OCR alevel chemistry module 5

• How does measuring pH help in monitoring the progress of a reaction?

  Measuring pH helps determine the change in concentration of H+ ions during the reaction.
• What instrument can be used to measure the pH of a substance at regular intervals?

  A pH meter can be used for this purpose.
• How can mass loss be used to measure the rate of a reaction?

  Mass loss can indicate the amount of gas produced during a reaction.
• What is a common method to measure the volume of gas produced in a reaction?

  A gas syringe can be used to measure the volume of gas produced.
• Why is it important to set up the gas syringe correctly during an experiment?

  Incorrect setup can lead to gas escaping and inaccurate measurements.
• What is the ideal gas equation used for in the context of measuring reaction rates?

  The ideal gas equation is used to calculate the number of moles of gas produced in a reaction.
• What is a colorimeter used for in measuring reaction rates?


  A colorimeter measures the absorptivity of light in a colored sample to monitor concentration changes.
• What is the common reaction example given for using a colorimeter?

  The reaction between propanone and iodine is a common example.
• How does the concentration of iodine affect the absorbance measured by a colorimeter?

  As the concentration of iodine increases, the absorbance also increases.
• How can a calibration curve be used in conjunction with a colorimeter?


  A calibration curve allows for the determination of unknown concentrations based on measured absorbance.
• What is the significance of drawing a line of best fit on a graph of reaction rates?

  The line of best fit helps to visualize the overall trend in the data collected during the reaction.
• How is the gradient of a graph related to the rate of reaction?

  The gradient of the graph represents the change in volume of gas produced over time, indicating the rate of reaction.
• What type of content is available on the Alibi Chemistry channel?

  Free videos for revision
• What is the formula for calculating the gradient of a line on a graph?

  The gradient is calculated as the change in Y over the change in X.
• What does the term "dynamic equilibrium" refer to in chemistry?

  It refers to the state where the rate of the forward reaction equals the rate of the backward reaction
• In what type of system does dynamic equilibrium occur?

  In a closed system
• What are the units for measuring the rate of reaction when using a gas syringe?

  The units are typically centimeters cubed per minute.
• What is the difference between concentration and amount of reactants and products at dynamic equilibrium?

  The concentration remains constant, but the amount of reactants and products may differ
• How do you find the initial rate of a reaction from a graph?

  The initial rate is found by calculating the gradient of the tangent at zero minutes on the graph.
• What is the equilibrium constant denoted as?

  • The equilibrium constant is denoted as $K_c$.
  • It is calculated from the molar concentrations of reactants and products.
• What is the challenge of calculating the gradient from a curved graph?

  The gradient changes along the curve, requiring the use of a tangent to find the rate at a specific point.
• How do you write the $K_c$ expression for the reaction $2a +$$b \rightleftharpoons 2c +$$d$?


  $K_c =$$\frac{[c]^2[d]}{[a]^2[b]}$
• What should you do if the graph is squashed into a small area of the paper?

  You should try to use a larger section of the graph paper to improve readability and reduce errors.
• What do square brackets indicate in the context of $K_c$ expressions?


  Square brackets indicate the concentration of a species
• What is the significance of the term "initial rate" in the context of reaction rates?

  The initial rate refers to the rate of reaction at the very beginning of the reaction.
• Given the reaction $2SO_2 +$$O_2 \rightleftharpoons 2SO_3$, how would you express $K_c$?


  $K_c =$$\frac{[SO_3]^2}{[SO_2]^2[O_2]}$
• Why is it important to have a tolerance when calculating the gradient of a tangent?

  A tolerance is important because it accounts for the difficulty in obtaining exact figures from experimental data.
• What is the main difference between homogeneous and heterogeneous systems in terms of $K_c$?


  In homogeneous systems, all reactants and products are in the same state, while in heterogeneous systems, some are in different states
• For the reaction $C_{(s)} +$$O_{2(g)} \rightleftharpoons CO_{2(g)}$, what is the $K_c$ expression?


  $K_c =$$\frac{[CO_2]}{[O_2]}$
• Why are solids and pure liquids not included in the $K_c$ expression for heterogeneous reactions?


  Because their concentrations remain constant and do not affect the equilibrium
• How do you calculate the equilibrium concentrations using the ICE method?

  • I: Initial moles of each species
  • C: Change in moles during the reaction
  • E: Equilibrium moles after the reaction
• How do you calculate the number of moles of a substance from its mass and molar mass?

  Number of moles = mass / molar mass
• In the reaction $2NO_2 \rightleftharpoons 2NO +$$O_2$, how do you determine the change in moles for each species?


  By using the stoichiometry of the reaction and the initial moles
• If you have 33.2 grams of nitrogen dioxide (NO2) and its molar mass is 46 g/mol, how many moles do you have?

  0.72 moles
• How do you find the number of moles of oxygen (O2) at equilibrium if you have 6.88 grams?

  By dividing 6.88 grams by the molar mass of O2, which is 32 g/mol
• What does the acronym ICE stand for in the context of equilibrium calculations?

  Initial, Change, Equilibrium
• What is the initial rate of a reaction defined as?

  The initial rate is the rate right at the start of the reaction.
• How do you determine the change in moles for reactants and products during a reaction?

  By observing the stoichiometric coefficients in the balanced equation
• How can the initial rate be determined?

  The initial rate can be found using the gradient of a tangent at zero minutes.
• At what time is the tangent used to find the initial rate?

  The tangent is taken at zero minutes, right at the start of the reaction.