EXPERIMENT-1: Cleaning Laboratory Glassware - General Procedure

Which statement best explains why laboratory glassware must be both chemically clean and grease‑free before use?

• Residual films can buffer solutions and distort colorimetric or volumetric results.

• Grease layers only make glassware slippery but do not interact with reagents.

• Only visible dirt affects measurements; invisible residues are inconsequential.

• Sterility alone guarantees accurate mass and volume measurements.

A newly purchased glass beaker arrives slightly alkaline. According to the protocol, what is the appropriate initial treatment before first use?

• Rinse with 5% HCl to neutralize surface alkali, then rinse with distilled water.

• Boil in deionized water for 30 minutes, then dry in an oven.

• Soak in saturated sodium bicarbonate to stabilize the surface, then air dry.

• Rinse directly with acetone to remove water and residual salts.

Which type of glassware does NOT require the 5% HCl pretreatment described for new items?

• Borosilicate glassware

• Newly purchased soda‑lime glassware

• Autopipette tips made of glass

• Measuring cylinders used for staining

In the general cleaning sequence, when should acetone first be used and for what purpose?

• After initial rinsing to remove excess organic oils or stains as an organic solvent.

• Before any water contact to avoid swelling of residues.

• Only after oven drying to remove adsorbed moisture from hot glass.

• At the very end to neutralize residual acids from the 5% HCl treatment.

Which ordered pair correctly matches the cleaning step with the rationale?

• Group similar glassware during cleaning — ensures uniform access of brush to curved surfaces.

• Use warm tap water with detergent and a brush — improves removal of residues from the inside and outside surfaces.

• Rinse immediately after use — allows stains to set firmly for easier scrubbing.

• Avoid deionized or reverse osmosis water — prevents leaching of ions from glass.

A lab wants to minimize hard‑water stains during rinsing. Based on the procedure, which approach is recommended?

• Use deionized or reverse osmosis water for the final rinse to wash away tap‑water deposits.

• Increase detergent concentration and rely on warm tap water only.

• Skip water rinses and rely on acetone to dissolve mineral salts.

• Dry glassware at room temperature to avoid precipitation of minerals.

Which sequence best reflects the recommended order for general cleaning of used glassware?

• Immediate rinse → hot water soak → detergent wash with brush → warm tap‑water rinse → deionized water rinse → acetone rinse → hot‑air oven drying

• Detergent wash → acetone rinse → hot water soak → deionized water rinse → warm tap‑water rinse → oven drying

• Acetone rinse → immediate rinse → hot water soak → warm tap‑water rinse → detergent wash → oven drying

• Immediate rinse → deionized water rinse → acetone rinse → warm tap‑water rinse → hot‑air oven drying

A lab technician finds glassware cloudy with coagulated organic residue. According to the special cleaning guidance, which chemical cleaning approach is appropriate and why?

• Use chromic acid or nitric acid because they can remove stubborn organic material

• Use only soap solution because acids etch glass surfaces irreversibly

• Use sodium bicarbonate because it neutralizes all organic residues

• Use only distilled water rinses because organics dissolve readily in pure water

Chromic acid cleaning solution is prepared from potassium dichromate, distilled water, and sulfuric acid. Which sequence reflects the correct preparation steps?

• Dissolve potassium dichromate in water, then slowly add sulfuric acid, and allow solution to turn dark brown before labeling

• Add sulfuric acid to dry potassium dichromate, then add water quickly, and use immediately while orange

• Add water to concentrated sulfuric acid first, then sprinkle potassium dichromate, and heat to boiling

• Mix potassium dichromate and sulfuric acid dry, then add water dropwise until light yellow

Given the specified quantities for chromic acid preparation—potassium dichromate 4.0 g, distilled water 40.0 ml, sulfuric acid 4.0 ml—what is the correct statement about measurements?

• Mass of potassium dichromate must be measured accurately at 4.0 g

• Potassium dichromate should be approximated by volume since it dissolves

• Sulfuric acid volume is irrelevant because color change controls concentration

• Water amount should be halved to accelerate dark brown color formation