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Frage 1 Bericht
If a stable neutral atom has a mass number of 31, the number of electrons and neutrons respectively are
Antwortdetails
To answer this question, let's break it down step by step:
Mass Number: The mass number is the total number of protons and neutrons in an atom's nucleus. In this case, the mass number is given as 31.
Stable Neutral Atom: A stable neutral atom has no overall electrical charge, meaning the number of protons (positively charged) must equal the number of electrons (negatively charged).
If we symbolize the number of protons by the atomic number (Z), we can say:
1. **Protons = Electrons** in a neutral atom.
2. **Mass Number (A) = Protons + Neutrons**.
Given that the mass number is 31, we have the equation:
A = Protons + Neutrons = 31.
Assuming a commonly known stable element like Phosphorus, which has an atomic number (Z) of 15, it means:
1. **Protons = 15**.
2. **Electrons = 15** (because it's a neutral atom).
3. To find Neutrons: Neutrons = Mass Number - Protons = 31 - 15 = 16.
So, in this scenario, the number of electrons is 15 and the number of neutrons is 16. This combination is found in the first option given.
Frage 2 Bericht
127g of sodium chloride was dissolved in 1.0dm3 of distilled water at 250 C . Determine the solubility in moldm−3 of sodium chloride at that temperature. [Na = 23, Cl = 35.5]
Antwortdetails
To determine the solubility of sodium chloride (NaCl) in mol/dm3 at the given temperature, you need to first calculate the number of moles of NaCl dissolved.
Step 1: Calculate the molar mass of NaCl.
The molar mass of a compound is found by adding the atomic masses of its constituent elements:
- Sodium (Na) has an atomic mass of 23.
- Chlorine (Cl) has an atomic mass of 35.5.
Thus, the molar mass of NaCl = 23 + 35.5 = 58.5 g/mol.
Step 2: Calculate the number of moles of NaCl.
The formula to calculate moles is:
Number of moles = Mass (g) / Molar mass (g/mol)
Given mass of NaCl = 127 g,
Number of moles = 127 g / 58.5 g/mol ≈ 2.17 mol
Step 3: Calculate the solubility in mol/dm3.
Since the sodium chloride is dissolved in 1.0 dm3 of water, the solubility is the same as the number of moles, since the volume is already 1.0 dm3.
Therefore, the solubility of sodium chloride at that temperature is 2.17 mol/dm3.
Rounded to the options given, 2.17 mol/dm3 is approximately equal to 2.2 mol/dm3.
Frage 3 Bericht
Calculate the number of moles of Copper that will be deposited, if 2 Faraday of electricity is passed through the copper during the electrolysis of copper(II)tetraoxosulphate(VI)
[1F = 96500C ]
Antwortdetails
The electrolysis of copper(II) tetraoxosulphate(VI) involves the deposition of copper at the cathode. To understand how many moles of copper are deposited when 2 Faraday of electricity is passed through, we need to consider Faraday's first law of electrolysis. Faraday's first law states that the mass (or number of moles) of a substance deposited at an electrode is directly proportional to the quantity of electricity that is passed through the electrolyte.
A Faraday (or Faraday constant) is the charge of one mole of electrons, which is approximately **96500 coulombs** (C). During electrolysis, the chemical reaction occurring at the cathode for copper deposition can be represented by the following equation:
Cu2+ + 2e- → Cu
This equation shows that **2 moles of electrons** (represented by 2e-) are needed to deposit **1 mole of copper (Cu)**.
If we have **2 Faradays** of electricity, it means we have **2 x 96500 C = 193000 C**. Since **1 Faraday (96500 C)** is required to deposit **0.5 mole** of copper, **2 Faradays** will deposit twice that amount:
0.5 mole of copper deposited per Faraday x 2 Faradays = **1.0 mole** of copper
Thus, when **2 Faradays** of electricity are passed through copper(II) tetraoxosulphate(VI) solution, **1.0 mole** of copper will be deposited.
Frage 4 Bericht
What accounts for the low melting and boiling points of covalent molecules?
Antwortdetails
The low melting and boiling points of covalent molecules are primarily due to the presence of weak intermolecular forces between the molecules. While covalent molecules consist of atoms bonded together by strong covalent bonds, the forces between separate molecules, known as van der Waals forces or London dispersion forces, are much weaker. These weak forces require significantly less energy to overcome, which explains why covalent molecules tend to have lower melting and boiling points.
Although covalent molecules have definite shapes and possess shared electron pairs, these characteristics have little influence on the melting and boiling points. The focus is instead on how much energy is needed to separate the molecules from one another.
Covalent molecules are not typically three-dimensional structures like ionic compounds or metals which form intricate lattices and require more energy to disrupt. Thus, the primary reason for their lower melting and boiling points is the presence of weak intermolecular forces that can be more easily overcome with minimal energy input.
Frage 5 Bericht
C2 H4(g) + 3O2(g) → 2CO2(g) + 2H2 O(g)
The above equation represents the combustion of ethene.If 10cm3 of ethene is burnt in 50cm3 of oxygen, what would be the volume of oxygen that would remain at the end of the reaction?
Antwortdetails
Gay Lussac’s Law of Combining Volumes states that when gases react, they do so in volumes which bear a simple ratio to one another, and to the volume of the product(s) formed if gaseous, provided the temperature and pressure remain constant.
C2 H4(g) + 3O2(g) → 2CO2(g) + 2H2 O(g)
1 mole : 3 moles
Total volume required: 10 cm3 50 cm3
Reacted Volume: 10 cm3 30 cm3
Residual volume: 0 (50 - 30) = 20 cm3
Frage 6 Bericht
The reaction between alkanoic acids and alkanols in the presence of an acid catalyst is known as
Antwortdetails
The reaction between alkanoic acids and alkanols in the presence of an acid catalyst is known as esterification.
An alkanoic acid, also known as a carboxylic acid, is a type of organic acid that contains a carboxyl group (-COOH). An alkanol, commonly referred to as an alcohol, contains a hydroxyl group (-OH).
When an alkanoic acid reacts with an alkanol in the presence of an acid catalyst (commonly sulfuric acid), they combine to form an ester and water. This particular reaction is termed esterification. The acid catalyst speeds up the reaction by donating protons, which helps in breaking and forming new bonds.
Here's a simplified view of the reaction:
1. Alkanoic Acid (R-COOH) + Alkanol (R'-OH) -> Ester (R-COOR') + Water (H2O)
The key characteristics of esterification are:
Therefore, in summary, the process described is esterification.
Frage 7 Bericht
If 11.0g of a gas occupies 5.6 dm3 at s.t.p., calculate its vapour density (1 mole of a gas occupies 22.4 dm3 ).
Antwortdetails
The problem requires calculating the **vapor density** of the gas. Vapor density is defined as the mass of a certain volume of a gas compared to the mass of an equal volume of hydrogen, where the hydrogen standard is 2 g/mol (as the molecular weight of hydrogen gas, H₂, is 2).
Here's a step-by-step explanation:
The calculated vapor density of the gas is 22.
Frage 8 Bericht
CH3 -CH2 -OH and CH3 -O-CH3
The relationship between the two compounds above, is that they are
Antwortdetails
The relationship between the two compounds is that they are isomers.
To understand why these compounds are isomers, let's break down their structures and definitions:
1. Structures of the Compounds:
2. Definitions:
Both compounds have the same molecular formula: C2H6O. However, they have different arrangements of their atoms. Ethanol has a hydroxyl group (-OH) attached to an ethyl group (CH3-CH2-), while dimethyl ether involves two methyl groups (CH3-) bonded to an oxygen atom (O). This difference in structure leads to different chemical and physical properties, despite having the same molecular formula. Hence, these two compounds are classified as isomers.
Frage 9 Bericht
If a salt weighs 2g and upon exposure to the atmosphere weighs 1.5g, this is as a result of
Antwortdetails
The observation that a salt initially weighs 2g, but reduces to 1.5g after exposure to the atmosphere is primarily due to the process called efflorescence.
Efflorescence occurs when a salt loses water molecules from its crystal structure when exposed to air, which is why the weight of the salt decreases over time. This loss of water is because some salts contain water of crystallization, and when such salts are exposed to the atmosphere, they can release this water, leading to a reduction in weight.
In this specific case, the salt has lost 0.5g of water, leading to the weight change from 2g to 1.5g. This process is different from hygroscopy, which involves absorbing moisture from the atmosphere, or deliquescence, where a substance absorbs moisture and eventually dissolves in it. It's also not related to effervescence, which is the escape of gas from an aqueous solution.
Frage 10 Bericht
Biuret test is a chemical test used for detecting the presence of
Antwortdetails
The Biuret test is a chemical test used for detecting the presence of proteins. When you perform a Biuret test, you are looking for peptide bonds, which are the connections between the amino acids in a protein. This is how it works:
The test is specifically tailored to proteins because carbohydrates, amines, and alkanoates do not exhibit the required peptide bonds necessary for this color change. Therefore, the Biuret test is not suitable for detecting these compounds.
Frage 11 Bericht
25.0g of potassium chloride were dissolved in 80g of distilled water at 300 C. Calculate the solubility of the solute in mol dm3 . [K =39, Cl = 35.5]
Antwortdetails
To calculate the solubility of potassium chloride (KCl) in mol dm3, we need to follow these steps:
Molar mass of KCl = 39 + 35.5 = 74.5 g/mol
Moles of KCl = Mass of KCl / Molar mass of KCl = 25.0 g / 74.5 g/mol = 0.3356 mol
Convert ml to liters: 80 ml = 0.080 L
Concentration = Moles of solute / Volume of solvent in liters = 0.3356 mol / 0.080 L = 4.195 mol/dm3
The solubility of potassium chloride at 30°C in mol/dm3 is therefore approximately 4.2 mol/dm3.
Frage 12 Bericht
An example of a physical change is
Antwortdetails
A physical change involves a change in the physical properties of a substance, without a change in its chemical composition. This means that the substance remains the same at the molecular level, despite how it might appear differently.
An example of a physical change from the given options is the liquefaction of liquids. In this process, a substance transitions from a solid or gas to a liquid state. This change is purely physical because the molecular structure of the substance does not change; only its state or form does. Importantly, such a change is usually reversible, meaning the substance can return to its original state. For instance, water can change into ice (frozen) or steam (vapor), and can still revert back to liquid water.
On the other hand, the other options involve chemical changes, where the original substances undergo chemical reactions to form new substances with different properties, thus altering the molecular structure depending on the option.
Frage 13 Bericht
An oxide of nitrogen that can rekindle a glowing splint is
Antwortdetails
The ability to rekindle a glowing splint is an indicator of the presence of an oxidizing agent, typically oxygen or a substance that releases oxygen. Among oxides of nitrogen, only a few are capable of doing this.
Nitrogen(I) oxide, commonly known as nitrous oxide (N2O), is not a strong enough oxidizer to rekindle a glowing splint.
Nitrogen(II) oxide, known as nitric oxide (NO), is not stable in the presence of oxygen and does not have the ability to rekindle a glowing splint because it does not actively release oxygen.
Nitrogen(IV) oxide or nitrogen dioxide (NO2), can support combustion by releasing oxygen as it decomposes. It is a brown gas and an effective oxidizer.
Dinitrogen tetraoxide (N2O4) is in equilibrium with nitrogen dioxide (NO2). However, at standard conditions, it is not as effective an oxidizer for rekindling a glowing splint as pure NO2.
In conclusion, the oxide of nitrogen that can rekindle a glowing splint is nitrogen(IV) oxide or nitrogen dioxide (NO2) due to its ability to release oxygen and support combustion.
Frage 14 Bericht
Rust on the surface of a metal sheet contains
Antwortdetails
Rust on the surface of a metal, specifically on **iron**, is primarily composed of **hydrated iron(III) oxide**. The rusting process occurs when **iron** reacts with **oxygen** and **water** from the environment. This chemical reaction typically produces a compound called **iron(III) oxide**, which is then combined with water molecules, resulting in **hydrated iron(III) oxide**. This hydrated state gives rust its characteristic flaky and reddish-brown appearance.
Frage 15 Bericht
The empirical formula of an organic liquid hydrocarbon is XY. If the relative molar masses of X and Y are 72 and 6 respectively, it's vapour density is likely to be
Antwortdetails
To determine the vapor density of the organic liquid hydrocarbon with the empirical formula XY, we first need to determine the **molecular formula** of the compound, which represents the actual number of atoms of each element in a molecule.
The **relative molar masses** of X and Y are given as 72 and 6, respectively. To find the molar mass of XY, we can add these values together:
Molar mass of XY = Molar mass of X + Molar mass of Y = 72 + 6 = 78 g/mol
Vapor density is defined as half of the molar mass of the compound, since vapor density is often compared to hydrogen, where hydrogen is taken as the standard with a molar mass of 2 g/mol. Therefore, vapor density can be calculated using the formula:
Vapor Density = (Molar Mass of the Compound) / 2
Substituting the molar mass of XY:
Vapor Density of XY = 78 / 2 = 39
Therefore, the vapor density of the hydrocarbon with the empirical formula XY is **39**.
Frage 16 Bericht
The hybridization scheme in ethyne is
Antwortdetails
Ethyne, also known as acetylene, is a simple alkyne with the chemical formula C2H2. In ethyne, each carbon atom is bonded to two other atoms: one hydrogen atom and the other carbon atom. The molecular structure of ethyne is linear, with a triple bond between the two carbon atoms.
To determine the hybridization scheme in ethyne, we need to examine the arrangement of the electron pairs around each carbon atom. In ethyne, each carbon atom is forming two sigma (σ) bonds and two pi (π) bonds. Let's explain:
When we consider the hybridization of the carbon atoms, we focus on the formation of sigma bonds and lone pairs. In ethyne, each carbon atom utilizes two orbitals to form sigma bonds: one with the hydrogen atom and one with the other carbon atom. This implies that each carbon atom in ethyne must use two hybrid orbitals.
The two hybrid orbitals formed by each carbon atom in ethyne are a result of mixing one s orbital with one p orbital. This hybridization is referred to as sp hybridization, characterized by a linear electron geometry. The remaining two unhybridized p orbitals on each carbon atom are responsible for forming the two pi bonds in the triple bond.
In conclusion, the hybridization scheme in ethyne is sp.
Frage 17 Bericht
Strong acids can be distinguished from weak acids by any of the following methods, EXCEPT
Antwortdetails
To distinguish between strong acids and weak acids, we can employ several methods based on their chemical properties:
Conductivity Measurement: Strong acids dissociate completely in water, releasing more ions. Because ion concentration is directly related to electrical conductivity, strong acids exhibit higher conductivity than weak acids, which only partially dissociate.
Litmus Paper: This method helps determine if a solution is acidic or basic but does not provide detailed information about the strength (strong or weak) of an acid. Both strong and weak acids turn blue litmus red. Therefore, **litmus paper cannot effectively distinguish between a strong and a weak acid.**
Measurement of pH: Strong acids have a lower pH because they fully dissociate to release more hydrogen ions (H+), whereas weak acids have a relatively higher pH as they do not dissociate completely. Thus, pH measurement can distinguish the extent of acidity.
Measurement of Heat of Reaction: The heat of reaction can give insights into the strength of an acid because it involves the degree of ionization and the energetics associated with it. A strong acid will exhibit a different calorimetric response compared to a weak acid.
In summary, **litmus paper is not suitable for distinguishing between a strong and a weak acid**, as it only indicates acidity but does not reveal the strength of the acid.
Frage 18 Bericht
The amount of water a substance chemically combined with is called water of
Antwortdetails
The amount of water that is chemically combined with a substance is referred to as water of crystallization. This is the water present in the crystalline form of a compound, necessary to maintain the structure of the crystals.
When certain substances crystallize from an aqueous solution, they incorporate a specific amount of water molecules into their crystal lattice structure. These water molecules are an integral part of the crystal and often affect its color, stability, and solubility. The water is combined in stoichiometric amounts, which means it is present in a fixed ratio relative to the rest of the molecule.
An example of this is copper(II) sulfate pentahydrate, which consists of copper(II) sulfate combined with five molecules of water per formula unit, represented as CuSO4·5H2O.
Frage 19 Bericht
The group VIII elements are the inert gases because they
Antwortdetails
The group VIII elements, also known as the noble gases, are called inert gases primarily because they all have completely filled valence shells. In a very simplified explanation:
1. Complete Valence Shells: All the noble gases have their outermost shells completely filled with electrons. This configuration is considered very stable and requires no additional electrons to reach stability, unlike other elements that may gain, lose, or share electrons to achieve a full valence shell.
2. Highly Stable: Due to this completely filled valence shell, the noble gases do not readily react with other elements to form compounds. Their stability comes from the fact that they do not need to bond with other elements to achieve a more stable state.
3. Examples: For instance, Helium (He) has two electrons filling its first shell, Neon (Ne) has eight electrons in its second shell, and similarly, other noble gases also have fully occupied outer shells.
This property is why the noble gases are termed "inert," which means they are largely non-reactive.
Frage 20 Bericht
The number of molecules of helium gas contained in 11.5g of the gas is
Antwortdetails
To find the number of molecules of helium gas in a given mass, we can use Avogadro's number and the molar mass of helium.
Step 1: Determine the molar mass of helium.
Helium is a noble gas with an atomic mass of approximately 4 grams per mole (g/mol).
Step 2: Calculate the number of moles in 11.5 grams of helium.
The formula to find the number of moles is:
Number of moles = Mass (g) / Molar Mass (g/mol)
So for helium:
Number of moles = 11.5 g / 4 g/mol = 2.875 moles
Step 3: Use Avogadro's number to find the number of molecules.
Avogadro's number is 6.022 x 1023 molecules per mole.
The formula to find the number of molecules is:
Number of molecules = Number of moles x Avogadro's Number
Number of molecules = 2.875 moles x 6.022 x 1023 molecules/mole
Number of molecules ≈ 1.73 x 1024 molecules
Therefore, the number of molecules of helium gas in 11.5g of helium is approximately 1.73 x 1024.
Frage 21 Bericht
The constituents of Alnico are Aluminium, Nickel and
Antwortdetails
Alnico is a type of alloy that is known for its strong magnetic properties. The name "Alnico" comes from the elements it is primarily composed of: Aluminum (Al), Nickel (Ni), and Cobalt (Co). These elements are combined to form an alloy that retains its magnetism well and can operate at high temperatures, making it ideal for applications like electric motors, sensors, and various electronic devices.
While there are different variations of Alnico, the presence of Cobalt (Co) is essential for enhancing the magnetic properties of the alloy. The other elements listed, such as Magnesium (Mg), Manganese (Mn), and Copper (Cu), are not typical core constituents of Alnico. Although trace amounts of other elements like copper may sometimes be included in specific formulations, the primary and most significant component responsible for Alnico's powerful magnetic characteristics is Cobalt (Co).
Frage 22 Bericht
Biodegradable pollutants are not safe in water systems because they can cause
Antwortdetails
Biodegradable pollutants are substances that can be broken down by natural processes and microorganisms. However, when they are present in water systems, they can lead to several environmental and health issues. One of the main concerns is their potential to cause ill health. Here's why:
When biodegradable pollutants such as organic waste are introduced into water bodies, they are decomposed by bacteria and other microorganisms. This process consumes dissolved oxygen in the water. As the oxygen levels decrease, aquatic life such as fish and plants may suffer or die due to a lack of oxygen, disrupting the entire aquatic ecosystem.
This situation is known as eutrophication, which can lead to the excessive growth of algae, commonly referred to as algal blooms. These blooms often produce toxins that are harmful to both aquatic life and humans. Furthermore, when this polluted water is used for drinking, agriculture, or recreational purposes, it poses serious health risks to humans. These risks may include gastrointestinal infections, neurological disorders, and skin problems.
In addition, as the pollutants decompose, foul smells may be released, which can affect air quality in the vicinity, although the primary concern with biodegradable pollutants in water is related to how they affect water quality and health.
Therefore, it is crucial to properly manage and treat biodegradable pollutants before they enter water systems to prevent these health hazards. Failure to do so can result in significant environmental and health issues.
Frage 23 Bericht
In the conductance of aqueous CuSO4 solution, the current carriers are the
Antwortdetails
In the conductance of aqueous CuSO4 solution, the current carriers are the hydrated ions.
Here's why:
The other options can be understood as follows:
The correct answer is therefore hydrated ions because they enable the conduction of electricity through the aqueous solution.
Frage 24 Bericht
What method is suitable for the separation of gases present in air?
Antwortdetails
The suitable method for the separation of gases present in air is the fractional distillation of liquid air. This method is used due to the differing boiling points of the gases present in the air. Let me explain this in simple terms:
Air is a mixture of different gases, primarily nitrogen, oxygen, and argon, along with small amounts of other gases like carbon dioxide, neon, and krypton. Each of these gases turns into a liquid at different temperatures.
The process begins by cooling the air until it becomes a liquid. This is done at very low temperatures (around -200 degrees Celsius). Once the air is in liquid form, it is slowly warmed up in a distillation column. As it heats up, each gas boils off or evaporates at its respective boiling point and can be collected separately.
For example, nitrogen, which has a boiling point of about -196 degrees Celsius, will evaporate first and can be collected at the top of the distillation column. Following nitrogen, oxygen will evaporate at its boiling point of around -183 degrees Celsius. Finally, argon and other gases will do so at their respective temperatures.
In summary, fractional distillation of liquid air is effective because it takes advantage of the different boiling points to separate each gas from the air mixture.
Frage 25 Bericht
The pH of a 0.001 mol dm−3 of H2 SO4 is
[Log10 2 = 0.3]
Antwortdetails
The question is asking about the pH of a 0.001 mol dm−3 solution of H2SO4 (sulfuric acid). To find the pH, we need to understand how sulfuric acid dissociates in water.
Step 1: Dissociation of H2SO4
Sulfuric acid, H2SO4, is a strong acid and dissociates completely in water in two steps:
1. The first dissociation: H2SO4 → H+ + HSO4-
2. The second dissociation: HSO4- → H+ + SO42-
For dilute solutions, particularly below 0.1 M, the first dissociation provides the major contribution to the H+ concentration. The second dissociation also contributes slightly to the acidity, but for simplicity and due to the dilute nature of this solution, the first step's contribution is primarily considered.
Step 2: Calculate the H+ Concentration
Since this is a strong acid and dissociates completely, for every 1 mole of H2SO4, we get 2 moles of H+. Therefore, for a 0.001 mol dm−3 solution of H2SO4, the concentration of H+ ions will be:
2 x 0.001 = 0.002 mol dm−3
Step 3: Calculate the pH
The pH is calculated using the formula: pH = -log[H+]
Substitute the H+ concentration:
pH = -log(0.002)
We know that log(10-2) = -2 and log(2) = 0.3 (as provided), so:
pH = -(log(2) + log(10-3))
pH = -(0.3 - 3)
pH = 3 - 0.3
pH = 2.7
Therefore, the pH of the 0.001 mol dm−3 H2SO4 solution is 2.7.
Frage 26 Bericht
An example of highly unsaturated hydrocarbon is
Antwortdetails
To determine a highly unsaturated hydrocarbon, we must first understand the concept of saturation in hydrocarbons. **Saturated hydrocarbons** are compounds that contain the maximum possible number of hydrogen atoms, single-bonded to carbon atoms, and they are alkanes. **Unsaturated hydrocarbons** have one or more double or triple bonds between carbon atoms, which reduces the number of hydrogen atoms that can be bonded.
Examining the given options:
Based on this analysis, **C2H2** (ethyne) is a highly unsaturated hydrocarbon due to the presence of a **triple bond**. The triple bond signifies a greater level of unsaturation compared to double bonds in hydrocarbons like ethene (C2H4).
Frage 27 Bericht
If the solubility of KNO3 at 300 C is 3.10 mol/dm3 a solution containing 303g/dm3 KNO3 is likely to be
Antwortdetails
To determine the condition of the solution containing KNO3 at 300C, let's start by calculating the molarity of the given solution.
The molecular weight of KNO3 (Potassium Nitrate) is approximately:
Thus, KNO3 = 39 + 14 + (16 * 3) = 101 g/mol.
Now, to determine the molarity of the given solution:
Compare with the solubility at 300C:
If we compare the values:
Hence, the solution is unsaturated because it can still dissolve more KNO3 until it reaches the solubility limit of 3.10 mol/dm3.
Frage 28 Bericht
Aqueous solution of sodium hydroxide can be used to test for the presence of : I. Ca2+ , II. Zn2+ , III. Cu2+
Antwortdetails
Aqueous solution of sodium hydroxide (NaOH) is a versatile reagent in chemistry, often used to test for the presence of metal ions. When sodium hydroxide is added to solutions containing certain metal ions, it forms precipitates that are characteristic of those ions. Here's how it interacts with each of the mentioned ions:
Calcium ions (Ca2+): When NaOH is added to a solution containing calcium ions, a white precipitate of calcium hydroxide (Ca(OH)2) can form. However, the precipitate is only slightly soluble in water, and this reaction is not the most definitive test for calcium ions.
Zinc ions (Zn2+): When sodium hydroxide is added to a solution containing zinc ions, a white gelatinous precipitate of zinc hydroxide (Zn(OH)2) forms. This precipitate is soluble in excess NaOH, leading to a clear, colorless solution. This reaction is used to test for zinc ions.
Copper ions (Cu2+): When NaOH is added to a solution containing copper ions, a pale blue precipitate of copper(II) hydroxide (Cu(OH)2) forms. This precipitate is insoluble even in excess NaOH, and the formation of this blue precipitate is a common test for copper ions.
Therefore, an aqueous solution of sodium hydroxide can be used to test for the presence of all three ions: calcium (Ca2+), zinc (Zn2+), and copper (Cu2+). The reaction and precipitate formation with each ion serve as indicators of their presence. Thus, the correct answer is:
I, II and III.
Frage 29 Bericht
The reaction of hydrogen and chlorine to produce hydrogen chloride gas is explosive in
Antwortdetails
The reaction between hydrogen and chlorine to produce hydrogen chloride gas is explosive in sunlight. This is because sunlight contains a broad range of electromagnetic radiation, including ultraviolet (UV) light, which is energetic enough to initiate the reaction.
Here is a simplified explanation:
In contrast, other forms of light like diffused light, infrared light, and Raman light do not provide enough energy to initiate this explosive reaction because they lack the necessary UV component found in sunlight.
Frage 30 Bericht
The amount of Faraday required to discharge 4.5 moles of Al3+ is
Antwortdetails
To determine the amount of Faraday required to discharge 4.5 moles of Al3+ ions, it is essential to understand Faraday's laws of electrolysis and the concept of moles in chemistry.
When discharging Al3+ ions to form aluminum metal (Al), the reduction half-reaction involved is:
Al3+ + 3e- → Al
From this equation, it can be seen that 3 moles of electrons (e-) are required to discharge 1 mole of Al3+ ions to form 1 mole of aluminum metal.
A Faraday is the amount of electric charge carried by one mole of electrons. Therefore, 1 Faraday corresponds to the charge needed to discharge 1 mole of electrons.
Now, to discharge 4.5 moles of Al3+, we need:
4.5 moles of Al3+ × 3 moles of electrons (e-)/mole of Al3+ = 13.5 moles of electrons
Since each Faraday discharges 1 mole of electrons, 13.5 moles of electrons correspond to 13.5 Faradays of charge.
Hence, the amount of Faraday required to discharge 4.5 moles of Al3+ ions is 13.5 Faradays.
Frage 31 Bericht
In a chemical reaction, surface area of reactants can affect
Antwortdetails
The surface area of reactants affects the rate of a reaction between limestone and hydrochloric acid because it increases the number of collisions between the particles of the reactants. For example, if you have a large marble chip of calcium carbonate and hydrochloric acid, the acid can't reach all the calcium carbonate in the middle of the chip. If you break the marble chip into smaller pieces, you'll have a larger surface area for the acid to react with, and the reaction will happen faster.
Frage 32 Bericht
The molecular formular of a hydrocarbon with an empirical formula of CH3 and a molar mass of 30 is
Antwortdetails
To find the molecular formula of a hydrocarbon given its empirical formula and molar mass, you need to compare the empirical formula mass with the given molar mass.
The empirical formula given is CH3. The molar mass of the empirical formula is calculated as follows:
Total empirical formula mass = 12 + 3 = 15 g/mol
The provided molar mass of the compound is 30 g/mol. To determine how many empirical units are in the molecular formula, divide the molecular mass (given) by the empirical formula mass:
Number of empirical units = 30 g/mol / 15 g/mol = 2
Therefore, the molecular formula is twice the empirical formula:
Empirical formula: CH3
Molecular formula: (CH3)2 = C2H6
The correct molecular formula is C2H6.
Frage 33 Bericht
A gas when mixed with oxygen, it produces a very hot and early controllable flame. What is the name of the flame and where is it used?
Antwortdetails
The Oxy-ethylene flame is a type of flame produced when oxygen is mixed with a gas called ethylene. This mixture results in a flame that is extremely hot and can be easily controlled. Such a flame is often used in industrial applications related to cutting and welding metals. The heat generated by an oxy-ethylene flame is sufficient to melt metals, allowing them to be welded together or cut apart efficiently.
Frage 34 Bericht
Hydrogen chloride gas and ammonia can be used to demonstrate the fountain experiment because they are
Antwortdetails
In the fountain experiment, hydrogen chloride gas (HCl) and ammonia (NH₃) are used to demonstrate the creation of a visible 'fountain' due to their high solubility in water. Here's a simple explanation:
When hydrogen chloride gas and ammonia gas come into contact with water, they dissolve very quickly and react vigorously. This is because both gases are very soluble in water. As they dissolve, a vacuum-like pressure is created inside the container where the gases are held, pulling water up into it, creating the 'fountain' effect.
Moreover, when HCl and NH₃ gases react with each other, they form a white, solid product known as ammonium chloride (NH₄Cl), which is a demonstration of how both gases can effectively dissolve and react with not just water, but also with each other.
Thus, the ability of these gases to create a fountain effect is primarily because they are very soluble in water, which allows them to dissolve rapidly and create the pressure differential necessary for the water to be pulled into the container dynamically.
Frage 35 Bericht
When Calcium ethynide is decomposed by water, the gas produced is
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When water reacts with calcium ethynide, the gas produced is ethyne (also known as acetylene), which is represented by the chemical formula C2H2.
The chemical reaction involved is as follows:
CaC2 + 2 H2O → C2H2 + Ca(OH)2
Let's break down this process to make it understandable:
The key point to remember here is that the gas produced is **ethyne (C2H2)**, which is useful in various industrial applications, such as welding and as a precursor for other chemicals.
Frage 36 Bericht
Alkanoates are naturally found in
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Alkanoates, also known as fatty acid esters, are primarily found in lipids. Lipids are a broad group of naturally occurring molecules that include fats, waxes, sterols, fat-soluble vitamins (such as vitamins A, D, E, and K), and others. One of the main components of lipids is fatty acids and their derivatives, such as alkanoates.
To be more specific, alkanoates can be found in the form of triglycerides, which are the main constituents of body fat in humans and animals, as well as vegetable fat. Triglycerides are composed of glycerol bound to three fatty acids, and these fatty acids are usually present in the form of alkanoates.
Unlike proteins and rubber, which are made up of amino acids and polymers of isoprene respectively, lipids are the primary class of biomolecules where these alkanoate compounds can be found in significant amounts.
Frage 37 Bericht
A gas that turns lime water milky is likely to be from
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The gas that turns lime water milky is **Carbon Dioxide**. This is because carbon dioxide reacts with calcium hydroxide, which is the main component of lime water, to form calcium carbonate. This chemical reaction can be represented by the equation:
Ca(OH)2 (aq) + CO2 (g) → CaCO3 (s) + H2O (l)
In this equation, calcium hydroxide ({Ca(OH)2}) in the lime water reacts with carbon dioxide ({CO2}) to produce calcium carbonate ({CaCO3}) and water ({H2O}).
The result is a milky or cloudy appearance due to the formation of insoluble calcium carbonate precipitate in the lime water. This reaction is a common test for the presence of carbon dioxide gas.
Among the options given, **Trioxocarbonate(IV)** is another name for the Carbonate group involving the gas carbon dioxide ({CO2}). Hence, the gas related to Trioxocarbonate(IV) is the one that turns lime water milky.
Frage 38 Bericht
The principle which states that no two electrons in the same orbitals of an atom have same value for all four quantum numbers is the
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The principle that states that no two electrons in the same orbitals of an atom can have the same value for all four quantum numbers is the Pauli Exclusion Principle.
To understand this principle, it's important to know a bit about the structure of an atom and what quantum numbers are:
Quantum Numbers:
1. **Principal Quantum Number (n):** This describes the energy level or shell of the electron.
2. **Angular Momentum Quantum Number (l):** This describes the subshell or shape of the orbital (s, p, d, f...).
3. **Magnetic Quantum Number (ml):** This describes the specific orbital within a subshell where the electron is located.
4. **Spin Quantum Number (ms):** This describes the spin direction of the electron, which can be either +1/2 or -1/2.
The Pauli Exclusion Principle asserts that each electron in an atom has a unique set of these four quantum numbers. While electrons can share the first three quantum numbers if they are in the same orbital (meaning they share the same energy level, the same subshell, and the same specific orbital within that subshell), they must have different Spin Quantum Numbers. This means that in any given orbital, one electron can have a spin of +1/2 and the other must have a spin of -1/2. This principle is fundamental in explaining the electronic structure of atoms and, consequently, the behavior and properties of elements.
Frage 39 Bericht
The main constituent of water-glass is
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The main constituent of water-glass is sodium trioxosilicate(IV). Water-glass, also known as liquid glass, is common terminology for a mixture of sodium silicate and water. The primary chemical component in water-glass is sodium silicate, which includes sodium ions (Na+) bonded with silicate ions (SiO44-).
Essentially, when sodium silicate is dissolved in water, it results in a viscous liquid that can be utilized in various applications such as in cements, passive fire protection, textile and lumber processing, and as a sealant. Sodium trioxosilicate(IV) forms a significant part of this mixture as it reacts with other compounds to create a hardened, glass-like structure when it dries. Therefore, when water-glass is mentioned, it is mostly referring to solutions that have sodium trioxosilicate(IV) as their principal compound.
Frage 40 Bericht
Which of the following is used in forming slag in the blast furnace for the extraction of iron?
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In the process of extracting iron in a blast furnace, CaCO3, or calcium carbonate, plays a crucial role in forming slag. Here is a simple and comprehensive explanation of how it works:
1. Role of Calcium Carbonate (CaCO3):
Calcium carbonate is commonly used as a flux in the blast furnace. When it is introduced into the furnace, it undergoes a decomposition reaction due to the high temperatures, breaking down into calcium oxide (CaO) and carbon dioxide (CO2).
2. Formation of Slag:
The calcium oxide (CaO) produced then reacts with silicon dioxide (SiO2) present in the iron ore. This reaction forms a liquid slag of calcium silicate. The slag serves two main functions:
Thus, calcium carbonate (CaCO3) is crucial for forming slag by providing the necessary calcium oxide (CaO) that reacts with impurities to form slag during the extraction of iron in a blast furnace.
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