ChemCore9-10

  Modern Periodic Table and Its Salient Features Introduction The periodic table is the most powerful tool in chemistry, systematically organizing all known elements based on their atomic number and properties. It helps scientists predict element behavior, reactivity, and trends. The Modern Periodic Law , proposed by Henry Moseley in 1913 , states: "The physical and chemical properties of elements are periodic functions of their atomic numbers." This means elements with similar properties appear at regular intervals. The periodic table is structured into periods (rows) and groups (columns), forming a logical arrangement of elements. For a deeper understanding of the periodic table’s structure, check out our detailed article: Exploring Periodic Table Structure . Historical Background of the Periodic Table 1. Dobereiner’s Triads (1817) Johann Wolfgang Döbereiner grouped elements into triads based on atomic masses, but this system was limited to only a few elements. ...

  Acids and Bases: MCQs with Answers and Explanations (i) Which acid is not used as a food or mixed with food? (a) Tartaric acid (b) Ascorbic acid (c) Citric acid (d) Formic acid ✔ Explanation: Formic acid is highly corrosive and not safe for consumption, whereas tartaric, ascorbic, and citric acids are commonly found in food and beverages. (ii) While baking, which gas is responsible for raising the bread and making it soft? (a) Oxygen (b) Carbon dioxide ✔ (c) Nitrogen (d) Carbon monoxide Explanation: Baking soda or baking powder releases carbon dioxide (CO₂) when heated or mixed with acids, causing dough to rise and become soft. (iii) Predict the main characteristics of the reactions of metals with acids. (a) Metals are dissolved (b) Metals are converted into salts (c) Hydrogen gas is evolved (d) All the above-mentioned characteristics are true ✔ Explanation: Metals react with acids to form salt and release hydrogen gas, which is why all the mentioned cha...

  Acid Rain and Its Effects Introduction to Acid Rain Imagine waking up one day to find your favorite plants withered, lakes and rivers lifeless, and historical buildings crumbling. This isn't a scene from a science-fiction movie; it's a real environmental threat caused by acid rain . Acid rain is a type of precipitation (rain, snow, fog, or even dust) that contains high levels of acidic pollutants, primarily sulfuric acid (H₂SO₄) and nitric acid (HNO₃). It results from emissions of sulfur dioxide (SO₂) and nitrogen oxides (NOₓ), which react with water, oxygen, and other chemicals in the atmosphere. Acid rain affects ecosystems, human health, and even man-made structures. In this article, we will explore acid rain in detail—how it forms, its devastating effects, and what we can do to prevent it. Causes of Acid Rain Acid rain originates from both natural sources and human activities . However, human activities contribute the most to this environmental problem. 1. Human ...

  1. Introduction to Acids and Bases Imagine you take a bite of a lemon and feel that sharp, sour taste on your tongue. That sourness comes from citric acid. Now, think about soap—when you touch it, it feels slippery. That’s because soap is made from a base. Acids and bases are everywhere around us, from the food we eat to the cleaning products we use. But what exactly are acids and bases? In simple terms: Acids are substances that taste sour, react with metals, and turn blue litmus paper red. Bases are substances that taste bitter, feel slippery, and turn red litmus paper blue. Scientists have created different definitions of acids and bases to explain their behavior. Let’s explore them in detail. 2. Early Theories of Acids and Bases Scientists have proposed different theories to explain acids and bases. The three most important theories are: a. Arrhenius Theory (1884) Swedish scientist Svante Arrhenius gave one of the first definitions of acids and bases: Acid...

  Exercise: Tick (✓) the Correct Answer (i) The following reaction is an exothermic reaction: H2 + Cl2 = 2HCl (a) By collisions between the molecules (b) From sunlight (c) From the surrounding (d) By collisions of the molecules with the walls of the container Answer: (b) From sunlight Explanation: This is a photochemical reaction , meaning light energy (from sunlight) initiates bond breaking in H₂ and Cl₂ , leading to HCl formation. (ii) Which of the following reactions has the least value of activation energy? (a) H₂(g) + ½ O₂(g) → H₂O(g) (b) C₆₀(s) + O₂(g) → CO₂(g) (c) NaCl(aq) + AgNO₃(aq) → AgCl(s) + NaNO₃(aq) (d) H₂(g) + I₂(g) → 2HI(g) Answer: (a) H₂(g) + ½ O₂(g) → H₂O(g) Explanation: Combustion reactions typically have low activation energy and are highly exothermic . The reaction between hydrogen and oxygen to form water releases significant energy and has low activation energy . (iii) Formation of which hydrogen halide from the elements is an end...

  . Understanding the Role of Molecules in Chemical Reactions Introduction: The World of Molecules Have you ever wondered how the food you eat is broken down into energy or why rust forms on iron over time? The answer lies in the invisible world of molecules! Molecules are the building blocks of everything around us, and they are always involved in chemical reactions. Whether in the air you breathe or the water you drink, chemical reactions are happening all the time. In this article, we’ll explore the fascinating role molecules play in chemical reactions, how they interact, and why understanding these processes is essential for chemistry. What Are Molecules? Before diving into how molecules work in chemical reactions, let’s first understand what they are. Molecules are made up of atoms—tiny particles that make up everything in the universe. These atoms are bonded together by forces, forming molecules. For example: Water (H₂O) : A molecule made of two hydrogen atoms and o...

  Gases and Gas Laws in Chemistry: A Simple Guide for all students Introduction to Gases Have you ever blown up a balloon or felt the air coming from a balloon when it deflates? That’s gas in action! Gases are all around us, but we usually don't notice them. They're one of the three states of matter, along with solids and liquids. Gases, unlike solids and liquids, don’t have a fixed shape or volume. They spread out and fill whatever space they are in. Some examples of gases include the air we breathe, the carbon dioxide in fizzy drinks, and even the gas inside a balloon. Gases behave in some pretty interesting ways, and understanding how they work is key to understanding a lot of chemistry! What is Pressure? Pressure is a way to talk about the force that gas particles exert when they collide with the walls of a container. Picture a balloon. Inside the balloon, tiny gas particles are constantly moving around, bumping into each other and the inside of the balloon. These col...

  Changing Physical Condition of a Chemical Reaction Introduction Imagine you are making tea. If you put cold water on the stove, it takes time to boil. But if you increase the flame, the water boils faster. What changed? The temperature ! This simple example shows how physical conditions affect chemical reactions. Chemical reactions happen everywhere—when you cook food, breathe, or even when your phone battery charges. But did you know that you can control the speed of a reaction? You can make it faster or slower just by changing certain conditions like temperature, pressure, concentration, surface area, or by adding a catalyst. In this article, we’ll explore how these physical conditions affect chemical reactions in a simple, relatable way. Factors That Affect Chemical Reactions A chemical reaction is like a race between molecules. Some reactions happen quickly, like an explosion, while others are slow, like rusting iron. The speed of a reaction is called the reaction ra...

  Dynamic Equilibrium What is Dynamic Equilibrium? Imagine you are filling a bucket with water while a hole at the bottom lets water leak out. At some point, the water level the same because the water entering is equal to the leaking out. This is what happens in dynamic equilibrium —a process where things continue to change, but overall, nothing appears different. In chemistry, dynamic equilibrium occurs when the rate of a forward reaction (reactants turning into products) is equal to the rate of the reverse reaction (products turning back into reactants). This means that even though molecules are reacting, their overall amounts remain constant. Key Points About Dynamic Equilibrium In a closed system (no substances can enter or leave). The forward and reverse reactions happen at the same speed . The amounts of reactants and products stay constant , but molecules are still moving. Types of Dynamic Equilibrium 1. Chemical Equilibrium When a chemical reaction goes in bo...

  1. Question: What happens when the concentration of a reactant is increased in a system at equilibrium? A) The reaction stops B) Backward reaction increases C) Forward reaction increases D) No change occurs ✓ C) Forward reaction increases Explanation: According to Le Chatelier’s Principle, when the concentration of a reactant is increased, the system shifts in the direction that consumes the added reactant, which is the forward reaction. 2. Question: What happens to the equilibrium constant () when the temperature of an exothermic reaction is increased? A) Increases B) Decreases C) Remains the same D) Becomes zero ✓ B) Decreases Explanation: In exothermic reactions, heat is a product. Increasing temperature shifts equilibrium towards the reactants, decreasing the concentration of products and therefore decreasing the equilibrium constant (). 3. Question: What is the effect of a catalyst on a system at equilibrium? A) Increases the equilibrium constant ...