BACE Solution Preparation and Calculations 2

Question 1

How much NaCl (MW = 58.44 g/mol) is needed to prepare 500 mL of a 0.9% (w/v) saline solution?

Accepted Answer

4.5 g

Answer

0.45 g

Answer

9.0 g

Answer

0.9 g

Question 2

A laboratory stock solution of HCl is labeled '12 M'. How much stock is needed to make 100 mL of 1 M HCl?

Accepted Answer

8.33 mL

Answer

1.2 mL

Answer

12 mL

Answer

120 mL

Question 3

What does 'pH 7.4 with NaOH' typically mean when listed in a buffer preparation protocol?

Accepted Answer

After dissolving all buffer components, measure pH and adjust to 7.4 by adding NaOH (to raise pH) or HCl (to lower pH) dropwise

Answer

Add NaOH until the solution becomes colorless

Answer

Prepare the buffer using NaOH as the sole pH-determining component

Answer

Add a fixed amount of 7.4 mL of NaOH to the solution

Question 4

A protocol requires a '10x PBS' stock solution. What concentration of NaCl would you expect in the stock, compared to the 1x working solution that contains 137 mM NaCl?

Accepted Answer

1,370 mM (137 mM x 10)

Answer

13.7 mM (one-tenth the working concentration)

Answer

137 mM (same as working — stocks are not more concentrated)

Answer

274 mM (2x the working concentration)

Question 5

When preparing a calibration standard curve for a Bradford assay, why must standards be prepared in the same buffer as the protein samples?

Accepted Answer

Because buffer components can affect the Bradford dye color reaction, potentially causing systematic error if standards and samples are in different buffers

Answer

To ensure the standard proteins denature at the same temperature as the samples

Answer

To allow both standards and samples to be autoclaved together for sterility

Answer

Buffer-matched standards are only required for mass spectrometry not colorimetric assays

Question 6

What is the molar concentration of a glucose solution prepared by dissolving 18.02 g of glucose (MW = 180.2 g/mol) in water to a final volume of 1 liter?

Accepted Answer

0.1 M

Answer

0.01 M

Answer

1.0 M

Answer

10 M