Balances, laboratory

Analytical balances are higher accuracy laboratory balances with capacities up to 400 g, and up to 20 million displayed divisions. 

Mass spectrometry allows us to measure masses of individual atoms. Still, there is an enormous difference between the mass of one atom and the masses of samples measured in the laboratory. For example, a good laboratory balance measures mass values from about 10 to 10 g. An atom, on the other hand, has a mass between 10 and... 

Measure the mass of a piece of weighing paper to 0.1 g using a laboratory balance. Record this mass in Data Table 1. 

Using a laboratory balance, measure the mass of a second piece of weighing paper and record the mass in Data Table 1. Place 0.1 g of sodium acetate on the weighing paper and record the combined mass. Calculate the mass of sodium acetate and record this value in Data Table 1. Place the sodium acetate in the test tube containing the phthalic anhydride. 

Since the laboratory balance does not weigh out in moles, convert this quantity to grams ... 

The maximum error is close to that of a common modem laboratory balance, which has a sensitivity of 1 mg. The minimum error is approximated by a good quality analytical balance. 

Densities of solids are determined by determining the volume of the solid, either by measurement of the solid s dimensions or by displacement of a liquid and then determining the mass on a laboratory balance. The density can also be determined by weighing the object and then weighing it again when suspended in a liquid of known density. 

Using a laboratory balance, measure the mass of an empty test tube and record the value in Data Table 1. Add about 8.0 g of BHT to the test tube. Measure the total mass of the test tube and BHT and record the measurement. 

The range of cell types that must be prepared, cultured and manufactured on a just in time basis, the number of detection systems that must be accommodated, the complex scheduling of incubation periods, sample preparation and analysis procedures, the form and fashion of data and post-analytical processing all contribute to a very complex laboratory, balancing a complicated set of demands. 

Eye protection — safety glasses or goggles - is mandatory whenever any pyrotechnic composition is being prepared or tested. Necessary equipment includes a mortar and pestle, a laboratory balance, a soft bristle brush, several 2-3 inch lengths of fireworks-type safety fuse (available from many hobby stores), and a fireproof stone or composite slab on which to conduct burning tests. 

Other laboratory equipment and reagents visible light microscope, hemacytometer, Trypan blue solution, laboratory balance, refrigerated centrifuge, household bleach 10% solution, automated cell counter (Coulter Z1 Counter, Beckman-Coulter, Miami, FL), flow cytometer (EPICS Elite II, Beckman-Coulter). 

Determine the volume of cell suspension using a laboratory balance. 

Mass measurements of objects are carried out with the laboratory balance. Many types of balances are available for laboratory use. The proper choice of a balance depends upon what degree of accuracy is needed for a measurement. The standard units of mass are the kilogram (kg) in the SI system and the gram (g) in the metric system. Some conversion factors are listed below. 

There are four classes of balances, each based on their ability to split hairs as it were, or, more specifically, based on the number of intervals used within the scale capacity. For example, if a laboratory balance has a capacity of 200.00 grams and it reads to two decimals, it would have 20,000 scale intervals. The formal identifi-... 

Lest you think that the laboratory balance has been made perfect by the servomotor, realize that the servomotor is electronic and therefore is susceptible to various types of interference. Sources of interference include ... 

Class 3 and Class 4 weights are used with moderate-precision laboratory balances. 

Determination of mass using common laboratory balances... 

Figure 2.2 Photograph illustrating typical laboratory balances and weighing equipment.

A solution contains an unknown amount of table salt dissolved in water. List as many ways as you can think of to measure or estimate the concentration of salt in the solution without leaving the kitchen of your home. The only instruments you are allowed to bring home from work are a thermometer that covers the range - 10°C to 120°C and a small laboratory balance. (Example Make up several solutions with known salt concentrations, and compare their tastes with that of the unknown solution.)... 

Your task this time is to estimate the heat capacity of an unknown liquid. You have available a laboratory balance, a very well-insulated container, a sensitive thermometer that can measure liquid temperatures, and a thermocouple that can measure temperatures of solids. The container is a very poor conductor of heat, so that virtually all heat transferred to or from its contents goes entirely into changing the temperature of those contents. If you need anything else (within reason), you can get it. Devise as many ways as you can to estimate Cy, which you may assume is independent of temperature. [Example Mix in the insulated flask a known mass, mi, of your liquid at temperature T, and a known mass, m2, of hot water at temperature T2, and measure the final temperature Tf. Since you can calculate the heat lost by water, Q m2Cyw(T2 — Tf), and you know Q must also equal the heat gained by the other liquid, miCy(Tf Ti), you can solve for Cy.]... 

To determine the number of moles of a given substance, we use the chemist s most powerful tool, the laboratory balance. If a sample of iron weighs 8.232 g, then... 

So, a 1-liter bottle of water contains 55.6 moles of water molecules. This represents about 33,500,000,000,000,000,000,000,000 molecules (55.6 moles x 602,000,000,000,000,000,000,000 molecules/mole) Remember Because each water molecule contains 3 atoms, one liter of water represents approximately 100,000,000,000,000,000,000,000,000 atoms (33,500,000,000,000,000,000,000,000 molecules x 3 atoms/molcculc) If a liter of water contains this many atoms, could we ever hope to measure the mass of a dozen, a score, or even a million atoms on our laboratory balances The answer is no, and that is why we group them in such large sets. 

To start with, you could find the mass of your aluminum by placing it on your laboratory balance. Let s say, for the sake of argument, that the mass of your sample was 60.0 g. You could then find the molar mass of aluminum by simply looking at the periodic table. The table tells us that the atomic mass of aluminum is 27.0 u/atom. Therefore the molar mass of aluminum is 27.0 g/mole (as explained in Lesson 7-1). 

RS kept in a desiccator 30 min to 1 h not clear what proper drying agent and proper time means RS weighed using second precision class laboratory balances VLP-200 g... 

Class S weights are used for calibrating balances. In the clmical laboratory, balances should be calibrated at least monthly and before conducting very accurate analytical work. 

Keep the reagent shelf and the laboratory balance clean and neat. Clean up any spills immediately, even though someone else is waiting to use the same chemical or reagent. 

In most analyses, an analytical balance must be used to obtain highly accurate masses. Less accurate laboratory balances are also used for mass measurements when the demands for reliability are not critical. 

Use auxiliary laboratory balances for weighings that do not require great accuracy. 

Auxiliary balance A generic term for a balance that is less sensitive but more rugged than an analytical balance synonymous with laboratory balance. 

Laboratory balance Synonymous with uu.xiliaiy balance. Laminar flow Streamline flow in a liquid near and parallel to a solid boundary. In a tube, this results in a parabolic llow profile near an electrode surface, this results in parallel layers of liquid that slide by one another. 

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