Empirical Data Collection and Analysis

Science: Systematic study of the world through observation and experimentation.

Need for Standardization: Scientists in different countries use different units. To ensure proper communication and avoid confusion, we need to share ideas and standardize our approach.

Example: If scientists in one country measure lengths in meters and another in feet, we face problems in converting them.

SI Units (International System of Units): Scientists agreed to adopt standard and user-friendly units called SI. Makes communication easy worldwide, allows scientists to share data easily.

Seven Base Units:

• Meter (m): Standard unit of length. Distance travelled by light in vacuum in about 1/300 millionth of a second
• Kilogram (kg): Standard unit of mass. Defined as mass of 1000 cm³ of water. A block kept in France is taken as standard
• Second (s): Standard unit of time. Time that elapses during 9,192,631,770 cycles of radiation from cesium-133 atom
• Kelvin (K): Standard unit of temperature. Thermodynamic temperature of triple point of water
• Mole (mol): Base unit of amount of pure substance. Defined as exactly 6.022×10²³ particles

Derived Units: Mathematically derived from base units. Examples: Pascal (pressure), Joule (energy), Newton (force)

Common SI Prefixes:

• Kilo (k) = 10³
• Deci (d) = 10⁻¹
• Centi (c) = 10⁻²
• Milli (m) = 10⁻³
• Micro (μ) = 10⁻⁶

Why Smaller Units in Chemistry: In Chemistry, quantities in laboratory are small. Using grams instead of kg is sensible and prevents excessively large or small values.

Temperature: Celsius scale most often used because more convenient. 100 divisions total, compatible with base ten. Easy conversion: K = °C + 273

Volume: Cubic centimeter (cm³) instead of cubic meter (m³) because easier to measure and calculate smaller volumes in laboratory.

Error: Every measurement carries a level of uncertainty, known as error. Difference between measured value and actual value.

Causes of Errors:

• Limitations of measuring instruments
• Skill of student making measurement

1. Systematic Errors: Errors that naturally occur when using tools meant for measurement. Can be removed by adding or subtracting constant adjustment. Affects accuracy. Example: Pipette, burette, measuring cylinder may deliver volume slightly different from indicated graduation.

2. Random Errors: Type of error student commits during measurement. Causes one measurement to differ slightly from next. Comes from unpredictable changes. Affects precision. Example: Reading volume from different angles, surrounding air affecting balance.

Accuracy: Measures how close results are to the true or known value.

Example: True volume = 25 cm³. Student measures 27 cm³ three times. Not accurate (not exact result).

Precision: The closeness of two or more measurements to each other.

Example: If you weigh substance five times and get 3.2 kg every time, measurement is precise but not necessarily accurate.

Relationship: Precision independent of accuracy. Student may be accurate but not precise, or precise but not accurate.

Avoiding Errors:

• Systematic: Improve experimental techniques, select better instruments, remove personal bias
• Random: Take multiple readings and average the results