chemistry paper 2 2023

• What gas is produced during the reaction between zinc and sulfuric acid?

  Hydrogen gas
• Why must a stopper be inserted into the conical flask as quickly as possible?

  To prevent the escape of hydrogen gas
• Describe the process by which hydrogen gas is collected in the experiment

  • Hydrogen gas is produced from the reaction of zinc and sulfuric acid
  • The gas travels through a delivery tube
  • The gas enters a measuring cylinder
  • Bubbles of gas displace water
  • The volume of hydrogen gas collected is measured in the measuring cylinder
• What is the unit of rate of reaction used in Table One?

  $\text{cm}^{3} \text{ per second}$
• How is the mean rate of reaction calculated when one result is anomalous?

  • Identify any anomalous results
  • Exclude the anomalous results from the data set
  • Calculate the sum of the remaining values
  • Divide the sum by the number of remaining values
• What equation is used to calculate the rate of reaction?

  Rate = Volume / Time
• What is the mean time taken to collect $20 \text{ cm}^{3}$ of gas in seconds?


  25 seconds
• What two changes would increase the mean time taken to collect $20 \text{ cm}^{3}$ of gas?


  • Using sulfuric acid of a lower concentration
  • Using a lower temperature
• What term describes a gas not fitting the general pattern in a set of data?

  Anomalous
• How does changing the concentration of sulfuric acid affect the rate of reaction?

  • Lower concentration: Fewer reactant particles, slower rate, longer time to collect $20cm^{3}$
  • Higher concentration: More reactant particles, faster rate, shorter time to collect $20cm^{3}$
• What effect does temperature have on the rate of reaction?

  • Higher temperature: More collisions, faster rate, shorter time to collect $20cm^{3}$
  • Lower temperature: Fewer collisions, slower rate, longer time to collect $20cm^{3}$
• What is the test for hydrogen gas?

  Burning splint
• What result is expected when a burning splint is used with hydrogen gas?

  Squeaky pop sound
• How does the energy released per gram vary with the number of carbon atoms in an alcohol molecule?

  • The energy released per gram generally increases with the number of carbon atoms
  • More carbon atoms lead to more energy stored in the bonds, resulting in more energy released when burned
• What is the energy released per gram of heptanol?

  38.9 KJ per gram
• What is the energy released per gram of ethanol?

  29.6 KJ per gram
• What mass of ethanol must be burned to release the same amount of energy as burning 1 gram of heptanol?

  1. 34 grams
• What is the general trend observed when plotting the energy released per gram of alcohol versus the number of carbon atoms?

  The energy released per gram generally increases with the number of carbon atoms
• Estimate the energy released when one gram of octanol is burned

  • Draw a line of best fit on Figure Two
  • Find where the line intersects the x-axis at 8 carbon atoms
  • Read the corresponding y-value to estimate the energy released per gram
• What is the expected range for the energy released when one gram of octanol is burned?

  40.4 to 40.8 KJ per gram
• When carbon dioxide is bubbled through lime water, what color change occurs?

  The lime water turns cloudy or milky
• What compound is lime water a solution of?

  Calcium hydroxide
• What is the group in ethanoic acid?

  $\text{COOH}$
• What functional group is present in ethanol?

  $\text{-OH}$
• How does ethanoic acid differ structurally from ethanol?

  • Both contain carbon and hydrogen atoms
  • Ethanoic acid has an additional oxygen atom in the carboxyl group
• What reagent is used to convert ethanol to ethanoic acid?

  • An oxidizing agent
• What are the products when ethanol reacts with ethanoic acid?

  • Ester: ethyl ethanoate
  • Water
• What are the products when ethanoic acid reacts with sodium carbonate?

  • Salt: sodium ethanoate
  • Water
  • Carbon dioxide
• What are the three common gas tests?

  Hydrogen, oxygen, carbon dioxide
• How is chlorine gas identified?

  By reacting it with halogens
• What are the main steps involved in a flame test for potassium ions?

  • Place the sample on a clean metal wire
  • Dip the wire into the hottest part of the Bunsen flame
  • Observe the color of the flame
• What color flame is observed for potassium ions in a flame test?

  Lilac
• What two ions must a chemist demonstrate the presence of in a medicine sample containing potassium bromide?

  • Potassium ions $(K^{+})$
  • Bromide ions $(Br^{-})$
• What pieces of equipment are necessary to perform a flame test?

  • Bunsen burner
  • Metal wire
• What are the equipment requirements for a flame test used to detect cations?

  • Bunsen burner
  • Metal wire
• Why is the metal wire used in a flame test made as clean as possible?

  To prevent the sample from being contaminated, ensuring that the flame test result is only for the target ions and nothing else.
• What chemical is used to clean the metal wire before a flame test?

  Hydrochloric acid or another strong acid.
• What is the first step in performing a flame test?

  Add the sample to the metal wire.
• Which part of the Bunsen flame should the sample on the metal wire be placed into?

  The hottest part, which is the blue area.
• What flame color indicates the presence of potassium ions in a flame test?

  Lilac flame.