Safety Rules: The Big Ones 1.Pour acid into water slowly (PAWS) 2.Tie your hair back 3.Wear goggles and an apron when working with chemicals, fire, or glass 4.Wear gloves when working with chemicals and bacteria 5.Don’t pour unknown chemicals down the sink, or return them to unlabeled containers, etc
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
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 visible B at a 180° angle from the flame C toward a ventilated area D 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 products B avoid splashing chemicals into the face of any person C protect the respiratory tract against potentially harmful vapors D 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.
Common Equipment 1. Be familiar with common lab equipment and their uses. 2. Be able to read measurements accurately and in metrics. 3. Be able to chose the BEST equipment that would help achieve the desired results in an experiment. 4. Be able to chose equipment that will give the MOST precise results. Graduated cylinder: measures volume Triple beam balance: measures mass Beaker: measures large volumes of liquids Which is MORE precise, the graduated cylinder or the beaker? Graduated cylinder because it has units in increments of 1 mL
Accuracy verses Precision Accuracy: 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)
Choosing Equipment Which piece of equipment would be used to precisely measure the volume of an acid? Eliminate choice A (balance measures mass) & D is a Bunsen burner Correct answer: Choice C because the graduated cylinder gives a more precise measure than the beaker. Precisely – want lots of increments Volume – need something that measures in mL
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 mL38 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.
Reading a Burette Which is the best estimate of the volume of solution released from the burette? A 47.3 mL B 47.7 mL C 48.3 mL D 48.7 mL Initial volumeFinal Volume Final volume – Initial volume = 48.5mL – 0.8 mL =________ 47.7 mL Correct answer: B 0.8 mL48.5 mL
Choosing Appropriate Lab Equipment An experiment was conducted to test the effectiveness of four different fertilizers on plant growth. Two grams of each fertilizer were to be diluted in 9 milliliters (mL) of water before adding to a plant. Which of the following measuring devices would introduce the least error into the measurement of the 9 mL of water? F 10 mL graduated cylinder G 20 mL graduated cylinder H 50 mL graduated cylinder J 100 mL graduated cylinder Use the graduated cylinder that holds the least volume that is required to ensure the least error (most precise) measurement. Correct Answer: F Choice F holds the least volume