CHEMISTRY LABORATORY AND APPARATUS
Chemistry is studied mainly in a science room called a school chemistry laboratory. The room is better ventilated than normal classroom. It has electricity, gas and water taps. A school chemistry laboratory has a qualified professional whose called Laboratory technician/assistant. All students user in a school chemistry laboratory must consult the Laboratory technician/assistant for all their laboratory work. A school chemistry laboratory has chemicals and apparatus.
A chemical is a substance whose composition is known. All chemical are thus labeled as they are. This is because whereas physically a substance may appear similar, chemically they may be different. All Chemicals which are not labeled should never be use.
Some chemicals are toxic/poisonous, explosive, corrosive, caustic, irritants, flammable, oxidizing, carcinogenic, or radioactive. Care should always be taken when handling any chemical which have any of the above characteristic properties.
Common school chemistry laboratory chemicals include:
(i) Distilled water
(ii) Concentrated mineral acid which are very corrosive (on contact with skin they cause painful open wounds)
(iii) Concentrated alkali/bases which are caustic (on contact with skin they cause painful blisters)
(iv) Very many types of salts
The following safety guideline rules should be followed by chemistry laboratory users:
(i) Enter the laboratory with permission in an orderly manner without rushing/pushing/scrabbling.
(ii) Do not try unauthorized experiments. They may produce flammable, explosive or toxic substances that affect your health.
(iii) Do not taste any chemical in the laboratory. They may be poisonous.
(iv) Waft gas fumes to your nose with your palm. Do not inhale/smell gases directly. They may be highly poisonous/toxic.
(v) Boil substances with mouth of the test tube facing away from others and yourself.
Boiling liquids spurt out portions of the hot liquid. Products of heating solids may be a highly poisonous/toxic gas.
(vi) Wash with lots of water any skin contact with chemicals immediately.
Report immediately to teacher/laboratory technician any irritation, cut, burn, bruise or feelings arising from laboratory work.
(vii) Read and follow safety instruction. All experiments that evolve/produce poisonous gases should be done in the open or in a fume chamber.
(viii) Clean your laboratory work station after use. Wash your hand before leaving the chemistry laboratory.
(ix) In case of fire, remain calm, switch of the source of fuel-gas tap. Leave the laboratory through the emergency door. Use fire extinguishers near the chemistry laboratory to put of medium fires. Leave strong fires wholly to professional fire fighters.
(x) Do not carry unauthorized item from a chemistry laboratory.
They are scientific tools/equipment used in performing scientific experiments. The conventional apparator used in performing scientific experiments is called standard apparator/apparatus. If the conventional standard apparator/apparatus is not available, an improvised apparator/apparatus may be used in performing scientific experiments. An improvised apparator/apparatus is one used in performing a scientific experiment for a standard apparator/apparatus.
Most standard apparatus in a school chemistry laboratory are made of glass because:
(i) Glass is transparent and thus reactions/interactions inside are clearly visible from outside
(ii) Glass is comparatively cheaper which reduces cost of equipping the school chemistry laboratory
(iii) Glass is comparatively easy to clean/wash after use.
(iv) Glass is comparatively unreactive to many chemicals.
Apparatus are designed for the purpose they are intended in a school chemistry laboratory:
(A) Apparatus for measuring volume
- Measuring cylinder
Measuring cylinders are apparatus used to measure volume of liquid/ solutions.
They are calibrated/graduated to measure any volume required to the maximum. Measuring cylinders are named according to the maximum calibrated/graduated volume e.g.
“10ml” measuring cylinder is can hold maximum calibrated/graduated volume of “10mililitres” /“10 cubic centimetres”
“50ml” measuring cylinder is can hold maximum calibrated/graduated volume of “50mililitres” /“50 cubic centimetres”
“250ml” measuring cylinder is can hold maximum calibrated/graduated volume of “250mililitres” /“250 cubic centimetres”
“1000ml” measuring cylinder is can hold maximum calibrated/graduated volume of “1000mililitres” /“1000 cubic centimetres”
Burette is a long and narrow/thin apparatus used to measure small accurate and exact volumes of a liquid solution.
It must be clamped first on a stand before being used.
It has a tap to run out the required amount out.
They are calibrated/graduated to run out small volume required to the maximum 50ml/50cm3.
The maximum 50ml/50cm3 calibration/graduation reading is at the bottom .This ensure the amount run out from a tap below can be determined directly from burette reading before and after during volumetric analysis.
Burettes are expensive and care should be taken when using them.
Pipette is a long and narrow/thin apparatus that widens at the middle used to measure and transfer small very accurate/exact volumes of a liquid solution.
It is open on either ends.
The maximum 25ml/25cm3 calibration/graduation mark is a visible ring on one thin end. To fill a pipette to this mark, the user must suck up a liquid solution upto a level above the mark then adjust to the mark using a finger.
4. Pipette filler
Pipette filler is used to suck in a liquid solution into a pipette instead of using the mouth.
It has a suck, adjust and eject button for ensuring the exact volume is attained.
This requires practice.
5. Volumetric flask.
A volumetric flask is thin /narrow but widens at the base/bottom. It is used to measure very accurate/exact volumes of a liquid solution. The maximum calibration /graduation mark is a visible ring. Volumetric flasks are named according to the maximum calibrated/graduated volume e.g. “250ml” volumetric flask has a calibrated/graduated mark at exact volume of “250mililitres” /“250centimetres”
“1l” volumetric flask has a calibrated/graduated mark at exact volume of “one litre” /“1000 cubic centimetres”
“2l” volumetric flask has a calibrated/graduated mark at exact volume of “two litres” /“2000 cubic centimetres”
6. Dropper/teat pipette
A dropper/teat pipette is a long thin/narrow glass/rubber apparatus that has a flexible rubber head. A dropper/teat pipette is used to measure very small amount/drops of liquid solution by pressing the flexible rubber head.
The number of drops needed are counted by pressing the rubber gently at a time .
(B)Apparatus for measuring mass
- Beam balance
A beam balance has a pan where a substance of unknown mass is placed. The scales on the opposite end are adjusted to “balance” with the mass of the unknown substance. The mass from a beam balance is in grams.
- Electronic/electric balance.
An electronic/electric balance has a pan where a substance of unknown mass is placed. The mass of the unknown substance in gramsis available immediately on the screen.
(C) Apparatus for measuring temperature
A thermometer has alcohol or mercury trapped in a bulb with a thin enclosed outlet for the alcohol/mercury in the bulb. If temperature rises in the bulb, the alcohol /mercury expand along the thin narrow enclosed outlet.
The higher the temperature, the more the expansion. Outside, a calibration /graduation correspond to this expansion and thus changes in temperature. A thermometer therefore determines the temperature when the bulb is fully dipped in to the substance being tested. To determine the temperature of solid is thus very difficult.
(D) Apparatus for measuring time
The stop watch/clock is the standard apparatus for measuring time. Time is measured using hours, minutes and second. Common school stop watch/clock has start, stop and reset button for determining time for a chemical reaction. This requires practice.
(E) Apparatus for scooping
A spatula is used to scoop solids which do not require accurate measurement. Both ends of the spatula can be used at a time. A solid scooped to the brim is “one spatula end full” A solid scooped to half brim is “half spatula end full”.
- Deflagrating spoon: A deflagrating spoon is used to scoop solids which do not require accurate measurement mainly for heating. Unlike a spatula, a deflagrating spoon is longer.
(F) Apparatus for putting liquids/solid for heating.
- Test tube.
A test tube is a narrow/thin glass apparatus open on one side. The end of the opening is commonly called the “the mouth of the test tube”.
- Boiling/ignition tube.
A boiling/ignition tube is a wide glass apparatus than a test tube open on one side. The end of the opening is commonly called the “the mouth of the boiling/ignition tube”.
Beaker is a wide calibrated/graduated lipped glass/plastic apparatus used for transferring liquid solution which do not normally require very accurate measurements
Beakers are named according to the maximum calibrated/graduated volume they can hold e.g. “250ml” beaker has a maximum calibrated/graduated volume of “250mililitres” /“250 cubic centimetres”
“1l” beaker has a maximum calibrated/graduated volume of “one litre” /“1000 cubic centimetres”
“5 l” beaker has a maximum calibrated/graduated volume of “two litres” /“2000 cubic centimetres”
- Conical flask.
A conical flask is a moderately narrow glass apparatus with a wide base and no calibration/graduation. Conical flasks thus carry/hold exact volumes of liquids that have been measured using other apparatus. It can also be put some solids. The narrow mouth ensures no spirage.
Conical flasks are named according to the maximum volume they can hold e.g. “250ml” Conical flasks hold a maximum volume of “250mililitres” /“250 cubic centimetres” “500ml” Conical flasks hold a maximum volume of “500ml” /“1000 cubic centimetres”
- Round bottomed flask
A round bottomed flask is a moderately narrow glass apparatus with a wide round base and no calibration/graduation. Round bottomed flask thus carry/hold exact volumes of liquids that have been measured using other apparatus.
The narrow/thin mouth prevents spirage. The flask can also hold (weighed) solids. A round bottomed flask must be held/ clamped when in use because of its wide narrow base.
- Flat bottomed flask
A flat bottomed flask is a moderately narrow glass apparatus with a wide round base with a small flat bottom. It has no calibration/graduation. Flat bottomed flasks thus carry/hold exact volumes of liquids that have been measured using other apparatus. The narrow/thin mouth prevents spirage. They can also hold (weighed) solids. A flat bottomed flask must be held/ clamped when in use because it’s flat narrow base is not stable.
(G) Apparatus for holding unstable apparatus (during heating).
- Tripod stand
A tripod stand is a three legged metallic apparatus which unstable apparatus are placed on (during heating). Beakers. Conical flasks, round bottomed flask and flat bottomed flasks are placed on top of tripod stand (during heating).
- Wire gauze/mesh
Wire gauze/mesh is a metallic/iron plate of wires crossings. It is placed on top of a tripod stand:
(i) Ensure even distribution of heat to prevent cracking glass apparatus
(ii) Hold smaller apparatus that cannot reach the edges of tripod stand
3 Clamp stand
A clamp stand is a metallic apparatus which tightly hold apparatus at their “neck” firmly. A clamp stand has a wide metallic base that ensures maximum stability. The height and position of clamping is variable. This require practice
- Test tube holder
A test tube holder is a hand held metallic apparatus which tightly hold test/boiling/ignition tube at their “neck” firmly on the other end.
Some test tube holders have wooden handle that prevent heat conduction to the hand during heating.
- Pair of tong.
A pair of tong is a scissor-like hand held metallic apparatus which tightly hold firmly a small solid sample on the other end.
- Gas jar
A gas jar is a long wide glass apparatus with a wide base. It is open on one end. It is used to collect/put gases. This requires practice.
(H) Apparatus for holding/directing liquid solutions/funnels (to avoid spirage).
- Filter funnel
A filter funnel is a wide mouthed (mainly plastic) apparatus that narrow drastically at the bottom to a long extension. When the long extension is placed on top of another apparatus, a liquid solution can safely be directed through the wide mouth of the filter funnel into the apparatus without spirage.
Filter funnel is also used to place a filter paper during filtration.
- Thistle funnel
A thistle funnel is a wide mouthed glass apparatus that narrow drastically at the bottom to a very long extension. The long extension is usually drilled through a stopper/cork. A liquid solution can thus be directed into a stoppered container without spirage
- Dropping funnel
A dropping funnel is a wide mouthed glass apparatus with a tap that narrow drastically at the bottom to a very long extension. The long extension is usually drilled through a stopper/cork. A liquid solution can thus be directed into a stoppered container without spirage at the rate determined by adjusting the tap.
- Separating funnel
A separating funnel is a wide mouthed glass apparatus with a tap at the bottom narrow extension. A liquid solution can thus be directed into a separating funnel without spirage. It can also safely be removed from the funnel by opening the tap. It is used to separate two or more liquid solution mixtures that form layers/immiscibles. This requires practice.
(I) Apparatus for heating/Burners
- Candle, spirit burner, kerosene stove, charcoal burner/jiko
Are some apparatus that can be used for heating.
Any flammable fuel when put in a container and ignited can produce some heat.
- Bunsen burner
The Bunsen burner is the standard apparatus for heating in a Chemistry school laboratory. It was discovered by the German Scientist Robert Wilhelm Bunsen in 1854.
(a) Diagram of a Bunsen burner
A Bunsen burner uses butane/laboratory gas as the fuel. The butane/laboratory gas is highly flammable and thus usually stored safely in a secure chamber outside Chemistry school laboratory. It is tapped and distributed into the laboratory through gas pipes.
The gas pipes end at the gas tap on a chemistry laboratory bench .If opened the gas tap releases butane/laboratory gas. Butane/laboratory gas has a characteristic odour/smell that alerts leakages/open gas tap. The Bunsen burner is fixed to the gas tap using a strong rubber tube.
The Bunsen burner is made up of the following parts:
(i) Base plate –to ensure the burner can stand on its own
(ii) Jet-a hole through which laboratory gas enters the burner
(iii) Collar/sleeve – adjustable circular metal attached to the main chimney/burell with a side hole/entry. It controls the amount of air entering used during burning.
(iv) Air hole – a hole/entry formed when the collar side hole is in line with chimney side hole.
If the collar side hole is not in line with chimney side hole, the air hole is said to be “closed” If the collar side hole is in line with chimney side hole, the air hole is said to be “open”
(v) Chimney- tall round metallic rod attached to the base plate.
(b) Procedure for lighting/igniting a Bunsen burner
- Adjust the collar to ensure the air holes are closed.
- Connect the burner to the gas tap using rubber tubing. Ensure the rubber tubing has no side leaks.
- Turn on the gas tap.
- Ignite the top of the chimney using a lighted match stick/gas lighter/wooden splint.
- Do not delay excessively procedure (iv) from (iii) to prevent highly flammable laboratory gas from escaping/leaking.
(c) Bunsen burner flames
A Bunsen burner produces two types of flames depending on the amount of air entering through the air holes. If the air holes are fully open, a non-luminous flame is produced. If the air holes are fully closed, a luminous flame is produced. If the air holes are partially open/ closed, a hybrid of non-luminous and luminous flames is produced.
Luminous flame has three main regions:
(i) The top yellow region where there is incomplete combustion/burning
(ii) The region of un-burnt gas below the yellow region where the gas does not burn
(iii) Blue region on the sides of region of un-burnt gas where there is complete burning
Non-luminous flame has four main regions:
(i) The top colourless region
(ii) Blue region just below where there is complete burning. It is the hottest region
(iii) Green region surrounded by the blue region where there is complete burning
(ii) The region of un-burnt gas at the innermost surrounded by green and blue regions. No burning takes place here.