How Science Works
1
Lifestyle, health and risk
■ HSW 1.1: Criterion 5 – Water as a liquid at room temperature
Criterion 5: Analysis and interpretation of data to recognise correlations and causal relationships
Consider the water molecule, its properties and its physical state.
Water has a relative molecular mass (Mr) of only 18, yet it is a liquid at room temperature.
This is surprising; it contrasts with other small molecules, which are usually gases at such temperatures. Examples include methane (CH4, Mr ϭ 16), ammonia (NH3, Mr ϭ 17), and carbon dioxide (CO2, Mr ϭ 44). But, unlike water, none of these latter molecules contains hydrogen bonds.
In gases, molecules are widely spaced and free to move about independently. In liquids, molecules are closer together. The observation that water is liquid under conditions when similar molecular substances are gases provides evidence that in water it is hydrogen bonds that pull the molecules very close to each other.
As a result, at the temperatures and pressures that exist over much of the Earth’s surface, water is a liquid and provides a medium that is exploited by all forms of life.
■ HSW 1.2: Criteria 2, 3, 4, 5, 8 and 10 – The effects of temperature on heart rate in
Daphnia
Criterion 2: Using knowledge to pose scientific questions, define problems and present arguments and ideas
What knowledge of the biology of Daphnia is essential to the design of this experiment?
Criterion 3: Using appropriate methods to answer scientific questions and solve problems
Why are Daphnia cultures ‘pre-incubated’ for 5 minutes under specified conditions, prior to experimentation? Criterion 4: Risk management – laboratory work
Safety issues arise in all practical work, whether laboratory-based or field studies. In science laboratories there are a range of potential hazards that must be identified. Think about these, bearing in mind the experiment to be undertaken.
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List the common circumstances that
Lifestyle, health and risk
■ HSW 1.1: Criterion 5 – Water as a liquid at room temperature
Criterion 5: Analysis and interpretation of data to recognise correlations and causal relationships
Consider the water molecule, its properties and its physical state.
Water has a relative molecular mass (Mr) of only 18, yet it is a liquid at room temperature.
This is surprising; it contrasts with other small molecules, which are usually gases at such temperatures. Examples include methane (CH4, Mr ϭ 16), ammonia (NH3, Mr ϭ 17), and carbon dioxide (CO2, Mr ϭ 44). But, unlike water, none of these latter molecules contains hydrogen bonds.
In gases, molecules are widely spaced and free to move about independently. In liquids, molecules are closer together. The observation that water is liquid under conditions when similar molecular substances are gases provides evidence that in water it is hydrogen bonds that pull the molecules very close to each other.
As a result, at the temperatures and pressures that exist over much of the Earth’s surface, water is a liquid and provides a medium that is exploited by all forms of life.
■ HSW 1.2: Criteria 2, 3, 4, 5, 8 and 10 – The effects of temperature on heart rate in
Daphnia
Criterion 2: Using knowledge to pose scientific questions, define problems and present arguments and ideas
What knowledge of the biology of Daphnia is essential to the design of this experiment?
Criterion 3: Using appropriate methods to answer scientific questions and solve problems
Why are Daphnia cultures ‘pre-incubated’ for 5 minutes under specified conditions, prior to experimentation? Criterion 4: Risk management – laboratory work
Safety issues arise in all practical work, whether laboratory-based or field studies. In science laboratories there are a range of potential hazards that must be identified. Think about these, bearing in mind the experiment to be undertaken.
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List the common circumstances that