Scientific Measurements: Metric System

Introduction to Scientific Measurements

• The lab explores scientific measurements using the metric system.
• The English system is outdated and cumbersome and is mainly used in the USA, Liberia, and Myanmar.
• The metric system, abbreviated as "SI" (Système International), is used instead of the English system and is standardized internationally.
• Metric system conversions are based on multiples of ten, simplifying unit changes.
• Length, mass, and volume measurements are taken during the course.

Metric System Base Units and Prefixes

• Length: The base unit for length is the meter, and its unit symbol is m.
• Mass: The base unit for mass is the gram, with the unit symbol g.
• Volume: The base unit for volume is the liter, and its unit symbol is L.
• Metric prefixes indicate fractions or multiples of the base unit by factors of ten.
• "Centi-" represents the fraction 1/100 or 0.01

Metric Table of Equivalencies (Examples)

• Giga (G): Multiplier of 10^9, e.g., 1 gigameter (Gm) is 1,000,000,000 meters.
• Kilo: Multiplier of 10^3.
• Centi: Multiplier of 10^-2
• Base Unit: Multiplier of 10^0 which equals 1
• Milli (m): Multiplier of 10^-3
• Micro (µ): Equivalent to 0.000001
• Nano : No exponential factor given
• Unit symbols are case sensitive and are not abbreviations, so they do not have plural forms and require a space before them (e.g., 1 km).

Unit Conversions

• Metric unit conversions involve powers of 10.
• To convert 300 cm to meters, use the conversion factor 1 m = 100 cm, resulting in 3 m.
• Two-step conversions are needed when converting between units that are not directly related.
• To convert 2000 mm to nm, first convert mm to m (1 m = 1000 mm) and then m to nm (1 m = 1,000,000,000 nm).

Scientific Notation

• Scientific notation expresses very large or small numbers using a mantissa and exponents of ten.
• To express 9,000 m in scientific notation: the mantissa is 9.0, move the decimal place 3 times resulting in 9.0 x 10^3 m.
• To express 0.01 L, it is written as 1 x 10^-2 L; the negative exponent indicates the decimal place was moved to the right.

Significant Figures

• Significant figures indicate the accuracy of a measurement.
• Writing 147.0 instead of 147 communicates the measuring instrument's accuracy to the nearest tenth of a pound.
• Nonzero digits (1-9) are always significant.
• Zeros with a line over them are significant.
• Leading zeros are not significant.
• Trailing zeros to the right of the decimal are significant.
• Trailing zeros to the left of a decimal are only significant if they are to the left of the decimal point as well.
• Zeros within a number are always significant.
• An estimation of one decimal place past the units of your measuring device is required in measurements.

Precision vs. Accuracy

• Precision: The ability of a measuring device to repeatedly give consistent values so the scale has good precision if it always measures 147 lbs but has low accuracy if your weight is 157lbs.
• Accuracy: An instrument's ability to provide measurements close to the true value.
• A scale is reasonably accurate vs precise if it measures different values that are close to the true value

Today's Lab: Measuring Length

• Practice measuring length in the metric system and compare results with a partner to identify discrepancies.

Today's Lab: Measuring Mass

• Mass is the quantity of matter and should not be confused with weight.
• Weight is the force of gravity on an object, which varies depending on the gravitational force (e.g., on the moon).
• Grams (g) are used as the metric unit of mass, but Newtons (N) are used as the metric unit for force.
• Mass is measured using a balance, while weight is measured using a scale.
• Density (D), also known as specific mass, is mass per unit volume, calculated as mass (g) / volume (cm³).

Today's Lab: Measuring Volume

• Volume is the space an object occupies, measurable for regular shapes (cube volume: V = s^3).
• Volume for Irregular objects is measured by submerging the object in liquid to measure volume displacement
• Liquid volume is measured using instruments with varying degrees of accuracy and precision.
• Beakers & Erlenmeyer flasks: They provide coarse measurements with a large error range .
• Graduated cylinders: The common liquid-measuring vessel with a lower error.
• Burets, pipets, & volumetric flasks: Volumetric instruments, which have the best accuracy.

Lab Procedures

• Review procedures before the laboratory session.
• Completing lab procedures and cleaning up within the specified time is your responsibility.

Materials

• Index Card
• Meter Stick
• Balance
• 150 mL Beaker
• 100 mL Graduated Cylinder
• Metric Ruler
• Density Cube
• Density Cube Literature Value Table
• Weigh Boats
• Tap Water
• 100 mL Volumetric Flask

Measuring Length

• Measure two objects using a metric ruler or meter stick with a lab partner
• Record and convert measurements to scientific notation.
• Compare data with your lab partner.

Measuring Mass

• Record a metal cube's assigned metal type.
• Find the density value from the provided table.
• Measure the volume of the metal block.
• Obtain a weigh boat to measure metal cube mass
• Determine density by dividing the mass by volume and compare it with the literature value.

Measuring Volume

• Measure the percent error with a 150 mL beaker, and a 100 mL graduated cylinder, and a 100 mL volumetric flask.
• Record the weight of each empty vessel in grams before each use and ensure your balance is tared before each measure
• Fill each vessel with 100 mL of tap water and ensure the meniscus rests along the graduation mark
• separately weigh the filled vessels and record the measure
• Calculate the mass of water by finding the difference between filled and empty mass of the vessel (Mass of Water (g) = Mass of Filled Vessel (g) – Mass of Empty Vessel (g))
• Final percent error calculation: Percent Error (%) = ((Mass of Water (g) – Expected Mass (g)) / Expected Mass (g)) x 100

Lab Clean-Up

• Dispose of used materials and water in the appropriate containers
• Return material to their designated drawers and be sure not to mix drawer items in the lab bench
• Disinfect lab areas

Post-Lab Results Checklist Includes

• (A) Length data, measuring device used, comparison to partner's data.
• (B) Mass data, literature values, density calculations, and answers to questions.
• (C) Volume data, weights of empty and filled vessels, calculations, and percent error.

Post-Lab Conclusion

• Summarize lab activities, results for each section, and discuss unexpected results or errors.
• Evaluate the effects of classmates test to your own and why this my be true or not
• Make sure to identify how was the calculated density comparing to litterature values
• Be sure to review and identify which vessel was most and least accurate through your data collection
• Why is the calibration of measuring devices so important
• How can you make measurements more effective
• Discuss why it is important to write the unit associated with your measurement for every measurement