Topic 7 Ideas About Science

• What needs to be considered when investigating a phenomenon scientifically

  1. Collect data

  2. Analyse data
• Hypothesis


  A possible explanation for something which has been observed
• Prediction


  A statement about how the effect of a factor will affect the outcome, based on the hypothesis
• Experiments


  Test the prediction
• Independent variable


  • The thing that you change in the experiment
• Dependent variable


  • The thing that you measure in the experiment
• Control variables


  • Things which must be kept constant throughout the experiments
• Control variables are important to ensuring a fair test
• Control variables must be kept the same throughout the experiments, otherwise they may affect the results of the experiment, making the experiment invalid
• Control variables when investigating the effect of light intensity on the rate of photosynthesis of pondweed

  • Species of pondweed
  • Carbon dioxide concentration
  • Temperature
  • Time allowed for gas formation
• Control variables are easy to control as it often just involves ensuring the reaction has been done for the same amount of time using a stopwatch, and using a water bath to control the temperature
• Sample size


  The number of measurements taken in an experiment
• Range of values


  The set of values that will be measured in an experiment
• When choosing a sample size or a range of values, it is important that it is big enough so that a reasonable correlation/conclusion can be taken from the results, but not too big that it will take an unnecessary amount of time for results to be collected and processed
• Appropriate equipment


  • Equipment that is suitable for the job and ensures the data is as precise, valid and accurate as possible
• The method must be clear, concise and repeatable - it is important that other people can recreate the experiment and get the same results
• Hazard


  Something which could cause harm
• Risk


  The chance that the hazard will cause harm
• Experimental hazards can involve chemicals, electricity, fire and glass
• It is important to identify all possible hazards in an experiment, so that procedures can be put in place to reduce the risk
• Reducing the risk


  Using lower concentrations of chemicals, putting a bunsen burner on a heat proof mat, and removing any glassware which is not in use
• When working with hydrogen peroxide, always wear safety glasses and gloves as it is an irritant. This will reduce the risk of the acid burning your skin and eyes
• Processes needed to draw conclusions from data

  1. Collect data

  2. Present data

  3. Analyse data
• Significant figures


  The number of digits in a measurement that are known with certainty
• Experimental measurements must all be taken to the same number of significant figures, and in any further calculations involving the results, the answers must be rounded to the lowest number of significant figures given
• IUPAC chemical nomenclature


  The worldwide system used for naming chemical compounds
• SI units


  The standard units used all over the world
• SI base units


  • Second, s
  • Metre, m
  • Joule, J
  • Kilogram, kg
• Prefixes


  Used to make the size of numbers easier to process
• Interconverting units


  Converting between different units
• Random errors


  Errors that occur due to changes in environmental conditions, a worn out measuring instrument, or a person taking an incorrect measurement
• Systematic errors


  Errors that are wrong by the same amount every time
• Anomalous result


  A result which does not fit the trend of the other results
• If there is a clear reason supporting an anomalous result, it should not be included in the processing of the results
• Tables


  • Used to organise data, must have a header and include units
• Bar charts


  • Used to present data split into categories, allow for easy comparison
• Graphs


  • Used to present continuous data, the dependent variable goes on the y-axis and the independent variable goes on the x-axis
• Range bars


  Lines drawn on a graph to indicate uncertainty or variation in the results
• Rate of reaction


  Can be calculated from the gradient of a graph if the amount of product formed/reactant used has been plotted against time
• Extrapolation


  Continuing the trend on a graph further to obtain more data points just outside the range