Analía Bellizzi – Chemistry Classes

Ronald Reagan Senior High School

# Measurements Notes IGCSE

Measuring means how to express a measurement including the uncertainty.

#### How to Measure LENGTH

The steps to follow are the same regardless the instrument you are using:

• 1.Observe what is the value for the smallest division in your instrument represents.
• 2.Divide this number by 2.
• 3.This number represents the error you will show in your measurements.
• 4.Do not forget to include units in these numbers

For the same object we use two different rulers:

If you use ruler 1, you can tell that the actual value is between 5.1 cm and 6.1 cm

Using ruler 2, the value will be between 5.50 cm  and 5.60 cm.

Which ruler you think will give you a more accurate value?

#### How to Measure VOLUME

For measuring Volumes, we use graduated cylinders, burettes or Pippetes. In all of them we follow the same procedure:

• A meniscus is the curve of the surface of the water in a graduated cylinder.
•  Water “sticks” to the walls of the graduated cylinder, but only on the sides and not the middle.
• When measuring liquids be sure that your eyes are aligned with the bottom of the meniscus.

#### Step by step:

• 1.Observe what amount the smallest division in your instrument represents.
• 2.Divide this number by 2.
• 3.This number represents the error you will show in your measurements.
• 4.Do not forget to include units in these numbers
• 5.Be careful when you look at the smallest division value

• When measuring liquids in a burette be sure that your eyes are aligned with the bottom of the meniscus as always.
• Be aware that the scales are inverted in burettes since we measure the liquid we poured into a container.
• look for the value between the lines.
• In this case, the correct measurement on the left with error included should read:
• Volume on the left burette: 3.30 mL ± 0.05 mL.
• Volume on the right burette: 3.90 mL ± 0.05 mL.

#### How to Measure MASS using a triple beam balance

1. Be sure that your triple beam balance is “zeroed”
2. Place an object on the pan.
3. Slide the rider with the largest mass along its beam until the pointer drops below zero.
4. Move it back one notch.
5. Repeat the process on each beam until the pointer stays at zero.
6. Add the masses on each beam to find the mass of the object.
7. Calculate the error and express the amount USING UNITS.

#### Step by step:

1. Observe what amount the smallest division in your instrument represents
2. Divide this number by 2.
3. This number represents the error you will show in your measurements.
4. Do not forget to include units in these numbers
5. Be careful when you look at the smallest division value

#### How to measure TEMPERATURE

1. The metric system uses the Kelvin (or sometimes Celsius) scale to measure temperature. However, temperatures are still measured on the Fahrenheit scale in the U.S.
2. IMPORTANT: ZERO KELVIN: ABSOLUTE ZERO: temperature at which particles do not move.
3. Water freezes at 0° Celsius and boils at 100 ° Celsius which is a difference of 100 °
4. To convert from Celsius to Kelvin just add 273.15° to the temperature in Celsius.
(for more information in how to convert between different temperature scales go to: http://www.metric-conversions.org/conversion-calculators.htm

#### Step by step:

1. Observe what amount the smallest division in your instrument represents.
2. Divide this number by 2.
3. This number represents the error you will show in your measurements.
4. Do not forget to include units in these numbers
5. Be careful when you look at the smallest division value. SOME  THERMOMETERS HAVE DIVISIONS EVERY 2 DEGREES.