1. 1
   A student adds dilute nitric acid to a sample of an unknown white powder and immediately sees vigorous bubbling. The gas produced is passed into a test tube of limewater.

   (a)

   Which observation would confirm that the powder is a carbonate?

   [1 mark]

   • AThe limewater turns cloudy white
   • BA squeaky pop is heard from the gas
   • CThe limewater turns blue
   • DNo reaction is observed at all

   (b)

   Which gas is responsible for the bubbling and the observed change in the limewater?

   [1 mark]

   • AHydrogen
   • BOxygen
   • CCarbon dioxide
   • DChlorine

   (c)

   Write a word equation for the general reaction between a metal carbonate and an acid, and use this to explain why bubbling is observed when the acid is added to the unknown powder.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A geologist tests a rock sample by dropping dilute hydrochloric acid onto its surface, and observes fizzing along with a hissing sound.

   (a)

   Which conclusion can the geologist draw from this initial observation alone?

   [1 mark]

   • AThe rock definitely contains iron
   • BThe rock may contain a carbonate mineral, but this needs confirming
   • CThe rock is definitely pure calcium carbonate
   • DThe rock contains no carbon at all

   (b)

   To confirm the fizzing gas is carbon dioxide, the geologist directs the gas into a test tube of limewater using a delivery tube. What result would provide this confirmation?

   [1 mark]

   • AThe limewater stays completely clear
   • BThe limewater boils vigorously
   • CThe limewater changes from red to blue
   • DThe limewater turns cloudy/milky white

   (c)

   Explain why the geologist should not conclude the rock is a carbonate based on fizzing alone, without carrying out the limewater test.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A soil scientist wants to test whether a sample of agricultural soil contains chalk (calcium carbonate) added to reduce soil acidity, which would affect how much extra lime the farmer needs to add.

   (a)

   Describe the procedure the scientist should use to test the soil sample for the presence of carbonate.

   [3 marks]

   (b)

   The scientist observes only very faint, slow bubbling from the soil sample, making it hard to judge whether carbonate is genuinely present in a meaningful amount. Explain possible reasons for this weak result, and suggest how the scientist could adapt the experiment to obtain a clearer, more reliable conclusion.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A construction materials inspector needs to determine whether a delivery of building aggregate, meant to be crushed limestone (calcium carbonate), has been contaminated with a different, non-carbonate rock type, since this would affect the aggregate's suitability for making concrete.

   (a)

   Describe, in detail, a thorough testing procedure the inspector could use to check multiple samples from the delivery for the presence of carbonate.

   [6 marks]

   (b)

   Across the samples tested, the inspector finds that most give a strong positive carbonate result, but one sample from the bottom of a delivery pile gives only a very weak, barely-detectable result. Evaluate the significance of this single weak result, and discuss what further steps the inspector should take before deciding whether to accept or reject the entire delivery.

   [6 marks]

   Total for question 4: 12 marks

End of questions