Question 1

Suppose you are setting up an assay in which patient samples are run in duplicate.All duplicate patient results match except for one.Which of the following would be a reasonable explanation (or explanations) for the lack of reproducibility for the patient results?

A)The pipet tip for one of the patient analyses was not placed tightly on the micropipet.
B)The patient sample was "wicked" out when wiping the pipet tip.
C)The technologist did not depress the piston of the micropipet to the second stop when delivering patient sample in one of the analyses.
D)All of the above

All of the above

Accepted Answer

Micropipets work on the principle of air displacement.If the disposable micropipet tip is not placed on the micropipet tightly, there will be improper air displacement, resulting in errant volume delivery.Likewise, if care is not taken when wiping extraneous droplets from the pipet tip, some patient sample will be removed (wicked) from the tip, also causing errant volume delivery.Finally, depressing the piston of the micropipet to the second stop is important in complete volume delivery.

Question 2

According to the Hazards Identification System developed by NFPA, the blue diamond indicates:&#10;A)the reactivity-stability hazard of the chemical&#10;B)any special hazard information about the chemical&#10;C)the flammability hazard of the chemical&#10;D)the health hazard associated with the chemical

Accepted Answer

The blue diamond is located on the left side of the NFPA diamond and serves to identify the health hazard associated with the chemical on a scale of 0 to 4.

Question 3

How many mL of 0.819 M acetic acid (MW = 60; pK&#8336; = 4.76) should be added to 350 mL of 0.368 M sodium acetate (MW = 82) to produce a final pH of 4.89?&#10;A)95.41 mL&#10;B)116.5 mL&#10;C)128.8 mL&#10;D)130.6 mL

Accepted Answer

Plugging the pKₐ and desired pH into the Henderson-Hasselbalch equation, the ratio of [Salt]/[Acid] is determined to be 1.35/1.As long as this ratio of salt to acid is maintained for this buffer, the pH of the buffer will be 4.89.In the problem, it is given that there are 350 mL of 0.368 M salt.Thus there are a total of 128.2 mmol of salt.Given that the required ratio of salt to acid is 1.35 to 1, and there are 128.2 mmol of salt, the following ratio can be set up:
 $ 1.35 \quad 128.2 \mathrm{mmol} $
$ 1 \quad \mathrm{x} \quad \times=95.41 \mathrm{mmol} $
In this equation, $ 95.41 \mathrm{mmol} $ of acid is necessary to maintain the $ 1.35 $-to-1 ratio. As per the problem, the $ 95.41 \mathrm{mmol} $ of acid is to be derived from a solution of $ 0.819 \mathrm{M} $ of the acid. Thus:
$$
\frac{95.41 \mathrm{mmol}}{0.819 \mathrm{mmol} / \mathrm{mL}}=116.5 \mathrm{~mL}
$$

Question 4

A material that is used to absorb and remove water from the air is known as a:&#10;A)teratogen&#10;B)desiccant&#10;C)carcinogen&#10;D)reference material

Accepted Answer

A desiccant is a material used to absorb and remove water from the air.

Question 5

Sodium azide is used in small amounts as a preservative in laboratory reagents.What is the safety concern associated with sodium azide?&#10;A)it can become explosive&#10;B)it can become volatile&#10;C)it is an environmental hazard&#10;D)it acts as a strong acid

Accepted Answer

Azides form explosive salts with metals such as iron and copper.Buildup of these metallic salts in laboratory sinks and sewers can be detonated by mechanical shock.

Question 6

The units for specific gravity are:&#10;A)g/mL&#10;B)mol/L&#10;C)mg/L&#10;D)%

Accepted Answer

The units for specific gravity are g/mL.

Question 7

What is the molarity (M) of a solution prepared by placing 10 g of NaOH (MW = 40) in a flask and diluting to 500 mL?&#10;A)0.25 M&#10;B)0.5 M&#10;C)1.0 M&#10;D)2.5 M

Accepted Answer

The solution prepared in the problem has a concentration of 10 g/500 mL.The definition of a molar (M) solution is the number of moles of solute per liter of solution, mol/L.This problem requires converting g/mL to mol/L.For the numerator, the molecular weight is used to convert 10 g to 0.25 mol.At this point, 10 g/500 mL is equal to 0.25 mol/500 mL.These units do not, however, meet the definition of the units for a molar solution.For the denominator, the desired unit is L (which is equal to 1000 mL).To make this conversion, multiply the numerator and the denominator by 2.This gives 0.5 mol/1000 mL which equals 0.5 mol/L, the proper units for molarity.This solution is a 0.5 M solution.

Question 8

How many mL of a 17.6 % solution of compound X (MW 142) would be required to prepare 450 mL of a 0.75 M solution?&#10;A)1.24 mL&#10;B)142 mL&#10;C)176 mL&#10;D)272 mL

Accepted Answer

The equation to use to solve this problem is V₁C₁ = V₂C₂.However, the units for concentration do not match.The first step is to convert % to M: 17.6 % = 17.6 g/100 mL = 176 g/L.The definition of a 1 M solution is the number of gram molecular weights per liter of solution.
 Thus $ 1 \mathrm{M} $ compound $ \mathrm{X} $ equals $ 142 \mathrm{~g} / \mathrm{L} $.
$$
\frac{142 \mathrm{~g} / \mathrm{L}}{176 \mathrm{~g} / \mathrm{L}}=\frac{1 \mathrm{M}}{\mathrm{x}} \mathrm{x}=1.24 \mathrm{M}
$$
The $ 17.6 \% $ solution of compound $ \mathrm{X} $ is equal to a $ 1.24 \mathrm{M} $ solution. Now, solving for $ \mathrm{V}_{1}: \mathrm{V}_{\mathrm{l}}(1.24 \mathrm{M})=450 \mathrm{~mL}(0.75 \mathrm{M}), \mathrm{V}_{\mathrm{l}}=272 \mathrm{~mL} $ of the compound $ \mathrm{X} $ solution.

Question 9

Pipets that must be rinsed in order to deliver the measured volume are known as ______ pipets.Pipets that deliver the measured volume without rinsing are known as ______ pipets.______ pipets are not to be blown out when delivering the full volume of the pipet.

A)to contain (TC), to deliver (TD), serological
B)to contain (TC), to deliver (TD), volumetric
C)to deliver (TD), to contain (TC), serological
D)to deliver (TD), to contain (TC), volumetric

Accepted Answer

To contain (TC) pipets must be rinsed out in order to deliver the volume measured by the pipet.To deliver (TD) pipets will deliver the measured volume without rinsing.Volumetric pipets deliver the exact volume measured with a high degree of accuracy after draining and require no "blow out."

Question 10

Which laboratory glassware should be selected to ensure accuracy in the preparation of a 100 mL of 0.5 N HCl solution?&#10;A)a beaker&#10;B)a graduated cylinder&#10;C)an Erlenmeyer flask&#10;D)a volumetric flask

Accepted Answer

Volumetric flasks are essential for the accurate preparation of solutions of known concentration.

Question 11

Which of the following water purification techniques is most effective in removing dissolved ionized gases?&#10;A)distillation&#10;B)deionization&#10;C)reverse osmosis&#10;D)ultrafiltration

Accepted Answer

The answer of Which of the following water purification techniques...

Question 12

What dilution is necessary to make an 18 mg/L solution from a 30 mg/L solution?&#10;A)1:5 dilution&#10;B)3:5 dilution&#10;C)2:3 dilution&#10;D)1:3 dilution

Accepted Answer

The answer of What dilution is necessary to make an...

Question 13

A solution of unknown concentration of compound X (MW = 150) has an absorbance of 0.600.It had an absorbance of 0.300 at a concentration of 9 mg/dL.What is the molarity of the solution?&#10;A)0.0012 M&#10;B)0.18 M&#10;C)1.2 M&#10;D)18 M

Accepted Answer

The answer of A solution of unknown concentration of compound...

Question 14

Which of the following laboratory containers should be selected to store an organic hydrocarbon solvent?&#10;A)borosilicate glass&#10;B)polyethylene&#10;C)polycarbonate&#10;D)polyvinyl chloride (PVC)

Accepted Answer

The answer of Which of the following laboratory containers should...

Question 15

How many mL of a 10 mg/L solution must be diluted to 100 mL to produce 100 mL of a 0.1 mg/dL solution?&#10;A)1 mL&#10;B)5 mL&#10;C)10 mL&#10;D)50 mL

Accepted Answer

The answer of How many mL of a 10 mg/L...

Question 16

In the metric system, 1 L is equal to how many fL?&#10;A)10-12&#10;B)10-15&#10;C)1012&#10;D)1015

Accepted Answer

The answer of In the metric system, 1 L is...

Question 17

The force produced by centrifugation is relative centrifugal force (RCF).The units for RCF are expressed as:&#10;A)rpm&#10;B)radius&#10;C)number of times greater than gravity&#10;D)there are no units for RCF

Accepted Answer

The answer of The force produced by centrifugation is relative...

Question 18

A fire associated with actively operating electrical equipment is classified as a ______ fire.The most appropriate type of fire extinguisher for this type of fire would be ______.&#10;A)Class A, halotron&#10;B)Class B, carbon dioxide&#10;C)Class C, halotron&#10;D)Class A and B, dry chemical

Accepted Answer

The answer of A fire associated with actively operating electrical...

Question 19

How would you prepare 400 mL of 0.85% NaCl?&#10;A)place 0.85 g of NaCl in a flask and dilute to 400 mL&#10;B)place 3.4 g of NaCl in a flask and dilute to 400 mL&#10;C)place 8.5 g of NaCl in a flask and dilute to 400 mL&#10;D)place 34 g of NaCl in a flask and dilute to 400 mL

Accepted Answer

The answer of How would you prepare 400 mL of...

Question 20

Taring an electronic balance refers to:&#10;A)verifying balance performance using Class S weights&#10;B)leveling the balance by adjusting the foot screws&#10;C)zeroing the weight of the weighing vessel&#10;D)adding counterweights to determine the true weight of the material being measured

Accepted Answer

The answer of Taring an electronic balance refers to:&#10;A)verifying balance...

Deck 1: Basic Laboratory Principles and Techniques