L2 MEASURING MASS

• (5) Types of Analytical Balance

  •Macro balance

  •Semimicroanalytical balance

  •Microanalytical balance

  •Traditional analytical balance

  •Single-pan analytical balance
• it has a maximum capacity ranging between 160 and 200g; measurements can be made with a standard deviation of ±0.01mg.

  Macro balance
• have a maximum load of 10 to 30g with a precision of ±0.01mg

  Semimicroanalytical balance
• has a capacity of 1 to 3g and a precision of ±0.01mg

  Microanalytical balance
• it has two pans attached either end of the lightweight beam that pivoted about a knife edge located in the center of the beam.

  Traditional Analytical Balance
• More convenient and weigh the sample faster than the traditional analytical balance.

  Single-pan analytical balance
• • Modern single pan analytical balance made by L. Oertling Ltd, London England. The type R.20 scales are capable of weighing to a

  hundredth of a gram using a system of substitute weights that are placed at the other end of the balance beam. • These are moved by the use of rods and levers

  operated by a series of rotary knobs. The weight is indicated by the values of the various knobs when the beam is balanced as shown bya circle of light projected onto an etched glasset reticule at the front.


  Single analytical balance
• is a class of balance designed to measure small mass in the sub-milligram range. The measuring pan of an analytical balance (0.1 mg or better) is inside a transparent enclosure with doors so that dust does not collect and so any air currents in the room do not affect the balance’s operation.

  Electronic Analytical Balance
• Method of weighing that gets the weight of the sample after getting the difference of the weight of container with sample and weight of the container alone.

  WEIGHING BY ADDITION
• WEIGHING BY ADDITION FORMULA?

  Weight of sample= Weight of container w/sample – weight of container
• •this procedure involves repetitive weighings of a weighing bottle containing a quantity of solid reagent. •the most accurate method to measure q. •quantitatively the mass of a solid sample.

  WEIGHING BY DIFFERENCE
• (4) WEIGHING ERRORS?

  •TEMPERATURE •MOISTURE GAIN AND EVAPORATION •ELECTROSTATIC CHARGE •BOUYANCY ERROR
• is the weighing error that develops when the object being weighed has a significantly different density than the standard weights.

  is the weighing error that develops when the object being weighed has a significantly different density than the standard weights.This error has its origin in the difference

  in the buoyant force exerted by the medium (air) on the

  object and on the weights.