Acids, alkalis and indicatorsIB MYP Chemistry: Subtopic test

1. 1
   Students at a school in Singapore test four household liquids with litmus paper: lemon juice, vinegar, soapy water and oven cleaner.

   (a)

   What colour does blue litmus paper turn in lemon juice?

   [1 mark]

   • ARed
   • BIt stays blue
   • CGreen
   • DIt turns colourless

   (b)

   Which ion is present in larger amounts in all acidic solutions?

   [1 mark]

   • AOH⁻
   • BCl⁻
   • CNa⁺
   • DH⁺

   (c)

   Soapy water is an alkali. State what happens to red litmus paper in soapy water and name the ion that makes the solution alkaline.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A student compares two acids of the same concentration. Hydrochloric acid turns universal indicator red, but ethanoic acid turns it orange-yellow. When identical strips of magnesium ribbon are added, bubbles of gas appear much faster in the hydrochloric acid than in the ethanoic acid.

   (a)

   Which conclusion is best supported by the results?

   [1 mark]

   • ABoth acids are strong acids
   • BHydrochloric acid is a strong acid and ethanoic acid is a weak acid
   • CEthanoic acid is more concentrated than hydrochloric acid
   • DEthanoic acid is an alkali

   (b)

   Which gas is produced when magnesium reacts with an acid, and how is it identified?

   [1 mark]

   • AOxygen, it relights a glowing splint
   • BCarbon dioxide, it turns limewater milky
   • CHydrogen, it burns with a squeaky pop
   • DHydrogen, it bleaches damp litmus paper

   (c)

   Identify two control variables that the student must keep the same for a fair comparison of the two acids.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A science teacher in Nairobi makes an indicator by boiling red cabbage leaves in water. She adds a few drops to three colourless liquids: lemon juice turns it pink, distilled water leaves it purple, and a solution of washing soda turns it green. Later, the class compares the cabbage indicator with litmus paper and universal indicator.

   (a)

   State what the results show about each of the three liquids.

   [3 marks]

   (b)

   Explain why universal indicator gives more information than litmus paper when testing the liquids.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A lake in a mountainous region of Sweden has been affected by acid rain, which is caused by gases released from factories and power stations. Universal indicator turns orange in the lake water and many fish have died. The local authority sprays powdered limestone, which is a base, over the lake. Some residents say this is a sensible fix, while others say the factories' emissions should be cut instead.

   (a)

   Explain what the universal indicator result shows about the lake water and how adding limestone changes the water.

   [6 marks]

   (b)

   Evaluate adding limestone to the lake compared with cutting the factory emissions that cause acid rain.

   [6 marks]

   Total for question 4: 12 marks

End of questions