CHEM LAB FINAL EXAM
General Laboratory Notebook Guidelines
- Laboratory notebooks can have lined, blank, or graph paper pages. The bound edge must be sewn. Pages should never be torn out of a sewn bound notebook. - All entries must be in ink. The ink should be permanent. - Entries in the notebook should be legible. - Data should not be "obliterated" by erasure, blacking-out, or whiteout. If there is an incorrect entry made, simply draw a strikeout line though the data. To indicate large amounts of incorrect data or text, use a diagonal line or "x" out the page. - Do not leave empty space, use a diagonal line or "x" to indicate large areas (a quarter of the page or more) of unused space. - As a general rule, there should be no loose material in the notebook. If the notebook is turned up and shaken, nothing should fall out. You may tape or staple special information (such as a diagram or graph) into the book by one edge, but do not do this to "cover up" a mistake or tape down all sides.
What to do before your first experiment
- Make sure you name, course and section number, and contact information for returning a lost notebook are on indicated on the cover (inside or out). - Create a page labeled "Table of Contents" at the place in the notebook where the work for this semester will start. - For each experiment, you will want to record the experiment title and the page it begins on the "Table of Contents" page. - Pre-number your pages. The reason for this is that if a page is torn out, the break in the numerical sequence will be obvious
What to do during each experiment
- Outline the experimental steps with enough detail that someone with your level of experience would be able to repeat the experiments and obtain the results you did. - Collect data in your organized data table with units. - Show sample calculations with units. - Report observations. Include color changes, temperature changes, formation or dissolution of precipitates, gas bubbles produced in a reaction, distinguishable odors. Make sure to waft the odor towards your face - never try to smell a container with a chemical directly and do so only when instructed to. - If you collect data in a data file during the experiment, make sure to record your file name in your notebook.
What to do to prepare for all experiments
- Write a purpose statement based on the narrative in the laboratory manual. To write a purpose statement, answer the question, "why is this experiment conducted?". Your statement should be short - a maximum of one to two sentences. - Read the whole experiment that will be performed that day. Pay attention to experimental section and any safety information. Safety information specific to chemicals and/or process should be noted in your notebook in a section between the purpose statement and the experimental section. - You can construct your data tables based on the suggested ones in the Laboratory Manual. Also include the important pieces of information that are required to record data.
Solvent
A liquid substance capable of dissolving other substances
Which of the following describe a consequence from contact with a physical hazard.
A shock from a hot plate. A burn from hot glass. Frostbite from dry ice.
What is one way to prepare when working with an acid, such as nitric acid?
Wearing an apron and splash-proof goggles
For the Molecular Weight lab, you will be performing ____ trials.
two
The rate law for the reaction A + B → C was found to be rate = k[A][B]. One experimental trial with the [A] = 0.26 M and [B] = 0.17 M had an initial rate of product formation of 0.35 M/s. What is the value of the rate constant for this reaction? Remember your units.
0.35 M/s = k [0.26][0.17] k = 7.9 1/Ms
An ideal gas sample was collected in a 0.410 L container at 3.28 atm and 301 K. The sample was found to have a mass of 0.751 g. What is the molecular weight of this sample?
13.8 n = PV/RT n = 3.28 atm (0.410 L) / 0.08206 (301 K) n = 0.054445344 MW = g/n MW = 0.751 g / 0.054445344 mol MW = 13.8 g/mol
An ideal gas sample was collected in a 0.301 L container at 4.24 atm and 308 K. The sample was found to have a mass of 0.733 g. What is the molecular weight of this sample?
14.5 n = PV/RT n = 4.24 atm (0.301 L) / 0.08206 (308 K) n = 0.050495203 MW = g/n MW = 0.733 g / 0.050495203 mol MW = 14.5 g/mol
The data below were obtained from an unknown liquid following this lab procedure. Calculate the molecular weight of the unknown. weight of flask 149.652 g weight of flask + unknown 150.702 g temperature of water bath 96.8 °C barometric pressure 677.7 mm Hg volume of flask 299.2 mL
150.702 g flask + unknown - 149.652 g flask = 1.05 g condensed liquid 96.8 °C + 273.15 = 369.95 K ≈ 370 K 677.7 mmHg x (1 atm / 760 mmHg) = 0.8917 atm ≈ 0.892 atm 299.2 mL x (1 L / 1000 mL) = 0.2992 L PV = nRT n=PV/RT n = (0.892 atm) (0.2992 L) / (0.08206 L atm/mole K) (370 K) = (0.267) / (30.4) = 0.00878 moles of unknown substance Molecular weight = grams/moles (1.05 g condensed liquid) / (0.00878 moles of unknown substance) = 119.5899 g/mole ≈ 120 g/mole
The Ka of an unknown weak acid is 1.7 x 10-9. Determine the pKa of the weak acid
8.77
To put out a fire in a classmate's hair or clothes, use:
A fire blanket to smother the flame.
Solute
A substance that is dissolved in a solution.
Broken glassware in the lab is a hazard because:
A. if in the sink, someone might cut themselves trying to dispose of it properly. B. if left on the lab bench, someone might cut their arm after leaning on the lab bench. C. if left on the floor, someone might cut their foot after stepping on it. D. All of the above. Answer: All of the above
Jewelry is a hazard in the lab because:
A. Jewelry that dangles could become hung in a piece of equipment and cause an accident. B. Chemicals may react with the materials in jewelry. C. Chemicals may become trapped under jewelry causing chemical exposure and potential chemical burns. D. All of the above. Answer: All of the above
What is the chemical formula for aluminum phosphide? For answers with subscripts, include number after the chemical symbol. DO NOT INCLUDE SPACES!
AlP
Determine if the scenarios below violate the academic integrity policy. A student emails another student in the lab section to determine the color change present from the indicator used in a titration experiment in lab. The solution color change description is required in a lab report. A student retakes introductory chemistry lab. The data the student collected this semester did not graph correctly. However, when the student took the course last semester, the graph appeared as it should. The student uses the data and graph from the previous semester to complete a lab report. A student consults with another student in the lab section about how multiple calculations are completed on the lab report.
All three are violations of academic integrity
Match the following descriptions to the appropriate term. Rate of reaction Rate law Rate constant
Always has units of amount per time (e.g. M/S or M/min) A formula that relates reactant concentration to reaction rate Can have different units such as M/s, 1/s, etc. depending on the reaction order
Select all the true statements regarding chemical equilibrium. Select one or more: The concentrations of reactants and products are equal the rates of the forward and reverse reactions are equal. Reactants are still being converted to products (and vice versa) The concentrations of reactants and products remain constant
B, C, and D
What is the chemical formula for carbon trioxide? For answers with subscripts, include number after the chemical symbol. DO NOT INCLUDE SPACES!
CO3
According to the SDS for 0.2 M Nitric Acid, this very dilute acid has which hazard statement?
Causes severe skin burns and eye damage.
Which of the following is not a required label element in the GHS?
Chemical formula
Select all of the ways you can minimize risk in the laboratory.
Eliminate a hazard. Wear appropriate PPE. Use low concentrations of chemicals when possible.
Of the following choices, which is the most effective way to minimize risk?
Elimination
In the hierarchy of controls, which of the following is/are more effective than PPE in minimizing risk.
Elimination of hazard Follow an administrative standard operating procedure Substitute with a less hazardous chemical
Safety in the laboratory is the responsibility of:
Every person working in the lab.
How are the orders of the iodide and persulfate ions determined in this experiment?
Experimentally, by calculating the change in rate and the change in concentration for given trials
___________ and consequences must be assessed to accurately decide the level of danger posed by a hazard.
Exposure
Unused chemicals may be disposed of by:
Following your instructor's guidelines with disposal in labeled containers or diluted with water and flushed down the sink.
Suppose that during the freezing point depression experiment, you forgot to tare the balance before weighing your solid unknown. How would this specifically affect the calculated molecular weight of your unknown?
Forgetting to tare the balance and weighing the solid unknown with the weigh paper would lead to an erroneously large molecular weight. The freezing point depression would still reflect the actual concentration of solute. However, the molecular weight determination would have an inaccurately large value for the mass of solute. Therefore, when dividing the grams of solute by moles of solute, the molecular weight will would be erroneously high.
Chemical hazards can be recognized using the GHS. What does the acronym GHS mean?
Globally Harmonized System
What is the chemical formula for sulfuric acid? Include appropriate state of matter . For answers with subscripts, include number after the chemical symbol. DO NOT INCLUDE SPACES!
H2SO4(aq)
Suppose that you didn't make a pin hole in the aluminum foil. How would this specifically affect the calculated molecular weight of the unknown for this particular trial?
If the pin hole was never made in the aluminum foil none of the unknown substance would be allowed to escape the flask. The mass of the flask with the cap, band, and condensed liquid would consequently be an erroneously high measurement. The calculated grams of unknown substance would therefore be higher as well. When using the formula for molecular mass the erroneously high calculation for grams of unknown substance would be used and cause the molecular weight for the unknown substance to be calculated as erroneously high.
Upon completion of the experiment, where should you place all solutions (E.g. standard solution, experimental solutions, and excess reagents?)
In a labeled waste beaker and then pour entire contents of the beaker in the appropriate labeled container in the hood
In the course of your lab exercise, you fail to label a beaker and do not know what chemical it contains. You should:
Inform your instructor and ask what to do with the unknown chemical.
The temperature unit to use in the gas laws is
Kelvin
Which of the following items are appropriate clothing that minimizes chemical exposures and injuries while in lab:
Long-sleeve shirts and jeans
An alkaline earth hydroxide, M(OH)2, was taken to lab for analysis. The unknown powder was poured into a flask and swirled in room temperature DI water until a saturated solution formed. This solution was then slowly filtered to remove the undissolved solid hydroxide. 27.5 mL of this saturated solution was titrated with 0.143 M HCl (aq). Endpoint required 25.90 mL of the HCl (aq) solution. Calculate the Ksp for this alkaline earth hydroxide
Molarity of HCl = 0.143 M Volume HCl added = 25.90 mL 25.90 mL HCl x (1 L / 1000 mL) = 0.02590 L HCl 0.02590 L HCl * 0.143 M HCl = 0.003703 mol HCl ≈ 0.00370 mol HCl 0.00370 mol HCl x (1 mol OH- / 1 mol HCl) = 0.00370 mol OH Volume of saturated solution titrated = 27.5 mL 27.5 mL saturated solution x (1 L / 1000 mL) = 0.0275 L saturated solution 0.00370 mol OH- / 0.0275 L saturated solution = 0.1345 M ≈ 0.135 M OH x = [OH- ] / 2 [OH- ] = 0.135 M x = 0.135 M OH- / 2 x = 0.0675 M Ksp = (x)(2x)^2 Ksp = 4x3 Ksp = 4(0.0675M)3 Ksp = 1.22 x 10-3
Show the calculation for obtaining the molarity of your unknown acid. Molarity of NaOH = 0.1445 M Volume NaOH at equilibrium = 18.93 mL 24.91 mL unknown weak acid
Moles base = (M NaOH) x (L NaOH at equivalence point) 18.93 mL NaOH x (1L / 1000 mL) = 0.01893 L NaOH 0.1445 M NaOH x 0.01893 L NaOH = 2.735 x 10-3 moles NaOH At Equilibrium: moles of acid = moles of base 2.735 x 10-3 moles unknown weak acid Volume unknown weak acid added = 24.91 mL 24.91 mL unknown weak acid x (1L / 1000 mL) = 0.02491 L M of weak acid = (moles of unknown weak acid / L of unknown weak acid added) 2.735 x 10-3 moles unknown weak acid / 0.02491 L = 0.1098 M
Was your K constant (or mostly constant) for all trials? Should it have been? Explain. What side of the equilibrium is favored for this reaction? Explain.
My K value consisted of a moderate amount of variation between trials. The K value should theoretically remain constant as long as the temperature remains the same. This is because the K value is independent from the initials concentrations of reactants or products. The average equilibrium constant suggests that this reaction is very product-favored, because any reaction with a value for K>1 is product-favored.
What is the chemical formula for sodium nitrate? For answers with subscripts, include number after the chemical symbol. DO NOT INCLUDE SPACES!
NaNO3
Does the numerical value of the rate constant, k, depend on initial reactant concentrations? Does the numerical value of the rate of the reaction depend on initial reactant concentrations? Does the presence of a catalyst affect the rate constant?
No, the rate constant acts independently from initial reactant concentrations. Yes, a higher initial concentration increases the reaction rate and vice versa. Yes, the rate constant is dramatically altered by the presence of a catalyst.
When 0.684 g of menthol is dissolved in 25 g of cyclohexane, the freezing point of the solution is lowered by 4.87 oC. The freezing point and Kf constant for cyclohexane is 20.8 oC/m. Calculate the molar mass of menthol.
Tf = (Kf)m 4.87 oC = 20.8 oC/m (m) m = 0.234 m = moles of solute / kg of solvent 0.234 = moles of solute / 0.025 kg moles of solute = 0.00585 MW = g solute / moles soute MW = 0.684 g / 0.00585 mol MW = 117 g/mol
Determine the molecular weight of the unknown from the following data collected from a freezing point depression experiment. freezing point of pure p-xylene 10.9 °C freezing point of p-xylene + unknown 8.7 °C mass of test tube + cork 96.643 g mass of test tube + cork + p-xylene 127.052 g mass of unknown added to p-xylene 1.661 g
Tf = 10.9 °C freezing point p-xylene - 8.7 °C freezing point p-xylene + unknown = 2.2 °C Tf = 2.2 °C 127.052 g mass of test tube + cork + p-xylene - 96.643 g mass of test tube + cork = 30.409 g p-xylene Tf = (Kf)m Tf = 2.2°C (Kf) = 4.30°C/m 2.2°C = (4.30°C/m)m 2.2°C / (4.30°C/m) = m 0.5116 = m m ≈ 0.51 m = moles of solute / kg of solvent 30.409 g solvent * (1 kg / 1000g) = 0.030409 kg 0.51 m = moles of solute / 0.030409 kg 0.51 m * 0.030409 kg = moles of solute 0.0155 = moles of solute 0.016 ≈ moles of solute MW = g solute / moles solute MW = 1.661 g unknown solute / 0.016 moles solute MW = 103.8 g/mol MW ≈ 100 g/mol
Upon completion of experiment 1, where should you place the liquid waste?
There is no waste generated in the experiment, the flask is simply rinsed several times with DI water
What will happen to the reaction in the kinetics experiment if you don't add the starch indicator?
There will be no color change.
For face to face events like attending class, lab, or meeting with faculty in office hours, a face mask must be worn at all times.
True
You heat a piece of glassware and now want to pick it up. You should:
Use tongs
What is the chemical formula for zinc chloride? For answers with subscripts, include number after the chemical symbol. DO NOT INCLUDE SPACES!
ZnCl2
What is the solubility product expression for Al(OH)3(s)?
[Al3+][OH-]3
A hazard may be simply defined as
any source of potential injury, damage, or harm.
When should you put on your safety goggles?
as soon as you enter the lab
What signal word can be found on the SDS for 0.2M nitric acid?
danger
The addition of NaCl to water cause the vapor pressure to ____ , the boiling point to ____ , and the freezing point to ____
decrease, increase, decrease
How can you experimentally determine the pKa of acetic acid?
determine the pH of the solution 1/2 way to the end-point on the pH titration curve for acetic acid
According to the SDS for 0.2M nitric acid, if the chemical is ingested, induce vomiting immediately.
false
Alkaline earth metals form hydroxides that are reasonably soluble.
false
The first step in the RAMP process is to Record the risk.
false
The only hazards that you need to think about in your chemistry laboratory are those from the chemicals you are using.
false
What is the name of the glassware shown?
graduated cylinder
The GHS classifies chemicals into three broad categories. They are
health, physical, and environmental
The numerical value of Keq is of/on initial concentration of reactants and products
independent
For the reaction shown here 8H2S (g) ↔ 8H2 (g) +S8 (g) The equilibrium concentrations were found to be [H2S]=0.338 M [H2]=0.507 M [S8]=0.720 M What is the equilibrium constant for this reaction? Give your answer to 3 significant figures.
k = ([0.507 M]^8 * [0.720 M]) / [0.338 M]^8 k = 18.5
Risk is a measure of the severity of the danger and the ____________________ of the exposure to the hazard.
likelihood
Unauthorized experiments in the laboratory are:
not allowed
In the acronym RAMP, the "P" represents ___________________________.
prepare for emergencies
What is the chemical name for Na2CO3 ? Spelling and spacing matter, make sure to follow the spacing rules outlined in your textbook and only put 1 space between words.
sodium carbonate
What is the principal difference between a strong and weak acid?
strong acids completely ionized while weak acids only partially ionize
A hazard is an intrinsic property of a chemical.
true
Asking the question, "What would I need to lessen the consequences or respond to an emergency effectively?" is another way of preparing for emergencies.
true
One way to minimize risk is to eliminate a hazard.
true
Performing a risk assessment is just one part of a risk management system.
true
When assessing a risk, asking the question "What level of danger is posed by the hazards?" is a great starting place.
true
