1. © SSER Ltd. How Science Works Selecting & Using Apparatus

2. Calibration All measuring instruments are calibrated by the manufacturer.  Attaching an appropriate scale to the instrument, e.g. this ruler is calibrated in millimetres... Calibration by the manufacturer involves:  Checking and adjusting the accuracy of the instrument throughout the range of values that it is supposed to measure.

3. Some measuring instruments need to be calibrated before use. Example: You need to check that a balance is set to zero. If this is not done properly, all subsequent readings will be incorrect. Calibration

4. A very sensitive balance is needed - one which measures in grams or milligrams. To measure the change in mass that occurs in a chemical reaction, bathroom scales would not be sensitive enough. Selecting Appropriate Apparatus “When you select apparatus to use in an investigation, you must select the most appropriate one.”

5. The sensitivity of a measuring instrument is the smallest difference that it can detect and display. A more sensitive instrument that is calibrated properly will be more precise. Accuracy, Precision & Sensitivity Precision in instruments is about the quality and reliability of the instrument. A more precise instrument will give closer readings for repeated measuring of the same value of a variable. Precise instruments lead to precise measuring. Accuracy is how close the measured value is to the true value. We don’t know what the true value is, but we do know how to improve accuracy. Greater accuracy results from using a properly calibrated, quality instrument. The more precise and sensitive the instrument, the greater the accuracy it can produce.

6. The smallest division on the scale must be smaller than the value you are trying to measure. Take the measurements as carefully as possible, using the proper technique. Repeat the measurements three times and use the mean as the result. Accuracy, Precision & Sensitivity In order for you to measure accurately and precisely: The instrument needs to be calibrated in the units that you are measuring to, e.g.  If you are trying to measure to the nearest degree, then the thermometer you use should be calibrated in degrees.

7. Choosing Appropriate Units The units that you use to measure, should be appropriate for the variable being measured… Select the most appropriate unit for the following tasks...

8. Measuring Cylinders

9. When designing an investigation, it is important that you select the most appropriate apparatus. This means selecting the apparatus that will provide you with the appropriate level of accuracy. Suppose you have been asked to measure out 7.5cm 3 of water as accurately as possible. To do this you have been provided with three measuring cylinders. Selecting a Measuring Cylinder All three measuring cylinders would hold the 7.5cm 3 of water that you need to measure out...

10. Which measuring cylinder will you use? Selecting a Measuring Cylinder

11. Before using a measuring cylinder, it is important you know how to use one properly.  The level of the liquid is not completely flat - it curves up slightly at the sides of the cylinder. The surface forms a meniscus. Using a Measuring Cylinder  Stand it on a flat surface.

12. Before using a measuring cylinder, it is important you know how to use one properly.  You then read the volume at the bottom of the meniscus, as shown above.  The level of the liquid is not completely flat - it curves up slightly at the sides of the cylinder. The surface forms a meniscus. Using a Measuring Cylinder  Make sure that your eye is level with the surface of the meniscus.  Stand it on a flat surface.

13. Complete the volume readings in the spaces below... Using a Measuring Cylinder

14. Burette

15.  The volume in a burette is read from the bottom of the meniscus, as with a measuring cylinder. Burette A burette can be used to measure volumes of liquids.  The scale reads downwards - not upwards, because as you open the tap at the bottom, the liquid exits. The reading on the scale tells you how much liquid you have used.  Each small division is worth 0.1cm 3. This instrument provides a very accurate volume measurement.  The burette must be set properly before use. This is done by filling the burette to above the 0cm 3 line and then letting the liquid flow out of the burette. Care must be taken to let the meniscus settle on a reading such as 0cm 3.

16. Thermometer

17.  Digital - usually given to two decimal places Thermometer There are three main types of thermometer:  Alcohol - each small division is usually worth 1 º C  Mercury - each small division is usually worth 1 º C “When you are measuring the temperature using a thermometer, it is important that you use a thermometer with an appropriate level of sensitivity.”

18. Choosing a Thermometer

19. Stop Clock There are a whole range of stop clocks and watches available. Many are sensitive to the nearest millisecond. “When timing an experiment, you need to record the time using a timepiece with an appropriate level of accuracy.”

20. Scales Which of these scales would give the most accurate results? “When measuring mass in an experiment, you need to record the mass using the most accurate set of scales available.” The digital scales on the right.

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