Revision KNEC Questions and Answers on Lab Cleaning and Sterilization

is easier to clean
can be reused quite frequently.
Improved transparency of glass offers enhanced visibility of graduation marks for accurate readings.
Glassware also provides improved chemical resistance against acids and any alkaline solutions.

State any four methods for disinfecting surface water in the laboratory.

Use of chlorine
Use of alcohol
Use of phenols and Lysols
subjecting to UV rays

State four available sources of radiation.
- Exposure to X rays
- Radioactive chemicals
- UV radiations
- Lesser beams radiating equipment and instruments
Outline the precautions taken while handling potassium dichromate as a cleaning agent

Avoid contact with skin and eyes
Avoid formation of dust and aerosols
Provide good ventilation in process area to prevent formation of vapor
Wash hands and other exposed areas with mild soap and water before eating, drinking or smoking and when leaving work.
Take any precaution to avoid mixing with Combustibles.
Keep away from sources of ignition – No smoking.

Outline the procedure for cleaning a dirty glassware in the laboratory

To remove organic residues, rinse glasware briefly with an organic solvent (acetone or ethanol). The used rinse will then be discarded into the organic waste.
Use warm tap water and a brush with soapy water to scrub the inside of curved glassware. This waste water can go down the sink.
Remove soapsuds with deionized water to avoid harsh water stains. The DI water rinse should form a smooth sheet when poured through clean glassware. If this sheeting action is not seen, more aggressive cleaning is needed. To expedite the glass-drying process, rinse again with acetone to remove water. The residual acetone will go into the organic waste container.

Give any two reasons for washing laboratory apparatus immediately after use

It is much easier to clean the glassware before residues in them become dry and hard.
Some stains may stick permanently on the glassware if left to deposit on them for long

State four requirements of a cleaning agent

Able to clean and remove clinically relevant soils. Nonabrasive. Less damage means fewer replacements and reduced cost.
Compatible with the materials being cleaned (and the cleaning equipment).
Low-foaming. Free-rinsing.
Environmental friendliness is more important than ever.
Able to provide adequate use and shelf life.
Able to rapidly dissolve and disperse soils.
Cost-effective.

(a) State five properties of ceramic wares

High hardness.
High resistance to corrosion and chemical attack.
High weather resistance.
High melting point.

Give any two precautions taken when washing large glassware apparatus in the laboratory sink

Hold with both hands
Ensure its not placed at the edges of the sink
Ensure firm grip so as not to slip and break

Explain why aquaregia should never be used to clean platinum ware

Aquaregia solutions are extremely corrosive to platinum wares and may result in explosion or skin burns if not handled with extreme caution

List four types of waste disposed in each of the following waste bin container found in the lab
Red bins

For Contaminated and highly infectious Pathological

waste

b.Yellow bins

Moderately infectious wastes eg soiled cotton wool

White (or translucent)

For Sharps waste eg used syringes, broken glass, scalpels

Black bins

General wastes eg waste papers ,food wastes etc

Describe how to clean
1. Laboratory sinks

First pick or collect large solid particles or papers out of the sink. Apply some soap on moisten towel and wash off by wiping the sides and base of the sink. Rinse with running water. If stain persists, try scrubbing with hard brush, warm water and apply an appropriate solvent. Then rinse with clean cold water and dry it.

Pipettes and burettes

Wash with hot soapy water, rinse thoroughly with tap water, and then rinse 3-4 times with deionized water. Burets need to be thoroughly clean to be used for quantitative lab work.

Crucibles

Crucibles should be kept chemically clean and always avoid using reagents in which platinum is soluble e.g. aquaregia, HCl, liquids mixtures which evolve bromine or iodine, concentrated H₂SO₄ and H₃PO₄. The process of cleaning crucibles is called tarring. The process involves

Placing the crucible in concentrated potassium dichromate to remove stains
Washing in distilled water
Add some dilute nitric acid then heat
Pour away the nitric acid then wash with distilled water
If the stain persist , rub with moist sand
Wash it in tap water , heat it with nonluminous flame for 15 min
If incase the stain still persist , leave it alone because this means that it is now part of the crucible and therefore harmless
Petri dishes used for microbial cultures

They are cleaned by sterilization in an autoclave
Before placing in an autoclave , they should be wrapped in porous brown paper and their edges carefully secured with autoclave tapes
Place the containers and other items in a wire basket or in the autoclave drum.
Pour distilled water or tap water into the autoclave drum to the level indicated by the manufacturer.
Place the basket or drum containing the items to be sterilized in the autoclave.
Close the lid and screw the lid clamps firmly and connect the horse to the air outlet.
Switch on the autoclave electric or gas plug or place it on a suitable heat source e.g. charcoal jiko.
As the water boils, a mixture of air and steam escape through the air outlet. Leave it to escape for about 5min.
Test if all the air has been expelled out by placing the other end of the horse inside a water bucket. the presence of air is indicated by bubbles , pure steam produce cracking sound as it condense into water
When all air have been expelled , close the air outlet and watch the pressure and temperature gauge .when pressure reaches 15 psc , reduce the heat and leave it for the recommended sterilization time using a timer clock
Turn off the heat and wait until the pressure gauge reach zero, open the outlet then open the lid and unpack.
Some autoclaves have indicator strips on the autoclave tapes, which changes color after sterilization.
NB: indicator strips are sometimes not reliable.
1. Cuvettes

Clean the cuvettes using soft material e.g. Lens cleansing tissue or cotton gauze to avoid scratching them. Do not touch the sides of the cuvettes with fingers.

Chromic acid, aquaregia are cleaning agents in the laboratory. For each of this cleaning agent, describe
1. Their preparation

Aquaregia is prepared by mixing concentrated HNO₃ and conc. HCl in a ratio of 1:3 in a fume chamber

Chromic acid is prepared by weighing out 10 g of sodium dichromate crystals, make it into a slurry with a few mls of water, then dissolve in 250mls conc. sulphuric acid with stirring and cooling (ice-bath), to give a thick syrupy dark brown mixture.( it is very corrosive!)

Their application

Fill the container with chromic acid solution and allow it to stand for an overnight, pour away the acid and thoroughly rinse the apparatus with distilled water and allow it to dry .Pipettes should be left standing in chromic acid solution in a tall plastic cylinder.

Aquaregia is used for removing organic stains. Much of the time, detergent and tap water are neither required nor desirable. You can rinse the glassware with the proper solvent, and then finish up with a couple of rinses with distilled water, followed by final rinses with deionizer water

State safety measures while handling aquaregia

Ensure you wear appropriate PPEs
All handling of aqua regia MUST be done with glassware inside a fume hood. Never remove a container with aqua regia from the fume hood. Keep the sash as low as possible to capture the toxic fumes. Never raise it above the indicated position

Explain why aquaregia should not be used to clean platinum ware

Because it can dissolve the platinum materia

State and explain two categories of dirty glassware in the laboratory

Dirt on laboratory glassware can be divided into

Superficial dirt
Obstinate dirt
Superficial dirt is easy to clean by simply applying a brush and a commercial washing detergent containing an abrasive, which do not scratch the apparatus
Obstinate dirt is hard to remove. They can however be removed using warm 15 % Trisodium phosphate solution in which an abrasive powder have been added.

Briefly explain how you would attempt to remove oil and grease from a pippete.

Clean using a more efficient cleaning liquid mixed with concentrated sulfuric acid and fuming nitric acid in equal proportions. Alternatively ,it can be removed by filling with warm soapy water and leaving for 15 min then rinsing with water followed by concentrated HCl and finally with distilled water .

Outline the process of washing glassware in the laboratory

To remove organic residues, rinse glasware briefly with an organic solvent (acetone or ethanol). The used rinse will then be discarded into the organic waste.

Use warm tap water and a brush with soapy water to scrub the inside of curved glassware. This waste water can go down the sink.

Remove soapsuds with deionized water to avoid harsh water stains. The DI water rinse should form a smooth sheet when poured through clean glassware. If this sheeting action is not seen, more aggressive cleaning is needed. To expedite the glass-drying process, rinse again with acetone to remove water. The residual acetone will go into the organic waste container.

Identify the most suitable cleaning method for the following
1. Precision instrument laboratory floor

By not dusting or sweeping but mobbing using a detergent and water

Glassware with obstinate dirt

They can however be removed using warm 15 % Trisodium phosphate solution in which an abrasive powder have been added.

Name the reagents used in the removal of the following types of stains from glassware
1. Grease

Describe the preparation of potassium dichromate solution for cleaning purposes

Transfer 6 g of potassium dichromate (K2Cr2O7) to a platinum dish and dry at 120°C for 4 h. Cool in a desiccator.
Place 4.9 g of the dried K2Cr2O7 in a 1-L volumetric flask, and.
Add 100 mL of water. …
Store the solution in a glass-stoppered bottle.

Describe any two commonly used chemicals in the cleaning of platinum ware apparatus in the laboratory.

They should be kept chemically clean by cleaning them using Potassium dichromate and dilute nitric acids.
It is necessary to avoid reagents in which platinum is soluble e.g. aquaregia, HCl, liquids mixtures which evolve bromine or iodine, concentrated H₂SO₄and H₃PO₄.

Outline the cleaning procedure used for laboratory glassware.

Soak the glassware overnight in warm soapy water. The glassware may require scrubbing with a brush. Rinse with tap water followed by 3-4 rinses with deionized water.

Outline the proper procedure of cleaning laboratory glassware to be safe for use both chemically and biologically.

Chemical cleaning is achieved by cleaning the glass wares physically using appropriate cleaning detergent or reagent then rinsing the glassware with distilled or deionized water and finally rinsing the glass ware with the solution in which the apparatus is intended to be used for .

Biological cleaning is a bit more involving because it involves total killing of microorganism’s present on the apparatus. The method is called sterilization.

To test whether the apparatus is thoroughly clean , fill the apparatus with distilled water , if water flows out in an broken film then it means the apparatus is clean but if it flows in droplets then the apparatus is dirty and must be cleaned again

Explain why chromic acid is not a recommended cleaning agent

Chromic acid is very corrosive agent, leaves some carbon stains on surfaces, and is known to release toxic fumes during preparation.

State the precautions to be taken when handling chromic acid.
- One must wear protective clothing
- The reagent must always be prepared in the fume chamber
- The items to be cleaned must be rinsed with a lot of water before using them
After laboratory practicals , laboratory benches are usually disinfected ,Explain the importance of disinfecting laboratory benches

Ensures no harmful organisms are left on the surface of the bench Ensures leftover dirt or other materials do not contaminate future projects. Ensure dangerous substances don’t end up in the wrong places, possibly damaging equipment or cause a colleague harm.

State any two reasons for washing laboratory apparatus immediately after use.

Apparatus must be cleaned immediately because stains will have not had sufficient time to form complex stains on the surface of the apparatus and hence are easy to be removed by only soap and warm water if cleaning is done immediately and may not require more sophisticated stain removers or cleaning agents

Explain why aquaragia should never be used to lean platinum ware

Because platinum material is soluble in aquaregia, its mixture may evolve bromine or iodine, concentrated H₂SO₄ and H₃PO₄.

Describe the general cleaning of laboratory glasswares
1. To remove organic residues, rinse glasware briefly with an organic solvent (acetone or ethanol). The used rinse will then be discarded into the organic waste.
2. Use warm tap water and a brush with soapy water to scrub the inside of curved glassware. This waste water can go down the sink.
3. Remove soapsuds with deionized water to avoid harsh water stains. The DI water rinse should form a smooth sheet when poured through clean glassware. If this sheeting action is not seen, more aggressive cleaning is needed. To expedite the glass-drying process, rinse again with acetone to remove water. The residual acetone will go into the organic waste container.
Cleaning Burets
- Wash with soapy water
- Rinse thoroughly with tap water
- Then rinse three to four times with deionized water. The rinse should form a smooth sheet when poured through clean glassware. If this sheeting action is not seen, more aggressive cleaning is needed.
- Burets need to be thoroughly cleaned to be used for quantitative work such as titrations. To expedite the glass drying process, rinse again with a small volume of acetone to remove water. The used acetone will then go into organic waste.
Cleaning Pipetes and Volumetric Flasks
- Clean pipets and volumetric flasks using warm soapy water
- Rinse with tap water followed by three to four rinses with deionized water. This water rinse should form a smooth sheet when poured through clean glassware. If this sheeting action is not seen, more aggressive cleaning may be needed.
- Dry using acetone to remove water. This acetone rinse will be disposed of in the organic waste container.

NB/ If water will affect the final solution, you can rinse with the solution you’re using to remove the water. Then, triple rinse with the solution you’re using to remove the alcohol or acetone.

Remove stoppers and stopcocks when they are not in use. Otherwise, they may “freeze” in place.
You can de-grease ground glass joints by wiping them with a kimwipe soaked with hexane or acetone. Do this in the hood vent to prevent you from breathing in the chemicals.
Do NOT dry glassware with a paper towel or forced air. This can introduce fibers or impurities. Normally, you can allow glassware to air dry on the shelf. Otherwise, if you need to turn in glassware to the stockroom you can use a solvent as described above.

List four methods used for drying glasswares

Air drying,
Blow drying,
Drying using dry cloth,
Roasting,
Organic solvent drying

Define the term waste disposal

waste disposal, the collection, processing, and recycling or deposition of the waste materials

List six heath effects resulting from proper waste disposal

Improper disposal can lead to adverse health outcomes, for example through water, soil and air contamination. Hazardous waste or unsafe waste treatment such as open burning can directly harm waste workers or other people involved in waste burning and neighbouring communities.

State four methods of carcass disposal

Methods of carcass disposal include burial, landfill, incineration or combustion, rendering, composting , and alkaline hydrolysis (chemical digestion).

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