Chemistry

Silicon and oxygen are the most abundant elements in the Earth’s crust, primarily found in silicate minerals.

A physical change involves alterations in the state or appearance of a substance without changing its chemical composition (e.g., melting ice). The change can be reversed

Solids have a definite shape and volume and are generally not compressible. The particles in solids are closely packed and have fixed positions

Metalloids exhibit properties of both metals and non-metals. They can have metallic luster but are brittle and poor conductors compared to metals.

A compound is a pure substance formed from two or more elements combined in fixed ratios, not just any combination of substances

Diffusion is the process where particles move from an area of higher concentration to an area of lower concentration until equilibrium is reached. The statement is incorrect because it describes the opposite of how diffusion works

An emulsion is a mixture of two immiscible liquids where one is dispersed in the other

Water is not considered an organic solvent; it is a polar solvent. Organic solvents include substances like propanone, alcohol, and turpentine.

Evaporation is the process where molecules at the surface of a liquid gain enough energy to transition into the gas phase at temperatures below the boiling point.

Metals are generally malleable (can be hammered into shape) and ductile (can be drawn into wires). Brittleness is typically a property of non-metals

A diluted solution contains a small amount of solute compared to solvent.

Silicon is the second most abundant element in the Earth’s crust, primarily found in silicate minerals

Silicon is a well-known metalloid, exhibiting properties of both metals and non-metals. Gold, carbon, and silver are not metalloids

Mixtures do not have fixed proportions; the components can vary in amount

In a tincture of iodine, iodine is the solute that is dissolved in alcohol (the solvent). The tincture is a solution used as an antiseptic

An aerosol is a mixture where tiny liquid or solid particles are dispersed in a gas.

Gas particles are in constant motion and have no fixed positions. They occupy all available space in a container, unlike solids and liquids

Compounds can be represented by chemical formulas, while mixtures cannot, as they do not have a consistent composition.

In a solution, the solvent typically makes up the greater volume compared to the solute

Brine is a saturated solution of salt (sodium chloride) in water

A pure substance consists of only one type of particle and has a uniform composition. Impure substances contain multiple components

An element is a fundamental substance that cannot be decomposed into simpler substances through chemical reactions. Atoms and ions are components or forms of elements, but they are not standalone substances

Matter is anything that has mass and occupies space. It is the substance that makes up all physical objects in the universe.

Oxygen is a gas and not an organic solvent. Propanone and benzene are examples of organic solvents, while turpentine is also organic.

Chemistry is the scientific discipline that studies the properties, composition, and changes of matter, including how substances interact and react with each other

Brass is an alloy primarily made of copper and zinc. In the context of alloys, the main component (in this case, copper) is considered the solvent, while the other metal (zinc) acts as the solute

Elements are generally classified into metals and nonmetals based on their physical and chemical properties.

The three primary states of matter are solid, liquid, and gas. “Dense” is not a state of matter.

A concentrated solution has a high amount of solute relative to the amount of solvent

A compound is a substance formed from two or more elements that are chemically bonded together in fixed ratios, unlike mixtures where the components retain their individual properties

The Tyndall effect describes the scattering of light by particles in a colloid, making the path of the light visible.

Non-metals generally have low densities compared to metals. Most non-metals are gases at room temperature, and those that are solid (like sulfur and phosphorus) are also less dense than metals

Metals are excellent conductors of heat and electricity. This characteristic is crucial for their use in electrical applications

Sedimentation is the process where suspended solid particles settle out of a fluid under the influence of gravity.

A saturated solution contains the maximum amount of solute that can dissolve at a given temperature.

Oxygen and silicon are the most abundant element in the Earth’s crust and is essential for life.

A gel is a colloidal system where a solid is dispersed in a liquid, giving it a jelly-like consistency

Brine is a solution, not a colloid. Honey, glue, and milk are colloidal solutions.

Steel is an alloy primarily made of iron, with carbon as the solute. The carbon is dissolved in iron to improve its strength and hardness

Sand is primarily composed of silicon dioxide (SiO₂), which consists of silicon and oxygen.

Liquids take the shape of their container. Solids maintain their shape, while gases expand to fill the entire volume of the container.

Most metals have high melting points. While some non-metals can have low melting points, metals are usually solid at room temperature with higher melting points

Matter is anything that has mass and occupies space. It is the substance that makes up all physical objects in the universe.

Water is indeed immiscible with oil, as oil and water do not mix due to their differing polarities. The other statements about water being a universal solvent, polar, and dissolving organic solutes are true

Compounds are generally classified into organic (containing carbon) and inorganic (typically lacking carbon)

Non-metals are generally brittle and cannot be easily shaped, unlike metals which can be stretched and drawn. However, some non-metals can exist in forms that can be molded.

In osmosis, the solvent (usually water) moves from an area of lower solute concentration to an area of higher solute concentration through a semipermeable membrane. The solute itself does not move in osmosis.

Liquids take the shape of their container and have a definite volume. They are fluid at room temperature and are not easily compressed compared to gases

An atom is the smallest unit of an element that retains the chemical properties of that element. Ions are charged particles derived from atoms, and delimiters are not relevant to this context

A chemical change results in the formation of new substances with different properties. This change is generally irreversible (e.g., burning wood).

In an aqueous mixture of sodium chloride (salt) and sand, sand is insoluble in water. When you perform filtration, the sand (solid) will remain on the filter paper, while the sodium chloride (dissolved in water) will pass through as part of the filtrate. Afterward, you can obtain pure sodium chloride by evaporating the water from the filtrate.

A separating funnel is specifically designed to separate two immiscible liquids based on their different densities.

Sublimation is the process where a solid transitions directly to gas without becoming liquid.

Entropy is a measure of disorder or randomness in a system. As temperature increases, particles move more rapidly and the disorder in the system increases.

When warm air meets the cold surface of the bottle, water vapor condenses into droplets.

Centrifugation uses centrifugal force to separate solids from liquids in a colloidal suspension by causing the solid particles to settle at the bottom.

Chromatography separates components of a mixture based on their different affinities to a stationary phase and a mobile phase, making it effective for colored substances.

Distillation is the best method to separate water from a sugar solution, as it uses differences in boiling points to evaporate the water, leaving the sugar behind.

burn is a chemical reaction in which a substance combines with oxygen, often resulting in a change in the chemical composition and the formation of a new substance.

Chromatography is a technique used to separate components of a mixture based on differences in their movement through a medium. It is effective for separating liquids.

Chromatography relies on the different adsorption properties of substances to separate them as they move through a medium

This statement is incorrect. An ion is formed when an atom gains or loses electrons, but the number of electrons gained or lost is equal to the ion’s charge, which corresponds to its valency, not twice its valency

Crystallization is a method used to separate a soluble solid from a solution by forming solid crystals, typically by evaporating the solvent.

Fractional distillation separates liquid mixtures based on differences in boiling points and densities.

Distillation separates components of a mixture based on differences in boiling points, not particle size. Other methods like sifting, filtration, and centrifugation can involve particle size.

Distillation is primarily used for separating liquids based on boiling points, not for separating solids.

Gravity is a force and not a separation method itself. Seiving, centrifugation, and chromatography can involve separation based on particle size.

Fractional crystallization separates solids based on their different solubilities in a solvent, allowing for the recovery of multiple solids.

Blood is a mixture because it contains various components, including red blood cells, white blood cells, platelets, and plasma, which are not chemically bonded and retain their individual properties. Sand is also a mixture, but the question specifies “an example,” so blood is a more complex example.

Vaporisation occurs when a liquid turns into a gas at its boiling point. This includes both boiling and evaporation, but at the boiling point, it specifically refers to the rapid conversion to gas.

A separating funnel is ideal for separating immiscible liquids like kerosene (a hydrocarbon) and water.

Crystallization is specifically used to separate solids from solutions, not for separating solid mixtures directly.

The change in color of zinc oxide with heating and cooling is a physical change, as it does not involve a change in the chemical composition of the substance

Residue refers to what is left behind after a process, whereas ion, atom, and molecule are all fundamental constituents of matter.

Crystallization allows for the recovery of solid solutes from a solution while leaving the solvent intact.

Sublimation is a method that can separate solids based on their ability to transition directly from solid to gas. For example, separating iodine from salt.

Kerosene is a hydrocarbon fuel that does not contain oxygen in its composition.

Molecular number is not a property typically used in the physical separation of mixtures. Properties like weight, solubility, and melting point are commonly used

Hand-picking: This method relies on the physical appearance (color, size) of the components to separate them manually.Centrifugation: This technique separates components based on their mass and density by spinning them at high speeds.Distillation: This method separates substances based on differences in their boiling points, not their color or mass.Filtration: This technique separates solids from liquids or gases based on particle size.

Boiling Point: Nitrogen and oxygen are separated from air through a process called fractional distillation. This method takes advantage of the different boiling points of these gases. Nitrogen has a boiling point of approximately -196°C, while oxygen has a boiling point of approximately -183°C. By cooling air and then distilling it, these gases can be effectively separated.

A compound is a pure substance formed when two or more elements chemically combine in fixed proportions, resulting in new chemical properties.

A chemical equation describes a chemical reaction rather than a physical property used for separation. Properties like color, size, and density are often used to separate mixtures.

Mercury is a pure substance, while the others are mixtures of various components.

This reaction involves combustion, which is a chemical change that results in the formation of new substances (ash, gases) from the original materials (wood)

Fractional distillation is used to separate mixtures of liquids with different boiling points, such as the various components of petroleum.

Distillation is used for separating components of a liquid mixture, not specifically for recovering solids from liquids.

Freezing ice-cream is a physical change because it involves a change in the state of matter from liquid to solid without altering the chemical composition of the ingredients. The ice-cream can be melted back to its original state.

Dissolving salt in water is a physical change, as no new substances are formed; the salt can be recovered by evaporation.

Sugar dissolves in water while sulfur does not. The mixture can be filtered to remove sulfur, and the sugar solution can then be evaporated to recover sugar.

Explanation: Ammonium chloride undergoes sublimation when heated, converting directly from solid to gas without becoming liquid. The white deposit observed is likely the result of gas cooling and solidifying.

Fractional distillation separates petroleum into its various components based on boiling points

This is a chemical change known as slaking, where quicklime (calcium oxide) reacts with water to form calcium hydroxide, resulting in a new substance.

Centrifugation is a technique that uses rapid spinning to separate components of blood based on their density. Blood cells settle at the bottom, while plasma remains on top

Distillation is effective for separating ethanol and water due to their different boiling points.

the molecule is the smallest particle of a compound which is capable of independent existence. An atom is the smallest unit of a compound capable of taking part in a chemical reaction

Bronze is an alloy a mixture of copper which is the solvent and tin which is the solute. Ie tin dissolved in copper. Bronze typically consists of about 90% copper and 10% tin,The addition of tin to copper improves the strength, corrosion resistance, and overall durability of the metal, making bronze suitable for various applications, including tools, weapons, and sculptures though the proportions can vary.

Distillation separates liquids based on their boiling points. It is commonly used to purify liquids or separate liquid mixtures.

Dissolution: Refers to the process of a substance dissolving in a solvent, not a separation method

This statement is incorrect because physical changes do not produce new substances; they only change the state or appearance of a substance. Chemical changes result in new substances being formed.

The f subshell has 7 orbitals, and since each orbital can hold 2 electrons, it can hold a total of 7×2=147×2=14 electrons.

The nucleus of an atom is made up of protons and neutrons. Electrons are not part of the nucleus; they orbit around it.

To find the relative atomic mass of the element with isotopes X-23 and X-24 existing in a ratio of 3:1, we can follow these steps:Step-by-Step Calculation: Isotope1 X-23 has a mass1 of 23 and exists in a ratio of 3. And Isotope2 X-24 has a mass2 of 24 and exists in a ratio2 which is 1. Calculate the weighted average:The relative atomic mass AA can be calculated using the formula: A=(mass1×ratio1)+(mass2×ratio2)/(ratio1+ratio2)=(23×3)+(24×1)/3+1=23.25

one molecule of Cl is monoatomic, one molecule of oxygen (O2) is diatomic, if the element contains 3 atoms it is triatomic eg , Ozone , O3 if the molecule of the element contains 4

The mass number is the sum of the number of protons and neutrons in an atom’s nucleus. It does not include electrons.

Each orbital can hold a maximum of 2 electrons due to the Pauli exclusion principle.

The Aufbau principle states that electrons fill orbitals starting from the lowest energy level to the highest.

In a neutral atom, the number of electrons equals the number of protons, which is the atomic number. Here, the atomic number is 8, so there are 8 electrons.

These are the three fundamental subatomic particles that make up an atom. Protons are positively charged, neutrons are neutral, and electrons are negatively charged.

The first electron fills the 1s orbital in the first shell.

filling the orbitals according to the energy level. Follow the order: 1s, 2s, 2p, 3s, 3p, 4s, 3d, 4p, 5s, 4d, 5p, 6s, 4f, 5d, 6p, 7s, 5f, 6d, 7p

A mass spectrometer is an instrument used to measure the mass-to-charge ratio of ions. It can accurately determine the atomic mass of an atom by analyzing the isotopes present. The other options (electrometer, hydrometer, thermometer) are not used for measuring atomic mass.

The mass number can be calculated using the formula: Mass Number=Atomic Number+NeutronsMass Number=Atomic Number+Neutrons For this atom, it would be: 8+7=158+7=15

Atomic Number: The atomic number of an element is defined as the number of protons in the nucleus of an atom and is always a whole number. It cannot be in fractions.

The d-subshell has five orbitals, which can hold a maximum of 10 electrons.

In a neutral atom, the number of electrons equals the number of protons, which is the atomic number. Here, the atomic number is 21, so there are 21 electrons.

An orbital is a region in an atom where there is a high probability of finding electrons

Hydrogen typically has one proton and one electron, but it usually has no neutrons in its most abundant isotope (protium). There are isotopes of hydrogen that contain neutrons (like deuterium and tritium), but the most common form of hydrogen (protium) does not have any neutrons.

The s-subshell has one orbital, which can hold a maximum of 2 electrons.

Key Definitions:Atomic Number (Z): The number of protons in an atom, which also determines the element’s identity. Mass Number (A): The total number of protons and neutrons in the nucleus of an atom. Neutrons: Calculated as the mass number minus the atomic number (A – Z). Electrons: In a neutral atom, the number of electrons equals the number of protons. Given: Mass Number (A) = 27 and Atomic Number (Z) = 17. Calculations: Number of Protons: This is equal to the atomic number..Protons = 17. Number of Neutrons: This is calculated as follows: Neutrons = Mass Number – Atomic Number = 27 – 17 = 10 Number of Electrons: In a neutral atom, the number of electrons equals the number of protons. Electrons = 17

An atom is electrically neutral when it has the same number of positively charged protons in the nucleus as negatively charged electrons surrounding the nucleus. This balance results in no overall charge.

Isotope A: Has a mass of 10 and a relative abundance of 70% (0.70). Isotope B: Has a mass of 11 and a relative abundance of 30% (0.30). Contribution of A=Mass of A×Relative abundance of A=10×0.70=7.0. Contribution of B=Mass of B×Relative abundance of B=11×0.30=3.3. adding the two gives 10.3

The p-subshell has three orbitals (px, py, pz), which can collectively hold a maximum of 6 electrons.

The maximum number of electrons in a shell can be calculated using 2n raised to power 2 or n-squared. For the 4th shell (n=4n=4): 2(4-squared)=2(16)=32

A mass spectrometer separates particles based on their mass-to-charge ratio. If an element shows two peaks in the mass spectrum, it means that there are two different masses present, which corresponds to the presence of two isotopes of that element. Isotopes are atoms of the same element that have different numbers of neutrons, resulting in different atomic masses

Protons carry a positive charge. The statement about protons being neutral is incorrect.

The atomic mass unit (amu) is defined relative to carbon-12, where one amu is one-twelfth of the mass of a carbon-12 atom. This isotope serves as the standard reference point for measuring and comparing the masses of all other atoms.

Neon (atomic number 10) has a complete outer shell with 8 valence electrons, which is the maximum for the outermost shell in the second period. Oxygen (8) has 6, phosphorus (15) has 5, and potassium (19) has 1 in its outermost shell.

The mass of an atom is actually estimated relative to carbon-12 (¹²C), not oxygen-16 (¹⁶O). The atomic mass unit (amu) is defined based on the mass of carbon-12, where 1 amu is a twelfth of the mass of a carbon-12 atom.

The f-subshell has seven orbitals, which can hold a maximum of 14 electrons.

The L shell can hold a maximum of 8 electrons. The total number of electrons in a shell can be calculated using the formula 2n22n2, where nn is the shell number (for L, n=2n=2).

The configuration is written some thing like 1s2-2s2-2p6. the first number is the shell number which is first written as whole number starting from 1 for K, 2 for L , 3 for M etc. then it is followed by the subshell which  is s, p,d or f and then the number of electrons in the subshell orbit is written last as superscript. so the 6 in 1p6 is the number of electrons

they are atoms of same elements with the same atomic number (Z) but different mass number. This means they have the same number of protons but different number of neutrons in their nucleus

Dalton’s atomic theory states that atoms combine in whole-number ratios to form compounds. The statement about combining in “small fractions” contradicts this principle.

In the quantum mechanical model, electrons do not move in fixed circular paths. Instead, they exist in probabilistic orbitals around the nucleus.

Electrons occupy the shells (energy levels) around the nucleus of an atom. Protons and neutrons are found in the nucleus.

The correct notation places the shell number before the subshell letter (e.g., 2s2s, 3p3p). The other statements are accurate in their descriptions.

Dalton’s atomic theory posits that atoms are indivisible and cannot be created or destroyed in chemical reactions. This statement contradicts that principle, as atoms can only rearrange during reactions but cannot be created from other atoms.

The electron configuration for 12 electrons is 1s2, 2s2, 2p6, 3s2, meaning the last electron is in the third shell.( the first shell has 2 electrons, the second shell holds 8 electrons and the remaining 2 go into the third shell

The mass of an electron is very small compared to that of protons and neutrons, so it does not significantly contribute to the overall mass of the atom.

To find the relative atomic mass of the element with isotopes X-16, X-17, and X-18 existing in a ratio of 3:1:1, we can use the following calculation: Step-by-Step Calculation:Identify the isotopes and their ratios:Isotope1 X-16 has a mass1 of 16 and exists in a ratio1 which is3. Then Isotope2 X-17 has a mass2 of 17 and exists in a ratio2 which is 1. Finally Isotope3 X-18 has a mass3 of 18 and exists in a ratio3 with is 1. Calculate the weighted average:The relative atomic mass =(mass1×ratio1)+(mass2×ratio2)+(mass3×ratio3)/(ratio1+ratio2+ratio3). Plugging the values into the forula: =(16×3)+(17×1)+(18×1)/(3+1+1)=16.6

The d subshell has 5 orbitals, and since each orbital can hold 2 electrons, it can hold a total of 5×2=105×2=10 electrons.

Protons have a positive charge, while electrons carry a negative charge. This statement is incorrect.

The number of neutrons can be calculated using the formula: Neutrons=Mass Number−Atomic NumberNeutrons=Mass Number−Atomic Number For this atom, it would be: 40−21=1940−21=19

To find the relative atomic mass of the element with isotopes X-20 and X-22 existing in a ratio of 3:1, we can use the following calculation:Step-by-Step Calculation:Identify the isotopes and their ratios: Isotope1 X-20 has a mass1 of 20 and exists in a ratio1= 3. Isotope2 X-22 has a mass2 of 22 and exists in a ratio2 of 1. Calculate the weighted average:The relative atomic mass formula: =(mass1×ratio1)+(mass2×ratio2)/(ratio1+ratio2). So if we plug the values into the formula: A=(20×3)+(22×1)/(3+1)= 22.5

The relative atomic mass of nitrogen is approximately 14.01, not 36. The other values are correct: carbon is 12, hydrogen is 1, and oxygen is 16.

An atom is composed of a nucleus (containing protons and neutrons) and electron shells (where electrons reside). The other options do not correctly represent the structure of an atom.

Atoms with a fully filled valence shell typically resemble noble gases and are chemically inert (non-reactive). This configuration is stable and is often referred to as the noble gas configuration.

The atomic mass scale is based on the carbon-12 isotope, which is commonly used as the standard reference for atomic masses. However, if you are specifically choosing from the options provided, the most direct answer is “carbon.”

Valence electrons are the electrons in the highest energy level (outermost shell) of an atom and are involved in chemical bonding.

Mass Number: The total number of protons and neutrons in the nucleus (protons + neutrons)

The atom has one valence electron in the outer shell (3rd shell), so its electrovalency is +1, not +2

When an atom receives an electron, it becomes negatively charged and is referred to as an anion, not a cation. A cation is formed when an atom loses an electron.

The valency of an element is the number of hydrogen atoms that can combine with or replace one atom of the element. Valency of an element is also called the combining power of the element or the oxidation number of the element. It is the number of electrons in the outermost orbit of an atom Some elements have more than one valency and they are said to have variable valences

when an electron gains energy, it moves to a higher energy level, not a lower one. Electrons emit energy when they drop to lower energy levels.

Ionic (or electrovalent) bonding occurs when one atom transfers its valence electrons to another atom, resulting in the formation of ions that achieve stable electronic configurations (noble gas structure)

Cathode rays, which are streams of electrons, travel in straight lines unless acted upon by an external magnetic or electric field. The statement about them running in curved paths is misleading without context regarding external forces.

The K shell corresponds to the principal quantum number n = 1. The value of n for the K shell is not 3; it is the first energy level.

Let’s analyze the given options regarding the atom and ion of sodium: Sodium Atom vs. Sodium Ion (Na⁺). Sodium Atom (Na): Atomic Number: 11 (has 11 protons and 11 electrons). Electron Configuration: 1s22s22p63s11s22s22p63s1. Sodium Ion (Na⁺): Formation: Formed when a sodium atom loses one electron. Protons: 11 (remains the same). Electrons: 10 (loses one electron) Options Analysis: The same chemical properties: Not Correct: Sodium (Na) and sodium ion (Na⁺) have different chemical properties due to the difference in their electron configurations. The ion is more stable and less reactive than the neutral atom. Electronic configuration: Not Correct: The electronic configuration of Na is 1s22s22p63s1, while for Na⁺ it is 1s22s22p6. They are different. Number of protons: Correct: Both the sodium atom and sodium ion have the same number of protons (11). Number of electrons: Not Correct: The sodium atom has 11 electrons, while the sodium ion has 10 electrons.

an atom that gains an electron becomes an anion, not a cation. Cations are formed when atoms lose electrons

Reduction refers to the gain of electrons, while metals lose electrons during ionic bond formation. Hence, the metal is oxidized, not reduced

J.J. Thomson discovered the electron in 1897 through his experiments with cathode rays. He demonstrated that cathode rays were composed of negatively charged particles, which he named electrons. This discovery was crucial in the development of atomic theory and our understanding of atomic structure.

The idea that electrons circle the nucleus of an atom in a manner similar to planets orbiting the sun was proposed by Niels Bohr in 1913. This model is known as the Bohr model of the atom.

The 3d orbitals are actually at a higher energy level than the 4s orbital. When filling orbitals, the 4s orbital is filled before the 3d orbitals because it has a lower energy level

The atom that gains the electron is commonly the metal.Explanation: This statement is incorrect because the atom that gains electrons is usually a nonmetal, which becomes negatively charged and forms an anion.

This statement is incorrect because protons are significantly more massive than electrons. A proton has about 1836 times the mass of an electron.

The cathode ray experiment revealed that the rays were composed of electrons, which are negatively charged particles.

Dalton did not discover the neutron; he proposed the atomic theory that included the existence of atoms but did not identify subatomic particles like neutrons.