Practical Skills Flashcards
What are some of the apparatus that are commonly used to accurately measure solution volumes? What are the respective volume capacity for each of the apparatus?
Measuring cylinder –> (10cm cube, 50 cm cube, 100 cm cube)
Pipette
(10.0cm cube, 25.0 cm cube)
Burette
(50.00cm cube)
What are some of the apparatus that are commonly used to accurate to contain solutions e.g. for a reaction to take place? What are the respective volume capacity for each of the apparatus?
Beaker
(100 cm cube, 250 cm cube)
Conical flask(100 cm cube, 250 cm cube)
Round-bottom flask (used for heating)
(100 cm cube, 500 cm cube, 1000 cm cube)
What are some of the apparatus that are commonly used to collect a gas and measure the gas volume? What are the respective volume capacity for each of the apparatus?
A graduated gas syringe or an inverted measuring cylinder may be used to collect a gas and measure the gas volume.
Gas syringe (100 cm cube)
Inverted measuring cylinder (collecting a gas by displacement of water) Note: the gas collected must not be soluble in water.
Heating of solids should be done using _____________.
Heating of solids should be done using a test-tube or boiling tube.
_________ and ________ are not used for strong heating of solids.
Conical flasks and beakers
Heating of liquids may be done in tubes, flasks or beakers ____________.
depending on the volume
An electronic balance is used to ____________.
measure mass
What are the things that you need to provide with and write about for procedures to an experiment?
Providing appropriate details regarding apparatus and materials used. ( the volume and reasoning)
The quantity of chemicals should be stated.
For e.g.
1. specify the mass, in grams, g, for solids
2. Specify the volume in cm cube or dm cube and concentration e.g. in mol dm to the power of -3, for solutions.
3. For titrations (is a laboratory technique that measures the concentration of a chemical in a solution) : state ‘add one or two drops’ of the indicator used and also describe the end-point colour change.
Examples:
(i) Measure 2.00g of copper (ii) oxide in a 100 cm cube beaker using an electronic or weighing balance.
(iii) To 1.00g of calcium carbonate, add 50.0 cm cube of 1.00 mol dm to the power of -3 dilute hydrochloric acid.
What are three examples of safety precautions one should take note of?
Experiments (general )–> safety precaution (avoid direct contact wth chemicals.) –> reason (chemicals may be toxic or corrosive)
Experiments (boiling liquid in a conical flask/ round-bottom flask e.g. in reactions involving synthesis. –> safety precautions (add boiling chips)–> reason (‘bumping’ may occur if boiling chips are not used and may result in chemicals spurting out.)
Experiments (heating a sample in a test-tube / boiling tube with a Bunsen burner)–> safety precautions (move the test-tube/boiling tube up and down . Do not heat at just one spot.–> reason (avoid contents of the test-tube/ boiling tube from spurting due to intensive heating at one spot.
How is reliability ensured for this experiment involving filtration to separate solid residue from a solution? Explain.
(The residue is the desired product).
Wash the residue (desired) on the filter paper with distilled water.
Discard the washing and the filtrate (not desired).
Explanation:
Any soluble impurity present on the residue will be removed. Otherwise, for example, the mass of the desired solid measured will be higher.
How is reliability ensured for this experiment involving filtration to remove insoluble impurities from a solution? (The filtrate is the desired product). Explain.
Reliability is ensured by washing the residue (not desired) on the filter paper with distilled water.
Collect the washings together with the filtrate (desired).
Explanation:
Any desired substance present on the residue will be washed and collected with the filtrate. If not washed, less of the desired substance will be collected.
How is reliability ensured for this experiment involving drying of product which is wet? Explain.
How reliability is ensured:
If solvent is water, dry the product in an oven of suitable temperature e.g. 50 degrees celcius [if solvent is a volatile liquid with low boiling point, heating product under an infra-red lamp will remove the solvent.]
After heating the product for some time (e.g. 10 min), cool the product, then weigh.
The process of heating for a short duration, cooling and weighing is repeated until two consecutive weighings give consistent mass.
Explanation
Ensures that a constant mass of the product with no solvent present is achieved.
Note:
If the mass of residue is important, drying a residue by pressing between pieces of filter paper is insufficient to remove solvent.
Heating the product in an oven or under an infra-red lamp is needed to remove the solvent (care should be taken that the product does not decompose under excess heat).
Note:
A general way to check for reliability is to repeat the whole experiment until consistent results are obtained.
