**Unit2: Measuring & Calculating**

**Unit2: Measuring & Calculating**

BJU Chemistry book: Ch. 3 "Measuring and Calculating"

Zumdahl Chemistry book: Ch. 1 "Chemical Foundations"

Glassware Fabrication and Lab Safety

__Reading__BJU Chemistry book: Ch. 3 "Measuring and Calculating"

Zumdahl Chemistry book: Ch. 1 "Chemical Foundations"

__Topics__- Metric system
- Conversion factors
- Significant digits
- Calculations involving the above
- The concept of 'density'

__Lab__Glassware Fabrication and Lab Safety

chemistry_measurement_class_notes_2021.docx |

Below: A rather dramatic demonstration of the energy which is contained in hydrogen gas (H2). Matter can exist as a gas, liquid, or solid... and a fourth category called 'plasma'. We will make small quantities of hydrogen gas - and safely study its properties - in a later lab.

__Lecture outline__

By around 1960, most nations had officially adopted the

**metric system**or

**System International (SI)**as their official measurement system. The metric system is based on "tens", and uses the meter, gram, liter, and second as basic units.

In the United States, we still use the

**Imperial System**(inches, feet, pounds, gallons) in many fields, but in Chemistry

*we use the metric system because it's easier and because it is the recognized standard*. Since Americans need to know

*both systems*, we use

**conversion factors**to convert back and forth between them. Historically, the Imperial System was used throughout the British Empire up through the mid-1900's, and since the British Empire included most of North America, we still have it.

Metric

**base units**and

**prefixes**shown below:

In the metric system, we also have

**derived units,**such as*area, volume, density, and pressure*.Density

- The density of something is its
__mass__divided by its__volume__. Density = mass/volume. - The density of water is 1,000 g/L (one thousand grams per liter).
- The density of rock is around 2,000 g/L. Therefore, a rock will sink in a beaker of water.

Accuracy vs. Precision

Significant Figures

- Accuracy is how close you are to the "true" value. Shooting an arrow directly in the bullseye is being 'accurate'.
- Precision has to do with 'repeatability', or how tightly grouped your measurements are. Shooting 10 arrows near the bullseye is 'precision'.
- Precision is also an indication of how small the scale 'gradations' are on your measuring instrument. A measurement like 5.125 L is "more precise" than 5.1 L, for example (even though neither one is perhaps very "accurate").

Significant Figures

- We have to be careful how many digits we show in our answer.
- For addition & subtraction, you can keep as many place values in your answer as the least precise measurement contains
- For multiplication & division, you can keep as many significant figures in your answer as the measurement with the least significant figures has

Scientific Notation

- Chemistry uses very small - and also very large - numbers. We use scientific notation to write these numbers.
- For example, 6 x 10^3 means a 6 with 3 zeroes, or 6,000 Or.... 6 x 10^23 means a 6 with 23 zeroes.

__Lab: Glassware Fabrication & Lab Safety__

Objectives: We will go over the safety rules pertaining to chemicals, glassware, and heat sources. Learn how to safely cut, bend, and draw glass. Make a functioning laboratory wash bottle. Read and sign the lab safety rules agreement.

_glassware_lab_student handout - print and bring to class |

lab_report instructions_-_glassware_fabrication_lab.docx |

lab_safety_rules_agreement_2021 - sign and return original.docx |

__AP take-home lab: Measurement, Significant Digits, and Graphing__

1._Lab Handout: Measurement_significant_digits_and_graphing_lab.doc |

1._Sig Figs_background_lecture.docm |

__Homework__

1._measurement_homework__problems.docx |