Apparatus and their uses

For delivering an accurately measured, variable volume of solution during a titration.

Graduated 0–50 cm³ in 0.10 cm³ divisions, and read to two decimal places with the second figure 0 or 5. Read the bottom of the meniscus, at eye level.

For delivering one fixed, accurately known volume of solution, usually 20.0 or 25.0 cm³, into the conical flask.

Filled with a pipette filler, never by mouth. The drop left in the tip is part of the calibration: touch it off against the flask wall, never blow it out.

For preparing and holding one exact volume of a standard solution: 100, 250, 500 or 1000 cm³.

It carries a single graduation mark on the neck, so it measures one volume and no other. Never dissolve a solid in it and never heat it.

For measuring volumes of solutions.

Approximate. Right for the 20 cm³ of dilute H₂SO₄ you add before a redox titration; never for a titre, an aliquot, or a volume that enters the calculation.

For holding liquids. The graduated beaker is used for measuring liquids.

Its graduations are the roughest of all: a guide for "about 50 cm³", nothing more. Its real job is as the vessel a solid is dissolved in.

For adding a liquid a drop at a time: the indicator into the flask, the last drops of water up to the calibration mark.

Two or three drops of indicator is the whole dose. More doesn’t sharpen the endpoint; it colours the solution so deeply that the change is harder to see.

For weighing a solid accurately, to two decimal places.

Tare it with the empty container on the pan, or every mass you record is out by the mass of the container. Never weigh a solid straight onto the pan.

For holding liquids and alkalis during titration.

The sloping sides let you swirl hard without splashing out. Rinsing it with distilled water does no harm: extra water changes the concentration but not the number of moles you pipetted in.

For holding small quantities of substances: a solid is weighed on it, or a solution evaporated slowly from it.

After transferring, wash the particles left on the watch glass into the beaker with distilled water. Solid left behind was weighed but never dissolved, so the concentration is lower than the one you calculated.

For taking chemicals from their containers.

Never return unused solid to the stock bottle, and never dip a wet or dirty spatula into one: the whole bottle is contaminated for everyone after you.

For stirring a solid into solution until it all dissolves, and for guiding liquid down into a funnel when pouring.

Rinse the rod into the volumetric flask along with the beaker: solution clinging to it is solution that never reached the flask.

For delivering distilled water in a fine jet: rinsing the beaker, the rod and the funnel into the flask, and washing residue down the sides.

For storing water, acids and alkalis.

A large bottle with a tap at the base, so liquid is drawn off without lifting or tilting the whole vessel.

For storing a test reagent with its own dropper in the stopper, so it can be added drop by drop.

Each dropper belongs to one bottle. Moving a dropper between reagents is how a whole shelf gets contaminated.

For carrying out reactions on a small scale. The boiling tube is the larger, thicker one, used when the mixture must be heated.

Never fill past a third, and always point the mouth away from yourself and from everyone else at the bench.

For standing test tubes upright side by side, so a set of tests can be compared against one another.

The comparison is the point: in qualitative analysis you run the same reagent on several portions and read the differences between the tubes.

For grinding a solid sample to a fine powder before it is dissolved or tested.

Powder dissolves faster because it exposes far more surface: the same reason powdered limestone fizzes harder in acid than a lump does.

For heating: the bench source of a flame.

Air hole open gives the blue, roaring flame you heat with; air hole closed gives the yellow luminous flame, which is the safety flame and deposits soot.

For supporting beakers and other vessels over the flame during heating.

Usually placed on a tripod stand to reduce direct heating.

It spreads the flame across the base of the vessel. Without it the flame strikes one spot and the glass cracks.

For holding substances to be burnt in gas jars.

How sulphur or sodium is burnt in a jar of oxygen: ignite the solid in the spoon, then lower it in. The long handle keeps your hand out of the jar.

For heating a solid strongly, and for evaporating a solution down to its solid.

Heating to CONSTANT MASS means heat, cool, weigh, and repeat until two weighings agree: that’s the proof that all the water of crystallisation has gone.

For holding a hot test tube, crucible or evaporating dish without touching it.

For holding a trace of a salt in the flame during a flame test.

Cleaned by dipping in concentrated HCl and holding in the flame until it colours the flame no longer. Nichrome and platinum are used because neither gives a flame colour of its own.

For testing gases: lighted for hydrogen, glowing for oxygen, and for lighting the Bunsen.

A lighted splint gives a squeaky pop with hydrogen and is put out by CO₂; a GLOWING splint relights in oxygen. Using the wrong one is a wasted test.

For viewing a flame test through, so that the strong yellow of sodium is filtered out.

Sodium is everywhere and drowns everything. Through cobalt glass its yellow disappears and potassium shows as lilac, otherwise a trace of sodium hides the potassium completely.

For cooling a heated solid without letting it take up moisture from the air again.

Skip it and a hygroscopic solid gains mass as it cools: the water you just drove off walks straight back in, and the result is too low.

For separating an insoluble solid (the residue) from the liquid that passes through (the filtrate), under gravity.

In solution preparation the same funnel does a different job: guiding the solution into the narrow neck of the volumetric flask. Rinse it in afterwards.

For filtration under pressure: the funnel sits in the thick-walled flask, whose side-arm is connected to a pump.

Reduced pressure pulls the liquid through far faster than gravity and leaves a much drier solid behind.

For fractional distillation.

Separates miscible liquids whose boiling points are close: ethanol from water. Repeated condensation and re-evaporation up the column enriches the vapour in the more volatile liquid.

For separating two immiscible liquids, oil and water, by running the lower layer out through the tap.

Close the tap the instant the boundary reaches it, or the two layers mix again in the receiver.

For cooling vapour back to liquid in distillation, so the distillate can be collected.

Cooling water enters at the LOWER end and leaves at the upper, so the jacket stays full and the vapour meets the coldest water last.

For collecting gases.

Covered with a greased lid or glass plate. A gas denser than air (CO₂, Cl₂, SO₂) is collected by downward delivery, jar upright; a lighter one (H₂, NH₃) by upward delivery, jar inverted.

For supporting a gas jar over water in a trough, when collecting a gas over water.

Only for gases that are insoluble, or nearly so, in water: hydrogen and oxygen yes, ammonia and hydrogen chloride never.

For carrying a gas from the flask where it is generated to the jar, trough or test tube where it is collected or tested.

Take the delivery tube OUT of the liquid before you stop heating, or cold liquid is sucked back into the hot tube and it cracks.

For adding acid to the solid in a gas generator without taking the flask apart.

Its stem must dip below the surface of the liquid; otherwise the gas you’re making escapes back up the funnel instead of going down the delivery tube.

For holding the burette vertical at a workable height, and for supporting flasks and tubes over the flame.

Clamp the burette at eye level so it can be read without stooping: a burette read from below gives a volume that’s too small.

To see the end-point or colour change readily.

Placed under the conical flask. Against a white background the first permanent pink is obvious; against a dark bench it’s missed, and the titre comes out too high.

For carrying out a test on one drop of solution at a time, in its shallow wells.

Saves reagent, and the white glaze shows a faint precipitate or colour the way a test tube can’t.

For electrolysis: two inert electrodes dipping into the electrolyte, connected through an ammeter and a switch to a D.C. supply.

Carbon (graphite) or platinum, because both are unreactive and conduct. The supply MUST be direct current: with a.c. the electrodes swap over many times a second and nothing is collected. Anode to positive, cathode to negative.