine you’re mixing things in the kitchen. Sometimes, sugar completely disappears in water. Other times, flour just sits at the bottom. And then there’s milk, which looks uniform but isn’t quite clear. These are all examples of how substances mix, and we’ll learn the scientific terms for them: Solutions, Colloidal Solutions, and Suspensions.

1. True Solutions: The Perfect Blend

Let’s start with what we call a Solution, or sometimes, a True Solution. This is like when you add sugar to water and stir it until you can’t see the sugar anymore. It’s completely gone!

• A solution is a mixture where solute particles are completely homogenized in the solvent.
• Let’s break that down:
  • Solute: The substance that dissolves (like sugar). (وہ چیز جو حل ہو جائے، جیسے چینی)
  • Solvent: The substance that does the dissolving (like water). (وہ چیز جس میں کوئی اور چیز حل ہو، جیسے پانی)
  • Homogenized: Means the solute particles are spread out so evenly that the mixture looks uniform throughout. You can’t tell them apart! (مکمل طور پر یکساں ہو جانا، اس طرح کہ حل شدہ ذرات نظر نہ آئیں)
• The solute particles in a true solution are so tiny that they cannot be seen by the naked eye.
• If you try to filter a true solution (like salt water) through a filter paper, these tiny particles will pass right through the pores of the filter paper, leaving no solid behind (no precipitate).

Common examples include the dissolution of sodium chloride (table salt) or copper sulphate in water.

2. Suspensions: When Things Don’t Mix Well

Now, let’s talk about Suspensions. This is like mixing sand in water. No matter how much you stir, the sand doesn’t truly dissolve, right?

• A suspension is a mixture in which solute particles do not dissolve in the solvent. They just float around for a while.
• We can actually see these particles with our naked eye because they are much larger.
• If a suspension is left undisturbed for some time, these heavier particles will settle down at the bottom.
• If you try to filter a suspension (like muddy water), the particles are too big and cannot pass through the pores of filter paper. They will be collected as a solid (a precipitate) on the filter paper.

A common example is a mixture of chalk in water or muddy water.

(سسپنشن میں، حل ہونے والے ذرات سالوینٹ میں حل نہیں ہوتے۔ ہم انہیں اپنی آنکھوں سے دیکھ سکتے ہیں، اور کچھ دیر رکھنے پر وہ نیچے بیٹھ جاتے ہیں۔ فلٹر کرنے پر یہ ذرات فلٹر پیپر سے نہیں گزرتے۔)

3. Colloidal Solutions: The In-Betweeners

Besides true solutions and suspensions, there’s a third fascinating form of mixture called a Colloidal Solution, or simply a Colloid. These are a bit like the middle child – they have properties that are between true solutions and suspensions.

• In this type, the solute particles do not homogenize completely with the solvent in the same way as a true solution, but they also don’t settle like a suspension.
• These particles are a little bit bigger than those present in a true solution, but not big enough to be seen with the naked eye like the particles in a suspension. Think of them as microscopic.
• If kept for some time, the particles of a colloidal solution do not settle down. This is a key difference from suspensions.
• On filtration, these particles pass through the filter paper like the particles of a true solution. This is because, while larger than true solution particles, they are still small enough to pass through typical filter paper pores.

Starch solution and the white of an egg (when dissolved in water) are common examples of colloidal solutions. Milk is another great example!

(کولائیڈل سلوشن میں ذرات نہ تو مکمل طور پر حل ہوتے ہیں اور نہ ہی نیچے بیٹھتے ہیں۔ یہ ذرات اتنے چھوٹے ہوتے ہیں کہ آنکھ سے نظر نہیں آتے لیکن سچے سلوشن کے ذرات سے بڑے ہوتے ہیں۔)

Comparing Solutions, Colloids, and Suspensions

To help you understand the differences clearly, let’s look at a comparison table. Click on the tabs to see the properties of each type!

Formation of Unsaturated and Saturated Solutions: How Much Can Dissolve?

Now, let’s talk about how much solute can actually dissolve in a solvent. It’s not unlimited!

Unsaturated Solution

Imagine you have about 100 grams of water in a beaker. Add 5 grams of table sugar and stir it. The sugar will dissolve easily. Then, add another 5 grams of sugar and stir. This will also dissolve.

This solution is called an unsaturated solution. It means it’s not “full” yet!

• A solution which can dissolve more amount of a solute at a particular temperature is called an unsaturated solution.

(ایک انسیچوریٹڈ سلوشن وہ ہے جس میں کسی خاص درجہ حرارت پر مزید حل ہونے والا مادہ (سولیوٹ) حل کیا جا سکتا ہے۔)

Saturated Solution

Now, let’s continue our sugar experiment. Keep adding sugar to the solution. As the quantity of sugar in water increases, its dissolution becomes more and more difficult. You’ll have to stir harder and longer.

Eventually, a stage comes when no more sugar will dissolve in water at that specific temperature. Any more sugar you add at this stage will just settle down at the bottom of the beaker, no matter how much you stir.

This solution is called a saturated solution at that particular temperature. It’s “full” to its maximum capacity!

• A saturated solution is one in which the maximum amount of the solute has been dissolved in a particular amount of a solvent at a particular temperature.

(ایک سیچوریٹڈ سلوشن وہ ہے جس میں کسی خاص درجہ حرارت پر سالوینٹ کی دی گئی مقدار میں سولیوٹ کی زیادہ سے زیادہ مقدار حل ہو چکی ہو۔ اس کے بعد مزید سولیوٹ حل نہیں ہو سکتا۔)

Solubility and Solubility Comparison: Not All Things Dissolve Equally

We just talked about saturated solutions. The maximum amount of solute that can dissolve in a given amount of solvent at a specific temperature is called its solubility.

Different Solutes Have Different Solubilities

It’s important to know that different solutes have different solubilities in a particular solvent. For example, if you try to prepare saturated solutions of table sugar and sodium chloride (salt) in water at room temperature, you’ll find a difference:

• The concentration of sodium chloride saturated solution is about 5.3 molar at room temperature.
• The concentration of sugar solution is about 3.8 molar at room temperature.

In simpler words, you can dissolve much more sodium chloride in water than sugar at the same temperature. The solubility of sodium chloride in water is far greater than that of sugar at room temperature.

Reason for Solubility Difference

Why is this so? This is due to the fact that the attraction of sodium and chloride ions with water are far stronger than the attractions between sugar molecules with water. Water molecules pull on salt ions more strongly than they pull on sugar molecules, helping salt dissolve better.

Interesting Information! Solutions All Around Us

Solutions are not just a chemistry concept; they are closely related to our everyday lives! You might be surprised to know how many things around you are actually solutions:

• The air we breathe is a gaseous solution (nitrogen, oxygen, etc.).
• The liquid and other foods we consume are often complex solutions (juices, sodas, even tea).
• The fluids in our body (like blood plasma) are vital solutions.
• Even solids like steel (an alloy of iron and carbon) are solid solutions!

So, understanding solutions helps us understand the world around us much better!

Effect of Temperature on the Solubility of Solutes: Heating Things Up (or Cooling Down)!

Temperature plays a big role in how much solute can dissolve.

Definition of Solubility (Revisited)

Just to be clear, the solubility of a solute is defined as the amount of solute which can dissolve in 100 grams of a solvent at a particular temperature to form a saturated solution.

Temperature’s Effect on Solubility: It’s Not Always the Same!

Change in temperature has different effects on the solubility of different compounds. While it’s a common idea that heating makes things dissolve more, this cannot be taken as a general rule. Let’s see why!

Solubility Curves: Visualizing Solubility

Scientists often use solubility curves to visually represent how the amount of solute that can dissolve changes with temperature.

• These are graphs that show the amount of solute (usually in grams per 100 g of water) that can dissolve at different temperatures.
• On such a graph:
  • The saturated zone lies directly on the curve.
  • Points below the curve represent unsaturated solutions (more solute can dissolve).
  • Points above the curve represent supersaturated solutions (where more solute is dissolved than normally possible at that temperature, usually by carefully cooling a saturated solution).

Example: You would see a graph showing the solubility curve of KNO₃ in H₂O, where the line goes sharply upwards, indicating its solubility increases greatly with temperature. (Please imagine this visual representation in your mind or refer to your textbook for the actual graph!)

Solubility and Temperature: Revisiting Sugar

Let’s go back to our sugar example to solidify this concept.

Take 100 grams of water in a beaker and prepare a saturated solution of sugar at room temperature. Now, heat the beaker on a spirit lamp. Add a little more sugar to it and stir it.

Will this extra sugar dissolve in it?

You will notice that by heating the solution, the quantity of sugar dissolved in water has increased. This means the solubility of sugar has increased with temperature.

Solubility Trends of Other Solids

Similarly, the solubilities of copper sulphate and sodium nitrate also increase with an increase in temperature.

However, as we learned, the solubility of calcium hydroxide decreases with the increase in temperature.

Exercise

Think about what we’ve learned and try to answer this question:

More Interesting Information!

Let’s look at a couple of practical applications of what we’ve learned:

1. Purification through Crystallization

The increase in the solubility of solids in liquids with an increase in temperature is very useful for purifying them.

How does it work? You dissolve an impure solid in a hot solvent to make a saturated solution. Then, as the solution cools down, the solubility of the pure solid decreases, and it starts to separate out as beautifully shaped crystals, leaving the impurities dissolved in the remaining liquid.

Example: This is how we get pure crystals of Potassium Nitrate or even table sugar from raw solutions.

2. Solubility of Gases and Temperature

As we just discussed, generally, the solubility of gases decreases with an increase in temperature.

This is why carbon dioxide gas is more soluble in water at low temperature. This principle is used in the beverage industry.

Soda water bottles are thus stored in the refrigerator to keep carbon dioxide gas dissolved in water for a longer period of time, keeping your drink fizzy and enjoyable!

Key Points Recap (Lessons 1-4)

Before we conclude, let’s quickly review the main ideas we’ve covered so far in our chemistry journey!

1. Definition of Chemistry

   Chemistry is that branch of science which deals with the composition of matter, changes in matter, and the laws which govern these changes. It’s all about what things are made of, how they change, and why!

2. Branches of Chemistry

   To understand the vast and complex subject of Chemistry, it is divided into many branches. Physical chemistry, inorganic chemistry, and organic chemistry are its main branches among so many others. Each branch focuses on a different aspect of matter.

3. States of Matter

   Matter exists mainly in three states: solid, liquid, and gas. They are different from each other due to the different characteristics of the particles they contain – how close they are, how they are arranged, and how strongly they attract each other.

4. Plasma – The Fourth State of Matter

   Plasma is regarded as the fourth state of matter which is not normally observed in our everyday world. It’s a super-energetic, ionized gas. Most of the matter present in the rest of the universe (like stars) exists in this state.

5. Intermediate States of Matter

   Matter also exists in fascinating intermediate states which are at the borderline of its two principal states, such as between liquid and gas (like supercritical fluids) and between liquid and solid (like liquid crystals). Supercritical fluids and liquid crystals are some examples of such states.

6. Basic Forms of Matter

   Matter exists in the form of distinct entities called elements, compounds, and mixtures. These are the fundamental categories for classifying substances.

7. Properties of Elements, Compounds, and Mixtures

   Elements, compounds, and mixtures have distinct properties individually, and they are very different from one another in terms of their composition, how they are formed, and how they can be separated.

8. Forms of Mixtures

   Solutions, suspensions, and colloidal solutions are different forms in which mixtures usually exist. They each have their own characteristic properties related to particle size, visibility, and how they behave on standing or filtration.

Great job everyone! You’ve covered a lot of ground in these first few lessons. Keep reviewing and practicing!