Term 2

• Method on how to obtain red cabbage indicator:

   1. Tear the red cabbage leaf into small pieces.

   2. Put the red cabbage into the mortar with a little sand.  Grind the cabbage with the pestle.

  3. Put the red cabbage into a beaker and about 100cm3 of water and heat.

   4.  Filter the mixture and collect the filtrate.  Save this for testing.

  5. Put a small amount of a chemical in a clean test tube.  Add a few drops of the red cabbage indicator.
• Colour of indicator when testing:

  Sodium hydroxide: yellow

  Ammonia: green

  Tap water: purple

  Ethanoic acid: pink

  Hydrochloric acid: red

  Sodium carbonate: green
• Colour chart of the universal indicator:


  Colour chart:

  
• Colour chart of red cabbage indicator: 


  Colour chart:

  
• Extraction is the process of removing or obtaining something from a source, often by separating it from other substances.
• Why was the crushed cabbage heated with water?

  The crushed cabbage was heated with water to extract the pigments from the cabbage, which are responsible for the color change in the red cabbage indicator.
• Name the method used to separate the leaves from the solution of the indicator.

  The method used to separate the leaves from the solution of the indicator is filtration.
• What colour would you expect the red cabbage indicator to become in aqueous potassium hydroxide which has a pH of 13? 

  In aqueous potassium hydroxide with a pH of 13, the red cabbage indicator would likely turn a deep blue or purple color.
• What colour would you expect the red cabbage indicator to become in aqueous nitric acid which has a pH of 1? 

  In aqueous nitric acid with a pH of 1, the red cabbage indicator would likely turn a bright red or orange color.
• If a solution turned the red cabbage indicator yellow, what effect would it have on Universal Indicator?

  If a solution turned the red cabbage indicator yellow, it would likely indicate that the solution is acidic. Universal Indicator would also likely show a similar acidic response, displaying colors in the red to orange range to indicate acidity.
• Word equation for Neutralisation:

   ALKALI  +  ACID                →           SALT  +  WATER
• Neutralisation is a chemical change.

  When an acid and an alkali are mixed together they react to make new chemicals. These chemicals are a salt and water (a salt is a type of chemical that is related to an acid and is usually made from acids.
• If the acid and alkali are added in the exact amounts so that no acid or alkali is left over, and only a salt and water are present, then the pH will be 7 and the solutions have been neutralised (made neutral).
• Reacting an Acid and an Alkali to Show neutralisation

  Method:

  1. Place 20 cm3 of ethanoic acid in a beaker and add 10 drops of universal indicator. Note down the colour and pH.
  2. Add 5 cm3 of sodium carbonate solution. Stir until the bubbling stops. Note the colour of the indicator and the pH.

     3. Repeat step 2, adding 5 cm3 portions until a total of 40 cm3 of the sodium carbonate has been added.
• Estimate the volume of sodium carbonate that you would need to add to make the solution neutral.

  20 cm3
• This reaction produced bubbles of carbon dioxide (CO2) gas. How would you identify the gas?

  Bubble the gas through limewater. The limewater turns milky white.
• DETERMINING THE PERCENTAGE OXYGEN IN THE AIR

  This technique involves passing a known volume of air over a heated metal which reacts with and therefore removes the oxygen from the air.

  Two gas syringes are connected together with a delivery tube. In the tube is some freshly cut copper metal. In one gas syringe there is 100cm3 of air; the other is empty.
• Diagram for determining the percentage of oxygen in the air 


  Diagram:

  
• Method for DETERMINING THE PERCENTAGE OXYGEN IN THE AIR:

  1. Set up the apparatus so that there is 100 cm3 of air in one gas syringe and none in the other.
  2. Heat the copper metal strongly using the blue Bunsen flame and pass the air in the syringe slowly back and forth over the heated metal.
  3. Note the volume of air each time you pass the air over the metal and continue until the volume no longer decreases.
  4. Leave the apparatus to cool for a few minutes and read of the final volume of gas left in the syringe.
• Results from the DETERMINING THE PERCENTAGE OXYGEN IN THE AIR practical.

  (i)  VOLUME OF AIR AT START = 100 cm3

  (ii)  VOLUME OF AIR AT END = 80 cm3

  (iii)  THEREFORE VOLUME OF OXYGEN REMOVED = 20 cm3

  iv)    THEREFORE % OXYGEN =  20%

   

  The 80cm3 of gases left in the syringes are called the RESIDUAL GASES.
• Use the results below to calculate the % of oxygen in the air:

  VOLUME OF AIR AT START = 60cm3

  FINAL VOLUME OF AIR = 50cm3

  THEREFORE VOLUME OF OXYGEN = 10 cm3

  % OF OXYGEN IN AIR = 16.7%

  Why is this value less than expected?

  Not all of the oxygen has been removed.

  What error might the student have made during the procedure?

  The apparatus was not heated until the volume stopped going down.
• How does copper change its appearance during the DETERMINING THE PERCENTAGE OXYGEN IN THE AIR

  experiment?

  From: brown

  To: black
• Write a word equation for the reaction – DETERMINING THE PERCENTAGE OXYGEN IN THE AIR practical

  copper + oxygen → copper ll oxide
•  How does the copper change in mass in the DETERMINING THE PERCENTAGE OXYGEN IN THE AIR experiment?

  It increases in mass.
• Give a use for each of the following gases;

  
  

  Carbon dioxide:  for fizzy drinks and fire extinguishers

  Argon: to fill light bulbs
•  Describe an alternative method of finding the percentage of oxygen in the air.

  Rusting iron in a gas jar: When the iron rusts, it reacts with the oxygen and water vapour from air. As the oxygen is used up a vacuum is created. The water level inside the gas jar rises upwards to take the place of the used up oxygen.

  The water level at the start and end of the experiment are marked on the scale. This shows how much oxygen is used up and can be used to calculate the % of oxygen in air.
•  Describe another alternative method of finding the percentage of oxygen in the air.

  The Burning of a Candle in a Glass jar

  1. Prepare the gas jar by marking a scale on it.

  2. Fill the water bowl 1/2 with water.

  3. Place a candle in a crucible on the water surface.

  4. Light the candle

  5. Invert the gas jar over the candle.

  6. Mark the starting water level on the scale.

  7. Wait till the candle extinguishes, marking the new water level.

  8. Use the scale to find the percentage of oxygen in the air using the formula: Percentage of Oxygen= (Finish Level – Start Level) × 100 / Total on scale
• What is the chemical name of rust?

  Hydrated Iron (lll) oxide
• A candle is made from a compound that contains the elements carbon and hydrogen. Name two gases that could form when a candle burns.

  Carbon dioxide and water vapour
• Hydrogen peroxide dissolved in water makes a colourless solution. Hydrogen peroxide slowly decomposes to make water and the colourless gas OXYGEN.

  HYDROGEN PEROXIDE → WATER + OXYGEN

  The reaction can be made much faster by adding the black solid compound, MANGANESE (IV) OXIDE. 
• The apparatus for the Laboratory Preparation of Oxygen.

  Diagram:

  
• Method for the laboratory preparation of oxygen:

  1. The apparatus is set up as in the diagram with some hydrogen peroxide in the flask.

  2. A spatula full of manganese (IV) oxide is added to the hydrogen peroxide.

  3. The gas is collected over water.

  4. After collecting the gas hold a glowing splint in it and note down the result.
• What is the colour of oxygen gas?  

  colourless
• What is the symbol for oxygen? 

  O
• What is the formula of oxygen gas? 

  02
• Oxygen gas exists as diatomic molecules. What does this mean?

  Made up by two atoms
• Which gas forms the major part of the air?  

  nitrogen
• This gas (nitrogen) is inert. What does this mean?

  It's nonreactive.
• This is a list of the apparatus used in this Manganese (IV) Oxide Catalyses the Decomposition of Hydrogen Peroxide.

  experiment

  Filter paper, test-tube with manganese (IV) oxide, filter funnel, 250cm3 beaker, 250cm3 conical flask, measuring cylinder, hydrogen peroxide solution, crystallising dish.
• Method for Showing that Manganese (IV) Oxide Catalyses the Decomposition of Hydrogen Peroxide.

  1. Measure 25cm3 of hydrogen peroxide into a beaker.

  2. Place manganese (IV) oxide on filter paper and weigh together.

  3. Add manganese (IV) oxide to hydrogen peroxide solution.

  4. Filter mixture, ensuring all manganese (IV) oxide is captured.

  5. Let filter paper dry for 10-15 minutes.

  6. Label and store filter paper with manganese (IV) oxide in a crystallizing dish in a fume cupboard.

  7. Retrieve filter paper next week and weigh again.