Unit 12: Empirical Data Collection and Analysis — Short Questions

SI units are used almost everywhere in the world. It allows scientists to use a single standard in exchanging scientific data. This fact brings accuracy, consistency and universal understanding in scientific communication. A measurement taken in part of the world can be easily understood and verified in another part without any confusion.

When scientists belonging to different countries and cultures collaborate on research, they need a common language to share their results. Using SI units enables scientists to compare results, replicate experiments and take benefit of each other work. That's why, SI units are user friendly.

Systematic error affect the accuracy of the measurement. All measuring instruments contribute to systematic error e.g. pipette, burette and measuring cylinder may deliver the volume slightly different from the one indicated by their graduation.

It is a type of error which a student commits during measurement is called a random error.
Reasons:
Random error causes one measurement to differ slightly from the next measurement. It comes from unpredictable changes during an experiment. The main reasons for random errors are limitations of instruments, environmental factors and slight variation in procedure.

Systematic Error | Random Error
When we use tools meant for measurement we assume that they give correct results. However, these tools may not always be right. In fact they have errors that naturally occur and these errors are called systematic errors. | It is a type of error which a student commits during measurement is called a random error. Random error causes one measurement to differ slightly from the measurement. It comes from unpredictable changes during an experiment. The main reasons for random errors are

The following systems of units are commonly used in the world:
i. SI System (International System of Units)
ii. CGS System (Centimeter-gram-second System of Units)
iii. MKS System (Meter-kilogram- second System of Units)
iv. Imperial (System of Units)

It is the standard unit of length. Symbol m is used for meter. Meter is the distance travelled by light in vacuum in about 300 millionth of a second.

When scientists belonging to different countries and cultures collaborate on research, they need a common language to share their results. Using SI units enables scientists to compare results, replicate experiments and take benefit of each other work.
SI units allow scientists to work together effectively, advancing the frontiers of our knowledge. All of this ensures safety, reliability, reproducibility and progress.

Reliable Results | Reproducible Results
Reliability refers to the consistency of results when the same experiment is repeated under the same conditions. If an experiment yields similar results every time it is conducted, it is considered reliable. This means that the measurement or observation is dependable and can be trusted to reflect what it is supposed to measure. | Reproducibility, refers to the ability of other researchers to obtain the same results when they conduct the same experiment independently, using the same methods and conditions. This is crucial for validating findings in science.
For example, if a scientist measures the boiling point of water multiple times and consistently gets 100°C at sea level, those results are reliable. | For example, if another scientist takes the original experiment's procedure and performs it in a different lab and still finds that water boils at 100°C, then the results are reproducible.

SI units have brought harmony in the scientific community in several ways:
Universal Language: SI units serve as a universal language for scientists across the globe. By using a standardized system, researchers from different countries and disciplines can communicate their findings without confusion. This common ground fosters collaboration and understanding in a field that often involves complex data and measurements.
Consistency in Research: The use of SI units ensures that measurements are consistent and comparable. When scientists report their results in SI units, it allows others to replicate experiments and validate findings accurately. This consistency is crucial for building on previous research and advancing scientific knowledge.

The student's work is precise but not accurate.
Explanation:
Precision refers to the closeness of repeated measurements to each other. In this case, the student consistently got a reading of 5.2 grams each time he weighed the substance, indicating precision.
Accuracy, refers to the closeness of a measurement to the true value. Since the true weight of the substance is five grams and the student consistently measured 5.2 grams, the measurements are not accurate.
Therefore, the student's work is precise (consistent readings of 5.2 grams) but not accurate (the measured value is not close to the true weight of five grams).

One of the most usual problem which is faced. by the scientific community is the issue of unit. If scientists in one country are measuring lengths in meters and in another country in feet, then we will have to face problems in converting them. Comparing quantities in different units is not only confusing but the wastage of time as well. For the reasons mentioned above scientists have agreed to adopt standard and user-friendly units called SI or System International Units. Things become a lot easier when we use these units.

SI units are used almost everywhere in the world. It allows scientists to use a single standard in exchanging scientific data. This fact brings accuracy, consistency and universal understanding in scientific communication. A measurement taken in part of the world can be easily understood and verified in another part without any confusion.

There are seven base units in SI system for physical quantities out of which we use five in Chemistry. These physical quantities are length, time, amount of substance, mass and temperature.

Quantity | Unit
Length | Meter (m)
Time | Second (s)
Amount of substance | Mole (mol)
Mass | Kilogram (kg)
Temperature | Kelvin (K)

Its symbol is (kg) and it is the standard unit of mass. A block is kept in France which is taken as a standard unit of mass. It is also defined as the mass of 1000 cm³ of water.

It is the standard unit of time with a symbol (s). it is the time that elapses during 9,192,631,770 cycles of the radiation produced by the transition between two levels of the cesium-133 atom.

It is represented by (K) and it is the standard unit of temperature. It is 1/273rd of the thermodynamic temperature of the triple point of water. It is a point at which all the states of water exist at the same time.

It is the base unit of the amount of pure substance and it is denoted by mol. It is defined as having exactly 6.022 x 10²³ particles of substance.

The subject of chemistry needs a consistent way to measure and to communicate the quantities like mass, volume, temperature, amount and time. To make sure that all of us can understand each other, scientists all over the world have adopted a common system of units which is based upon the metric system and it is called SI units.

Mathematically, these are derived from base units.
Examples: The derived units used in chemistry are given in the following table.

Quantity | Unit
Volume | Cubic meter (m³)
Density | kg per cubic meter (kgm⁻³)
Area | Square meter (m²)

Since the SI system of units is a metric system, it is based around the number 10 for convenience. A set unit of prefixes has been developed which indicates whether the unit is a multiple or a fraction of the base ten. It allows the reduction of zeros of a very small number or a very large number. These SI prefixes also have a set of symbols that precede the unit symbol.

In Chemistry, we measure the masses of the reactants in grams. It is essential because the unit of measurement of molar mass consists of grams per mole. Therefore, given a mass measured in grams as well as a corresponding molar mass, enables us to find the mole of a substance. Moreover, in Chemistry the quantities involved in the laboratory are likely to be small. The choice of gram rather than kg is therefore sensible and normal. Using grams provides more manageable numbers for calculation and prevents the need for excessively large or small values.

Celsius scale is most often used to measure temperature in Chemistry rather than Kelvin because it is more convenient to use it. Celsius scale has 100 divisions in total which makes it more compatible with the base ten format of SI system. Another reason is that it is easier to convert temperature on Celsius scale into Kelvin scale.

The unit of measurement of volume in Chemistry is cubic centimeter instead of cubic meter because it is easy to measure and calculate with it and it is precise. In laboratory, we usually measure smaller volumes of liquid which are more manageable in cubic centimeter rather than cubic meter.

i. Symbols are not changed in plural forms
ii. Uses a space between units N m⁻² not Nm⁻²

Every measurement carries a level of uncertainty which is known as error. An error may be defined as the difference between the measured value and the actual value.
For example, if two students use the same tool or instrument for measurement, it is not necessary that both of them get similar results. The difference between the measurements is called an error.

An error may occur due to two factors:
i. The limitation of the measuring instrument.
ii. The skill of the student making the measurement.

Precision | Accuracy
The closeness of two or more measurements to each other is called precision. | Accuracy measures how close results are to the true or known value.
e.g. If you weigh a given substance five times and every time you get 3.2kg reading, then your measurement is precise. | e.g. Volume of liquid is 26cm³. A student measures its volume three times and find the result as 27cm³. The student is not accurate but if it measures 26cm³ then it would be accurate.

The SI system and the MKS system are both metric systems used for measuring physical quantities. but they have some differences in their units.
SI System:
In the SI (International System of Units), the base units are:
i. Meter (m) for length
ii. Kilogram (kg) for mass
iii. Second (s) for time
iv. Ampere (A) for electric current
v. Kelvin (K) for temperature
vi. Mole (mol) for the amount of substance
vii. Candela (cd) for luminous intensity
MKS System:
The MKS system is a subset of the SI system, where MKS stands for Meter, Kilogram, and Second. It primarily focuses on these three units:
i. Meter (m) for length
ii. Kilogram (kg) for mass
iii. Second (s) for time

There are seven base units in SI system for physical quantities out of which we use five in Chemistry. These physical quantities are length, time, amount of substance, mass & temperature.

Basic Quantity | Basic Unit
Length | Meter (m)
Time | Second (s)
Amount of substance | Mole (mol)
Mass | Kilogram (kg)
Temperature | Kelvin (K)

The following systems of units are commonly used in the world:

Quantity | Unit
Volume | Cubic meter (m³)
Density | kg per cubic meter (kgm⁻³)
Area | Square meter (m²)

Mass In Chemistry, we measure the masses of the reactants in grams. It is essential because the unit of measurement of molar mass consists of grams per mole. Therefore, given a mass measured in grams as well as a corresponding molar mass, enables us to find the mole of a substance.
Volume:
The unit of measurement of volume in Chemistry is cubic centimeter instead of cubic meter because it is easy to measure and calculate with it and it is precise. In laboratory, we usually measure smaller volumes of liquid which are more manageable in cubic centimeter rather than cubic meter.

If scientists in one country are measuring lengths in meters and in another country in feet, then we will have to face problems in converting them. Comparing quantities in different units is not only confusing but the wastage of time as well.

For the reasons mentioned above scientists have agreed to adopt standard and user-friendly units called SI or System International Units. Things become a lot easier when we use these units.