Chemistry: Scientific Measurements, Notation, and Significant Figures

Flashcards cover mass, weight, density, volume, accuracy vs. precision, error sources and improvements, scientific notation, and significant figures based on the provided lecture notes.

What is mass?

A fundamental property of matter quantifying substance amount, measured in kilograms (kg) or grams (g), and independent of location.

What is the difference between mass and weight?

Mass is the amount of matter in an object (measured with a balance; units g or kg; does not change with location). Weight is the force of gravity on that mass (measured in newtons; depends on gravity; varies with location).

What is density and its SI units?

Density is mass per volume (ρ = m/V); SI units are g/cm³ and kg/L; denser materials have more mass per unit volume.

What is volume and its common units?

Volume is the amount of space occupied by a substance; SI unit is cubic meters (m³), with common units of liters (L) and milliliters (mL) for liquids.

What is the formula for density in terms of mass and volume?

Density ρ = m/V.

What is the formula for volume in terms of mass and density?

Volume V = m/ρ (mass divided by density).

What does mass tell us in a lab measurement?

How much matter is present in an object.

What does volume tell us in a lab measurement?

How much space the object occupies.

What does density tell us in a lab measurement?

How tightly packed the matter is within a given volume; calculated from mass and volume.

What is precision?

How consistent or repeatable measurements are across trials, regardless of whether they are close to the true value.

What is accuracy?

How close measurements are to the true or accepted value.

Why are accuracy and precision important in experiments?

They ensure trustworthy results, valid data, and help identify problems with methods or tools when measurements are off.

What does it mean if data is accurate and precise?

Measurements are both close to the true value and consistently clustered together.

What is a common density-lab example that demonstrates accuracy and precision?

If trials 7.83, 7.84, 7.85 g/cm³ are obtained for a true density of 7.85 g/cm³, the results are accurate and precise.

What is Instrument Error?

Errors due to measuring tools not being calibrated or zeroed (e.g., a balance not zeroed).

What is Human Error?

Errors arising from human mistakes such as misreading a ruler or not keeping the instrument at eye level.

What is Environmental Error?

Errors caused by surroundings, like wind, vibrations, or temperature changes during an experiment.

What is Procedure Error?

Errors from not following the procedure correctly, such as spilling water, using the wrong unit, or skipping steps.

How can you improve measurement reliability when a scale isn’t calibrated?

Calibrate or reset the instrument to zero before using it.

How can you reduce parallax error in readings?

Always read measurements at eye level to avoid parallax error.

What should you do if your method is inconsistent?

Follow the step-by-step procedure carefully and standardize the method.

What should you do if the tool is not suitable for the measurement?

Use the correct measuring tool for the object or quantity being measured.

Why should you repeat trials in experiments?

To obtain an average and improve reliability by reducing random error; typically at least three trials are recommended.

What is scientific notation?

A way of writing very large or very small numbers in the form a × 10^n, where a is between 1 and 10 and n is an integer.

Why is scientific notation used in chemistry?

To make numbers easier to read/write and to reduce calculation errors; used for atoms, masses, distances, and times.

What is the format of scientific notation?

a × 10^n, where a is between 1 and 10 and n is the exponent indicating decimal movement.

How do you convert 500,000 to scientific notation?

5.0 × 10^5.

How do you convert 0.00034 to scientific notation?

3.4 × 10^-4.

What is the purpose of significant figures (sig figs)?

To express how exact or precise a measurement is and to show precision limits of the measurement tool.

Why are significant figures important in chemistry?

Results must reflect the precision of the tools used; they prevent overstatement of accuracy.

Rule 1 for sig figs

All non-zero digits are significant (e.g., 345 has 3 sig figs; 72.4 has 3 sig figs).

Rule 2 for sig figs

Zeros between non-zero digits are significant (e.g., 205 has 3 sig figs; 1002 has 4 sig figs).

Rule 3 for sig figs

Leading zeros are not significant (e.g., 0.003 has 1 sig fig).

Rule 4 for sig figs

Trailing zeros are significant if there is a decimal point (e.g., 20.0 has 3 sig figs; 100.00 has 5 sig figs).

What does P20 with a decimal imply about measurement precision?

Without a decimal (P20) it could be P20.01 or P19.99; with a decimal (P20.00) it indicates measurement to the nearest hundredth.

When should you use scientific notation for very big or very small numbers?

When numbers are too large or too small to write conveniently, to avoid long strings of zeros and reduce errors.