1). In which chemical reaction, does the exchange of ions or groups between two substances takes place?
i. Combination
ii. Double displacement
iii. Addition
iv. Neutralization
Ans: ii. Double displacement
2). What happens when dilute hydrochloric acid is added to an iron nail?
i. No reaction takes place.
ii. Hydrogen gas and iron chloride are produced.
iii. Chlorine gas and iron hydroxide are produced.
iv. Iron salt and water are produced.
Ans: ii. Hydrogen gas and iron chloride are produced.
3). Which necessary condition is essential for green plants to make glucose as food using carbon dioxide and water?
i. Sunlight
ii. Heat
iii. Catalyst
iv. Pressure
Ans: i. Sunlight
4). Hydrogen reacts with sulphur to produce hydrogen sulphide. What type of reaction is this?
i. Decomposition synthetic
ii. Neutralization
iii. Displacement
iv. Neutralization
Ans: iii. Displacement
5). Which one of the following undergoing reactions is a neutralization reaction?
i. Zinc reacts with dilute hydrochloric acid.
ii. Sodium reacts with chlorine.
iii. Calcium carbonate reacts with sulphuric acid.
iv. Sodium hydroxide reacts with hydrochloric acid.
Ans: iv. Sodium hydroxide reacts with hydrochloric acid.
6). Nitrogen reacts with hydrogen to form ammonia gas. Out of the given necessary conditions, which one is not required?
i. UV light
ii. high pressure
iii. Iron catalyst
iv. high temperature
Ans: i. UV light
7). Differentiate between:
a. Physical change and chemical change
| Physical change | Chemical change |
| Involves a change in the physical properties of a substance without altering its chemical composition. | Involves a change in the chemical composition of a substance, resulting in the formation of new substances with different properties. |
| Generally reversible, and the original substance can usually be obtained back. | Generally reversible, and the original substance can usually be obtained back. |
| Melting ice, crushing a can, boiling water. | Burning wood, digestion of food, rusting of iron. |
b. Reactant and product
| Reactant | Product |
| A substance that undergoes a chemical change or reaction. | A substance that is formed as a result of a chemical reaction. |
| Present at the beginning of a chemical reaction. | Formed as a result of the chemical reaction. |
| Participates in the chemical reaction and gets transformed into products. | The outcome of a chemical reaction, formed from the reactants. |
| Shown on the left side of a chemical equation. | Shown on the right side of a chemical equation. |
c. Single displacement reaction and double displacement reaction
| Single displacement reaction | Double displacement reaction |
| Involves a reaction where one element replaces or displaces another element in a compound. | Involves a reaction where parts of two ionic compounds switch places to form two new compounds. |
| One element replaces another element in a compound, resulting in the formation of a new compound and a different element. | Involves two compounds in the reaction, and the positive and negative ions of the compounds exchange places. |
| Involves both metals and non-metals. | Typically involves ionic compounds. |
Zinc displacing copper from copper sulfate: Zn + CuSO₄ → ZnSO₄ + Cu. | Formation of precipitate when silver nitrate reacts with sodium chloride: AgNO₃ + NaCl → AgCl + NaNO₃. |
8). What are the parts of a chemical equation?
Ans: The parts of a chemical equation include:
1.Reactants
2. Arrow Symbol (→)
3. Products
4. Coefficients
5. Subscripts
6. State Symbols (optional)
9). Name the chemical reaction in which two substances exchange ions.
Ans: The chemical reaction in which two substances exchange ions is called a “double displacement reaction.”
10). Define acid-base reaction with an example.
Ans: An acid-base reaction is a type of chemical reaction where an acid, which is a substance capable of releasing hydrogen ions (H⁺), reacts with a base, which is a substance capable of accepting hydrogen ions, to form water and a salt.
Example: HCl (acid) + NaOH (base) → H₂O (water) + NaCl (salt)
11). Identify the type of chemical reaction taking place when silver chloride turns black on exposure to sunlight.
Ans: The type of chemical reaction taking place when silver chloride turns black on exposure to sunlight is a “photochemical decomposition reaction.”
13). Name the gases that are evolved at anode and cathode during the electrolysis of acidified water.
Ans: During the electrolysis of acidified water, the gases evolved at the electrodes are:
At Anode:
Oxygen gas (O₂) is evolved at the anode.
At Cathode:
Hydrogen gas (H₂) is evolved at the cathode.
14). Give one example of the reaction in which a catalyst increases the rate of reaction.
Ans: One example of a reaction in which a catalyst increases the rate of reaction is the decomposition of hydrogen peroxide. A catalyst like manganese dioxide (MnO2) speeds up the breakdown of hydrogen peroxide (H2O2) into water (H2O) and oxygen gas (O2).
Chemical Equation:
2 H2O2→2H2O+O2
15). What substance causes a chemical reaction without itself being affected?
Ans: The substance that causes a chemical reaction without itself being affected is called a “catalyst.”
16). Does a chemical reaction always result in a new substance being formed?
Ans: Yes, a chemical reaction usually creates new substances with different properties, although there are exceptions in certain equilibrium reactions.
17). How do you know if you have made a chemical reaction?
Ans: We can know if a chemical reaction has occurred by observing one or more of the following signs:
Formation of Precipitate:
A change in color indicating a transformation at the molecular level
Color Change:
A change in color indicating a transformation at the molecular level.
Gas Production:
Formation of gas bubbles, often visible as fizzing or effervescence.
Temperature Change:
A noticeable change in temperature, indicating energy changes during the reaction.
Odor Change:
A distinct change in odor or the release of a new smell.
Change in Physical State:
A change from solid to liquid, liquid to gas, etc.
18). How can a chemical reaction be accelerated?
Ans: A chemical reaction can be accelerated or speeded up by employing the following methods:
1. Catalysts
2. Increase in Temperature
3. Pressure Changes
4. Increase in Concentration
5. Particle Size Reduction:
6. Radiation
19). How does pressure affect the rate of gaseous reaction?
Ans: Higher pressure in a gaseous reaction increases the concentration of gas molecules, leading to more frequent and forceful collisions, ultimately accelerating the reaction rate.
21). What is a chemical reaction? What are the conditions required for a chemical Reaction?
Ans: A chemical reaction is a process where substances, called reactants, undergo a transformation, resulting in the formation of new substances, known as products.
Conditions Required for a Chemical Reaction:
1. Reactants:
Chemical reactions require at least two or more reactants, which are substances undergoing the transformation.
2. Collision and Activation Energy:
Reactant molecules need to collide with a certain minimum force called activation energy for the reaction to occur. This collision imparts sufficient energy to break existing bonds and form new ones.
3. Orientation:
The reactant molecules must collide with the correct orientation to form the desired product. Not all collisions lead to a reaction; the reactants must align properly during collision.
22). Explain addition reaction and single displacement reaction with an example.
Ans:
1. Addition Reaction:
An addition reaction is like putting two things together to make a new thing. It’s when two reactants combine to form a single product.
Example of Addition Reaction – Formation of Water:
Imagine you have hydrogen gas (H2) and oxygen gas (O2), and you combine them. They react and form water (H2O) – a new substance.
Chemical Equation: H2+O2→H2O
2. Single Displacement Reaction:
A single displacement reaction is like a switch. One element in a compound is replaced by another element, resulting in a new compound and a different element.
Example of Single Displacement Reaction – Zinc and Copper Sulfate:
Suppose you have zinc (Zn) and copper sulfate (CuSO₄). Zinc displaces copper in copper sulfate, forming zinc sulfate (ZnSO₄) and copper (Cu).
Chemical Equation: Zn+CuSO4→ZnSO4+Cu.
23). What is a catalyst? How does a catalyst affect the rate of reaction?
Ans: A catalyst is like a helper in a chemical reaction. It’s a substance that helps the reaction happen faster, but it doesn’t get used up in the process. It’s like a magic wand that makes things go quicker.
- Imagine you are building a tower with blocks. Normally, it takes a long time to stack them one by one. Now, if you have a tool that helps you stack them faster without being used up, that tool is like a catalyst.
- In a chemical reaction, a catalyst makes the reactant molecules collide more effectively, sort of like giving them a nudge to react faster. It lowers the energy needed to start the reaction, so the reaction happens faster.
So, a catalyst is a helper that speeds up a chemical reaction, making it go faster without getting used up itself. It’s like the turbo boost for reactions.
24). Carbon reacts with oxygen to give carbon dioxide. What type of chemical reaction is this? Write its chemical equation.
Ans: The reaction of carbon with oxygen to produce carbon dioxide is a combustion reaction.
Chemical Equation:
C+O2→CO2
25). Silver bromide is stored in dark bottles in the laboratories.
Ans: Silver bromide is stored in dark bottles in laboratories because it’s sensitive to light. If exposed to light, it can change or break down. Storing it in dark bottles protects it from light and helps to keep it stable and usable for experiments.
26). It is important to understand chemical reactions.
Ans: Understanding chemical reactions is important because it helps us know how substances interact and change.
27). The conversion of magnesium ribbon into white powdered ash on burning is a chemical change.
Ans:When magnesium ribbon burns and turns into white powdered ash, it’s a chemical change because the magnesium atoms in the ribbon combine with oxygen from the air to create a new substance, magnesium oxide. The original magnesium ribbon is no longer there; it transformed into a different material with different properties.
28). The rate of a chemical reaction is important in real life.
Ans: The rate of a chemical reaction is important in real life because it tells us how fast or slow a reaction happens. Imagine cooking – if the food takes forever to cook, it’s not practical. Similarly, in chemistry, knowing how fast a reaction occurs is crucial.
29). Iron fillings rust faster than an iron nail.
Ans: Iron fillings rust faster than an iron nail because of their size and surface area.
30). Acid base reaction is also called a neutralization reaction.
Ans: An acid-base reaction is termed a neutralization reaction because it involves the combination of an acid and a base, resulting in the formation of water and a salt.
31). The colour of copper sulphate solution changes when an iron nail is dipped into it.
Ans: The color of copper sulfate solution changes when an iron nail is dipped into it because of a chemical reaction between the iron and copper sulfate. The iron from the nail reacts with the copper sulfate, leading to the formation of a new substance. This new substance has a different color than copper sulfate, causing the solution to change color.
32). We apply paints on iron articles.
Ans: We apply paints on iron articles because it helps to protect them from rusting and to enhance their appearance.This layer acts as a barrier, preventing direct contact between the iron and moisture in the air.
33). Finely divided solid reactants react more quickly than solid lump reactants.
Ans: Finely divided solid reactants react more quickly than solid lump reactants because of their increased surface area.The more surface area, the more places where the reaction can occur.
