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Question 1 Report
What is the vapour density of 560cm3 of a gas that weighs 0.4g at s.t.p?
[Molar Volume of gas at s.t.p = 22.4 dm3 ]
Answer Details
To find the vapour density of a gas, you can use the formula:
Vapour density = (Molar mass of gas) / 2
However, first, we need to determine the molar mass of the gas. One can find the molar mass using the given data:
We know that at standard temperature and pressure (s.t.p.), 1 mole of any gas occupies 22.4 dm3. We need to convert the volume from cm3 to dm3 because the molar volume is given in dm3:
560 cm3 = 0.560 dm3
Now, let's find the number of moles in 0.560 dm3:
The number of moles (n) = Volume of gas (dm3) / Molar volume at s.t.p. (dm3/mol)
n = 0.560 dm3 / 22.4 dm3/mol
n = 0.025 moles
Given that the mass of the gas is 0.4 grams, we can find the molar mass by using the relation:
Molar Mass = Mass / Number of Moles
Molar Mass = 0.4 g / 0.025 moles
Molar Mass = 16 g/mol
Now that we have the molar mass, we can find the vapour density:
Vapour density = Molar mass / 2
Vapour density = 16 g/mol / 2
Vapour density = 8.0
Hence, the vapour density of the gas is 8.0.
Question 2 Report
The volume in cm3 of a 0.12 moldm−3 HCl required to completely neutralize a 20cm3 of 0.20 moldm−3 of NaOH is
Answer Details
To find the volume of HCl that is required to completely neutralize the NaOH solution, we need to use the concept of a neutralization reaction. A neutralization reaction occurs when an acid and a base react to form water and a salt, thus neutralizing each other.
In this particular reaction, the balanced chemical equation is:
HCl + NaOH → NaCl + H2O
Here, the equation tells us that one mole of HCl reacts with one mole of NaOH. Therefore, the molar ratio of HCl to NaOH is 1:1.
First, let's determine the number of moles of NaOH present in 20 cm3 solution:
Number of moles of NaOH = Concentration (mol/dm3) × Volume (dm3)
= 0.20 mol/dm3 × 20 cm3 × (1 dm3 / 1000 cm3)
= 0.20 × 0.020
= 0.004 moles
Since the reaction is in a 1:1 ratio, the number of moles of HCl required is also 0.004 moles.
Now, let's determine the volume of HCl solution required:
Volume of HCl (dm3) = Number of moles / Concentration
= 0.004 moles / 0.12 mol/dm3
= 0.03333 dm3
Convert this volume from dm3 to cm3:
0.03333 dm3 × 1000 cm3 / dm3 = 33.33 cm3
Therefore, the volume of HCl required is 33.33 cm3.
Question 3 Report
The pH of a 0.001 mol dm−3 of H2 SO4 is
[Log10 2 = 0.3]
Answer Details
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.
Question 4 Report
Fog is a colloid in which
Answer Details
**Fog** is a type of colloid, which is a mixture where very small particles of one substance are evenly distributed throughout another substance. In the case of fog, it consists of tiny **liquid droplets** that are dispersed in a **gas**. Specifically, these are tiny droplets of water suspended in the air. When you walk through fog, you are essentially walking through air that contains these minute water droplets.
Thus, the correct description of fog as a colloid is that it consists of **liquid particles dispersed in a gas medium**. The liquid here is water, and the gas is air.
Question 5 Report
The scientist that performed the experiment on discharged tubes that led to the discovery of the cathode rays as a sub-atomic particle is
Answer Details
The **scientist who performed the experiment on discharge tubes that led to the discovery of cathode rays as a sub-atomic particle** is J.J. Thomson.
In the late 19th century, J.J. Thomson conducted experiments using a cathode ray tube. This device involved an evacuated glass tube with electrodes at each end, through which an electric current was passed. **When a high voltage was applied, Thomson observed a stream of particles traveling from the negative electrode (cathode) to the positive electrode (anode).** These streams of particles were what he called "cathode rays."
Through his experiments, J.J. Thomson discovered that these cathode rays were composed of negatively charged particles. **He concluded that these particles were much smaller than atoms, and named them "electrons," which are now known to be sub-atomic particles.** His work was fundamental in advancing the atomic model and in understanding the structure of the atom.
Thomson's discovery was pivotal because it provided the first evidence that atoms are not indivisible, but rather consist of smaller subatomic particles. This **challenged the then-prevailing notion of atoms as indivisible units**, thus marking the birth of modern particle physics.
Question 6 Report
The number of molecules of helium gas contained in 11.5g of the gas is
Answer Details
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.
Question 7 Report
Water gas obtained from the gasification of coke is made up of
Answer Details
The gasification of coke to produce water gas involves reacting coke, which is primarily composed of carbon, with steam. The main chemical reaction that occurs is:
C (s) + H2O (g) → CO (g) + H2 (g)
From this reaction, the main constituents of water gas are hydrogen (H2) and carbon monoxide (CO), also known as carbon(II) oxide. Therefore, water gas obtained from the gasification of coke is made up of hydrogen and carbon(II) oxide.
Question 8 Report
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?
Answer Details
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
Question 9 Report
23892 U + 10 n → 23992 U
The process above produces
Answer Details
The process described appears to depict a nuclear reaction involving a nuclear transmutation. Let's break down the process:
1. The starting element is initially denoted as "23892", which represents Uranium-238. In nuclear notation, "23892" indicates an atomic mass number of 238 and an atomic number of 92.
2. The next step so happens with the element "238"; however, the numbers remain: "92" indicates that the atomic number is unchanged, suggesting no change in the element. This often means a step in between of hypothetical notation.
3. Then there's the occurrence of adding a "U + 10", which again leaves the original atomic number "92".
4. In subsequent steps, it seems that the number "n" transitions to become "23992". The mass number has increased by one unit, turning the initial isotope into "23992", which represents Uranium-239.
The key point here is the transition from Uranium-238 to Uranium-239, which typically happens through the process of a neutron absorption in which a neutron is added, resulting in a change of the mass number. Such a process often leads to the creation of a radioactive isotope.
Therefore, the process described is indicative of producing a radioactive isotope, specifically Uranium-239.
Question 10 Report
A radioactive element of mass 1g has half-life of 2 minutes, what fraction of the substance would have disintegrated after 10 minutes?
Answer Details
Originalmass2n
= Residual mass
Where n = number of activity = exposuretimehalflife
Given:
Original mass = 1g, exposure time = 10 minutes , half life = 2 minutes, Residual mass = ?
Substituting all the given parameters appropriately, we have
n = 102
n = 5
Originalmass2n = Residual mass
125
5 = Residual mass
132 = Residual mass
Residual mass = 132
or 0.03125g
Question 11 Report
Concentrated sodium chloride solution is electrolyzed using mercury cathode and graphite anode. The products at the anode and the cathode respectively are
Answer Details
When a concentrated sodium chloride solution is electrolyzed using a mercury cathode and graphite anode, the products are hydrogen gas at the cathode and chlorine gas at the anode
At the anode, 2Cl− → Cl2 + 2e−
At the cathode, 2H+ + 2e− → H2
During the electrolysis, hydrogen and chloride ions are removed from solution whereas sodium and hydroxide ions are left behind in solution. This means that sodium hydroxide is also formed during the electrolysis of sodium chloride solution.
Question 12 Report
Hydrogen chloride gas and ammonia can be used to demonstrate the fountain experiment because they are
Answer Details
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.
Question 13 Report
When Sulphur(IV)oxide is passed into solution of acidified tetraoxomanganate(VII), the colour changes from
Answer Details
When Sulphur(IV) oxide (SO2) is passed into a solution of acidified tetraoxomanganate (VII) (KMnO4), it acts as a reducing agent. This reaction involves the reduction of potassium permanganate (KMnO4), which is characterized by a distinctive color change.
The tetraoxomanganate (VII) ion (MnO4-) is purple in color. During the reaction, SO2 gets oxidized while the MnO4- ion is reduced to Mn2+, which is almost colorless or pale pink, depending on the concentration.
Thus, the color of the solution changes from purple to almost colorless as the reaction progresses.
Question 14 Report
The ions responsible for permanent hardness in water are sulphates of
Answer Details
Permanent hardness in water is mainly caused by the presence of certain metal ions, specifically the **sulfates (SO₄²⁻)** and **chlorides (Cl⁻)** of calcium (Ca) and magnesium (Mg). These compounds do not precipitate out when the water is boiled, which means they remain dissolved and continue to contribute to the hardness of the water.
Among the options you provided, the ions responsible for permanent hardness in water are the **sulfates of calcium (Ca²⁺)** and **magnesium (Mg²⁺)**. The presence of calcium sulfate (CaSO₄) and magnesium sulfate (MgSO₄) in water keeps it hard.
When compared to temporary hardness, which can be removed by boiling the water to precipitate bicarbonates, **permanent hardness cannot be removed by boiling**. Instead, methods such as ion exchange or the use of water softeners are required to remove these ions from the water.
In summary, the ions causing permanent hardness in water are the **sulfates of calcium (Ca²⁺)** and **magnesium (Mg²⁺)**. These ions remain dissolved and continue to make the water hard, despite boiling.
Question 15 Report
The combustion of candle under limited supply of air forms
Answer Details
When a candle burns under a limited supply of air, it doesn't get enough oxygen to completely burn the hydrocarbons in the wax. In complete combustion (with enough air), the candle would ideally produce water (H2O) and carbon dioxide (CO2). However, under limited air supply, the process is incomplete and results in the formation of soot and carbon monoxide (CO).
Here's why:
In summary, under limited air conditions, the combustion of a candle primarily forms soot and carbon monoxide (CO).
Question 16 Report
The term that is not associated with petroleum industry is ?
Answer Details
Cracking, saponification and polymerization are all terminologies associated with the petroleum industry but fermentation is associated with the brewery industry.
Cracking is a chemical process that breaks down heavy hydrocarbon molecules into lighter, more useful ones.
Saponification is a chemical reaction that converts fats and oils into soap. It's not directly involved in petroleum, but it can be used to analyze petroleum products.
Polymerization is a process in the petroleum industry that converts light olefin gases into higher molecular weight hydrocarbons.
Fermentation is the process in which a substance breaks down into a simpler substance. Microorganisms like yeast and bacteria usually play a role in the fermentation process, creating beer, wine, bread,yogurt and other foods.
Question 17 Report
In a chemical reaction, surface area of reactants can affect
Answer Details
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.
Question 18 Report
In the graph above, y represents
Answer Details
To understand what y represents in the graph, we need to think about what graphs in chemistry, specifically regarding energy changes in reactions, generally show.
Chemical reaction energy diagrams often depict a reaction's energy change as a curve from the reactants to the products, showing different energy levels throughout the process. The energy required to start a reaction or to transform the reactants into an activated complex (also known as the transition state) is crucial.
The height of this energy barrier is called the activation energy. This is the minimum amount of energy required to start a chemical reaction. The activation energy is represented by the peak in the energy graph between the reactant energy level and the top of the curve.
Therefore, in this context, y represents the activation energy needed for the reaction to proceed. Understanding activation energy is vital as it determines how quickly a reaction will occur. Reactions with a high activation energy tend to happen more slowly because it is less probable that the necessary energy for the reaction to occur spontaneously will be present.
Question 19 Report
Fats and oils are esters of fatty organic acids combined with a trihydric alkanol commonly referred to as
Answer Details
Fats and oils are types of lipids that belong to the category of esters of fatty acids. These are organic compounds formed when fatty acid molecules react with an alcohol. In the case of fats and oils, the alcohol involved is a trihydric alkanol, meaning it has three hydroxyl (-OH) groups.
The trihydric alkanol commonly found in fats and oils is glycerol. Glycerol, also known as glycerine, has the chemical formula C3H8O3 and has three carbon atoms, each of which is attached to a hydroxyl group, making it a perfect candidate to form esters with three fatty acid molecules.
When these fatty acids react with the hydroxyl groups of glycerol, they form compounds called triglycerides. These triglycerides are the primary constituents of both fats and oils. Therefore, the correct answer is that fats and oils are esters of fatty organic acids combined with glycerol as the trihydric alkanol.
Question 20 Report
Aqueous solution of sodium hydroxide can be used to test for the presence of : I. Ca2+ , II. Zn2+ , III. Cu2+
Answer Details
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.
Question 21 Report
Boyle's law can be expressed mathematically as
Answer Details
Boyle's Law describes the relationship between the volume and pressure of a given amount of gas held at a constant temperature. It states that the pressure of a gas is inversely proportional to its volume. In simpler terms, if you decrease the volume of a gas, its pressure increases, provided the temperature remains constant, and vice versa.
The mathematical expression of Boyle's Law is PV = K, where:
This relationship implies that if you multiply the pressure by the volume, the result will always be the same constant as long as no other variables are changed. This is the classic formulation of Boyle's Law, illustrating the inverse relationship between pressure and volume for a gas at constant temperature.
Question 22 Report
The table above shows the formulae of some ions. In which of these compounds is the formula not correct?
Answer Details
To assess the correctness of the chemical formulae for the given compounds, let's break down each compound:
Aluminium Tetraoxosulphate(VI), Al2(SO4)3:
Aluminium ion is denoted as Al3+, and the sulphate ion is SO42-. To balance the charges between the positive and negative ions:
2 x (+3) from aluminium ions = +6
3 x (-2) from sulphate ions = -6
Thus, the charges balance out, making the formula correct.
Calcium Trioxonitrate(V), Ca(NO3)2:
Calcium ion is Ca2+, and the nitrate ion is NO3-. To balance the charges:
1 x (+2) from calcium ion = +2
2 x (-1) from nitrate ions = -2
The charges balance out, therefore, this formula is also correct.
Iron(III) Bromide, Fe3Br:
Iron(III) ion is Fe3+, and bromide ion is Br-. Each iron ion would pair with three bromide ions to balance the charges:
FeBr3, where:
1 x (+3) from iron = +3
3 x (-1) from bromide = -3
The charges balance out in the correct formula which should be FeBr3, making the given formula Fe3Br incorrect.
Potassium Sulphide, K2S:
Potassium ion is K+, and sulphide ion is S2-. To balance the charges:
2 x (+1) from potassium ions = +2
1 x (-2) from sulphide ion = -2
The charges balance out, making this formula correct.
Therefore, the compound with the incorrect formula is Iron(III) Bromide where the proper chemical formula should be FeBr3, not Fe3Br.
Question 23 Report
The difference in molecular mass between an alkene and alkyne with six carbon per mole is
Answer Details
To determine the difference in molecular mass between an alkene and an alkyne, let's first take a look at their general formulas.
Alkene: An alkene is a hydrocarbon with at least one double bond between carbon atoms. For an alkene with six carbon atoms, the general formula is CnH2n. Therefore, for 6 carbon atoms, the molecular formula is C6H12.
Alkyne: An alkyne is a hydrocarbon with at least one triple bond between carbon atoms. For an alkyne with six carbon atoms, the general formula is CnH2n-2. Therefore, for 6 carbon atoms, the molecular formula is C6H10.
Now let's calculate the molecular masses:
Molecular mass of alkene (C6H12):
Molecular mass of alkyne (C6H10):
The **difference** in molecular mass between the alkene and alkyne is **84 g/mol - 82 g/mol** = 2 g/mol.
Question 24 Report
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
Answer Details
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**.
Question 25 Report
H2 S(g) + Cl2 (g) → 2HCl(g) + S(s)
What is the change in oxidation state of sulphur from reactant to product?
Answer Details
To determine the change in oxidation state of sulfur, follow these steps:
In the given reaction:
H2S(g) + Cl2(g) → 2HCl(g) + S(s)
We observe:
Thus, the change in oxidation state of sulfur when moving from the reactants to the products is from **-2** to **0**. This indicates that sulfur is being oxidized.
The correct answer is that the oxidation state of sulfur changes from **-2 to 0**.
Question 26 Report
Which of the following is an air pollutant?
Answer Details
An air pollutant is any substance in the air, introduced by natural or human activity, that causes harm or discomfort to living organisms, or damages the environment. Let's analyze the substances mentioned:
1. O2 (Oxygen)
Oxygen is the gas we need to breathe. It's not considered an air pollutant because it is essential for human and animal life, as well as many natural processes.
2. CO (Carbon Monoxide)
Carbon Monoxide is a colorless, odorless gas that is produced by burning fuel (like in cars and factories). This gas can be very dangerous if there is a lot of it, as it can prevent oxygen from entering the bloodstream. Because of its harmful effects, it is considered an air pollutant.
3. H2 (Hydrogen)
Hydrogen, while a flammable gas, is generally not harmful to the air or to organisms when it is released into the environment. Therefore, it is not considered an air pollutant.
4. O3 (Ozone)
Ozone is a bit tricky because it is both good and bad. Higher up in the atmosphere, it forms a layer that protects us from the sun’s UV radiation. However, at ground level, it is a harmful air pollutant. Ground-level ozone can cause health problems such as respiratory difficulties, so in this context, it is considered an air pollutant.
In conclusion, the substances that are considered air pollutants in this context are Carbon Monoxide (CO) and ground-level Ozone (O3).
Question 27 Report
Alkanoates are naturally found in
Answer Details
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.
Question 28 Report
An example of a physical change is
Answer Details
An example of a physical change is the boiling of water. Let me explain why this is considered a physical change:
A physical change is a change where the substances involved do not change their chemical composition, meaning they remain the same substance, just in a different form or appearance. In the case of boiling water, when water is heated to its boiling point, it changes from a liquid to a gas (steam), but it is still comprised of water molecules (H2O). The change is reversible, so the gas can condense back into liquid water without any new substance being formed.
On the other hand:
Thus, boiling water is an excellent example of a physical change as it involves only the change in the state of matter without altering the substance's identity.
Question 29 Report
One of the following is not a water pollutant?
Answer Details
Water pollutants are substances that, when introduced into the water, cause harm to ecosystems, human health, and the overall quality of the water. Each of the options provided has the potential to be considered a water pollutant, except for one. Let's explain them:
1. Inorganic fertilizers: These are substances mainly composed of synthetic chemicals, including nitrates and phosphates. When these fertilizers enter water bodies, they can lead to nutrient pollution, which causes excessive growth of algae (eutrophication), leading to a decrease in oxygen levels in the water, harming aquatic life.
2. Warm water affluent: This refers to the discharge of heated water into natural water bodies. This heat contamination can change the temperature of the water, affecting the metabolism of aquatic life and leading to thermal pollution.
3. Oxygen gas: Oxygen gas is a fundamental component of the Earth's atmosphere and is not considered a water pollutant. In fact, dissolved oxygen is crucial for the survival of aquatic organisms. Rather than causing any harm, adequate levels of dissolved oxygen in water bodies are essential for maintaining healthy aquatic ecosystems.
4. Biodegradable waste: These are organic materials that decompose in the environment. When introduced in large quantities into water bodies, they can consume a significant amount of dissolved oxygen as they decompose, which can lead to depletion of oxygen levels and cause harm to aquatic life, making them pollutants in aquatic ecosystems.
Given the explanations above, oxygen gas is the option that is not a water pollutant. It is vital for the health of aquatic ecosystems, unlike the other options, which can all lead to some form of pollution in water bodies.
Question 30 Report
The composition of alloy permalloy is iron and
Answer Details
The alloy known as **permalloy** is composed primarily of **iron** and **nickel**. Permalloy is a well-known magnetic alloy that typically consists of about **80% nickel and 20% iron**. It is renowned for having high magnetic permeability, meaning it can become magnetized easily, which makes it extremely useful in a variety of electrical and magnetic applications, such as transformers, memory storage, and magnetic shielding. The nickel in permalloy enhances the magnetic properties of the iron, giving the alloy its unique characteristics.
Question 31 Report
The IUPAC nomenclature of the complex K4 Fe(CN)6 is
Answer Details
The compound in question is K4[Fe(CN)6]. To name this complex using IUPAC nomenclature, let's break it down into parts:
Next, consider the oxidation state of Fe:
Finally, we consider the oxidation state of the iron. Since calculations show that it is +2, the complex ion is named based on its oxidation state.
Hence, the IUPAC name of this compound is potassium hexacyanoferrate(II).
Question 32 Report
An example of a substance that does not change directly from solid to gas when heated is
Answer Details
When discussing the process of substances changing states, some substances can transition directly from a solid to a gas without passing through a liquid state. This process is called sublimation. However, not all substances exhibit this behavior. Let's examine the substances provided:
In conclusion, calcium carbonate (CaCO3) is the substance that does not change directly from a solid to a gas when heated, as it undergoes a decomposition process instead.
Question 33 Report
After breathing in a test tube that contains acidified K2 Cr2 O7 , a man noticed the change in the colour of K2 Cr2 O7 from orange to green. This suggests the presence of
Answer Details
When the acidified potassium dichromate (\(K_2Cr_2O_7\)) solution changes from orange to green, it indicates a chemical reaction is occurring where the chromium in the dichromate ion is being reduced. In this context, acidified \(K_2Cr_2O_7\) is commonly used as an oxidizing agent.
The change in color from orange (dichromate ion) to green (chromium ion) suggests that the dichromate ion is being reduced, and something in the person's breath is being oxidized.
The substances that can be oxidized in the breath are organic compounds, typically those containing functional groups with oxidizable hydrogen atoms or structures.
Therefore, when the color of acidified potassium dichromate changes from orange to green, it suggests the presence of an alkanol.
Question 34 Report
A liquid hydrocarbon obtained from fractional distillation of coal tar that is used in the pharmaceutical industry is
Answer Details
Benzene is a liquid hydrocarbon that is obtained from the fractional distillation of coal tar, and it is extensively used in the pharmaceutical industry. Let me break this down for you:
That's why benzene plays an important role in the pharmaceutical industry, making it a highly valued product obtained through the distillation of coal tar.
Question 35 Report
A type of isomerism that ClCH=CHCl can exhibit is
Answer Details
ClCH=CHCl can exhibit geometrical isomerism and positional isomerism. ClCH=CHCl can exhibit positional isomerism because the positions of the functional groups or substituent atoms are different. Positional isomerism occurs when compounds with the same molecular formula have different properties due to the difference in the position of a functional group, multiple bond, or branched chain.
Question 36 Report
Esterification reaction is analogous to
Answer Details
The **esterification reaction** is analogous to a **condensation reaction**. In chemistry, a **condensation reaction** is a type of chemical reaction where two molecules or functional groups combine to form a larger molecule, with the simultaneous loss of a small molecule, usually water. **Esterification** specifically involves the reaction between an acid (often a carboxylic acid) and an alcohol, resulting in the formation of an **ester** and the release of a molecule of water.
To explain this further, in an esterification reaction:
Conversely, the other types of reactions you've mentioned have different mechanisms:
Therefore, given the nature of how molecules join and release water, it's clear that the **esterification reaction** is analogous to a **condensation reaction**.
Question 37 Report
The volume occupied by 1 mole of an ideal gas at a temperature of 130 C and a pressure of 1.58 atm is
[ R = 0.082 atm dm3 K−1 mol−1 ]
Answer Details
According to the Ideal gas equation, PV = nRT
Given: P = 1.58 atm, V = ?, n = 1 mole, R = 0.082, T= 13 + 273K = 286K
Substituting all the given parameters,
V = nRTP
V = 1×0.082×2861.58
V = 14.84 dm3
Question 38 Report
The basicity of tetraoxophosphate(V) acid is
Answer Details
The term basicity of an acid refers to the number of hydrogen ions (H⁺) that an acid can donate when it dissociates in water. In simpler terms, it's the number of replaceable hydrogen ions in one molecule of the acid.
Tetraoxophosphate(V) acid is another name for phosphoric acid, which has the chemical formula H₃PO₄. In this molecule, there are three hydrogen (H) atoms bonded to the phosphate group (PO₄).
When H₃PO₄ dissolves in water, it donates hydrogen ions in three steps:
Therefore, phosphoric acid, or tetraoxophosphate(V) acid, can donate a total of three hydrogen ions. Hence, the basicity of tetraoxophosphate(V) acid is 3.
Question 39 Report
Scandium is not regarded as a transition metal because its ion has
Answer Details
Scandium is not regarded as a transition metal because its ion has no electron in the d-orbital.
To understand this, let's first define a transition metal. A transition metal is defined as an element that has an incomplete d-subshell in either its elemental form or in any of its common oxidation states.
When Scandium (Sc) loses electrons to form its most common ion (Sc3+), it loses three electrons. These electrons are removed from the 4s and 3d orbitals. The electron configuration for Scandium is [Ar] 3d1 4s2. Upon losing three electrons to form Sc3+, the resulting electron configuration is [Ar], which means there are:
As a result, there are no electrons in the d-orbital of the Scandium ion, which does not meet the criteria for a transition metal.
Question 40 Report
Nitrogen obtained from air is not absolutely pure because it contains the following except
Answer Details
Nitrogen obtained from air is not absolutely pure because it contains other gases, including:
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