The Nature of Science: Unit 1A

Safety, Safety Symbols and Measurement

Safety

Safety Rules: The Big Ones

1. Pour acid into water slowly (PAWS)2. Tie your hair back3. Wear goggles and an apron when working

with chemicals, fire, or glass4. Wear gloves when working with chemicals

and bacteria5. Don’t pour unknown chemicals down the

sink, or return them to unlabeled containers, etc

6. Use wafting to determine the contents of a container

7. Reactions that produce toxic gases should be preformed under a fume hood

Important Safety Terms & Symbols

1. Corrosive- Will corrode or eat away metal, skin, or other substances.

2. Volatile- Evaporates quickly, may form dangerous vapors

3. Flammable (may ignite)- will catch on fire or explode easily.

4. Ventilation- removing contaminated air and brining in fresh air

Explosive

Corrosive

Flammable

Poisonous

Radioactive Biohazard

Lab Safety

This picture indicates that the chemical represented is —

A pressurized

B corrosive

C flammable

D toxic

This is the safety symbol for ____________

Corrosive material

Correct answer: Choice B

Lab Safety Reactions that produce toxic gases should be

performed in a —

A laboratory fume hood B beaker with a watch glass on top C well-ventilated area of the lab D warm, airtight drying oven

Should we breath in toxic gases? NO!

How can we trap toxic gases?

Correct answer: Choice A; a lab fume hood will trap the gases so that we don’t breath in the fumes from the toxic gases!

Heating Chemicals in a Test Tube--- When a 10% hydrochloric acid solution is heated

in an open test tube, the test tube should always be pointed —

A so bubbles are visibleB at a 180° angle from the flameC toward a ventilated areaD away from nearby people

Safety rule: Always point test tube away from yourself and others

Correct answer: D Choice D BEST matches our safety rule

The reason for wafting or fanning a small amount of chemical vapors toward the nose as a means to detect odors in a test tube is to —

A avoid experimental error from excessive loss of mass of reactants or productsB avoid splashing chemicals into the face of any personC protect the respiratory tract against potentially harmful vaporsD determine the relative strength of the odor before smelling directly

Wafting Chemicals

Correct Answer: C; wafting allows a small amount of the chemicals vapors to be detected by your nose without you having to smell the “full” odor.

Accuracy verses PrecisionAccuracy:1. The accuracy of the instrument refers to how close the

measured value is to the true or accepted value.2. For Example : if an object has a real mass of 2 grams

and the balance used gives a reading of 2 grams, the measurement is accurate. If the balance reads 1.8 grams it is inaccurate.

Precision:1. Precision refers to how close together a group of

measurements actually are to each other.2. For Example: If an object has a true mass of 2 grams.

A person masses it as 5 grams three time in a row. The person shows precision (but NOT accuracy)

Measuring Accurately The illustration shows

volume levels of a liquid in a graduated cylinder before and after a sample was removed. According to this information, what was the volume of the sample to the nearest milliliter?

Record and bubble in your answer on the answer document.

47 mL 38 mL

Subtract: 47mL – 38 mL = 9.0 mL

Meniscus

The meniscus is the slightly curved surface that forms in a graduated cylinder. Always read at the bottom of the meniscus.