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Chemistry Tuition Flashcards > Physical Week 7 > Flashcards

Physical Week 7 Flashcards

Acids and Bases

1
Q

What is a Bronsted-Lowry base?

A

A Bronsted-Lowry base is a proton acceptor, like hydroxide ions (OH-). Hydroxide ions are still considered Bronsted-Lowry bases because they accept protons and form water.

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2
Q

What are conjugate pairs?

A

Conjugate pairs refer to the relationship between an acid and its corresponding base, or a base and its corresponding acid. In the context of acid-base reactions, conjugate pairs differ by one proton.

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3
Q

What is a Bronsted-Lowry acid?

A

A Bronsted-Lowry acid is a proton donor, such as Ammonium ions (NH4+). Acids release hydrogen ions in aqueous solution.

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4
Q

What are strong acids?

A

Strong acids are acids that completely dissociate in solution and release all of their H+ ions. They have a pH of about 0 to 1.

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5
Q

What is a conjugate acid-base pair?

A

A conjugate acid-base pair differ by one proton. In this example HCl and Cl- are a conjugate acid-base pair and H2O and H3O+ are another acid-base pair.

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6
Q

What is pH?

A

pH is a measurement of acidity or basicity on a scale from 0 to 14, indicating the presence of H+ ions in a solution. A pH of 0 is highly acidic with a high concentration of H+ ions, while a pH of 14 is highly basic with a low concentration of H+ ions.

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7
Q

What is the pH scale?

A

The pH scale is a logarithmic scale that measures the acidity or basicity of a solution. For every increase by 1 on the scale, the [H+] decreases by a factor of 10.

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8
Q

What is a Ka value?

A

Ka value refers to the acid dissociation constant, which is a measure of the extent to which an acid dissociates in water. In cases where two acids are present, the acid with a higher Ka value will act as the acid.

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9
Q

What happens when HCl reacts with water in an aqueous solution?

A

In aqueous solution, HCl reacts with water to produce hydronium ions and chloride ions.

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10
Q

What is the pH range of strong acids like hydrochloric acid?

A

Strong acids, like hydrochloric acid, have a pH of about 0 to 1.

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11
Q

How do conjugate acid-base pairs differ from each other?

A

Conjugate acid-base pairs differ by one proton.

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12
Q

What is the pH of a 0.1 mol dm-3 hydrochloric acid solution?

A

A 0.1 mol dm-3 hydrochloric acid solution has a pH of 1.

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13
Q

What is the H+ ion concentration in a solution with a pH of 3?

A

A solution with a pH of 3 has an H+ ion concentration of 10^-3 moldm^-3.

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14
Q

How does the pH scale represent the concentration of H+ ions?

A

The pH scale is logarithmic, with each increase of 1 representing a 10-fold decrease in [H+] concentration.

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15
Q

What assumption is made for strong acids when calculating pH?

A

For strong acids, the assumption is made that [HA] is equal to [H+].

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16
Q

Give examples of conjugate acid-base pairs.

A

Examples of conjugate acid-base pairs include HCl and Cl-, as well as H2O and H3O+.

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17
Q

What is an OH- ion?

A

The hydroxide ion (OH-) is formed when a water molecule acts as a base and accepts a hydrogen ion (H+) from another water molecule. It is a strong base and plays a crucial role in acid-base reactions.

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18
Q

What is a titration?

A

Titration is a technique used in chemistry to determine the concentration of a substance in a solution. It involves the gradual addition of a solution of known concentration (titrant) to a solution of unknown concentration (analyte) until the reaction between the two is complete.

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19
Q

What is a weak acid?

A

A weak acid is an acid that only partially dissociates into its constituent ions in a solution. It reacts with water to produce hydronium ions (H3O+) and the conjugate base.

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20
Q

What is a strong base?

A

A strong base is a base that completely dissociates into its constituent ions in a solution. It readily accepts hydrogen ions (H+) from water, resulting in a high concentration of hydroxide ions (OH-).

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21
Q

What is a strong acid?

A

A strong acid is an acid that completely dissociates into its constituent ions in a solution. It readily donates hydrogen ions (H+) to water, resulting in a high concentration of hydronium ions (H3O+).

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22
Q

What is dissociation?

A

Dissociation refers to the separation of a compound into its constituent ions in a solution. In the case of water, it dissociates into hydrogen ions (H+) and hydroxide ions (OH-), which can then participate in acid-base reactions.

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23
Q

What is the ionic product for water?

A

The ionic product for water, denoted as Kw, is an equilibrium constant that represents the concentration of hydrogen ions (H+) and hydroxide ions (OH-) in water. It is defined as [H+][OH-] and has a constant value of 1.00 x 10^-14 mol^2 dm^-6 at 25 degrees Celsius.

24
Q

What is a hydroxonium ion?

A

The hydroxonium ion, also known as the hydronium ion (H3O+), is formed when a water molecule acts as an acid and donates a hydrogen ion (H+) to another water molecule. It is a strong acid and plays a crucial role in acid-base reactions.

25
Q

What is a weak base?

A

A weak base is a base that only partially dissociates into its constituent ions in a solution. It reacts with water to produce hydroxide ions (OH-) and the conjugate acid.

26
Q

What is neutralisation?

A

Neutralisation is a chemical reaction between an acid and a base, resulting in the formation of a salt and water. The hydrogen ions (H+) from the acid react with the hydroxide ions (OH-) from the base to form water.

27
Q

What is the equivalence point?

A

The equivalence point is the point in a titration where the stoichiometrically equivalent amounts of acid and base have reacted. At this point, the solution is neutral, and the concentration of hydrogen ions (H+) is equal to the concentration of hydroxide ions (OH-).

28
Q

What is the value of the Kw at a temperature of 25 degrees Celsius?

A

At a temperature of 25 degrees Celsius, the Kw value for aqueous solutions is 1x10-14 mol2dm-6.

29
Q

Why does pure water have a pH of 7?

A

The pH of pure water is 7 because the concentration of hydrogen ions ([H+]) is equal to the concentration of hydroxide ions ([OH-]) due to the water’s ionic product (Kw)

30
Q

What is the calculation for the pH of a weak acid at half equivalence?

A

At half neutralisation, the assumption is made that [HA] = [A-] and the pH is equal to the pKa.

31
Q

What happens when ethanoic acid reacts with water?

A

Ethanoic acid reacts with water to produce hydroxonium ions and ethanoate ions. The reverse reaction occurs more frequently than the forward one, resulting in the recombination of ions to form the acid and water again.

32
Q

What is the pH of the resulting mixture when 25 cm3 of 0.4 mol dm-3 HCl is reacted with 45 cm3 of 0.5 mol dm-3 NaOH?

A

The resulting mixture has a pH of 13.25.

33
Q

How is the dissociation of weak acids represented?

A

The dissociation of weak acids is represented by the expression [H3O+][A-]/[HA(aq)].

34
Q

What is the pH of water at 60°C with a Kw value of 9.55 x 10^-14 mol2 dm-6?

A

The pH of water at 60°C, with a Kw value of 9.55 x 10^-14 mol2 dm-6, is 6.51, which is still neutral as [H+] = [OH-].

35
Q

What does the ionic product for water, Kw, represent?

A

The ionic product for water, Kw, is an equilibrium constant that represents the concentration of hydroxonium and hydroxide ions in water.

36
Q

How would you calculate the pH of a partially neutralised acid?

A

Calculate the number of moles in the initial acid solution and determine the moles of H+ ions. Then, find the moles of the added base and determine the moles of OH- ions. Finally, figure out which one is present in excess.

37
Q

What is a titration?

A

Titration is a laboratory technique used to determine the concentration of a substance in a solution by reacting it with a solution of known concentration. It involves the gradual addition of the titrant (solution of known concentration) to the analyte (solution of unknown concentration) until the reaction between the two is complete.

38
Q

What is the equivalence point?

A

The equivalence point is the point in a titration at which the acid and base have reacted in stoichiometrically equivalent amounts. At this point, the number of moles of acid is equal to the number of moles of base, resulting in complete neutralisation.

39
Q

What is a buffer solution?

A

A buffer solution is a solution that resists changes in pH when small amounts of acid or base are added. It consists of a weak acid and its conjugate base (or a weak base and its conjugate acid) in roughly equal concentrations.

40
Q

What is the end point?

A

The end point of a titration is the point at which the indicator changes color, indicating that the reaction between the acid and base is complete. It may or may not coincide exactly with the equivalence point, depending on the choice of indicator and the nature of the reaction.

41
Q

What are indicators?

A

Indicators are substances that change color in response to changes in pH. They are used in titrations to determine the endpoint, which is the point at which the indicator changes color and signals that the reaction between the acid and base is complete. Different indicators have different pH ranges over which they change colour, allowing them to be used in different types of titrations.

42
Q

What is the Ka?

A

Ka, also known as the acid dissociation constant, is a measure of the strength of an acid in solution. It represents the equilibrium constant for the dissociation of the acid into its ions.

43
Q

What is the point of inflection?

A

Ka, also known as the acid dissociation constant, is a measure of the strength of an acid in solution. It represents the equilibrium constant for the dissociation of the acid into its ions.

44
Q

What are pH curves?

A

pH curves, also known as titration curves, are graphical representations of the pH changes that occur during a titration. They show the relationship between the volume of the titrant (acid or base) added and the resulting pH of the solution.

45
Q

What would happen if you use phenolphthalein as an indicator in a titration with a weak base?

A

Phenolphthalein would not function effectively as its pH range does not match the steep section of the titration curve with a weak base.

46
Q

What is the purpose of using an indicator in acid-base titrations?

A

In acid-base titrations, an indicator is used to determine the end point of the titration when an acid and alkali have completely reacted. The change in color of the indicator marks this point.

47
Q

What steps should be followed to ensure the accuracy of a pH meter in a titration experiment?

A

To ensure the accuracy of a pH meter in a titration experiment, you should begin by checking the accuracy of the pH meter by measuring the pH of a known buffer solution. Then, use a pH probe and calibrate it by immersing it in a standard buffer solution. Finally, maintain a consistent temperature throughout the experiment to enhance accuracy.

48
Q

What are the steps involved in performing a titration?

A

Perform a titration by transferring 25cm³ of acidic solution into a conical flask and measuring the initial pH using a pH meter. Gradually add small amounts of alkaline solution while recording the volume and pH values.

49
Q

How does the strength of the base used affect pH curves and titrations?

A

PH curves and titrations are affected by the strength of the base used. A buffer solution is formed when excess acid is added, stabilising the pH curve.

50
Q

How can a pH curve of a titration be created?

A

A pH curve of a titration can be created by measuring the pH using a calibrated pH meter and maintaining a consistent temperature.

51
Q

Why is it important to choose the right indicator for titrations?

A

Choosing the right indicator is crucial for titrations, as it should match the equivalence point and exhibit a color change within the appropriate pH range.

52
Q

What should be done to sketch a pH curve during a titration?

A

Sketch a pH curve based on the type of acid and base used, ensuring the equivalence point is at the center of the vertical section.

53
Q

What is the difference between the equivalence point and the neutral point in a titration?

A

The equivalence point is when the solutions are mixed in the correct amounts based on the equation’s proportions, while the neutral point is when the pH is 7

54
Q

What is the purpose of measuring the initial pH and recording the volume and pH values during a titration?

A

The purpose is to track the changes in pH as the alkaline solution is added and to determine the equivalence point.

55
Q

What is the role of Phenolphthalein in titrations?

A

Phenolphthalein is used only in titration with strong bases, not weak bases. It changes color from colourless acid to pink alkali.

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