Lab Practical Flashcards
Appropriate Lab Attire
- always wear safety goggles
- pre-labs must be completed before lab
- clothing must fully cover the body
- shoes must cover the entire foot
Keep in Mind: Analytical Balance
- handle doors with care
- never move the balance
- never dispense liquid over balance
- never put chemicals directly on the balance
- never open the top slider
- be patient
- keep balance clean
- don’t sweep chemicals into hand
Analytical Balance Features
- tare (zero function)
- sliding doors
- decimal place (four decimal places)
how to find the mass of water in an analytical balance
weigh the beaker first and record mass. fill with water then weigh again. subtract beaker mass from beaker and water mass to get water mass.
volumetric pipette
red bulb suction thing
TD (amount of error calibrated into the device): +/-0.2 mL
volumetric pipette procedure
- bulb should be loosely placed on end of pipette
- draw liquid just past the desired line
- remove bulb quickly –
- replace with thumb to hold suction
- drain to line
- deliver liquid
- move slowly
- dont draw liquid into bulb
reporting quantitative measurements
- numerical value
- units (in grams)
- precision / accuracy (uncertainty)
- sig figs indicates precision
- the right most digit is always an estimate
- uncertainty expressed with a +/- sign
top loader balance
regular balance
- decimal places: 2
- implied precision: +/- 0.01g
precision
reproducibility
- how close measurements are to each other
- indicated with sig figs if no other information is available
- can be told by the standard deviation
accuracy
how close the value is to the actual value
- fundamentally unknowable
systematic error
- part of the experimental system
- ex. faulty device or inconsistent reading
- can be eliminated
random error
- caused by an unknown / unpredictable errors from the environment
- can never be eliminated
What type of error (systematic or random) is caused by viewing
the meniscus from an angle?
systematic error
standard deviation
- quantify the uncertainty or “spread” in data
- smaller SD = less uncertainty (more confidence)
Galvanized Nails, Quality Control, and an Introduction to Green Chemistry
- measure the length of a nail in millimeters using a calliper
- find the mass of each nail individually.
- Using a measurement device, five milliliters of hydrochloric acid was retrieved.
- The measurement device was filled to ten milliliters, then we waited for the device to adjust to five milliliters to ensure the appropriate amount of
solution was used. - One nail was placed into the hydrochloric acid and we started the timer for two
minutes, simultaneously. - Observations were discussed and reported during this waiting period.
- Once the timer ended, the mixture (with the nail still inside) was dumped into a shared waste beaker.
- A pair of forceps were used to pick up the nail from the waste beaker. While holding the nail with the forceps, distilled water was used to thoroughly rinse the nail, allowing the water to fall into the waste beaker below.
- The nail was then dried with tissues and placed on the analytical balance to determine the mass.
- The used nail was then disposed of in the proper location, underneath the fume hood in the lab
the rusting of nails is…
a chemical reaction
what protects something from corrosion
- paint
- keeping things dry
- a protective coating
- extending nail life with a zinc coating
why does zinc ideal to protect the nail
- zinc is more resistant to corrosion than iron
- zinc is low cost
how to assess if galvanized nails comply with industry
standards
use high quality vs low quality standards
what is green chemistry
is the design of chemical products and processes that reduce the use
and generation of hazardous substances
goals of green chemistry
- prevent waste rather than treat or clean up after
- minimize amount of materials used in the production of a product
- use and generate substances that are not toxic
- use less energy
- use renewable materials
- use materials that degrade into innocuous products at the end of their useful life
green waste management
1) Know your materials
2) Know your chemistry
3) Use your chemistry
how to find the density of copper
- the density of copper pieces that varied in shapes and sizes was found
by using the water displacement and the caliper method. - find mass of copper using an analytical balance.
For the water displacement method:
- a 10 mL volumetric pipette was used to extract 10 mL of water.
- The water was then placed in a graduated cylinder
- Each piece of copper (small cylindrical piece, large cylindrical piece, small rectangular piece, and the large rectangular piece) was individually placed in
the graduated cylinder and where the water rose to was noted.
- For the caliper method, the caliper tool was used to measure the diameter, height, length, and width of each piece of copper (the same pieces from the previous method).
- The volume was calculated using these measurements.
- The mass of the copper was then divided by the calculated volume to find the density
how to find the density of soda
- each individual was in charge of a different amount of soda and would conduct three trials.
- One student looked at 6 mL of regular soda, another looked at 11 mL of
regular soda, while another student looked at 15 mL of diet soda, and the final student looked at 20mL of diet soda. - The analytical balance was used to determine the mass of the empty beakers.
- Each student used a different sized volumetric pipette that was consistent with the condition (the amount of soda they were in charge of).
- The analytical balance was used again to find the mass of the beaker with soda, which produced a value that could be subtracted from the empty beaker to determine the mass of the soda, relevant to the respective condition. This mass was then divided by the volume of the soda assigned at the beginning of the experiment to provide the density.
copper / soda density claims
Claim 1: Of the two methods for calculating the density of copper blocks, the caliper method is more accurate.
Claim 2: The size and shape of copper does not affect density.
Claim 3: Regular coke is more dense than diet coke.
Determination of the Percent Oxygen in Air Procedure
- Grab a piece of steel wool and lay a piece of weight paper down on the analytical balance.
- Zero out the scale and then place the steel wool piece down to record its mass.
- While wearing gloves, spread the steel wool out to optimize its
surface area. - Dip the steel wool in the half water and half vinegar mixture, so it is fully submerged and let it sit for one minute. Remove the steel wool and wring it out in the vinegar waste beaker.
- Tightly coil and roll the steel wool and place it into the test tube. Use the stirring
rod to press it down so it reaches the bottom, without smashing it too far in. - Turn the tube upside down to make sure that the steel wool doesn’t fall out.
- Place the test tube in at least 300 milliliters of water upside down, allowing the mouth of the test tube to be at the bottom of the beaker.
- Simultaneously start a timer for five minutes. Record the temperature by pointing the laser of the infrared thermometer at the top of the test tube (the part pointing out of the solution).
- Record the height of the water level by carefully lifting the test tube so that the water inside equals the water outside of the tube.
- The measurement can be attained by utilizing the ruler that is already attached on the outside.
- Wait five minutes and record observable observations.
- When the timer ends, record the height of the water level using the same water level measuring process.
- Continue measuring water levels until it begins producing a consistent value (balancing out).
- Once a consistent value is obtained, record the final temperature using the same infrared thermometer process.
- Dispose of the vinegar waste and use forceps to remove the steel wool from the test tube.
cylindrical test tube
This tube is specifically designed to account for the non-cylindrical closed end.
How does the mass of iron impact the rate of reaction. Would the rate of reaction be slower or faster if the steel wool was in a tight wad instead of being spread out
- If the mass of the iron were to be higher, it would take longer for the rust to develop because the reaction takes longer.
- Similarly, if there was less iron, the rust would form quicker.
- The rate of reaction would be slower if the steel wool was not spread out because it would take longer for the iron to be exposed to moisture.
- There is more open space in the iron sample and less surface area, therefore the reaction happens faster.
Percent oxygen experiment: What is the role of acetic acid in this reaction? How does a catalyst function
The catalyst of this reaction was the acetic acid, which is the element of the reaction that increases the rate of reaction but is not consumed in the reaction. Soaking the iron in acetic acid before the reaction lowered its activation energy so that it would start to rust quicker
Stoichiometry: Determination of a Metal Carbonate Procedure
how to find the mass of an unknown
- Commonly done using precipitation reaction
- Uses the mass of a sample to determine the amount of the substance of interest
- Utilizes the Law of Conservation of Mass
- The known reactant needs to be in excess to fully precipitate product
conservation of mass
mass cannot be created or destroyed
vacuum filtration apparatus
funnel at the top with a vacuum that sucks stuff down. a waste beaker is located at the bottom to catch substances.
determining the mass of an unknown procedure
- Scoop the unknown carbonate onto the weight paper to determine mass.
- Pour the weighed amount into a beaker. Add 100 milliliters of deionized water to the beaker with the sample in it.
- Ensure the sample is thoroughly mixed into the beaker. Check the bottom
to see if any residual substance remains. Use the stir rod to mix the mixture further. - Gather 25 milliliters of strontium chloride and pour it into the beaker (ensuring it is in excess).
- Wait for a clear liquid layer to form at the top of the solution. Use a pipette to remove part of the clear liquid at the top and place it onto the well plate.
- Add a drop of sodium chloride and observe to see if any appearance changes occur.
- Ensure this liquid is clear enough before proceeding. Weigh the glass tray with the weight paper on top and record the mass.
- Record the tray number used, as well. Turn on the vacuum.
- Place the weight paper into the center of the funnel attached to the waste beaker. Use distilled water to wet the weight paper, this allows the paper to adhere to the funnel.
- Using the glass beaker, place the stir rod so it is pointing at the center of the weight paper and begin pouring slowly. Aim for the center to prevent the mixture from spilling towards the sides and falling under the weight paper Ensure the accumulated waste appears clear.
- Pour excess from the well plate into the center of the funnel. Rinse the beaker with distilled water to ensure remaining mass is still poured through the paper. Scrape residue on the sides onto the weight paper.
- Using tweezers, slide the weight paper onto the glass and put it in the oven to dry.
- Let dry for 25 minutes. Once cooled, take the final mass and use data to create calculations.
Qualitative observations lab overview
You will be running many different reactions – as such, waste management will be a critical part of this lab
Qualitative observations lab procedure
Part A1: Bring the test tubes from the lab station over to the designated area where the substances are located. Measure out a small portion of baking soda and place it into a test tube. Record initial observations of the baking soda in the test tube and observe the bottle of vinegar (acetic acid) briefly. Add 10-20 drops of the vinegar into the tube and observe reactions.
Part B2: Bring the test tubes to the designated work space. Use a clean tube and add approximately one milliliter of 0.1 M magnesium chloride. A reference test tube can help with this approximation. Report initial observations into a lab notebook. Add equal volume of sodium hydroxide and mix after each addition. Report final observations into the lab notebook.
Part C1: Use a small test tube with an approximation of two milliliters of 3.0 M of hydrochloric acid. Record initial observations of the substance and then locate a pea sized piece of steel wool. Drop the steel wool into the test tube and record observed changes.
Part D1: Familiarize oneself with how the Bunsen Burner works and its safety procedures. Place a small piece of a potato into a clean test tube using forceps. Fill the test tube with hydrogen peroxide (around 5%-6%) until it is around half way full. A rubber stopper should quickly be placed on top of the test tube lightly, refrain from creating a tight seal. Wait ten seconds and observe changes. Using the Bunsen Burner, light a wooden splint and let it burn for a couple seconds. Blow out the splint so it is still glowing a bit and place it into the test tube. Record observations in a notebook.
Part E1: Using a test tube, add two milliliters of 2.0 M of sodium hydroxide. Use a reference test tube to help with this approximation. Measure an equal volume of sulfuric acid into a tube. Record any observed changes.
Part F2: Remind oneself of how the Bunsen Burner works and its safety procedures. Grab a copper wire. Set a timer for one minute and simultaneously hold the copper wire over the lit Bunsen Burner until the timer ends. Scrape the sides of the wire using a metal tool. Dispose of the wire.
Determination of Heat Exchanged in Acid-Base Reactions Procedure
1st part
- scoop 5.6 g - 5.8 g of magnesium hydroxide onto the tray and record official mass
- Fill the graduated cylinder with 100 milliliters of water and pour it into the styrofoam cup that is sitting underneath the thermometer and stir rod.
- Press the start button and wait until the temperature events out. Record initial temperature.
- Wait 10-20 seconds and then begin slowly adding the magnesium hydroxide into the water.
- Monitor the temperature until it becomes stable for approximately one minute and then press the stop button.
- Calculate the change in temperature.
2nd part
- measure out substance.
- Press the green button again and begin stirring the magnesium hydroxide slurry.
- Once the magnesium hydroxide stabilizes, pour in the measured amount of citric acid and monitor the temperature.
- Once the temperature stabilizes for about a minute, press the stop button.
- Clean and dry the calorimeter cup and stir rod and pour waste into the class waste disposal bucket.
- Rinse the cup with distilled water over the bucket. The weight boat can be disposed of in a separate bucket.
3rd part
- Measure out 100 milliliters of water and pour it into the styrofoam cup using the graduated cylinder.
- Measure out the mass of the citric acid (use the same mass range from part two).
- Press the start button. Add the citric acid into the cup and monitor the temperature until it stabilizes, and then press the stop button.
4th part
- measure out 5.6 g - 5.8 g of solid magnesium chloride into a zeroed out weight boat on the analytical balance.
- Press the green button and begin stirring the slurry.
- Once the citric acid stabilizes, add the magnesium hydroxide into the mixture and monitor the temperature.
- Once the temperature stabilizes, press the stop button.
- Repeat the cleaning protocol from part two and quit Logger Pro.
calorimetry
the measurement of the quantity of heat exchanged
the first law of thermochemistry and the hess’s law
the total enthalpy change of a chemical reaction is the same whether the reaction occurs in a single step or a series of steps.
calorimeter components
- thermometer
- stirrer
- insulated container
- styrofoam cup
Verneir Logger Pro
application that measures temperature changes over time
energy changes
energy into system equals energy out of surroundings and vice versa
positive for endothermic, negative for exothermic
Caliper
wrench looking measurement device that can help determine diameter
- What is the purpose of galvanization? Are galvanized nails better than non-galvanized nails (explain)?
- Galvanization is used to defer the rusting process. For nails, this means applying a zinc coating that deters the rusting process.
determinant error
errors that are known and controllable errors e.g instrument errors, personal errors, etc.
indeterminant
caused by uncontrollable or unknown fluctuations in variables that may affect experimental results
why does zinc prevent corrosion
On exposure to air, it develops a thin gray oxide film (protects the nail), which prevents deeper oxidation (corrosion) of the metal
why does acid cause rust
they break down the oxide layer that forms on the surface of the metal, exposing the metal to oxygen and water hence accelerating the rusting process
what does the percent oxygen reaction tell us
When you soak the steel wool in vinegar it removes the protective coating of the steel wool and allows the iron in the steel to rust. When the protective coating is removed, oxygen in the atmosphere can reach the iron in the steel wool. Rusting (or oxidation) is a chemical reaction between iron and oxygen, this chemical reaction creates heat energy which increases the temperature inside the beaker.
