The tared mass of a sample is its mass without regard to its container Transfer liquids and solutions from a reagent bottle or beaker with the aid of a stirring rod. 20. 21. womnD A small est tube has a volume of -3 mL. 23. A litmus paper test for the acidity or basicity of a solution requires the use of a stirring rod to remove a portion of the solution to then be touched to the litmus paper After drying a hygroscopic solid in a drying oven, the solid should be cooled in a desiccator. The color change of the indicator at the endpoint of a titration should persist for 30 seconds. 24. 25. Answer True or False for the following statements that refer to Laboratory Techniques. Ask your instructor to identify the questions you are to complete. 1. All clean glassware should be air-dried naturally 2. While cleaning glassware, discard all washes and rinses from the delivery point of the glass vessel. 3. To avoid waste in the use of chemicals, share the unused portion with other chemists before discarding. 4. Never touch, taste, or smell a chemical unless specifically told to do so. 5. A chemical with a "blue hazard label (a number 3 rating) means that the chemical is highly reactive. -6. If uncertain as to how to dispose of a chemical, dumping it into the sink followed by copious amount of - water is a safe disposal procedure. 7. Use a spatula to transfer solid chemicals from a reagent bottle. 8. Most all chemicals used in experiments can be disearded into the sink. 9. The number of significant figures used to record the mass of a chemical should correspond to the sensitiv- ity of the balance used for the measurement. 10. A 3-inch test tube has a volume of 3 ml.; an 8-inch test tube must have a volume of 8 ml. 11. To transfer a solution, a stiring rod touches the delivery point of the reagent vessel and the wall of the receiving vessel. 12. The minimum number of centrifuge tubes placed in a centrifuge during its operation is two. 13. A test tube should be less than one-third full when heating with a "cool" flame. 14. Right-handed students should operate the stopeock of a buret with their left hand and swirl the Erlenmeyer (receiving) flask with the right hand. 15. The thumb is the digit of choice on controlling the flow of liquid from a pipet. 16. Blow out the solution remaining in the pipet tip after the solution has drained from the pipet 17. A buret must always he filled to the top (the zero mark) before every titration procedure. 18. The volume of solution in a buret should be read and recorded 10-15 seconds after completing the titration. -19, It is possible to add a half-drop of solution from a buret. 20. To test the acidity of a solution with pH paper, place the pH paper directly in the solution. 21. The odar of a chemical should not be tessed unless specifell instructed to do so. The vapors of the chem- 22. One must first calculate the number of moles of solute that are required before preparing a solution of ical should be fanned toward the nose. known concentration. Summarize the Disclaimer in your own words. 42 Laboratory Techniques