What ions are released when an acid dissolves in water?
Hydrogen ions (H⁺).
What ions are released when an alkali dissolves in water?
Hydroxide ions (OH⁻).
According to the Arrhenius theory, what element do acids contain?
Hydrogen (H).
According to the Arrhenius theory, what ion do alkalis produce?
Hydroxide ions (OH⁻).
What is the role of water in showing acidic properties?
Water enables the separation of hydrogen ions from acid molecules and acts as a medium in which acidic properties can be displayed.
What is the role of water in showing alkaline properties?
Water facilitates the separation of hydroxide ions from alkali molecules and acts as a medium for displaying alkaline properties.
What is a strong acid?
A strong acid is one that ionises completely in water, producing a high concentration of H⁺ ions.
What is a weak acid?
A weak acid is one that only partially ionises in water, resulting in a lower concentration of H⁺ ions.
What is a strong alkali?
A strong alkali is one that ionises completely in water, producing a high concentration of OH⁻ ions.
What is a weak alkali?
A weak alkali is one that only partially ionises in water, resulting in a lower concentration of OH⁻ ions.
Name three common strong acids.
Hydrochloric acid (HCl), nitric acid (HNO₃), and sulfuric acid (H₂SO₄).
Name three common strong alkalis.
Sodium hydroxide (NaOH), potassium hydroxide (KOH), and barium hydroxide (Ba(OH)₂).
Name two common weak acids.
Ethanoic acid (CH₃COOH) and methanoic acid (HCOOH).
Name one common weak alkali.
Ammonia (NH₃).
What is the chemical formula for a hydronium ion?
H₃O⁺.
What does the pH scale measure?
The pH scale measures the acidity or alkalinity of a solution.
What pH value indicates a neutral solution?
A pH value of 7.
What is the range of the pH scale for acidic solutions?
A pH range of less than 7.
What is the range of the pH scale for alkaline solutions?
A pH range of more than 7.
What is the significance of hydrogen ions (H⁺) in acidic solutions?
The presence of hydrogen ions (H⁺) gives acids their characteristic acidic properties.
Explanation Questions
Explain how water enables acids to show their acidic properties.
Water acts as a medium in which acids can ionise. When an acid dissolves in water, the covalent bond in the acid molecule is broken, resulting in the formation of H⁺ ions and negatively charged ions. The H⁺ ions then combine with water molecules to form hydronium ions (H₃O⁺), which are responsible for the acidic properties. Without water, acids cannot dissociate into ions and therefore will not show acidic properties.
Explain how water enables alkalis to show their alkaline properties.
Water acts as a medium for alkalis to ionise. When an alkali dissolves in water, the molecule separates to form positive ions and hydroxide ions (OH⁻). The presence of water allows these hydroxide ions to move freely, which is essential for demonstrating alkaline properties. Without water, alkalis cannot dissociate into ions, thus preventing them from exhibiting their alkaline characteristics.
Explain the process of ionisation of a strong acid in water.
A strong acid undergoes complete ionisation in water. This means that every molecule of the acid breaks apart into ions. For example, when hydrochloric acid (HCl) is dissolved in water, it completely dissociates into hydrogen ions (H⁺) and chloride ions (Cl⁻). This complete dissociation results in a high concentration of H⁺ ions in the solution, which is why it is a strong acid.
Explain the process of ionisation of a weak acid in water.
A weak acid only partially ionises in water. This means that only a fraction of the acid molecules will break apart into ions, while most will remain as whole molecules. For example, ethanoic acid (CH₃COOH) in water will only partially ionise to form hydrogen ions (H⁺) and ethanoate ions (CH₃COO⁻), leaving a significant number of CH₃COOH molecules un-ionised. Therefore, weak acids produce a lower concentration of H⁺ ions compared to strong acids.
Explain the process of ionisation of a strong alkali in water.
A strong alkali undergoes complete ionisation in water. This means that every molecule of the alkali breaks apart into ions. For example, when sodium hydroxide (NaOH) is dissolved in water, it completely dissociates into sodium ions (Na⁺) and hydroxide ions (OH⁻). This complete dissociation results in a high concentration of OH⁻ ions in the solution, which is why it is a strong alkali.
Explain the process of ionisation of a weak alkali in water.
A weak alkali only partially ionises in water. This means that only a fraction of the alkali molecules will break apart into ions, while most will remain as whole molecules. For example, ammonia (NH₃) in water will only partially ionise to form ammonium ions (NH₄⁺) and hydroxide ions (OH⁻), leaving a significant number of NH₃ molecules un-ionised. Therefore, weak alkalis produce a lower concentration of OH⁻ ions compared to strong alkalis.
Why is water crucial for acids and alkalis to demonstrate their characteristic properties?
Water is essential because it acts as a medium that allows acids and alkalis to ionise. Without water, the molecules of acids and alkalis cannot break apart into ions, which are responsible for acidic and alkaline properties. Water molecules interact with acids to form hydrogen or hydronium ions, and with alkalis to form hydroxide ions. These ions must be present in an aqueous solution for the substance to demonstrate its acidic or alkaline nature. Thus, water is a crucial component for acids and alkalis to show their characteristic behaviours.
How does the concentration of hydrogen ions (H⁺) determine the strength of an acid?
The strength of an acid is directly related to the concentration of hydrogen ions (H⁺) in an aqueous solution. A higher concentration of H⁺ ions indicates a stronger acid because it means more acid molecules have ionised. Strong acids, such as HCl, completely ionise, resulting in a high H⁺ concentration and low pH. Conversely, weak acids, such as CH₃COOH, only partially ionise, resulting in a low H⁺ concentration and higher pH.
How does the concentration of hydroxide ions (OH⁻) determine the strength of an alkali?
The strength of an alkali is directly related to the concentration of hydroxide ions (OH⁻) in an aqueous solution. A higher concentration of OH⁻ ions indicates a stronger alkali because it means more alkali molecules have ionised. Strong alkalis, such as NaOH, completely ionise, resulting in a high OH⁻ concentration and a high pH. Conversely, weak alkalis, such as NH₃, only partially ionise, resulting in a low OH⁻ concentration and lower pH.
Explain how the pH scale is related to the concentration of H⁺ and OH⁻ ions in a solution.
The pH scale is a measure of the acidity or alkalinity of a solution and is directly related to the concentration of hydrogen ions (H⁺) and hydroxide ions (OH⁻). The pH scale ranges from 0 to 14, with 7 being neutral. Solutions with a pH less than 7 are acidic and contain a higher concentration of H⁺ ions than OH⁻ ions. The lower the pH value, the greater the concentration of H⁺ ions and the stronger the acid. Solutions with a pH greater than 7 are alkaline and contain a higher concentration of OH⁻ ions than H⁺ ions. The higher the pH value, the greater the concentration of OH⁻ ions and the stronger the alkali. A pH of 7 indicates a neutral solution where the concentration of H⁺ and OH⁻ ions are equal. The pH scale thus provides a convenient way to describe the relative acidity or alkalinity of a solution by measuring the concentration of these ions.