# Particle model of matter - Six-mark questions

Six-mark questions are extended open response questions. These require longer answers than the structured questions with fewer marks. It is wise to plan your answer rather than rushing straight into it, otherwise you may stray away from the key points.

Six-mark questions are marked using a levels-based mark scheme because they are open ended. To gain full marks, you need to:

• support explanations using scientific knowledge and understanding
• use appropriate scientific words and terms
• write clearly, linking ideas in a logical way
• maintain a sustained line of reasoning, rather than getting lost or bogged down

You are likely to see command words such as:

• 'Describe' - you need to give an account but no reason
• 'Explain' - you must give reasons or explanations
• 'Devise' - you must plan or invent a procedure using your scientific knowledge and understanding
• 'Evaluate' - you must review information, including identifying strengths and weaknesses, and make a supported conclusion

Six-mark questions may be synoptic questions. These questions bring together ideas from two or more topics. For example, a question about atoms could include ideas about atomic structure, isotopes, radiation and nuclear reactions. Remember that the topics covered in the first paper are assumed knowledge for the second paper, so questions in the second paper may need knowledge and understanding of those topics too.

The answers shown here give marking points as bullet points. You do not usually need to include all of them to gain six marks, but you do need to write in full sentences, linking them logically and clearly.

Questions courtesy of Eduqas.

## Sample question 1 - Foundation

Question

A tree surgeon carries out an experiment on fir trees to find out whether or not they are diseased.

The tree surgeon needs to find the density of an irregular small piece of wood. He uses a method illustrated below to find the density of the piece of wood.

Describe how you would find the density of the wood sample from the information given in the diagrams. [6 marks]

The mass of wood sample is measured = 74.5 - 62.5 = 12 g.

An object that sinks must be used because wood floats on water.

The volume of the dense block = 72 - 62 = 10 cm3.

The volume of wood sample and dense block = 87 - 62 = 25 cm3.

Therefore the volume of the wood sample = 25 - 10 = 15 cm3 OR the volume of the wood sample = 87 - 72 = 15 cm3.

Density is calculated by: density = mass ÷ volume = 12 ÷ 15 = 0.8 g/cm3.

Answering tip: Briefly plan the key points you want to include in your answer. For example:

• you need to find the mass of the piece of wood
• you need to find the volume of the piece of wood
• use the equation for density
• describe each stage in your calculation

## Sample question 2 - Higher

Question

A gas is at constant temperature. Explain in terms of molecular motion and collisions why the pressure changes in the way it does if the volume is increased. What is the relationship between the volume and pressure? [6 marks]

As the volume increases, the molecules have further to travel between collisions with the container therefore they take a longer time to travel, so the rate of change of momentum is reduced. This reduces the force from any one molecule when in collision with the walls. Since pressure = force ÷ area, the decrease in the force gives a reason for a decrease in pressure. As the temperature remains constant, the pressure will halve as the volume doubles because pV = constant.

Answering tip: Briefly plan the key points you want to include in your answer. For example:

• consider the distance moved by the particles
• consider the force of the particles hitting the sides
• use the equation for pressure in your explanation
• use another formula from the list to describe the relationship