Experimental Design | Chemistry for Grade 11 (IGCSE) PDF Download

Time

• Time can be gauged using either a stopwatch or a stopclock, typically accurate to one or two decimal places.
• Common time units include seconds or minutes, though different units may be utilized for very slow reactions, such as rusting.
• 1 minute is equivalent to 60 seconds.

Temperature

• Temperature is determined using a thermometer or a digital probe.
• Laboratory thermometers usually offer a precision of half or one degree.
• Digital temperature probes, more accurate than traditional thermometers, often provide readings to 0.1 degrees Celsius.
• Traditional thermometers function based on the uniform expansion and contraction of a liquid substance with temperature, while digital probes can be equally or more precise.
• The standard unit of temperature is degrees Celsius (ºC).

Mass

• Mass is assessed using a digital balance, typically providing measurements to two decimal places.
• Balances need to be zeroed (tared) prior to usage.
• The primary unit of mass is kilograms (kg), although grams (g) are predominantly used in chemistry.
• 1 kilogram equals 1000 grams.

Volume - Liquids

• Determining the volume of a liquid depends on the required level of accuracy, and various apparatus are available for this purpose.
• For approximate volumes where high accuracy isn't crucial, measuring cylinders are employed.
• These cylinders are graduated, featuring a scale for measurement, and are typically offered in sizes ranging from 10 cm³ to 1 liter (1 dm³).
• Volumetric pipettes offer the most precise method for measuring a fixed liquid volume, usually 10 cm³ or 25 cm³.
• They include a scratch mark on the neck, aligned with the bottom of the meniscus for measurement.
• Burettes provide the most precise means of measuring a variable liquid volume between 0 cm³ and 50 cm³, commonly used in titrations.
• When using burettes, it's important to read the scale from top to bottom, with 0.00 cm³ positioned at the top of the column.
• Regardless of the apparatus used, markings may appear in milliliters (ml), equivalent to cubic centimeters (cm³).
• Diagram of a burette with conical flask and pipette with filler:
  

Volume-gases

• Gas volume measurement often requires collecting the gas in a graduated measuring device.
• Typically, a gas syringe serves as the primary apparatus for this purpose.
• Alternatively, an inverted graduated cylinder submerged in water may suffice, as long as the gas is not water-soluble.
• In instances where the gas is heavier than air and has coloration, the cylinder may be used in an upright position.
• Diagram of the set-up for an experiment involving gas collection:
  

Advantages & Disadvantages of Methods & Apparatus

• In laboratory settings, there are often various options for performing a particular task.
• Selecting the most suitable apparatus is essential for effective experimental planning and design.
• This involves understanding the advantages and disadvantages associated with different laboratory equipment.

Planning your method

• Effective experimental design involves addressing key questions such as:
  • Have I selected the right equipment for the measurement I intend to make?
  • Will the chosen equipment provide results within a reasonable timeframe?
  • Will it yield sufficient data for analysis and drawing conclusions?
  • Does it allow for repeated trials to assess result reliability?
  • Does my experimental plan encompass a suitable range of outcomes?
  • How can I ensure the accuracy of my results?
  • Have I opted for appropriate quantities without being wasteful or compromising safety?
• Exam questions may inquire about experimental methodologies, and your familiarity with practical chemistry techniques can help identify errors and propose enhancements.