chemistry lab midterm
A series of measurements in the lab led to an experimental result of 32.9 mL, with a calculated standard deviation of 0.3 mL. What is the standard way to report this result?
32.9 ± 0.3 mL
When using a properly stabilized balance, how should you ensure that you get the most accurate mass reading possible?
Close the side shields on the balance during reading. Measure the mass of the sample at room temperature.
What action is NOT necessary before lighting a Bunsen burner?
Leave the gas cock open for a few minutes before lighting to clear the line.
What is the first step for response to an emergency situation?
Remain calm and quiet, gather information, and assess the situation.
Suppose that two students perform a titration experiment multiple times, resulting in the average concentrations reported here. Student A 0.125 ± 0.008 MStudent B0.12 ± 0.03 M
Student A 0.125 ± 0.008 MStudent B0.12 ± 0.03 M The more precise work was done byStudent Abecausethat student's data has a smaller standard deviation.
Determine when to put on disposable gloves for work in the lab.
Before handling any glassware or chemicals for the experiment
When should lab participants look at the Safety Data Sheet (SDS) of a substance?
Before using the substance
Which chemical waste situation should always be supervised or performed by an instructor? Note that you still may need to alert your instructor about the described incident, even if you clean it up yourself.
Cleaning up a broken mercury thermometer
systematic error vs random
improper use of a measuring device random fluctuations in a measuring device
Once the separation is complete in a vacuum filtration, stop the process by first
Once the separation is complete in a vacuum filtration, stop the process by first opening the clamp or stopper on the solvent trap and then turning off the vacuum source.
PASS (fire extinguisher)
P- pull A- aim S- squeeze S- sweep
Under what conditions should a student inform the instructor of a lab injury?
The instructor must be informed of all laboratory injuries.
When should you start a new chemical waste container in the lab?
When the contents of the current container are a couple inches below the brim of the container
What is the last step of any spill cleanup procedure?
Wipe down the affected area with detergent and water.
How do you determine the last digit in any measured number?
Estimate one digit past the smallest precisely known digit or marking.
Determine whether each quantity is a measured value or an exact value.
144 grams of sugar Measured 2 avocados Exact 2 cups of milk Measured 18 meters Measured 3 teacups Exact 1 ft = 12 in Exact
Using the letters on the image, identify each component of the Bunsen burner.
A Barrel B Air inlet C Gas inlet D Gas regulator
Determine when you should remove your goggles in the lab room.
When everyone in the room is done handling any chemicals or glassware
Most chemicals can be cleaned up with a general spill kit, but a few chemicals require specialized spill procedures. For each substance listed, determine whether a general spill kit is sufficient or if a specialized spill kit is needed.
acetone general mercury special methanol general hydrofluoric acid special phosphoric acid general
In general, which characteristics are necessary for a location to be suitable for chemical storage?
cool dry dark
Which procedure cannot be performed on a hot plate, requiring a Bunsen burner instead?
Heating a crucible to remove water from a hydrate
Identify the precautions to take with exits in the lab.
Locate the exits prior to the start of lab. Do not block a door with an EXIT sign.
When drawing up liquid into a micropipette
When drawing up liquid into a micropipette, put the tip in the liquid at a 90 degree angle, push the plunger to the first point of resistance, and then release the plunger. When dispensing that liquid from the micropipette, hold the micropipette at a 45 degree angle in the desired container and push the plunger to the second point of resistance. Hold down the plunger until dispensing is done.
When inputting a formula into Excel or other spreadsheet software, what components are required for the formula to function properly?
An equal sign at the beginning of the formula Closing parentheses for any opening parentheses
how to remove gloves
Changing gloves often will minimize the spread of chemicals. To properly remove gloves, first, grasp the exterior of one glove with a gloved hand, and then, peel off the first glove . Then insert a bare finger between the interior edge of the second glove and the skin, and remove the second glove.
What is the charge delivered by a current with an average of 0.57 A over 22.3 minutes?
Charge, in Coulombs, is the product of current, in Amps, and time, in seconds. The time needs to be in seconds because 1 Amp is 1 Coulomb per second. Start by converting time given in minutes to time in seconds. time in seconds=22.3 min×60 s1 min Then, multiply the time in seconds by the current to find the charge delivered. charge in C=time in seconds×0.57 A=time in seconds×0.57 C/s
A student removes a chemical sample from a reagent bottle to be used in an experiment. What should he do with any excess chemical remaining from this sample after the experiment is complete?
Check and see if anyone else can use the chemical. If not, discard in the proper waste container.
What should you do if you are using a balance that has persistent fluctuations in mass?
Contact your TA or instructor to adjust the balance.
Which types of signs are posted to convey information about chemical storage?
Hazard signs such as "Flammable," "Oxidizer," and "Corrosive" National Fire Protection Association (NFPA) diamond Gas Cylinder sign
In the plot to determine Avogadro's number, the x-axis should be
In the plot to determine Avogadro's number, the x-axis should be moles of electrons and the y-axis should be number of electrons. The slope of the best-fit line should be Avogadro's number.
What should you do every time you are about to heat glassware on a hot plate?
Inspect the hot plate for frayed cords Check that there are no cracks in the glassware Ensure that the glassware is designed for heating
What is the purpose of the solvent trap in a vacuum filtration setup?
Keeping the running water from the sink away from the filtration apparatus, and keeping the filtered materials in the filtration apparatus
All lab participants must remain prepared to use safety equipment in case of emergency. Identify the components of effective preparation.
Knowing what safety equipment is available Understanding where the safety equipment is located Being familiar with how safety equipment is used
What information is needed in order to be prepared for an emergency?
Location of all exits Contact information for emergency personnel Location of lab phone and first aid kit Understanding of where to go should an emergency occur
Identify effective techniques for accurate pipet use. Select all that apply.
Measure liquid by aligning the meniscus with the volume line. Do not let liquid enter the pipet bulb or pump.
While setting up a beaker to boil a solution on a hot plate, you notice that the stirring is erratic and unstable. What should you do to stabilize the stirring solution?
Move the beaker to the center of the hot plate. Turn down the stirring speed.
What needs to be included in the label for each axis of a graph?
Name of quantity displayed on axis Units of quantity displayed on axis
Once the vacuum filtration set-up is complete
Once the vacuum filtration set-up is complete, start by adding a small amount of water in the filter funnel. Then, slowly decant the mixture into the middle of the filter paper.
Which signs are typically posted in areas of active lab work?
Personal protective equipment (PPE) sign Sign prohibiting food and drink Safety equipment signs Chemical storage signs
Determine whether each practice is recommended to keep a micropipette clean and functioning properly.
Save tips after removal to reuse them later. Not recommended Place the micropipette on a rack after using it. Recommended Place the micropipette on the bench between uses. do Not recommended Use a new tip any time you change solutions. Recommended Turn the micropipette upside down after loading with liquid. Not recommended
To experimentally determine Avogadro's number, you can apply a current to a metal circuit, causing the metal to lose electrons and dissolve as ions.
The number of moles of electrons lost from the metal can be calculated from the mass change and molar mass of the metal as well as the number of electrons lost in each ion formation. The total number of electrons involved in the process can be calculated from the total charge applied and the individual charge of an electron. Then, Avogadro's number is the total number of electrons divided by the number of moles of electrons.
Identify the true statements describing the experimental set-up in the Measuring Avogadro's Number experiment.
The plastic spacer should be placed between the two strips of metal. The metal strip with the red lead is the one that should have its mass measured.
Identify the recommended practices when putting a tip on a micropipette.
Use the tip size designed for the micropipette size in use. Gently push the micropipette into the tip and tap lightly to load the tip.
Determine the safest option in the lab if you need your vision to be corrected.
Wear corrective glasses or lenses under your safety goggles for the whole experiment, but always check with your TA or Instructor for your school's policy
Match each lab incident to the item of PPE that will protect you from it. Each item of PPE will only be used once.
While pulling an empty beaker off the shelf at the beginning of lab, it slips out of your hand onto the floor. Closed-toe shoes While transferring a solution from a flask to a beaker, the solution accidentally spills down the front of the lab bench. Lab coat While picking up a buret, an unknown solution left by a previous solution drips onto your hand. Gloves While checking on a stirring solution, the solution splashes up towards your face. Goggles
Which is NOT a good source of information about the hazards that affect waste disposal in a chemistry lab?
Your lab partner
Identify the safety equipment designed to deal with each emergency listed
chemicals on clothes safety shower chemicals in eyes eyewash station large fire on the benchtop fire extinguisher fire on a person fire blanket cuts or minor burns first aid kit
best way to prepare for lab
lose earrings-remove flowy sleeves- tie back or secure long necklaces- remove lose bracelets- remove long hair-tie back or secure
Identify the section in which each type of information can be found on a Safety Data Sheet.
recommendations in case of accidental contact with the chemical- First Aid Measures incompatibility or reactivity with other chemicals-Handling and Storage chemical name and formula-Identification recommended personal protective equipment (PPE)-Exposure Controls/Personal Protection possible dangers and health effects-Hazards Identification
When performing a multiplication or division calculation
significant figures in the calculated result are dictated by the significant figures of the measured numbers. The calculated result should have the same number of significant figures as the measured number in the calculation with the fewest significant figures.
When describing the uncertainty of a measurement
the term accuracy refers to the closeness between a measurement and its accepted value, whereas the term precision refers to the closeness among a set of measurements.
In a reaction, there are multiple ways to discuss the amount of compound produced. Identify the definition of each term related to the reaction yield.
The comparison of the experimental amount of product to the calculated amount Percent yield The calculated amount of product under ideal conditions Theoretical yield The amount of product experimentally produced Actual yield
Identify the following errors as systematic or random
The last digit on a pH meter fluctuates up and down as a measurement is taken. Random A micropipet is improperly calibrated, and the balance dispensed is always smaller than expected. Systematic A few drops of water are on a balance pan, causing the mass output on the balance to be high each time it is used. Systematic A thermometer is placed such that the bulb makes poor contact with the measured substance, giving erratic temperature readings. Random
What statements are always true about limiting reactants?
The limiting reactant is completely used up in the reaction. The limiting reactant dictates the amount of product. There will be an excess of other reactants at the end of the reaction.
Identify the true statements concerning Avogadro's number as it applies to atoms or electrons.
The mass of Avogadro's number of atoms depends on the element. Avogadro's number of electrons is 6.022×10236.022×1023 electrons
The purpose of the best-fit line on an experimental scatterplot is to
The purpose of the best-fit line on an experimental scatterplot is to identify any linear trend in scattered data. The best-fit line allows us to predict behavior between measured data using its slope.
When using the Tare function on a balance
start by placing the glassware on the balance. Then, press the Tare/Zero button to cancel out that mass. Finally, add your sample to the glassware and record the mass of your sample.
When heating a solution to boiling on a hot plate
start by starting and stabilizing the stir function. Then, turn the heat to a medium heat setting to start. If necessary, turn up the heat setting after waiting about ten minutes without seeing boiling.
In the plot to determine Avogadro's number
the x-axis should be moles of electrons and the y-axis should be number of electrons. The slope of the best-fit line should be Avogadro's number.
