Revised Summer II 2016
CH111 PRELAB : HARDNESS OF WATER
- (a) Convert 9.13 x 10-5 g CaCO3/mL to ppm. (Hint: conversion factor on p. 17.)
(b) When titrating hardness with a soap solution, the endpoint is indicated by a lather. This lather is created by excess soap and a “blank” must be first determined by titrating a sample of distilled water (distilled water has zero hardness, so the soap used is only for the lather).
Calculate the “blank” ( mL soap / mL distilled water) if a student used 0.74 mL of soap to get a lather for a 20.00 mL sample of distilled water.
(c) When titrating water samples with hardnesses greater than zero, the soap first reacts with all the Ca2+ and then produces a full lather to get to the endpoint. Therefore, the amount of soap used for only the lather needs to be subtracted out of the total volume of soap used for the full titration in order to determine the amount of soap needed for the Ca2+(also called the corrected soap volume).
Calculate the corrected soap volume (the soap is required to react with just the Ca2+ ) if a 10.00 mL sample of hard water took a total of 5.13 mL of soap to get to the full lather endpoint.
corrected soap volume (mL) = total mL soap used – [ “blank”(from 1b) x (mL of water sample)]
- Describe the procedure for the experiment. This could be in an outline format or a flow chart format or paragraph format. It should not be copied directly from the manual. (This should be between ½ – 1 page, you may use the back of the page)
- Briefly discuss all safety precautions related to this experiment. (chemical and equipment related)
HARDNESS OF WATER
Chemical Handling and Waste Treatment
Normal laboratory safety practices must be followed at all times. MSDS sheets are available in the laboratory.
The soap solution is alcohol-based and therefore can be considered flammable. No sparks or flames are allowed in the laboratory.
The EBT (eriochrome black T) indicator is dissolved in 2-methoxyethanol. This solution is a combustible liquid and is considered harmful if inhaled, swallowed or absorbed through the skin. If skin contact occurs, promptly wash with soap and water.
The pH 10 buffer solution has a very high ammonia concentration, the vapor is very noxious and especially corrosive to skin and eyes. Avoid excessive inhalation, however if you do inhale the vapor, move away from the area to fresh air. Contact lenses SHOULD NOT BE WORN. If skin contact occurs, flush the affected area with lots of cold tap water and inform the instructor.
All completed titrations, can be disposed of by rinsing down the drain with lots of cold tap water.
Due at beginning of lab
ALL parts EXCEPT PROCEDURE
Introduction…as usual…state the purpose and explain the chemistry involved…do NOT just list all the calculations in the intro
Data: simply use lab computer print-out…be sure to attach it in the data section (NOT AT END)
Calculations: show all the calculations…there were 7 titrations…so show 7 equations and 7 calculations and 7 answers…be sure to give the equation used, use labels, units and proper significant figures.
Discussion: State the ppm results for the water samples (tap and unknown) for the 2 methods. Compare to the actual given values and compare the 2 methods to each other. % error is a good way to compare the 4 results. Comment on accuracy and precision. Discuss sources of experimental error.
(signed carbons attached at end)
CHEMISTRY LABORATORY GENERAL INFORMATION
This laboratory course is intended to present the basic concepts that are essential to a general understanding of the science called chemistry. The specific objectives are:
- Provide training in the application of specific principles, thus strengthening the power of logical reasoning.
- Develop an ability to discover facts through experimentation, an important step in learning to evaluate the work of others.
- Develop a feeling for quantities, such as the volume or mass of a substance used in the laboratory, or the degree of completeness to which a reaction proceeds.
- Identify and induce neat and precise work habits.
- Develop the ability to produce well-written prose which conveys the method of experimentation, the results of that experimentation, and the logic by which the results of the experimentation are analyzed.
Notebooks for the Laboratory
Each student is required to have a laboratory notebook. The laboratory notebook is a permanent, documented record of laboratory data and observations. The laboratory notebook must be a bound book. The notebook makes carbonless copies. This notebook should be a complete record of the ideas and actions which are part of the laboratory work. Keeping a proper laboratory notebook is an essential part of “real-life” science and research. Some specifics which have been developed over the last couple of centuries as part of the format for a laboratory notebook are given below:
- Each page number is pre-printed in the upper right-hand corner, use pages in numerical order as printed. Do not skip pages or tear out random pages.
- Your name, the date, the name(s) of your lab partner(s) (if any) and the title of the experiment should be recorded on every page used for the experiment. This should be done during the lab period while using the lab notebook.
- Only one side of each page is used. A carbon copy must be generated simultaneously. When using the carbonless notebook, be sure to put the cardboard separator between each set of pages.
- All data, calculations and details of the experiment must be recorded directly into the notebook, in ink, while you are performing the experiment. It is important that every detail is recorded as the event occurs. The notebook is a historical record, a diary, of what was actually done in the lab. Information is never collected on scraps of paper, the lab manual or other paper to be recorded
“later”. Always use the lab notebook for primary data recording.
- Both the original and the carbon copy pages must be initialed and dated by the instructor before you leave the laboratory. The carbon copy (the bottom copy) is perforated and is removed from the notebook to be taken home and is used as the basis of your final report. Never remove the original pages from the notebook. The laboratory notebook itself must remain in the laboratory drawer.
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- Since data and thoughts are being recorded directly into the notebook, errors will be made. These errors are deleted by drawing a single line through them. Never blot out or erase or “white-out” what are considered errors. Original thoughts and data must not be destroyed! These so-called errors often provide useful information. You should also record a brief explanation of why the item was changed.
- When calculations are recorded in the lab notebook, be sure to clearly identify the calculation, show equations used, labels and units as well as the worked out answer. If a calculation is incorrect and has to be re-done, be sure to show the new work. As with correcting data, just draw a single line through the error and place the new entry nearby.
- A laboratory notebook should be legible and the data should be easily decipherable with labels and units.
Plagiarism of any kind will not be tolerated. Copying from any text, the manual or any other person will not be accepted. Each student is expected to write and submit a unique report that represents their own ideas. Group work should not result in identical reports. Any instance of plagiarism or re-use of data (past or present) without consent of the instructor will seriously jeopardize your lab grade. It is important to remember that if you fail lab you fail the whole course.
The issue of digital plagiarism has raised concerns about ethics, student writing experiences, and academic integrity. Although you may never have engaged in intentional plagiarism, many students do incorporate sources without citations, which is a form of plagiarism. The University of Hartford subscribes to a digital plagiarism detection program called SafeAssign, which you will use to check lab reports for this course and see whether you may have included in your report material that requires a citation. In addition to the actual report, you will upload your work to Blackboard through SafeAssign so that it can be checked against web pages and databases of existing papers. Your paper will then automatically become part of that database for future use. Further instructions will be given in lab.
In addition to the universal rules banning any form of plagiarism, in the scientific disciplines, particularly with respect to patents, the intellectual ownership and correct representation of data are of utmost importance. Thus it is considered to be extremely unethical to use another person’s data, with or without that person’s permission, unless the data are clearly identified as being collected by a different person. It is unethical to “fudge” data or make up data. Every time an experiment is performed, it is a unique demonstration of a chemical principle. As such, it is unacceptable to present data that were collected on one day as data that were collected on a different day. Data from one run of an experiment may not be “reused” for a second run, even if the same person is performing the experiment. Data may not be added or eliminated from a data set without an explanation and justification.
There are a number of sources which expand upon these general principles. If a student is uncertain whether a certain behavior or use of data is scientifically ethical, it is the responsibility of the student to ask the laboratory instructor in advance.
Written Presentation of Your Work
All presentations of experimental work should be written in the past tense, since you have already done the experiment. A somewhat more involved concept is that of writing in the third-person passive voice. This formality is derived from the fact that the role of the experimenter in the laboratory is to make it possible for the natural course of events to take place. Thus, the experimenter does not actually react one chemical substance with another. As long as the procedure is strictly followed, the given reaction
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should take place in the same way, no matter who has brought the two species together (assuming competence on the part of the researcher)! So, instead of writing a description as “I mixed 15.0 mL of 1.03M acetic acid with 23.2 mL of 0.923M sodium hydroxide…”, it should be “Fifteen (15.0) mL of 1.03M
acetic acid were mixed with 23.2 mL of 0.923M sodium hydroxide…”. Nature will take it’s own course regardless of the personality of the experimenter, so no personal pronouns will appear in your writing. Finally, the reader should be led through your report one thought at a time. Even calculations need to have some words around them to lead the reader through your thoughts as the calculations are done.
A typical lab report has numerous sections. Pay attention to specific weekly report requirements (posted of BlackBoard) for each individual experiment, as not every report is a full one.
- The TITLE PAGE includes (as a separate page !)
- the title of the experiment (as written in the manual)
- the date(s) of the experiment
- the date the report is submitted
- name of the student submitting the report
- the name(s) of any partners for that experiment (if applicable)
- The INTRODUCTION should literally introduce the entire experiment. The first paragraph should present an overview of the experiment. In this paragraph briefly present the purpose of the experiment and the key experimental technique to be used. Any theory behind the experimental procedures or objectives should be presented in the introduction. Any expectations for the results can be presented. Important equations (chemical and algebraic) which are to be used during the experiment should be presented or derived (only if the equation was not derived in the lab manual) in the introduction Do not simply give a list of equations. Do not actually perform the calculations or state the results obtained. Keep in mind that you are trying to instruct the reader so that they will understand all the details and implications of the experiment during the rest of the report. Functionally, it is usually easiest to write this section last, since it is easier to write an introduction when you already have finished what you are going to introduce!
- The PROCEDURE section should be a detailed description of what actually happened during the experiment. It should include all procedures and observations. This section must be a faithful history of your experience in the laboratory (thus, as always, written in the past tense and the third- person passive voice). Your laboratory notebook should be your guide in writing this section. This section is in paragraph format, NOT simply a numbered or bulleted list of directions. The reader wants to know what you did and what you experienced, to a level of detail that the experiment could be exactly duplicated from you written word. It is your job to transport the reader to the laboratory to relive your experience. Specific data values and calculations should NOT be included in this section.
- The DATA, CALCULATION and GRAPH sections should be an orderly presentation of your primary data. Primary data are those values provided by the experiment, before they are used for any calculation. Thus, if a buret reading before a titration is 4.56 mL, and the reading after the titration is 45.94 mL, these two values are the primary data. The 41.38 mL which were delivered from the buret is a calculated quantity. It is necessary to calculate and present the 41.38 mL, but it would not be sufficient to report only the 41.38 mL value.
Data are generally organized into tables. Each table should be numbered and given a name (title). In many experiments, data are checked through interaction with a specifically- tailored computer program. These programs generally provide a print-out of all or part of the data for the experiment. The computer print-out should be used as all or part of the data section, as appropriate. Attach the
printout in the appropriate section in the report.
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Calculations: Before you actually write down an equation and solve for the desired quantity, your prose should indicate what it is that you will be calculating, and how. Then when you actually make the calculation, the reader will know what you are doing and thinking. As mentioned above, it is your job to continually lead the reader through the thoughts that are the logical development of the experiment and analysis. While all calculations are expected to be initially carried out in the lab notebook. The carbon copies of these pages which are attached to the final lab report are only used to evaluate your performance and do NOT qualify as the calculation section of your formal lab report. You should show the calculations neatly in this section using proper number of significant figures and label all units. Be sure to label each calculation with text (not just a sequential set of numbers). Give the equation used and show the worked out calculation with your data. Proper units and significant figures must always be used.
Any graphs necessary for the analysis of the data should be computer-generated. Sketches constructed from plain lined paper or on pages from the lab notebook are NOT acceptable. The graph should be a full page and the plotted points should be clearly shown and use up most of the page (not all squished into a corner). In general, each axis must be labeled, and each label must contain the dimension of that label (e.g. mL, C, sec, etc.). There generally should be from 4 to 6 demarcations on each axis (i.e. mL readings might be 10, 20, 30, 40, and not 1, 2, 3, 4…40 even though there may be 40 ruled lines comprising the axis). The demarcations should be some convenient number, usually a number easily divisible by 2 or 5. Data points should never be connected with a line unless that line is the result of calculation from a function which represents the data (i.e. best fit line or trend line). So, if the data are theoretically supposed to represent a linear function, it is perfectly acceptable to draw the best straight line superimposed upon the data. It is not acceptable to connect them as if it were a four-year-old’s connect-the-dots book. Any graph made during the lab period can be used in the report provided it is signed by the lab instructor and follows the specifications listed.
- The DISCUSSION section is the place where you discuss the outcome(s) of the experiment. All good experiments start with a certain expectation. This expectation should have been presented in the introduction section. Firstly, state your result(s), compare your result(s) with the expectation(s) and/or the true value and comment on this comparison. And finally discuss 3-4 possible sources of experimental error and how those errors could have affected the results of the experiment.
One part of your expectations involves the quality of your data. Since each measurement has a random uncertainty associated with it, there is an expectation that there will be some uncertainty (error) in your results. So, if all your measurements were made to 4 significant figures, and your data deviate from some expected value in the second significant figure, some part of the procedure either has a larger uncertainty than was immediately obvious, or there was some non-random error involved in the experiment (e.g. the solution was spilled over the bench top just before the final measurement!). The laboratory experiments are designed to bring you through numerous common scenarios involving different experimental uncertainties. Analysis of experimental uncertainty is constantly done by working scientists and engineers.
- The carbon copies of the notebook pages, initialed by the instructor, are attached at the end of the report. In the event that this cannot be done for a particular experiment, the instructor should be notified and some alternate arrangement made, before submitting the report. Without these pages, the report is considered incomplete and cannot be given a grade.
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Grading: The grade for each laboratory experiment in CH110 is calculated as follows:
1. The first 15% of the grade is based upon a Pre-Lab exercise to be submitted at the start of the
laboratory session, they will not be accepted late.
NOTE: The pre-lab questions are available on http://blackboard.hartford.edu in the CH110 ALL LABS
course. It is your responsibility to obtain them and submit them according to the schedule.
A video is available on Blackboard for each experiment with additional information. It is highly recommended that you read through the experiment write up in the manual and watch the video before attempting to complete the pre-lab.
This “pre-lab” consists of:
Answers to questions about the experiment. These questions are designed to prepare you for the experiment. They might include sample calculations with typical data, or they might be a definition or short answer-type question. Show your work for any calculations; do not copy any source or the manual for short-answer questions. If you are unable to answer any of these questions, it would be to your great advantage to get help well in advance of your lab period. A clear understanding of the pre-lab questions will be a tremendous asset to you during the experiment itself.
A brief description of the procedure for the experiment. This could be in an outline format or a flow chart format or paragraph format. It should not be copied directly from the manual. This part should be between 1⁄2 and one page.
An analysis of the safety procedures and disposal requirements specific to that experiment. It is not intended that every item from the safety contract be repeated. However, each experiment has specific safety and disposal details which should be summarized in this section.
The next 35% of the grade is based upon your performance during the laboratory period including, but not limited to, following safety guidelines, your general technique, appropriate care of measurement and understanding of the number of significant figures associated with each measurement, neatness, efficiency, considerations for fellow students, attitude, promptness to class, proper use of the laboratory notebook pages and accuracy of the results when appropriate.
The last 50% of the grade is based upon the finished report. This grade is based on the clarity of presentation, neatness, logical discussion and interpretation, correct calculations and their presentation, grammar, spelling, punctuation, use of the correct tense and voice. Lab reports are due at the next lab meeting. Late submissions will be penalized 10 points per week (pro-rated on a daily basis). Note: not every report will be a full written report; you are expected to follow the criteria provided by your lab instructor each week. In addition, some reports are required to be submitted to SafeAssign for plagiarism review, the report grade will receive a penalty if plagiarism is present or if the report is not submitted to SafeAssign.
Attendance at all laboratory periods and submission of all reports will result in the dropping of the lowest NON-ZERO grade upon calculation of the final laboratory average at the end of the semester. If an excused absence has occurred during the semester, that “grade” will be dropped. An unexcused absence is considered a zero (see below) and will not be dropped at the time of final-grade calculation.
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Unexcused or missed lab sessions will be graded as a zero. If you miss a lab, you must contact your lab instructor and the lab supervisor immediately with documentation for your absence. In general, make-up labs will not be arranged. However, if you have a serious reason for an absence, it might be possible, with permission of the lab supervisor to arrange for you to go to another lab section to do the experiment during the week the same experiment is scheduled. This must be arranged in advance. Excused absences can only be granted by the laboratory supervisor.
Student-Athletes should provide a copy of their practice/game schedule to their lab instructor or lab supervisor at the beginning of the semester or the beginning of their season. with any questions.
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LABORATORY SAFETY CONTRACT
University of Hartford – Chemistry Department
- Eye protection must be worn at all times in the laboratory. Failure to do so will result in expulsion from the laboratory. Acceptable safety goggles are supplied upon check-in for CH110 and are the students’ responsibility for subsequent lab courses, additional pairs are available for purchase from the chemistry department.
- SMOKING IS ABSOLUTELY PROHIBITED at all times in the laboratory and in the building.
- Eating and drinking are not permitted in the laboratory. This includes candy and gum. Water bottles or any beverage or food container must be stored in a closed backpack away from the lab bench areas.
- Cell phones or any other type of personal communication device may not be used during the laboratory period. These devices should be turned off for the duration of the lab period, (i.e. you will not receive nor make calls or text during the lab period). Also, iPods or any other types of personal listening device with ear/head phones are not allowed during the lab period.
- Horseplay, pranks and other acts of mischief are especially dangerous and are absolutely prohibited. Do not sit on laboratory bench areas. Place all personal belongings in designated area, keep bench area and floor clear of excess items such as books and bags. Use the wall hooks for coats, etc.
- Shoes must be worn in the laboratory at all times; sandals are not permitted. Rollerblades, “Heelys” or skateboards are NOT allowed in the laboratory at any time. Tie back long hair and loose clothing when in the laboratory. Shorts are not recommended.
- Students must be acquainted with the location and use of the following safety equipment: fire extinguisher, fire blanket, safety shower, eye wash fountain(s), emergency gas shut-off and exit from the laboratory. In any emergency, call the lab instructor immediately.
- Students are NOT permitted to enter the stockroom to obtain supplies. Any necessary item will be issued by the lab instructor or stockroom attendant.
- DISPOSAL: Used paper and towels should be placed in the large trash barrels. Broken glass should be placed in the glass disposal boxes. Any solid chemicals or metal items will be disposed of as directed by lab instructor. No solids are allowed in the sink; water-soluble liquids only may be poured down the drains. If in doubt, check with the instructor.
- All spills must be cleaned up immediately; this includes your work area, in the hoods, on side benches, near the balances and the floor. For spills inside the balance, consult the instructor.
- Mouth suction must never be used to fill pipets. Never taste any chemical or put it in your mouth. Wash hands thoroughly when finished with experiment.
- Never use chipped or broken glassware, obtain a new item from stockroom.
- Never leave an experiment unattended, particularly an open flame.
- Chemicals (reagents or products) may NOT be removed from the laboratory.
- At the end of each laboratory period, each student must clean his/her bench area with a wet sponge.
- All laboratory work in this course must be done during a regularly scheduled lab period with a lab instructor in attendance.
I HAVE READ, UNDERSTAND AND WILL FOLLOW THE ABOVE SAFETY RULES. I HAVE ALSO BEEN MADE AWARE OF THE LOCATION AND USE OF THE SAFETY EQUIPMENT.
Student signature CH course #
Date Lab Instructor
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Selected Techniques and Procedures
- Simple Statistics
The average or mean of a set of values can be calculated be taking the sum of the values, and dividing by the number of values. The average of the molarity in the following example is calculated,
average = 0.1212 + 0.1225 + 0.1217 = 0.1218 3
The precision of a set of values refers to the closeness of approach of the set of values to a common value (the average). Precision may be measured in terms of the deviations of the individual measurements of a series from the average value of that series. The average of the absolute values of the individual deviations is called the average deviation.
Example: In a series of titrations, the following values for the molarity of a solution were found:
(1) (2) (3)
Values 0.1212 M 0.1225 M 0.1217 M
Deviation from the Average
(0.1212 – 0.1218) = – 0.0006 (0.1225 – 0.1218) = + 0.0007 (0.1217 – 0.1218) = – 0.0001
Absolute Value of the Deviation
+ 0.0006 M + 0.0007 M + 0.0001 M
= 0.0014 ÷ 3
= 0.0005 M (Avg dev)
0.3654 ÷ 3 = 0.1218 M
Thus the molarity may be reported as 0.1218 M ± 0.0005 M.
Percent deviation is a convenient way to express the precision results. Percent deviation is easily determined by dividing the average deviation by the average value and multiplying by 100.
% dev = avg dev x 100 % dev = 0.0005 x 100 = 0.41 % dev average 0.1218
Accuracy refers to the nearness of a determination to the accepted value. Often this can be expressed by percent error. The percent error can be found by dividing the difference between the accepted value and the experimental value by the accepted value and then multiplying by one hundred.
Example: In an experiment, a student calculated a value for Absolute Zero to be -256°C. The accepted value for Absolute Zero is -273°C.
% error = accepted – experimental x 100 accepted
% error = (-273°C) – (-256°C) x 100 = 6.2 % error (-273°C)
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- Use of a Bunsen Burner
- – Close the thumbscrew and open 1/4 turn.
- – Close the air holes with the moveable sleeve.
- – Open the gas valve on the inlet pipe wide.
- – Light the burner with the striker.
- – Regulate the thumbscrew and the sleeve to produce a blue flame with a sharp pointed inner blue cone. (Note: The gas valve on the inlet pipe is not used to regulate gas flow. It should be used as an on/off valve only.)
- – A bright yellow tip indicates insufficient air. Open the sleeve to let in more air.
- – If the flame lifts off the burner (common when using a flame spreader), turn down the gas with the thumbscrew.
- Use of Pipets
Rinse the inside of the pipet by drawing in several milliliters of distilled water with the aid of a pipet bulb or pump, shaking, and then expelling all liquid from the pipet. As always in pipetting, take care that you do not draw any liquid into the pipet bulb or pump. If this does occur, remove the bulb or pump from the pipet and expel the liquid into the sink. If you draw some liquid other than water into the bulb or pump, rinse the bulb or pump by drawing water into it and thoroughly expelling all liquid. After the pipet is thoroughly rinsed, dry the outside of the pipet tip and draw several milliliters of the solution to be transferred into the pipet. Never place a pipet directly into a stock bottle, pour some of the solution into a beaker or graduated cylinder first. Rinse the pipet carefully with the solution by shaking, and discard the rinse solution. Do this once more, then fill the pipet to a few centimeters above the mark on the upper portion of the stem. Remove the bulb or pump and quickly place a finger or thumb over the top of the pipet. Allow the liquid meniscus to align with the mark on the pipet by slowly and carefully moving your finger off the pipet. If the meniscus drops below the line, use the bulb or pump again to draw the liquid up. When the meniscus is on the line, wipe the tip of the pipet, touch the tip of the pipet to the side of the container to which you wish to transfer the solution, and allow the liquid level to drain. With a singular volume pipet, the liquid should be allowed to drain, and the tip kept on the side of the flask 3 seconds after the solution has ceased flowing. The remaining liquid in the tip is NOT to be blown out by the pipet bulb.
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- Use of Burets
Before use, a buret should be thoroughly cleaned with soap solution and a long brush. The cleansing should be followed by a thorough rinsing with distilled water. If any water droplets adhere to the inner wall of the buret, it is not clean and should be re-cleaned. With the stopcock closed, add about 5 mL of the solution to be measured. Rotate the buret to wet the walls. Allow the liquid to drain through the stopcock. Repeat this rinse one more time. Clamp the buret to the ring stand with a buret clamp. Fill the buret above the zero mark with the solution. Allow the buret to drain past the zero mark to fill the tip with solution. Do not try to drain it to exactly zero as this introduces prejudicial error. Make sure no air bubbles are left in the tip or on the walls of the buret. Bubbles on the wall may be dislodged by gently tapping the sides of the buret. Note the initial position of the meniscus. Allow the solution to drain until either an endpoint is reached in a titration, or the desired volume of solution has been delivered. Note the final position of the meniscus. The exact volume delivered is the difference between the initial and final readings. Always read buret volumes to ±0.01mL.
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test tube brush
test tube holder
test tube rack
funnel rack clamp
Bunsen burner buret clamp