ROSSMOYNE CHEM

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Questions and Answers

Which of the following statements is/are correct for particles in the transition state of a chemical reaction? (i) They can quickly form reactants. (ii) They can quickly form products. (iii) They have maximum enthalpy.

all

Describe, in terms of all the forces formed and forces broken, the process of solid potassium sulfide dissolving in water.

-ionic bonds between ions in lattice are broken -ion dipole forces are formed between ions and water molecules -dissociation of ionic substances described/shown -formation of ions surrounded by polar water molecules described/shown

Explain, in terms of breaking of existing bonds and forming of new bonds, why this process of dissolving solid potassium sulfide in water causes the temperature of the water to decrease.

-This is endothermic reaction: more energy req'd to break strong ionic bonds -than is released when ion-dipole forces are formed between ions and water molecules -the net result is that energy is absorbed in the process -because total energy is conserved, this comes at the expense of decrease in kinetic energy of the water molecules, as that kinetic energy is converted to chemical energy held in bonds which accounts for the decrease in temperature of the water

Explain why the solution of potassium sulfide can conduct electricity when the following apparatus is used to test its conductivity.

-ions are free to move and function as charge carriers -meaning potassium ions can flow toward negative electrode and sulfide ions can flow toward positive electrode -the result of this flow of ions is that the solution can conduct electricity Signup and view all the answers

Explain why dissolving the same amount (in mole) of hydrogen sulfide gas (H2S) in water produces a solution that has a lower conductivity than that of K2S.

-H2S is a weak electrolyte -meaning it only partially ionises in solution -the solution of H2S will thus have lower concentration of ions than that of K2S which fully dissociated (is a strong electrolyte) -with a lower concentration of ions there are less charge carriers present to conduct electricity through the solution thus H2S has a lower conductivity Signup and view all the answers

define monoprotic acid

has one ionisable hydrogen per molecule Signup and view all the answers

stationary phase = polar and mobile phase = low polarity. Explain why hexachlorophene is most polar

-stationary phase is polar AND mobile phase has low polarity (MUST HV BOTH) -therefore most polar component will adsorb most strongly to the stationary phase -thus most polar component will move most SLOWLY and have the lowest retention factor Signup and view all the answers

Give one (1) reason that it cannot be known for certain that tribromsalan is in this cosmetic product.

Another chemical may have the same retention factor in identical conditions Signup and view all the answers

suggest two reasons why these treatments may be performed on the salt solution (periodically treating salt solution with chlorine, bromine or UV light)

-kill bacteria, fungi, virus, disinfect water Signup and view all the answers

define pH

negative log of the concentration of H+ (aq) in a solution Signup and view all the answers

Using example of sulfuric acid explain what is meant by strong acid, use an equation in answer

-a strong acid that fully ionises in solution -H2SO4(aq) -> H+(aq) + HSO4-(aq) -HSO4-(aq) -> H+(aq) + SO4(2-)(aq) -it is a diprotic acid, so it donates two H+ ions per molecule, with the first stage fully ionising, and the second partially ionising. (This increases concentration of H+ ions in solution) Signup and view all the answers

aliminium oxide is amphoteric (can act as acid or base). Explain why aliminium oxide is the substance chosen to complete the clean-up process

bc aliminium oxide will neutralise any excess acid and/or base Signup and view all the answers

Use your knowledge of reaction rates to explain why the aluminium oxide was used in a powdered form.

-powdered aliminium will have larger surface area -this will increase number of (successful) collisions between the particles in the acid/base and the aliminium oxide -there ROR increase Signup and view all the answers

what feature so period three elements have in common?

all have VALENCE ELECTRONS which occupy third energy shell Signup and view all the answers

define first ionisation energy and explain the increasing trend observed: As you move from left to right across period 3, both the first ionisation energy and electronegativity of the elements increase.

-first ionisation energy = energy required to remove one mole of electrons from one mole of atoms in the gaseous state -positive charge of nucleus increases as you move left to right across the period (in addition to decreased atomic radius) -therefore e- are more attracted to nucleus and -greater amount of energy is required to remove an electron -hence ionisation energy increases Signup and view all the answers

define electronegativity and explain the increasing trend observed as you move from left to right across a period

-the ability of an atom to attract electrons to itself within a covalent bond -with constant inner electron shielding and an increase in positive nuclear charge, the nucleus can attract electrons more effectively. -also results in decrease in atomic radius, which increases ability to attract more electrons as the electrons attracted will be closer to the nucleus Signup and view all the answers

Use the concepts of ionisation energy and electronegativity to explain why NaCl is an ionic substance, whilst Cl2 is a covalent substance.

-sodium has low IONISATION ENERGY and chlorine has high ELECTRONEGATIVITY -therefore e- are transferred from sodium to chlorine, forming cations and anions (ie. ionic bonding) -chlorine gas consists of two non-metal atoms with HIGH ELECTRONEGATIVITIES -therefore electrons are shared, forming an uncharged COVALENT molecule Signup and view all the answers

Explain why Cl2 is the only one of these covalent compounds to contain non-polar bonds.

-The two chlorine atoms within Cl2 have the same electronegativity. -Therefore the electron pair is shared equally by both atoms and no bond dipole is created. Signup and view all the answers

Explain why SiCl4 is classified as a non-polar molecule, despite containing polar bonds. Include the Lewis structure of SiCl4 in your answer.

| <ul> <li> <ul> <li></li> </ul> |</li> </ul> -shape of molecule is A SYMMETRICAL TETRAHEDRAL -therefore the bond dipoles cancel each other out and there is no net dipole (resulting in a non-polar molecule) Signup and view all the answers

Study Notes

Transition State

Transition state particles can quickly form reactants or products.
Transition states have the highest enthalpy.

Dissolving Potassium Sulfide

Solid potassium sulfide (K₂S) dissolves in water by breaking ionic bonds between potassium and sulfide ions.
Water molecules form hydration shells around the ions, surrounding them with their negative and positive ends.
The process of dissolving potassium sulfide requires energy to break existing bonds, resulting in a decrease in water temperature.

Electrical Conductivity

Potassium sulfide solution conducts electricity because it contains free-moving ions (K⁺ and S²⁻) that carry an electric current.

Comparing Conductivity of K₂S and H₂S

K₂S solution has a higher conductivity than H₂S solution because K₂S completely dissociates into ions in water, while H₂S only partially ionizes, resulting in fewer charge carriers.

Monoprotic Acid

A monoprotic acid can donate only one proton (H⁺ ion) per molecule.

Hexachlorophene Polarity

Hexachlorophene is more polar than tribromsalan because of its more electronegative chlorine atoms.

Absence of Tribromsalan

It is not certain if tribromsalan is present in the cosmetic product because it is not explicitly mentioned in the provided information.

Treating Salt Solutions

Salt solution is treated with chlorine or bromine to kill harmful bacteria and microorganisms.
UV light is used to disinfect the salt solution by breaking down harmful organic compounds and pathogens.

pH Definition

pH is a measure of the hydrogen ion concentration in a solution.

Strong Acid

A strong acid, like sulfuric acid (H₂SO₄), completely ionizes in water, releasing all its hydrogen ions:
- H₂SO₄ (aq) → 2H⁺ (aq) + SO₄²⁻ (aq)

Amphoteric Property of Aluminum Oxide

Aluminum oxide (Al₂O₃) is amphoteric because it can act as both an acid and a base:
- As an acid: Al₂O₃(s) + 2OH⁻(aq) → [Al(OH)₄]⁻(aq)
- As a base: Al₂O₃(s) + 6H⁺(aq) → 2Al³⁺(aq) + 3H₂O(l)

Aluminum Oxide Cleanup

Aluminum oxide was chosen to complete the cleanup process because it is amphoteric, allowing it to neutralize both acids and bases.

Powdered Aluminum Oxide

Powdered aluminum oxide was used to increase the surface area for faster reaction rates.

Period 3 Element Feature

Period 3 elements have the same number of electron shells.

First Ionization Energy

First ionization energy is the minimum energy required to remove one electron from an atom in its gaseous state.
It increases from left to right across Period 3 due to increasing nuclear charge and decreasing atomic radius.

Electronegativity

Electronegativity is the ability of an atom to attract electrons in a covalent bond.
It increases from left to right across Period 3 due to increasing nuclear charge.

NaCl and Cl₂ Bonding

NaCl is ionic because sodium (Na) has a low ionization energy and readily loses an electron, while chlorine (Cl) has high electronegativity and gains an electron.
Cl₂ is covalent because both chlorine atoms share electrons equally, forming a non-polar covalent bond.

Non-Polar Bonds in Cl₂

Cl₂ has non-polar bonds because both chlorine atoms have the same electronegativity and share electrons equally.

SiCl₄ Polarity

SiCl₄ is a non-polar molecule despite containing polar bonds due to its tetrahedral shape.
The four polar Si-Cl bonds cancel each other out, resulting in a non-polar molecule.

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Description

trends in periodic table, electronegativity, ionisation energy, bonding, exothermic/endothermic, ion-dipole