1. 1
   A soft drinks manufacturer dissolves sugar in water to make a flavoured syrup solution, then dilutes samples of this solution to test different sweetness levels before scaling up production.

   (a)

   A soft drinks manufacturer dissolves 40 g of sugar in water to make exactly 2 dm3 of a flavoured syrup solution for quality testing. What is the concentration of the sugar solution, in g/dm3?

   [1 mark]

   • A20 g/dm3
   • B80 g/dm3
   • C40 g/dm3
   • D2 g/dm3

   (b)

   The manufacturer then takes 500 cm3 of the 20 g/dm3 syrup solution for a smaller taste-test batch. Which statement correctly describes the concentration of this smaller sample compared with the original solution?

   [1 mark]

   • AThe concentration becomes zero because no more sugar is added to the smaller sample
   • BThe concentration decreases to 10 g/dm3 because only half the volume was taken
   • CThe concentration doubles to 40 g/dm3 because a smaller volume was taken
   • DThe concentration remains 20 g/dm3, because concentration does not depend on the volume of solution taken

   (c)

   Calculate the mass, in grams, of sugar present in the 500 cm3 sample taken from the syrup solution of concentration 20 g/dm3. (Note: 500 cm3 = 0.5 dm3.)

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A hospital pharmacy technician prepares an intravenous fluid solution containing a medicinal salt, following strict dosing guidelines, before doctors decide how much of the solution to administer to a patient.

   (a)

   A hospital pharmacy technician dissolves 15 g of a medicinal salt in water to make exactly 3 dm3 of an intravenous fluid solution, following strict dosing guidelines. What is the concentration of this solution, in g/dm3?

   [1 mark]

   • A15 g/dm3
   • B45 g/dm3
   • C5 g/dm3
   • D0.2 g/dm3

   (b)

   A doctor needs to administer exactly 10 g of the medicinal salt to a patient using the 5 g/dm3 solution prepared by the technician. Which calculation correctly finds the volume of solution, in dm3, that must be administered?

   [1 mark]

   • AVolume = mass x concentration = 10 x 5 = 50 dm3
   • BVolume = mass / concentration = 10 / 5 = 2 dm3
   • CVolume = concentration / mass = 5 / 10 = 0.5 dm3
   • DVolume = mass - concentration = 10 - 5 = 5 dm3

   (c)

   The doctor decides to administer 1.5 dm3 of the 5 g/dm3 medicinal salt solution to a different patient. Calculate the mass, in grams, of medicinal salt this patient will receive.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   An environmental scientist is testing river water samples for dissolved salt pollution downstream of a road-gritting site, comparing results from two different sampling points along the river to assess how salt levels change with distance from the road.

   (a)

   An environmental scientist is testing river water for dissolved salt pollution downstream of a road-gritting site. She dissolves the salt residue collected by evaporating 4 dm3 of river water and finds it has a mass of 0.8 g. Calculate the concentration of dissolved salt in the original river water sample, in g/dm3, showing your working.

   [3 marks]

   (b)

   At a second sampling point further downstream, the scientist collects 2.5 dm3 of river water and evaporates it, finding a salt residue of mass 0.3 g. Calculate the concentration of dissolved salt at this second point, and explain, using your two calculated concentration values, whether the data suggests the river dilutes the road-gritting salt as it flows further from the road.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A water treatment plant manager is training new staff on how disinfectant is added to reservoirs of very different sizes, to ensure the treated drinking water supplied to the local town is always both safe and effective against harmful microorganisms.

   (a)

   A water treatment plant manager needs to explain to new trainees why measuring the concentration of a chemical (mass per given volume of solution, such as g/dm3) is essential when adding disinfectant to a large reservoir, rather than simply adding a fixed mass of disinfectant regardless of the reservoir's volume. Explain fully, using the concept of concentration, why the relationship between mass of solute and volume of solution is important for making sure the treated water is both safe to drink and effective at killing harmful microorganisms, and describe what could go wrong if concentration were ignored.

   [6 marks]

   (b)

   The plant manager presents trainees with data showing that Reservoir X, with a volume of 5000 dm3, was treated with 2500 g of disinfectant, while Reservoir Y, with a volume of 2000 dm3, was treated with 1600 g of disinfectant. Using concentration calculations, evaluate which reservoir, if either, is likely to have received a more effective and appropriate treatment, given that the target safe concentration for this disinfectant is stated to be between 0.6 g/dm3 and 0.9 g/dm3.

   [6 marks]

   Total for question 4: 12 marks

End of questions