FREE BACE Preparing solutions Questions and Answers 2

Question 1

What equipment is required to accurately prepare a 1.00 M NaCl solution in a volume of exactly 100 mL?

Accepted Answer

A 100 mL volumetric flask, an analytical balance, and a magnetic stir plate

Answer

A beaker, a top-loading balance, and a graduated cylinder

Answer

A 100 mL beaker, a triple beam balance, and distilled water

Answer

A 250 mL Erlenmeyer flask, a digital scale, and a hot plate

Question 2

What is the purpose of adding sterile water to a lyophilized (freeze-dried) enzyme powder when reconstituting it for laboratory use?

Accepted Answer

To dissolve and hydrate the enzyme restoring its active three-dimensional conformation and activity

Answer

To denature any contaminating proteins present in the lyophilized powder

Answer

To dilute the enzyme to below the concentration that causes autocatalytic degradation

Answer

To lower the pH of the enzyme preparation to the optimal level for activity

Question 3

A protocol requires a 1:5 serial dilution series starting with a 1 mg/mL protein stock. What is the protein concentration of the third dilution in the series?

Accepted Answer

0.008 mg/mL

Answer

0.2 mg/mL

Answer

0.04 mg/mL

Answer

0.001 mg/mL

Question 4

When preparing a solution of a solid reagent, why should you add solvent to the solute rather than adding solute to a pre-measured volume of solvent?

Accepted Answer

Adding the solid first and then adding solvent while monitoring volume prevents overshoot of the target volume as dissolution can change the total volume

Answer

Adding solvent to solute prevents air bubbles from forming in the solution

Answer

Adding solvent to solute is faster because the solid dissolves more quickly when solvent is added dropwise

Answer

There is no difference — either order gives the same result if the final volume is checked

Question 5

What does anhydrous mean when referring to a reagent and why does it matter for solution preparation?

Accepted Answer

Anhydrous means the compound contains no water of hydration — important because hydrated forms have higher molecular weights and using the wrong form will give incorrect concentrations

Answer

Anhydrous means the compound has been purified by recrystallization from water

Answer

Anhydrous means the compound has been certified sterile and endotoxin-free for cell culture

Answer

Anhydrous means the compound is a liquid that has had its water content reduced by distillation

Question 6

How do you prepare 100 mL of a 20% (v/v) ethanol solution from pure (100%) ethanol?

Accepted Answer

Add 20 mL of 100% ethanol to a 100 mL volumetric flask and fill to the mark with water

Answer

Add 20 mL of water to 80 mL of 100% ethanol in a 100 mL flask

Answer

Add 100 mL of ethanol to 20 mL of water and mix

Answer

Dilute 100 mL of ethanol with enough water to make 20 mL total volume