Intro to Chemistry and Lab Safety
Start here if chemistry still feels new. In this unit, you will learn what chemistry is really about, how to stay safe in the lab, and how to measure in a way that will still hold up when you get to matter, calculations, and reaction work later on.
What you'll learn
1.1 Start Here: What Chemistry Is Actually About
Chemistry is the study of matter, energy, and change. Notice that this is bigger than "memorizing the periodic table." Chemistry asks what a substance is, how much of it you have, what changes, and what the evidence shows.
The four rows below show what chemistry actually asks — these same questions come back in every unit.
| Chemistry question | What you are trying to figure out |
|---|---|
| What substance is present? | Identify the material or particle involved. |
| How much is present? | Measure mass, volume, amount, or concentration correctly. |
| What changed? | Track how matter or energy changed during a process. |
| What do the measurements show? | Use data to support a conclusion. |
Why this unit matters
- This unit is your setup for the rest of the course. If measurement and safety feel automatic later, harder chemistry gets much easier.
- You will practice reading instruments, choosing the right tool, recording correct precision, and using evidence to support a claim.
- Do not miss this: these same habits show up again in Unit 02 on matter, mole work, and stoichiometry.
1.2 How Chemists Test an Idea and Defend a Claim
Scientists use evidence to answer a testable question. The process is not always perfectly linear, but the routine is the same: ask, test, measure, and justify the conclusion with data. If this feels shaky, slow down here, because later labs expect you to tell the difference between what you changed, what you measured, and what the data actually support.
Step 1: Ask a testable question
Write a question you can answer with observations or measurements. Example: "Does higher water temperature make an antacid tablet dissolve faster?"
Step 2: Use what is already known
Use what is already known to plan a better test. For the antacid example, you already know that temperature speeds up particle motion — that's what makes your hypothesis more than a guess.
Step 3: Write a real hypothesis
State what you predict and why. A hypothesis is testable. It is often written in if-then form.
Step 4: Set up a fair test
Choose one variable to change. Choose what to measure. Keep the other conditions the same. Include a comparison condition when needed.
| Variable type | Definition | In the example |
|---|---|---|
| Independent | What you deliberately change | Water temperature |
| Dependent | What you measure as a result | Time for the tablet to dissolve |
| Constants | Everything else held the same | Tablet brand, water volume, container, stirring |
| Comparison | Condition used for a fair check | Room-temperature water |
Step 5: Collect and organize the data
Record observations and measurements clearly. Organize the data so you can compare results.
Step 6: Make the conclusion match the evidence
Decide whether the data support the hypothesis. Explain your conclusion with evidence.
Step 7: Share the work so others can check it
Share the method and results so others can evaluate the work.
Common mix-up: theory vs. law
- A scientific law describes what happens consistently.
- A scientific theory explains why or how it happens.
- Neither word means "guess" in science. A theory is not a weak law, and a law does not explain the cause.
1.3 Lab Safety: What You Need to Do Before Anything Goes Wrong
Lab safety is not a list to memorize once and forget. Start here: match each hazard to the right action before you touch chemicals, glassware, or heat. That is how you protect yourself, your lab partner, and your data.
Personal Protective Equipment (PPE)
Safety goggles — worn whenever chemicals, heat, or glassware are in use. Regular glasses do not count.
Gloves — nitrile gloves protect skin from corrosive, toxic, or skin-absorbed chemicals. Remove before touching your face.
Lab apron/coat — protects clothing and skin from spills. Long pants and closed-toe shoes are required.
Before lab
These three happen before you touch anything. If you skip them, the rest of the list doesn't protect you.
- Read the entire procedure before beginning.
- Know the location of the eyewash station, safety shower, fire extinguisher, and first aid kit.
- Put on goggles and any required protective clothing before handling chemicals or glassware.
During lab
Notice: most of these are about habits, not knowledge. They only protect you if they become automatic.
- Never eat, drink, or apply cosmetics in the lab.
- Read labels carefully before using a chemical.
- Never smell a chemical directly — waft the vapors toward you with your hand.
- Add acid to water, not water to acid.
- Keep long hair tied back and loose items away from flames and chemicals.
If something goes wrong
- Report spills, breakage, and exposure to your teacher immediately.
- Use safety equipment right away when needed.
- Dispose of chemicals only as instructed.
Hazard Symbols (GHS)
Before any lab, check the chemical label. These are the symbols you'll see — and what each one tells you to do differently. Notice the pattern: the symbol is only useful if it changes what you do next.
1.4 Lab Equipment: Which Tool to Use and Why
Choose equipment based on the job. The most common mistake here is grabbing a beaker for everything. If precision matters, use equipment made for measuring, not just holding.
| Task | Best tool | Why |
|---|---|---|
| Hold or mix a liquid | Beaker | Good for holding and mixing, not for precise volume |
| Measure liquid volume accurately | Graduated cylinder | Better for measured volume than a beaker |
| Prepare one exact final volume | Volumetric flask | Built for one exact marked volume |
| Deliver a precise variable volume | Burette | Used when the delivered amount must be measured carefully |
| Transfer an exact volume | Pipette | Designed to measure and move a precise amount |
| Measure mass | Electronic balance | Reads mass directly; tare removes the container mass |
| Heat and stir a solution | Hot plate / stirrer | Designed for controlled heating and mixing |
| Support glassware over a heat source | Ring stand + clamps | Holds equipment in place during heating |
| Transfer solids | Spatula / scoopula | Moves solids cleanly without using your hands |
| Rinse glassware | Wash bottle | Lets you direct distilled water where you need it |
Quick choice check
- If the question asks for an accurate measured volume, choose a graduated cylinder, pipette, or burette, not a beaker.
- If the question asks for sample mass only, place the container on the balance first and press TARE before adding the sample.
- Important: "holds liquid" and "measures liquid" are not the same job. Beakers hold liquid but do not measure it accurately like a graduated cylinder, pipette, or burette.
1.5 Measurement and SI Units: Writing Data So It Actually Means Something
Science uses the International System of Units (SI) so measurements mean the same thing everywhere. Every measurement has a number and a unit. A number by itself is not enough. Later topics like moles, stoichiometry, and solutions only work if your units are under control.
Measurement routine: Identify the quantity, write the number and unit together, convert only if needed, and keep the units visible through the setup.
SI Base Units
| Quantity | Unit | Symbol |
|---|---|---|
| Length | meter | m |
| Mass | kilogram | kg |
| Time | second | s |
| Temperature | kelvin | K |
| Amount of substance | mole | mol |
| Electric current | ampere | A |
| Luminous intensity | candela | cd |
Common Metric Prefixes
| Prefix | Symbol | Multiplier | Example |
|---|---|---|---|
| mega- | M | 10⁶ | 1 Mm = 1,000,000 m |
| kilo- | k | 10³ | 1 km = 1,000 m |
| deci- | d | 10⁻¹ | 1 dm = 0.1 m |
| centi- | c | 10⁻² | 1 cm = 0.01 m |
| milli- | m | 10⁻³ | 1 mm = 0.001 m |
| micro- | µ | 10⁻⁶ | 1 µg = 0.000001 g |
| nano- | n | 10⁻⁹ | 1 nm = 10⁻⁹ m |
You'll use Celsius for everyday lab measurements. You'll need Kelvin when you get to gas laws and thermodynamics — that's where 273 becomes important.
- Chemists use Celsius (°C) for everyday lab measurements and Kelvin (K) for gas law and thermodynamics calculations.
- Many intro chemistry problems round 273.15 to 273. Follow the directions given.
- 0 K (absolute zero) is the coldest possible temperature — there are no negative Kelvin values.
1.6 Significant Figures: Which Digits Count and Which Do Not
Significant figures (sig figs) communicate the precision of a measurement. The big question is simple: which digits came from the measurement, and which zeros are only placeholders? If this feels shaky, fix it now. Sig figs keep showing up in calculations all the way through moles and stoichiometry.
For an analog instrument, record all certain digits plus one estimated digit. For a digital instrument, record all digits shown on the display.
Rules for Counting Sig Figs
| Rule | Example | Sig figs |
|---|---|---|
| All non-zero digits are significant | 4,523 | 4 |
| Zeros between non-zero digits are significant | 4,023 | 4 |
| Leading zeros are NOT significant | 0.0047 | 2 |
| Trailing zeros with a decimal point ARE significant | 2.500 | 4 |
| Trailing zeros without a decimal are NOT significant | 2500 | 2 |
| Scientific notation removes all ambiguity | 2.50 × 10³ | 3 |
In answer boxes, type it with e notation:
9.53e23.For small numbers, use a negative exponent: 4.56 × 10−4 is typed as
4.56e-4.
6.02e6 and 4.56e-4.Sig Figs in Calculations
This is where the two rules get mixed up. The operation type — not the number of digits — tells you which rule applies.
- Multiplication/Division: Answer has the same number of sig figs as the measurement with the fewest sig figs.
- Addition/Subtraction: Answer is rounded to the same decimal place as the measurement with the fewest decimal places.
- Exact numbers (counts, definitions) have unlimited sig figs and do not limit your answer.
12.36 + 1.2 = 13.56 → rounds to 13.6 (tenths place, limited by 1.2)
Common mistake
- Do NOT round intermediate steps.
- Carry extra digits through the entire calculation and round only the final answer.
- When you need to show that trailing zeros ARE significant, use a decimal point (2500.) or scientific notation (2.500 × 10³).
- Do not confuse decimal-place rules with sig-fig rules. Addition and subtraction care about decimal places. Multiplication and division care about sig figs.
1.7 How to Read a Graduated Cylinder Correctly
A graduated cylinder measures liquid volume. Liquids in glass form a curved surface called the meniscus. For most liquids, including water and aqueous solutions, the meniscus curves downward (concave). Read from the bottom of the meniscus at eye level. Reading from above or below creates parallax error, and that small mistake can turn into a wrong answer fast.
This reads 6.8 mL.
The recorded reading is 42.0 mL.
This reads 18.5 mL.
Precision rule: Read the bottom of the meniscus for most aqueous solutions. Record one estimated digit beyond the smallest marked interval.
1.8 How to Use an Electronic Balance Without Ruining the Measurement
An electronic balance measures mass in grams. Use the TARE function so the display shows the sample mass only, not the container plus the sample. This is one of the easiest mistakes to make and one of the easiest to prevent.
Correct Balance Technique
Why tare? Think of it this way: if you skip taring, the balance includes the container in its reading. You aren't subtracting it yourself — so it stays in the number, and the measurement is wrong before you even start. That is what TARE removes.
| Problem | Result |
|---|---|
| Forgot to tare | The display includes container + sample. |
| Did not record all shown digits | You lose precision. |
| Removed the tared container and kept going | The reading is no longer valid. |
Do Not Miss These Common Errors
- Parallax: Reading a graduated cylinder from above or below eye level gives an incorrect meniscus position.
- Forgetting to tare: Always tare the balance with the container before adding your sample.
- Rounding too early: Carry all digits through calculations; round only the final answer.
- Confusing mass and weight: Mass (kg, g) is a property of matter; weight is the gravitational force on that mass.
- Hypothesis ≠ prediction: A hypothesis must be testable and falsifiable. "I think plants will grow better" is not a hypothesis.
- Forgetting units: A number without a unit is not a measurement.