Lab experiments and types of research often require preparation of chemical solutions. Preparations of these chemical solutions are done by weight (w/v) and by volume (v/v).

1. PREPARING CHEMICAL SOLUTIONS – MEASURING AND HANDLING SOLID
CHEMICALS - MEASURING AND HANDLING LIQUID CHEMICALS –
REQUIREMENTS FOR MEASURING VARIOUS CHEMICALS.
PREPARING CHEMICAL SOLUTIONS
Lab experiments and types of research often require preparation of chemical solutions.
Preparations of these chemical solutions are done by weight (w/v) and by volume (v/v).
GLOSSARY
Buffer: A solution which tends to maintain a constant pH when excess acid or base is added.
Concentrated: For some commonly used acids and bases, the maximum solubility (at room
temperature) in an aqueous solution or as a pure liquid.
Concentration: The relative amount of solute and solvent in a solution.
Molality: A concentration unit (m); defined as the number of moles of solute divided by the
number of kilograms of solvent.
Molar Mass: The mass of a mole of any element or compound.
Molarity: A concentration unit (M); defined as the number of moles of solute divided by liters
of solution.
Normality: A concentration unit (N); defined as the number of equivalents of solute per liter
Solute: The substance which is dissolved, or has gone into solution (typically a solid).
Solvent: The substance which does the dissolving (typically a liquid, such as water or alcohol).
Must be greater than 50% of the solution.
Solution: A uniform homogeneous mixture of two or more substances. The individual
substances may be present in varying amounts.
Standard Solution: A very precise solution, usually to 3–4 significant figures, used in
quantitative analysis or an analytical procedure.
Saturated Solution: A solution that contains the maximum amount of a particular solute that
will dissolve at that temperature.
Supersaturated Solution: A solution that contains more solute than equilibrium conditions
allow; it is unstable and the solute may precipitate upon slight agitation or addition of a single
crystal.

2. INTRODUCTION TO PREPARATION OF SOLUTIONS
Many experiments involving chemicals call for their use in solution form. That is, two or
more substances are mixed together in known quantities. This may involve weighing a precise
amount of dry material or measuring a precise amount of liquid. Preparing solutions accurately
will improve an experiment's safety and chances for success.
SOLUTION 1: USING PERCENTAGE BY WEIGHT (W/V)
Formula
The formula for weight percent (w/v) is: [Mass of solute (g) / Volume of solution (ml)] x 100
Example
A 10% NaCl solution has ten grams of sodium chloride dissolved in 100 ml of solution.
Procedure
Weigh 10g of sodium chloride. Pour it into a graduated cylinder or volumetric flask containing
about 80ml of water. Once the sodium chloride has dissolved completely (swirl the flask gently
if necessary), add water to bring the volume up to the final 100 ml. Caution: Do not simply
measure 100ml of water and add 10g of sodium chloride. This will introduce error because
adding the solid will change the final volume of the solution and throw off the final percentage.

3. SOLUTION 2: USING PERCENTAGE BY VOLUME (V/V)
When the solute is a liquid, it is sometimes convenient to express the solution
concentration as a volume percent.
Formula
The formula for volume percent is: [Volume of solute (ml) / Volume of solution (ml)] x 100
Example
Make 1000ml of a 5% by volume solution of ethylene glycol in water.
Procedure
 First, express the percent of solute as a decimal: 5% = 0.05
 Multiply this decimal by the total volume: 0.05 x 1000ml = 50ml (ethylene glycol)
 Subtract the volume of solute (ethylene glycol) from the total solution volume:
 1000ml (total solution volume) - 50ml (ethylene glycol volume) = 950ml (water needed)
Dissolve 50ml ethylene glycol in a little less than 950ml of water. Now bring final volume of
solution up to 1000ml with the addition of more water. (This eliminates any error because the
final volume of the solution may not equal the calculated sum of the individual components).
So, 50ml ethylene glycol / 1000ml solution x100 = 5% (v/v) ethylene glycol solution.

4. SOLUTION 3: MOLAR SOLUTIONS
Molar solutions are the most useful in chemical reaction calculations because they
directly relate the moles of solute to the volume of solution.
Formula
The formula for molarity (M) is: moles of solute / 1 liter of solution or gram-molecular masses of
solute / 1 liter of solution.
Examples
The molecular weight of a sodium chloride molecule (NaCl) is 58.44, so one gram-molecular
mass (=1 mole) is 58.44 g. We know this by looking at the periodic table. The atomic mass (or
weight) of Na is 22.99, the atomic mass of Cl is 35.45, so 22.99 + 35.45 = 58.44.
If you dissolve 58.44g of NaCl in a final volume of 1 liter, you have made a 1M NaCl solution,
a 1 molar solution.
Procedure
To make molar NaCl solutions of other concentrations dilute the mass of salt to 1000ml of
solution as follows:
0.1M NaCl solution requires 0.1 x 58.44 g of NaCl = 5.844g
0.5M NaCl solution requires 0.5 x 58.44 g of NaCl = 29.22g
2M NaCl solution requires 2.0 x 58.44 g of NaCl = 116.88g
HANDLING SOLID CHEMICALS
Take an appropriate container to the reagent shelf where the general supply is kept.
Solids are somewhat more difficult to transfer than are liquids, so a wide-mouthed container such
as a beaker is preferable.
During the transfer, hold the stopper or lay it on the bench without contaminating the
stopper. Solid chemicals are most easily poured by tipping the general supply bottle and slowly
rotating it back and forth. Mere tipping of the bottle alone often causes large chunks to come out

5. very suddenly which leads to spills. If you use your own spatula, be sure that it is absolutely
clean. Return the proper stopper to the general supply bottle; do not interchange stoppers.
MIXING
If the solid is to be mixed with a liquid, add the solid to the liquid. Additions should be
made in small quantities except in certain circumstances.
DISPOSAL
If the laboratory instructor directs you to dispose of any solid chemicals in the sink, flush
it down the drain with copious amounts of running water. All other solids should be disposed of
in special containers provided for this purpose.
HANDLING LIQUID CHEMICALS.
Take an appropriate container to the reagent shelf. Avoid measuring volumes of strong
acids and alkaline solutions with your graduated cylinder held at eye level. Support your
graduated cylinder on your bench. Add hazardous liquids a little at a time, inspecting after each
addition.
REAGENT IN DROPPER BOTTLE
If the general supply bottle is equipped with a dropper, use it, but be sure that the dropper
never touches your container or the contents in it. Never put it down on the bench top, but return
it immediately to the right reagent bottle.
REAGENT IN STOPPER BOTTLE
If the general supply bottle is equipped with a stopper, the stopper should either be held
during the transfer or placed on its flat top. Do not lay the stopper on its side on the bench top.
Pour chemicals from the general supply bottle into your container. Be sure that the proper that
the stopper is returned to the right bottle.
MIXING
If liquid chemicals are to be mixed with water, always add the concentrated chemical to
water rather than water to chemical. This keeps the new solution dilute at all times and avoids
many accidents. Usually addition should be done slowly, using small quantities. It is important to
add acid to water, not the other way around because of the heat generated.

6. PIPETTING
Liquids are drawn into the pipet by applying a slight vacuum at the top, using a small
rubber suction bulb but never the mouth. Use pipette fillers.
HEATING
Liquids in beakers and flasks can be heated by placing them on a ring or tripod stand on
wire gauze with the container preferably supported by a clamp
DISPOSAL
Check with your laboratory instructor before disposing of any chemicals down the drain.
If the liquid chemical can be disposed of in the sink, dispose of it by rinsing it down the sink
with large quantities of water. Avoid unnecessary splashing.
TRANSFER, MEASURE AND MIX CHEMICALS
It is important, when we work with chemicals, that you know what you are doing and that
you always work in a safe way.

7. To make sure to do this, we need to follow correct procedures for handling and applying
chemicals.
TRANSFERRING CHEMICALS SAFELY
Chemical substances often need to be transferred from one container to another.
Transferring substances, especially when filling small containers from a larger one, can be quite
dangerous if the substance is explosive, flammable or corrosive.
Follow these guidelines when transferring chemicals to make sure you do it safely:
 Make sure that the large container is stable and in your control if you are lifting it to pour
liquid out of it.
 Use a funnel and pour slowly to prevent splashing and airlocks in the funnel.
 If the substance is flammable keep it away from any source of heat or ignition.
 If the substance releases dangerous fumes (for example, petrol), wear the correct
respirator and work in an open, ventilated area.
 If the substance is corrosive, wear gloves, a face shield and a rubber apron.
 Whenever possible use a hand-pump or siphon to transfer liquids, rather than pouring.
MEASURING CHEMICALS ACCURATELY
Chemicals often need to be measured accurately, otherwise, they may be too weak or too
strong and can become a safety hazard.
When measuring solid like powders and granules, use a scoop or a measuring spoon:
 Use a measuring spoon or scoop with the correct measurement you need.
 Take a scoop of the substance over-fills the scoop or spoon.
 Level the spoon or scoop by taking off the excess with a flat object.
When measuring liquids, always measure the substance on a flat surface and slowly pour or
decant the substance into a measuring cup, glass or cylinder tube until you have the correct
amount.
To observe if you have the correct volume
make sure that the eye level is at the same
level as the substance in the measuring
container. Should look at the measurement or
graduation from eye level – do not take the
measurement from above or below it.

8. MIXING CHEMICALS SAFELY
Mixing chemicals can be dangerous because they are often hazardous. Always wear the
correct personal protective clothing and equipment when mixing chemicals.
Follow these steps to mix chemicals safely:
1. Choose a suitable mixing area. The site should be away from plants, people, animals and
waterways. It needs to have good lighting and must be well ventilated. There should be first aid
equipment and materials to clean up any spills that may occur.
2. Make sure you have lots of clean, fresh water available. The water that you are using in your
mixture should be as clean as possible.
Check the product label for the chemical to find out how to mix a solution, including the
proportions or volumes needed. If you are unsure, contact the manufacturer or retailer for
instructions.
REFERENCES
 Michael N. Quigley. (1991). Student preparation of standard solutions, Journal of
Chemical Education, vol 68 (6), 505
 Rachel Wang., (2000). An Introductory Laboratory Exercise on Solution Preparation: A
Rewarding Experience. Journal of Chemical Education, vol 77 (2), 249.
 Francis. Marino.( 1993) General chemistry lab time to learn solutions. Journal of
Chemical Education, 70 (5) ,407
 http://delloyd.50megs.com/hazard/labsafety.html
 https://sielearning.tafensw.edu.au/toolboxes/TurfMgmt/html/pages/office/occupational_h
ealth/trans_mix.html
 https://www.sciencecompany.com/Preparing-Chemical-Solutions.aspx