Density and properties of matterIB MYP Chemistry: Subtopic test

1. 1
   A jeweller in Jaipur wants to check whether a small shiny bar is pure gold or a cheaper metal that looks similar. The bar is a cuboid measuring 2.0 cm by 1.5 cm by 2.5 cm. She finds its mass is 96.5 g.

   (a)

   What is the volume of the bar?

   [1 mark]

   • A6.0 cm³
   • B3.75 cm³
   • C7.5 cm³
   • D96.5 cm³

   (b)

   What is the density of the bar, to 3 significant figures?

   [1 mark]

   • A12.9 g/cm³
   • B0.078 g/cm³
   • C7.5 g/cm³
   • D104 g/cm³

   (c)

   Pure gold has a density of 19.3 g/cm³. Decide whether the bar is pure gold and justify your answer.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A student in São Paulo wants to find the density of an irregular piece of rock. She finds that the rock has a mass of 84 g. She half-fills a measuring cylinder with water and reads 50 cm³. She lowers the rock into the water on a thread and the water level rises to 82 cm³.

   (a)

   What is the volume of the rock?

   [1 mark]

   • A132 cm³
   • B32 cm³
   • C50 cm³
   • D82 cm³

   (b)

   Why does the student use displacement of water to find the volume of the rock?

   [1 mark]

   • AWater makes the rock heavier so it is easier to weigh
   • BDisplacement gives the mass of the rock
   • CThe rock must be wet before its density can be found
   • DThe rock has an irregular shape, so its volume cannot be calculated from simple length measurements

   (c)

   Calculate the density of the rock in g/cm³. Give your answer to 2 significant figures.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A student in Cape Town wants to find out how adding salt changes the density of water. She dissolves different masses of salt in 100 cm³ of water to make four solutions, all at the same temperature. For each solution she measures 50 cm³ in a measuring cylinder and finds the mass of the 50 cm³ sample using a balance.

   (a)

   Identify the independent variable, the dependent variable and one control variable.

   [3 marks]

   (b)

   The 50 cm³ samples had masses of 50.0 g (no salt), 53.2 g (10 g of salt), 56.0 g (20 g of salt) and 58.5 g (30 g of salt). Calculate the density of the solution with 30 g of salt, describe the trend in density, and suggest one way to improve the accuracy of the volume measurement.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   An engineer in Abu Dhabi is choosing a metal for the outer panels of a new skyscraper and compares three metals. Aluminium: density 2.7 g/cm³, resists corrosion, moderate price. Steel: density 7.9 g/cm³, strong and cheapest, but rusts unless it is painted regularly. Titanium: density 4.5 g/cm³, strong and resists corrosion, but very expensive. Each panel will be a flat rectangle 2.0 m long, 1.5 m wide and 4.0 mm thick.

   (a)

   Discuss the advantages and disadvantages of each metal for the outer panels, considering both physical and chemical properties and the economic and environmental implications. Reach a justified conclusion.

   [6 marks]

   (b)

   Calculate the mass of one aluminium panel. Give your answer in kg, in standard form.

   [6 marks]

   Total for question 4: 12 marks

End of questions