Sample Final Exam CHEM 1280 last four numbers of SSN- Name: Note: Read the entir

Question

Sample Final Exam CHEM 1280 last four numbers of SSN- Name: Note: Read the entire qaestion and make sure to follow ALL directions for each question. Fill in the bubbles for your Name and Student ID number AND write your name on the front of the Scantron sheet as well as this exam. 5 pts. will be deducted if this is not done comectly. Use the Scantron sheet for BOTH the TrueFalse and Multiple Choice sections of the exam. 1. You have Exam A. Fi n Bubble A on the Scantron sheet. 40 pts.)TRUE-FALSE: Identify the following statements astrue or false. Two points each. 2. In order to obtain accurate results, it is best to weigh something right after it is removed from an ice bath, 3. As a solution becomes more concentrated, the 9T 4. All storage containers should be labeled with a NFPA diamond label so th you know the hazards associated with working with that oompound. 5. A buret may be used when one wishes to deliver varying volumes that ae accurate to 002 mL 6. If the substance you are ve, itis okay to weigh it withoutusing weighing paper or a weighing pan. 7. The supernate is decanted from the filtrate. is okay to remove your goggles in labonce you are done using chemicals. 9. The sides of a cuvette do not need to be cleaned before itis nserted into a 0. Top-loading balances are used for quick determinations of massesto the nearest 0.1-0001 g 1. The meniscus is read at eye-level in order to avoid parallax 2. Bunsen burners are often used in experiments using ethanol and ether 13. When excess reagent has been removed from a container. it is okay to pour it back into the 4. A material safety data sheet (MSDS) for every compound that is used is available in each lab. 15. If you and your neighbor don't have pipette bulbs.then it is okay to pipet by mouth. 16. When preparing a solution of known dilution.it is okay to use a volumetric flask for the dilution. 7. When preparing solutions, concentrated acids should always be added to water 18. Well-plates allow for systematic testing of multiple solutions and small volumes. 19. A volumetric pipet is calibrated as a Volume Contained instrument and thus should never be blown out 20. When using a Buchner funnel you must first fold the filter paper in half twice. 21. Analytical balances are very sensitive to air draftsandtable movement. 40 pts) MULTIPLE CHOICES 22. If you plot volume on the ordinate and mass on the abscissa.the slope of the graphis the

Explanation / Answer

2. We must allow the substance to come to room temperature slowly before taking the weight. Therefore, the statement is false.

3. The absorbance of a solution (A) is related to the concentration as

A = *c*l where = absorptivity of the substance being analysed (constant for a particular substance at a particular wavelength), c = concentration of the solution and l = path length of the solution (constant for a particular spectrophotometer).

As the solution becomes more concentrated, i.e, c increases, A increases.

Now A is related to the percent transmittance (%T) as

A = 2 – log (%T)

As increases, %T must decrease. Therefore, the given statement is false.

4. The given statement is true. An user must be aware of all the risks associated with using the compound. The NFPA diamond label classifies a material on the basis of fire hazard, health hazard and reactivity.

5. The given statement is true. A buret may be used to deliver varying volumes of a solution that are as accurate as possible.

6. A corrosive substance leads to skin irritation on part of the user and has nothing to do with the weighing balance (it may react). A non-corrosive substance doesn’t lead to skin irritation but may react with the material used in making the balance or absorb moisture on contact with the balance. Hence the given statement is false.

7. A supernate is the liquid which remains above the solid after dissolution. One of the easiest ways of removing the supernate is to decant the supernate into a separate container. Hence, the given statement is true.

8. It is imperative that a worker has his goggles on while inside the lab. Even when the worker isn’t handling chemicals, the lab atmosphere may be contaminated with vapors which can infect the eyes. Hence, the given statement is false.

9. The sides of a cuvette are to be cleaned so that there are no stain marks or stray marks on the sides. Such marks will interfere in the transmission of light through the sample. Hence the statement is false.

10. Top-loading balances can be used to weigh masses that are accurate to 0.1 g. More a more accurate weight determination, an analytical balance is to be used. Therefore, the statement is false.

11. The statement is true.

12. Ethanol and ether are flammable and cannot be used with near open flames. Hence, the statement is false.

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