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Question 1 Report
What is the main source of carbon monoxide (CO) in urban areas?
Answer Details
The main source of carbon monoxide (CO) in urban areas is vehicle emissions.
When vehicles burn fuel, such as gasoline or diesel, they produce a variety of air pollutants, including carbon monoxide. This occurs because the fuel combustion process is not completely efficient, resulting in the release of carbon monoxide gas into the air.
Vehicle emissions are a significant contributor to air pollution in urban areas, especially in densely populated cities where there is a high concentration of vehicles. The exhaust from cars, trucks, buses, and motorcycles contributes to the elevated levels of carbon monoxide in the surrounding air.
Carbon monoxide is a colorless and odorless gas that is harmful to human health. It can be particularly dangerous in enclosed spaces, as it can build up to toxic levels and interfere with the body's ability to carry oxygen to vital organs.
To reduce the levels of carbon monoxide in urban areas, it is important to implement measures such as adopting cleaner transportation technologies, promoting public transportation, and improving vehicle emission standards. These efforts can help mitigate the negative impacts of carbon monoxide on air quality and public health.
Question 2 Report
Which of the following is a common property of non-metals?
Answer Details
A common property of non-metals is that they tend to gain electrons in chemical reactions.
Non-metals are a group of elements on the periodic table that have certain characteristics in common. One of these characteristics is their tendency to gain electrons during chemical reactions.
Electrons are negatively charged particles that orbit around the nucleus of an atom. Non-metals have a higher attraction for electrons compared to metals. This means that when non-metals come into contact with other elements, they have a greater likelihood of taking electrons from those elements.
This process of gaining electrons is called electron gainor electron capture. When non-metals gain electrons, they become negatively charged ions, also known as anions. This electron gain gives them stability and helps them achieve a full outer electron shell, similar to the noble gases.
The tendency of non-metals to gain electrons is an essential characteristic that distinguishes them from metals. Metals, on the other hand, tend to lose electrons during chemical reactions, leading to the formation of positively charged ions called cations.
Therefore, the property that matches the description is "Tend to gain electrons in chemical reactions," making it a common characteristic of non-metals.
Question 3 Report
The lanthanides and actinides are located in which block of the periodic table?
Answer Details
The lanthanides and actinides are located in the f-block of the periodic table.
The periodic table is organized into blocks based on the electron configuration of the elements. The f-block elements are located at the bottom of the periodic table, separated from the rest of the elements.
The lanthanides and actinides are a group of elements that have similar properties and electron configurations. They are also known as the "rare earth elements." These elements have electrons filling the 4f and 5f orbitals, hence they are placed in the f-block.
The f-block elements are very important in many scientific and technological applications. They are used in the production of magnets, catalysts, high-strength alloys, and various electronic devices. Some lanthanides and actinides are also used in medical imaging and cancer treatments.
Overall, the f-block elements play a crucial role in various fields of science and technology, and their placement in the periodic table helps to highlight their unique properties and characteristics.
Question 4 Report
Which of the following statements is true regarding the melting and boiling points of pure substances?
Answer Details
The correct statement regarding the melting and boiling points of pure substances is that the melting and boiling points can vary depending on the substance.
The melting point of a substance is the temperature at which it changes from a solid to a liquid state. On the other hand, the boiling point is the temperature at which a substance changes from a liquid to a gas state.
Both melting and boiling points are unique for each substance. The melting and boiling points are influenced by the strength of the forces of attraction between the molecules or atoms that make up the substance.
Substances with strong intermolecular forces will have higher melting and boiling points, while substances with weak intermolecular forces will have lower melting and boiling points. For example, metals tend to have high melting and boiling points because the metallic bonds between the metal atoms are strong.
Ionic compounds also have high melting and boiling points because of the strong electrostatic attraction between the positively and negatively charged ions. In contrast, molecular substances generally have lower melting and boiling points because the forces of attraction between their molecules are weaker.
This is why substances like water (H2O) have lower melting and boiling points compared to metals or ionic compounds. So, to summarize, the melting and boiling points of pure substances are not always the same and can vary depending on the substance.
The strength of the intermolecular forces determines the melting and boiling points, with substances having stronger forces generally having higher melting and boiling points.
Question 5 Report
What is the IUPAC name for the compound CCl4 ?
Answer Details
The IUPAC name for the compound CCl4 is tetrachloromethane
Question 6 Report
Which of the following substances is NOT hygroscopic?
Answer Details
Out of the given options, aluminum is the substance that is NOT hygroscopic.
Hygroscopicity refers to the ability of a substance to absorb or attract moisture from the surrounding environment.
Salt, sugar, and silica gel are all examples of substances that are hygroscopic.
When exposed to air, hygroscopic substances tend to absorb moisture and become damp or sticky. This is because they have polar molecules or ionic compounds that easily attract water molecules.
However, aluminum is a non-polar metal and does not have the same ability to attract or absorb moisture. Therefore, it is the substance that is not hygroscopic out of the given options.
Question 7 Report
What is the solubility product constant (Ksp) used for?
Answer Details
The solubility product constant (Ksp) is used to calculate the solubility of a solute in a given solvent. It helps us understand how much of a particular compound can dissolve in a specific solvent at a given temperature. : "To measure the total mass of a solute that can dissolve in a solvent" - This option is incorrect. The solubility product constant does not directly measure the mass of a solute that can dissolve. It calculates the maximum amount of solute that can dissolve in the solvent. : "To determine the concentration of a solute in a saturated solution" - This option is partially correct. The solubility product constant is involved in determining the concentration of a solute in a saturated solution. By knowing the Ksp value and the concentrations of the ions in the saturated solution, we can calculate the solute concentration. : "To calculate the solubility of a solute in a given solvent" - This option is correct. The solubility product constant is used to calculate the solubility of a solute in a given solvent. Solubility refers to the maximum amount of solute that can dissolve in a specific amount of solvent at a given temperature. : "To compare the solubilities of different solutes in the same solvent" - This option is not directly related to the solubility product constant. While Ksp values can be used to indirectly compare the solubilities of different solutes, the primary purpose of Ksp is to calculate solubility, not comparison. In summary, the solubility product constant (Ksp) is mainly used to calculate the solubility of a solute in a given solvent. It helps determine the maximum amount of solute that can dissolve in the solvent at a specific temperature.
Question 8 Report
Identify the reducing agent in the following reaction:
Zn + CuSO4
→ ZnSO4
+ Cu
Answer Details
In the given reaction, Zn reacts with CuSO4 to form ZnSO4 and Cu. To identify the reducing agent in this reaction, we need to understand the concept of oxidation and reduction. Oxidation is the loss of electrons, while reduction is the gain of electrons. In any redox reaction, there is an oxidizing agent (which causes oxidation) and a reducing agent (which causes reduction). Let's analyze the reaction: Zn + CuSO4 → ZnSO4 + Cu In this reaction, Zn is being oxidized because it loses two electrons to form Zn2+ ions in ZnSO4. On the other hand, Cu2+ ions in CuSO4 are being reduced because they gain two electrons to form Cu atoms. The reducing agent is the species that causes the reduction to occur. In this reaction, Zn is the reducing agent because it gives away its two electrons, causing the Cu2+ ions to be reduced to Cu atoms. Therefore, the reducing agent in this reaction is **Zinc (Zn)**.
Question 9 Report
At 2.0 atm pressure, the volume of a gas is 4.0 L. If the pressure is reduced to 1.0 atm while keeping the temperature constant, what will be the new volume of the gas?
Answer Details
In this scenario, we have a gas at an initial pressure of 2.0 atm and an initial volume of 4.0 L. We are told that the temperature is constant throughout the process.
The question asks us to determine the new volume of the gas if the pressure is reduced to 1.0 atm. To do this, we can use the Boyle's Law.
Boyle's Law states that if the temperature of a gas remains constant, then the pressure and volume of the gas are inversely proportional. In other words, as the pressure decreases, the volume increases.
Using Boyle's Law, we can set up the following equation:
P1 * V1 = P2 * V2
Where:
P1 = initial pressure
V1 = initial volume
P2 = final pressure
V2 = final volume (what we need to find)
Substituting the given values into the equation, we have:
(2.0 atm) * (4.0 L) = (1.0 atm) * (V2)
Simplifying the equation:
8.0 L atm = V2 * 1.0 atm
Since the pressure and volume are inversely proportional, we can solve for V2 by dividing both sides of the equation by 1.0 atm:
V2 = 8.0 L
Therefore, the new volume of the gas when the pressure is reduced to 1.0 atm while keeping the temperature constant will be 8.0 L.
Question 10 Report
Which type of chemical combination involves the transfer of electrons from one atom to another, resulting in the formation of oppositely charged ions?
Answer Details
The type of chemical combination that involves the transfer of electrons from one atom to another, resulting in the formation of oppositely charged ions, is ionic bonding.
In an ionic bond, one atom donates electrons to another atom. This happens when one atom has a stronger attraction for electrons than the other. The atom that donates electrons becomes positively charged (known as a cation), while the atom that receives the electrons becomes negatively charged (known as an anion).
The transfer of electrons occurs because atoms want to achieve a stable electron configuration, usually by having a complete outermost electron shell. By transferring electrons, atoms can achieve this stability. The resulting oppositely charged ions are attracted to each other due to the electrostatic force, forming an ionic bond.
For example, in the formation of table salt (sodium chloride), sodium (Na) donates an electron to chlorine (Cl). Sodium becomes a positively charged ion (Na+), and chlorine becomes a negatively charged ion (Cl-). The positive and negative charges attract each other, creating the ionic bond in sodium chloride.
Overall, ionic bonding involves the transfer of electrons, resulting in the formation of oppositely charged ions. This type of chemical combination is an essential concept in understanding various compounds and their properties.
Question 11 Report
Which functional group is present in alkanals?
Answer Details
The functional group present in alkanals is the carbonyl group (C=O).
In organic chemistry, functional groups are specific groups of atoms that are responsible for the characteristic chemical reactions and properties of a compound.
The carbonyl group consists of a carbon atom bonded to an oxygen atom with a double bond (C=O). It is often found at the end of the carbon chain in alkanals, which are a type of organic compound derived from alkanes.
The presence of the carbonyl group gives alkanals several important properties and reactivities. For example:
In summary, the presence of the carbonyl group (C=O) is the defining feature of alkanals, giving them specific chemical properties and reactivities.
Question 12 Report
Which of the following is a characteristic property of acids?
Answer Details
Acids are substances that can donate protons (H+) in aqueous solutions. When acids react with certain metals, they can release hydrogen gas (H2) as one of the products. This is a common behavior of many acids and can be used to distinguish them from other substances.
Question 13 Report
Which trace gas in the atmosphere plays a significant role in the greenhouse effect?
Answer Details
The trace gas in the atmosphere that plays a significant role in the greenhouse effect is carbon dioxide.
The greenhouse effect is a natural process that helps to regulate the Earth's temperature. When sunlight reaches the Earth's surface, some of it is absorbed and warms the planet. However, some of this heat is also radiated back into space.
Greenhouse gases, such as carbon dioxide, trap some of this heat and prevent it from escaping into space. They act like a blanket around the Earth, keeping it warm. Without these greenhouse gases, the Earth would be much colder and life as we know it would not be possible.
However, human activities, such as burning fossil fuels like coal, oil, and natural gas, have been increasing the concentration of carbon dioxide in the atmosphere. This excessive amount of carbon dioxide has enhanced the greenhouse effect, leading to global warming.
Global warming is the long-term increase in Earth's average temperature due to the increased levels of greenhouse gases. It is causing changes in climate patterns, melting of polar ice caps, rising sea levels, and extreme weather events.
So, in summary, carbon dioxide is the trace gas in the atmosphere that plays a significant role in the greenhouse effect and contributes to global warming.
Question 14 Report
Which of the following is a unique property of water compared to other liquids?
Answer Details
A unique property of water compared to other liquids is that it expands when freezing.
When most substances freeze, the molecules become more closely packed together and the substance contracts or becomes denser. However, water is different. As it cools below 4 degrees Celsius, the water molecules start forming a crystal lattice structure. This structure has a more open arrangement, causing the water molecules to move further apart and take up more space. This expansion causes ice to be less dense than liquid water. This expansion is why ice floats in liquid water. If water did not expand when freezing, ice would sink and bodies of water like lakes and oceans would freeze from the bottom up, endangering aquatic life. The expansion of water when freezing is also important for another reason. It helps prevent the environment from experiencing rapid temperature fluctuations. When the temperature drops, the top layer of a body of water freezes, acting as an insulating layer for the water below, and protecting aquatic life during cold winter months. Overall, the expansion of water when freezing is a unique property of water that has significant implications for the survival of organisms and the stability of ecosystems.Question 15 Report
Which group does calcium belong to in the periodic table?
Answer Details
Calcium belongs to the alkaline earth metals group in the periodic table.
The periodic table is a chart that organizes elements based on their properties and atomic number. It consists of rows, called periods, and columns, called groups or families.
The alkaline earth metals group is found in the second column of the periodic table, specifically group 2. This group includes elements such as beryllium, magnesium, calcium, strontium, and barium.
So, why does calcium belong to the alkaline earth metals group? It's because of its characteristics and behavior.
Firstly, alkaline earth metals are highly reactive and relatively soft metals. Calcium, like other elements in this group, readily loses its two outermost electrons to form a positive ion with a +2 charge.
Secondly, alkaline earth metals have similar chemical properties. They all react with water to form alkaline solutions and with non-metals to form compounds.
Lastly, calcium is found abundantly in Earth's crust, mainly as calcium carbonate in limestone and chalk. It is an essential element for living organisms and is involved in various biological processes, such as muscle contraction and bone formation.
In conclusion, calcium belongs to the alkaline earth metals group in the periodic table due to its reactivity, similar chemical properties to other group members, and abundance on Earth.
Question 16 Report
When a substance is oxidized, it
Answer Details
When a substance is oxidized, it loses electrons.
Oxidation is a chemical process in which a substance reacts with another substance or element, resulting in the loss of electrons from the oxidized substance. In other words, the oxidized substance gives away electrons to another substance or element.
This loss of electrons during oxidation is significant because electrons are negatively charged particles that play a crucial role in chemical reactions. By losing electrons, the oxidized substance becomes positively charged or oxidized.
It's important to note that oxidation doesn't necessarily involve the gain of oxygen atoms. While some reactions involving oxidation do include the addition of oxygen, it is not a defining characteristic of oxidation. The key factor is the loss of electrons, regardless of whether oxygen atoms are involved or not.
Question 17 Report
Answer Details
When an acidic solution is diluted by adding more solvent (usually water), the concentration of hydrogen ions (H+ ) decreases. As a result, the pH of the solution decreases, making it less acidic
Question 18 Report
An element has an atomic number of 8 and a mass number of 16. How many neutrons does this element have?
Answer Details
An element with an atomic number of 8 and a mass number of 16 has 8 neutrons.
Let's break down the information to understand why.
The atomic number of an element tells you the number of protons in its nucleus. In this case, the element has an atomic number of 8, which means it has 8 protons.
The mass number of an element is the sum of its protons and neutrons. In this case, the mass number is 16.
To calculate the number of neutrons, we subtract the atomic number from the mass number: Number of Neutrons = Mass Number - Atomic Number
So, in this case, the number of neutrons would be: 16 (mass number) - 8 (atomic number) = 8 neutrons.
Therefore, the element in question has 8 neutrons.
Question 19 Report
According to the kinetic theory of gases, the pressure exerted by a gas is due to
Answer Details
The pressure exerted by a gas is due to the collisions of gas particles with the container walls. This is explained by the kinetic theory of gases, which provides a simple model to understand the behavior of gases. According to the kinetic theory, a gas is made up of tiny particles (such as atoms or molecules) that are in constant random motion. These particles move in straight lines until they collide with each other or with the walls of the container. When gas particles collide with the walls of the container, they exert a force on the walls. This force is what we call pressure. The more frequently and forcefully the particles collide with the walls, the greater the pressure exerted by the gas. The other options mentioned - the vibrations of gas particles, the weight of the gas particles, and the attractive forces between gas particles - are not the primary factors contributing to the pressure exerted by a gas. While these factors may play a role in certain situations, they are not the main reason for the pressure in a gas. In summary, the pressure exerted by a gas is primarily due to the collisions of gas particles with the container walls. This concept is explained by the kinetic theory of gases, which helps us understand the behavior of gases and how they exert pressure.
Question 20 Report
What is the mass (in grams) of 500 mL of ethanol? (density of ethanol = 0.789 g/mL)
Answer Details
To calculate the mass of ethanol, we need to use its density and volume. The density of ethanol is given as 0.789 grams per milliliter.
First, let's convert the volume from milliliters to liters. Since there are 1000 milliliters in a liter, 500 mL is equivalent to 0.5 liters.
Now, we can use the formula:
Mass = Density x Volume
Substituting the value, we have:
Mass = 0.789 g/mL x 0.5 L
Multiplying these values, we find that the mass of 500 mL of ethanol is 0.3945 grams. Therefore, the correct answer is 394.5 g.
Question 21 Report
What is eutrophication?
Answer Details
Eutrophication is the excessive growth of algae in water bodies, such as lakes, rivers, and oceans, due to an increase in nutrients in the water. These nutrients, mainly nitrogen and phosphorus, come from various sources including agricultural runoff, wastewater discharge, and soil erosion.
When there is an excess of nutrients in the water, it acts as a fertilizer for algae and other aquatic plants. These plants grow rapidly and form dense colonies on the water surface, resulting in what we commonly call an "algal bloom".
During the algal bloom, the water becomes green or murky and can sometimes emit an unpleasant odor. This excessive growth of algae can have several negative impacts on the aquatic ecosystem.
As the algae die and decompose, they consume a large amount of oxygen from the water, leading to oxygen depletion. This reduction in oxygen levels can be harmful to fish and other organisms that depend on oxygen to survive. It can lead to the death of fish and other aquatic organisms, creating what is known as a "dead zone".
Furthermore, the dense layer of algae on the water surface can block sunlight from penetrating into the water, limiting photosynthesis for other aquatic plants and organisms. This can disrupt the balance of the ecosystem, affecting the biodiversity of the water body.
In summary, eutrophication is caused by an excess of nutrients in the water, leading to the rapid growth of algae and the subsequent negative impacts on oxygen levels and biodiversity in the aquatic ecosystem.
Question 22 Report
Balance the following redox reaction:
Fe2
O3
+ CO → Fe + CO2
Answer Details
The balanced equation for the given redox reaction is: Fe2O3 + 3CO → 2Fe + 3CO2 To balance this reaction, we need to make sure that the number of atoms of each element is the same on both sides of the equation. In the reaction, we have Fe, O, and C as the elements. Step 1: Balancing Fe There are 2 Fe atoms on the left side and only 1 Fe atom on the right side. To balance the Fe atoms, we need to put a coefficient in front of Fe on the right side. Hence, the equation becomes: Fe2O3 + 3CO → 2Fe + 3CO2 Step 2: Balancing O There are 3 O atoms in Fe2O3 and 3 O atoms in CO2 on the right side. To balance the O atoms, we need to make sure there are 3 O atoms on the left side as well. So we put a coefficient of 2 in front of Fe2O3: 2Fe2O3 + 3CO → 2Fe + 3CO2 Step 3: Balancing C There are already 3 C atoms on both sides, so no further balancing is needed for C. Now the equation is balanced with 2Fe2O3 + 3CO → 2Fe + 3CO2. So the correct option is: Fe2O3 + 3CO → 2Fe + 3CO2
Question 23 Report
A gas occupies a volume of 1.5 liters at a pressure of 2 atmospheres. If the pressure is increased to 4 atmospheres while the temperature remains constant, what will be the new volume of the gas?
Answer Details
According to Boyle's law (for constant temperature), the product of initial pressure and initial volume is equal to the product of final pressure and final volume. Therefore, (1.5 liters) × (2 atmospheres) = (new volume) × (4 atmospheres). Solving for the new volume gives us (new volume) = (1.5 liters × 2 atmospheres) / 4 atmospheres = 0.75 liters.
Question 24 Report
Which of the following statements is true for strong electrolytes?
Answer Details
Out of the given statements, the true statement for strong electrolytes is:
They completely dissociate into ions in solution.
Now, let's understand what a strong electrolyte is and why this statement is true.
An electrolyte is a substance that conducts electricity when dissolved in water or melted. Strong electrolytes are substances that completely dissociate or break apart into ions when dissolved in water.
When strong electrolytes dissolve in water, the bonds holding the molecules together are broken and they separate into their individual ions. These ions are then free to move and carry electrical charge, allowing the solution to conduct electricity.
On the other hand, weak electrolytes partially dissociate or break apart into ions when dissolved in water. Not all of the molecules separate into ions, resulting in a lower concentration of ions in the solution and less conductivity of electricity compared to strong electrolytes.
In summary, strong electrolytes completely dissociate into ions in solution, allowing for effective electrical conductivity. This is why the statement "They completely dissociate into ions in solution" is true for strong electrolytes.
Question 25 Report
If gas A has a molar mass of 32 g/mol and gas B has a molar mass of 64 g/mol, what is the ratio of their diffusion rates?
Answer Details
The diffusion rate of a gas is influenced by its molar mass. In simpler terms, the lighter the gas, the faster it will diffuse. To find the ratio of the diffusion rates between gas A and gas B, we need to compare their molar masses. Gas A has a molar mass of 32 g/mol, while gas B has a molar mass of 64 g/mol. To calculate the ratio, we can divide the molar mass of gas B by the molar mass of gas A: 64 g/mol ÷ 32 g/mol = 2. Therefore, the ratio of their diffusion rates is 2:1. This means that gas B will diffuse twice as fast as gas A.
Question 26 Report
Which of the following factors does NOT affect the rate of a chemical reaction?
Answer Details
The factor that does NOT affect the rate of a chemical reaction is the molecular weight of products.
The rate of a chemical reaction is influenced by various factors, such as:
However, the molecular weight of products does not directly affect the rate of a chemical reaction. The rate of a reaction is determined by the characteristics of the reactants and the conditions in which the reaction takes place, not the molecular weight of the resulting products.
Question 27 Report
Alkynes readily undergo addition reactions with which of the following?
Answer Details
Alkynes readily undergo addition reactions with hydrogen gas (H2) in the presence of a metal catalyst, such as palladium (Pd) or platinum (Pt), to form alkenes.
Question 28 Report
What happens when alkanoic acids react with alcohols in the presence of an acid catalyst?
Answer Details
When alkanoic acids react with alcohols in the presence of an acid catalyst, esterification occurs.
Esterification is a chemical reaction that results in the formation of an ester. An ester is a compound that is formed by the reaction between an acid and an alcohol. In this case, the alkanoic acid and alcohol react together to form an ester.
The reaction is initiated by the acid catalyst, which helps to speed up the reaction and increase the yield of the desired ester product.
During the reaction, the acid catalyst provides a proton (H+) to the alkanoic acid, which makes it more reactive. The alcohol then attacks the carbonyl carbon of the alkanoic acid, resulting in the formation of a new bond.
The final product of the reaction is an ester, which is a compound that has an oxygen atom connected to a carbon atom through a single bond, with the other end of the oxygen atom connected to an alkyl group.
To summarize, when alkanoic acids react with alcohols in the presence of an acid catalyst, esterification occurs, resulting in the formation of an ester compound.
Question 29 Report
What is the valency of an element with the electronic configuration 2, 8, 7?
Answer Details
The valency of an element is a measure of its ability to combine with other elements to form compounds. It is determined by the number of electrons an atom can gain, lose, or share in order to achieve a stable electronic configuration.
In the given electronic configuration 2, 8, 7, the element has a total of 17 electrons. In order to achieve a stable electronic configuration, the element needs to either gain one electron to complete its outermost shell or lose seven electrons to empty its outermost shell.
The valency of an element is typically determined by the number of electrons in its outermost shell, also known as the valence shell. In this case, the element has 7 electrons in its valence shell, which means it needs to gain one electron to achieve a stable configuration.
Therefore, the valency of the element with the electronic configuration 2, 8, 7 is 1, as it needs to gain one electron to achieve stability.
Question 30 Report
The process of rusting is an example of the formation of
Answer Details
The process of rusting is an example of the formation of an acidic oxide.
Rusting occurs when iron or steel react with oxygen and moisture in the presence of an electrolyte (such as water or salt). This reaction forms a reddish-brown substance called rust.
Rust is considered an acidic oxide because it reacts with water to form an acid. When moisture is present, iron reacts with oxygen to create iron(III) oxide, which is the main component of rust. This iron oxide reacts further with water to produce hydrated iron(III) oxide and releases H+ ions, making the resulting solution acidic.
For example, the reaction between iron, oxygen, and water can be represented by the following equations:
Iron + Oxygen → Iron(III) Oxide
Fe + O2 → Fe2O3
Iron(III) Oxide + Water → Hydrated Iron(III) Oxide + Acid
Fe2O3 + xH2O → Fe2O3·xH2O + H+
Therefore, it is clear that the formation of rust is an example of the formation of an acidic oxide.
Question 31 Report
When anhydrous cobalt chloride paper is exposed to water, what color change is observed?
Answer Details
When anhydrous cobalt chloride paper is exposed to water, the color change observed is from blue to pink.
Anhydrous cobalt chloride paper is a type of paper that contains cobalt chloride in a dry form. Cobalt chloride is a chemical compound that can exist in both anhydrous (without water) and hydrated (with water) form.
In its anhydrous form, cobalt chloride appears as blue crystals. These crystals do not contain any water molecules. When anhydrous cobalt chloride is exposed to water, it undergoes a chemical reaction called hydration.
During hydration, water molecules are absorbed by the cobalt chloride crystals, resulting in the formation of hydrated cobalt chloride. The hydrated form of cobalt chloride is pink in color.
So, when anhydrous cobalt chloride paper comes into contact with water, the blue crystals of cobalt chloride change into pink crystals of hydrated cobalt chloride. This color change is a clear indication that water is present.
Therefore, the color change observed when anhydrous cobalt chloride paper is exposed to water is from blue to pink.
Question 32 Report
Which of the following is an example of a primary cell?
Answer Details
An example of a primary cell is an alkaline battery.
Primary cells are non-rechargeable batteries, meaning once they have been depleted of their energy, they cannot be recharged and must be replaced. These types of batteries are commonly found in everyday household items like remote controls, toys, and flashlights.
The alkaline battery works by converting chemical energy into electrical energy. Inside the battery, there are two electrodes - a negative electrode (anode) and a positive electrode (cathode). These electrodes are separated by an electrolyte, which allows the flow of ions between them.
During use, a chemical reaction occurs at the anode, causing zinc ions to be released into the electrolyte. At the cathode, manganese dioxide reacts with the zinc ions and water, producing hydroxide ions. The movement of ions creates an electron flow from the anode to the cathode, generating an electric current.
As the reactions continue, the zinc anode gradually gets consumed, and the battery loses its ability to produce electricity. Once the chemical reactions are complete, the alkaline battery is considered "dead" and needs to be replaced.
In contrast, the other options given are not primary cells:
Question 33 Report
Which of the following alkanes has a straight-chain structure?
Answer Details
A straight-chain structure in organic chemistry refers to a carbon chain where the carbon atoms are connected in a linear or straight fashion, without any branches or loops.
Among the given options, the alkane that has a straight-chain structure is butane (C4H10).
Butane is composed of four carbon atoms (C4) and ten hydrogen atoms (H10). Its carbon atoms are arranged in a straight or linear chain without any branches.
In contrast, the other options have structures that deviate from a straight-chain. Cyclopentane (C5H10) forms a ring or cyclical structure, Isobutane (C4H10) has a branch coming off the main chain, and Benzene (C6H6) has a cyclic structure.
In summary, only butane (C4H10) has a straight-chain structure among the given options.
Question 34 Report
What is the chemical formula of rust, which is formed on the surface of iron in the presence of oxygen and moisture?
Answer Details
The correct chemical formula of rust, which is formed on the surface of iron in the presence of oxygen and moisture, is Fe2O3. Rust is a reddish-brown oxide that forms when iron reacts with oxygen and water. It occurs as a result of a chemical reaction called oxidation. When iron comes into contact with oxygen in the presence of moisture, a series of reactions occur that lead to the formation of rust. The formula Fe2O3 represents rust, where Fe represents iron and O represents oxygen. The number 2 indicates that there are two atoms of iron, and the number 3 indicates that there are three atoms of oxygen in the rust formula. To summarize, rust is formed on the surface of iron when it reacts with oxygen and moisture, and its chemical formula is Fe2O3.
Question 35 Report
A blue litmus paper turns red when dipped into a solution. What does this indicate about the solution?
Answer Details
The blue litmus paper turning red when dipped into a solution indicates that the solution is acidic.
Litmus paper is a commonly used indicator to determine the acidity or alkalinity of a solution. It undergoes a color change depending on the nature of the solution it is exposed to. Blue litmus paper is specifically used to test for acidity. In an acidic solution, which has a high concentration of hydrogen ions (H+), the blue litmus paper reacts with the hydrogen ions. This reaction causes the litmus paper to change from blue to red. This color change is a clear indication that the solution being tested is acidic in nature. Therefore, in this scenario, since the blue litmus paper turns red when dipped into the solution, it confirms that the solution is acidic. It is important to note that this indicates the nature of the solution and not a fault in the litmus paper itself.Question 36 Report
Sodium reacts vigorously with water to produce
Answer Details
When sodium reacts with water, it undergoes a very vigorous reaction. This means that the reaction is very fast and produces a lot of energy. The products that are formed during this reaction are sodium hydroxide (NaOH) and hydrogen gas (H2). Let's break down the reaction step by step: 1. Sodium (Na) is a highly reactive metal. When it is placed in water (H2O), it reacts with the water molecules. 2. The sodium atom loses an electron, becoming a positively charged sodium ion (Na+). This electron is transferred to a water molecule, causing it to split apart. 3. The water molecule (H2O) is made up of two hydrogen atoms and one oxygen atom. The hydrogen ions (H+) from the water combine with the remaining electron to form hydrogen gas (H2). 4. The remaining hydroxide ions (OH-) from the water combine with the sodium ions (Na+) to form sodium hydroxide (NaOH). In summary, when sodium reacts with water, it produces sodium hydroxide (NaOH) and hydrogen gas (H2). Therefore, the correct answer is sodium hydroxide (NaOH) and hydrogen gas (H2).
Question 37 Report
What is the common name for ethanoic acid?
Answer Details
The common name for ethanoic acid is acetic acid.
Acetic acid is a clear, colorless liquid with a strong, pungent odor. It is a weak acid commonly found in vinegar, giving it its sour taste and distinct smell. Acetic acid is also used in many industries, such as food production, pharmaceuticals, and cleaning products.
The name "acetic acid" is derived from the Latin word "acetum," which means vinegar. This is because acetic acid is the main component of vinegar.
In summary, the common name for ethanoic acid is acetic acid, which is a weak acid found in vinegar and used in various industries.
Question 38 Report
Which of the following methods can be used to remove temporary hardness from water?
Answer Details
One method that can be used to remove temporary hardness from water is boiling.
When water is heated and boiled, it causes the dissolved minerals that contribute to temporary hardness, such as calcium and magnesium bicarbonates, to precipitate out of the water. These precipitates settle at the bottom of the container or can be filtered out, resulting in the removal of temporary hardness.
Filtration can also help in removing temporary hardness from water. This method involves passing water through a filter that is designed to trap and remove the dissolved mineral ions responsible for hardness. The filter can be made of materials like activated carbon or ion-exchange resin, which have the ability to bind with calcium and magnesium ions and remove them from the water.
Distillation is another effective method for removing temporary hardness from water. Distillation involves heating the water to boiling point, and then collecting and condensing the steam to obtain pure water. As the water is heated and evaporates, the dissolved minerals are left behind, resulting in the separation of the excess minerals and the production of softened water.
Chlorination is not a method that can be used to remove temporary hardness from water. Chlorination refers to the process of adding chlorine or chlorine compounds to water to disinfect and kill harmful microorganisms. It does not have any direct effect on the mineral content of the water, and therefore cannot remove temporary hardness.
In summary, methods such as boiling, filtration, and distillation can be used to remove temporary hardness from water, while chlorination does not have any impact on hardness removal.
Question 39 Report
At room temperature and standard pressure, chlorine gas is in which state of matter?
Answer Details
At room temperature and standard pressure, chlorine gas is in the state of matter called gas.
In chemistry, there are three main states of matter: solid, liquid, and gas. The state of matter depends on the arrangement and movement of the particles that make up a substance.
Let's consider each state of matter one by one:
Solid: In a solid state, the particles are tightly packed together and have fixed positions. They vibrate in place but do not move around freely. Solids have a definite shape and volume. Examples of solids are a desk, a brick, or a piece of ice.
Liquid: In a liquid state, the particles are more spread out compared to solids. They have some freedom to move, but they still remain close to each other. Liquids can flow and take the shape of the container they are in. However, they still have a definite volume. Examples of liquids are water, milk, or oil.
Gas: In a gas state, the particles are far apart and move freely in all directions. They have much more energy compared to particles in solids or liquids. Gases do not have a definite shape or volume and can expand to fill the entire space they are contained in. Examples of gases are air, oxygen, or carbon dioxide.
Chlorine gas, at room temperature and standard pressure, exists as individual chlorine molecules that are far apart and move freely. Therefore, it is classified as a gas.
Question 40 Report
Which halogen is a gas at room temperature and is pale yellow in color?
Answer Details
Fluorine is a halogen that is a gas at room temperature and is pale yellow in color. Halogens are a group in the periodic table consisting of five chemically related elements: fluorine (F), chlorine (Cl), bromine (Br), iodine (I), and astatine (At). Among these, only Fluorine and Chlorine are gases at room temperature, but Chlorine is greenish-yellow, not pale yellow.
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