Tutorial Questions

Question

• Q1. What is a blank?
• Q2. What is masking?
• Q3. What is a calibration curve?
• Q4. Distinguish between a primary standard and a secondary
standard.
• Q5. Describe the procedure for preparing 250.0 mL of 0.04906
mol L-1 standard solution of sodium carbonate (Na2CO3).
• Q6. Describe how you would prepare a secondary standard of
an acid.
• Q7. What mass of potassium hydrogen phthalate, KH(C8H4O4),
in grams, must be weighed out in order to make 200.0 mL of
0.250 mol L-1 KH(C8H4O4) standard solution.

Answer 1

• A1. A blank is a sample that does not contain the analyte of interest and is used to calibrate the instrument or to establish a baseline for measurements.

• A2. Masking is a technique used in analytical chemistry to suppress or inhibit the interference of one or more components in a sample during analysis.

• A3. A calibration curve is a graph showing the relationship between the concentration of an analyte in a sample and the response of the instrument used for analysis. It is used to quantify the amount of analyte in unknown samples based on their instrument response.

• A4. A primary standard is a highly pure compound that can be used to prepare a standard solution for chemical analysis without requiring further purification. A secondary standard, on the other hand, is a substance that has been standardized against a primary standard and is used for routine analytical measurements.

• A5. To prepare 250.0 mL of 0.04906 mol L-1 standard solution of sodium carbonate, one would weigh out the appropriate amount of sodium carbonate (Na2CO3) based on its molecular weight and dissolve it in water to make a total volume of 250.0 mL.

• A6. To prepare a secondary standard of an acid, one would first prepare a primary standard solution of the acid using a primary standard substance. The primary standard solution is then standardized against a secondary standard base to determine its exact concentration.

• A7. To make 200.0 mL of 0.250 mol L-1 KH(C8H4O4) standard solution, one would need to weigh out 5.00 grams of potassium hydrogen phthalate (KH(C8H4O4)) based on its molecular weight.