Instrumentation Flashcards
mention the 2 types of primary balances that are found
analytical and top-loading balance
what are the balances used for
to weigh very small amounts of a substance with a high degree of accuracy
which balance would require little or no manual manipulation
balances that are not time consuming and do not require more manual manipulation
what is the basic principle of a quantitative measurement of mass
is to balance an unknown mass (a substance being weighed) with a known mass built into the object
explain the workings of an analytical balance
used in labs where extreme sensitivity is needed for weighing of items
measure small mass up to 4 decimal places
chemical analysis is always based upon mass so the results are not based on gravity at a specific location, which would affect the weight
measuring pan are enclosed in the glass box to prevent dust particles from setting in the pan
what is a top loading balance
it is a delicate piece of laboratory equipment in the lab that needs to be maintained and handled with care if it is to give accurate results
name the care measures that should be taken for a top loading balance
always try not to spill on the pan or surrounding areas
clean up any spillage
switch off the balance between routine use
position on a vibration free bench
position away from drought
what calibration aspects need to be taken into account concerning the top loading balance
top loading balances are able to weigh heavier masses
they read to fewer decimals
they come in varieties of sizes and shapes and levels of complexity
explain the electronic balance
it is a device used to find accurate measurement of weight
weighing chemicals to ensure a precise measurement of chemicals for use of various experiments
provide digital results
they are either top loading balances or analytical in design and permit weighing to be made in 5 seconds or less
how should the balances be maintained and operated
they should be located in an area in the lab that is free from droughts and vibrations and has relatively constant temperature
excessive vibrations can be detected when the vibration of the pointer or oscillation of numbers in the last decimal place of the digital display is observed
should be located in a relatively isolated part of the lab away from areas where corrosive chemicals are stored or used
should be placed on a heavy, solid dedicated weighing table
chemicals should be weighed on weighing paper, in plastic weighing boats and never placed directly on the balance
before the balance is used, its level should be checked by adjustment of the foot screws and centring of the bubble in the spirit level
the optical zero should be checked before weighing
mention the precautions to be taken with the balances
place in an air conditioned room
protect from drought, sunlight, heat fumes
place on a solid support
do not shake or bump the pan, case or support
keep the doors closed except when adding or removing material
do not weigh hot or cold substances
always use a weighing boat or container
check the balance is levelled before use
do not overload
keep the balance clean
after weighing:
check you have recorded the weight correctly
remove objects from the pan
close the doors
switch off
what is centrifugation
centrifugation is a method used in the separation of solid material from liquid material by application of increased gravitational force by rapid spinning or rotating
explain the use of a centrifuge
usually the solid particles are heavier than liquid and will settle at the bottom and some cases solid particles will be lighter than the liquid and will float
to recover the solid material suspensions e.g. urine sediments for microscopy
to separate blood into cells and serum or rod cells, buffy coat and plasma
what is a percipitate
the solid material packed at the bottom of the centrifuge tube
what is the supernatant
the liquid or top portion over the precipitate
