Weighing & Preparation of
Solutions of Different
strengths & their Dilution
Handling Techniques of
We will discuss..
2. Measuring Chemicals
3. Different chemical concentrations
4. Dilution of stock solutions
6. Lab safety
• Solution uniform homogenous mixture of two
or more substances i.e, solute and solvent.
Solution= solute + solvent
• Standard solution: 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 a solute that will dissolve at that
• Supersaturated solution: a solution that contains more solute
than equilibrium condition allow; it is unstable & the solute may
precipitate upon slight agitation or addition of single crystal
Solutions of known concentration can be prepared in a number of
different ways depending on the nature of the analyte and/or the
• Weighing out a solid material of known purity, dissolving it in a
suitable solvent and diluting to the required volume
• Weighing out a liquid of known purity, dissolving it in a suitable
solvent and diluting to the required volume
• Diluting a solution previously prepared in the laboratory
• Diluting a solution from a chemical supplier.
Basic protocol 1: measuring mass using a top-loading Balance
1. Turn on balance and wait for display to read 0.0 g.
2. Place weighing vessel on the balance pan (e.g., creased weighing
paper, weigh boat)
3. Press tare button so that display reads 0.0g.
4. Gently add the substance being weighed to the weighing sample.
5. Record mass.
6. Remove weighed sample.
7. Clean spills off balance with brush or absorbent laboratory tissue.
Discard any disposable weighing vessel.
• Basic protocol 2: measuring Mass using an analytical
1. Turn on balance and wait for display to read 0.0000 g.
2. Check the level indicator & do not lean on table while
3. Place weighing vessel on the balance pan (e.g., creased
weighing paper, weigh boat)
4. Close the sliding doors & wait for stability light
indicator, indicating that the weight is stable.
5. Press tare button so that display reads 0.0g.
6. Gently add the substance being weighed to the
7. Record mass.
8. Remove weighed sample.
9. Clean spills off balance with brush or absorbent
laboratory tissue. Discard any disposable weighing
Volumetric or transfer
Procedure for preparing a solution of known concentration from a
known amount of a solid material
Procedure for preparing a solution of known
concentration by dilution
Common Practical Units for
Moles of solute / litres of solution
Number of EWs solute / Litre of solution
Moles of solute / Kg of solvent
g of solute / 100 g of solution
mL of solute / 100 mL of solution
g of solute / 100 mL of solution
•Weight per unit volume e.g., g/L, mg/ml
•Parts per million(ppm) or ppb
1. Molar solutions
• Molarity is number of moles of a solute that are dissolved per liter of
• A 1 M solution contains 1 mole of solute per liter total volume.
A 1M solution of H2SO4 contains 98.06 g of sulfuric acid in 1 liter of
"mole" is an expression of amount
"molarity" is an expression of concentration.
• "Millimolar", mM, millimole/L.
– A millimole is 1/1000 of a mole.
• "Micromolar", µM, µmole/L.
– A µmole is 1/1,000,000 of a mole.
HOW MUCH SOLUTE IS NEEDED FOR A SOLUTION OF A PARTICULAR MOLARITY
(g solute ) X (mole) X (L) = g solute needed
x volume = g solute needed
TO MAKE SOLUTION OF GIVEN
MOLARITY AND VOLUME
1. Find the FW of the solute, usually from label.
2. Determine the molarity desired.
3. Determine the volume desired.
4. Determine how much solute is necessary by
using the formula.
5. Weigh out the amount of solute.
6. Dissolve the solute in less than the desired
final volume of solvent.
7. Place the solution in a volumetric flask or
graduated cylinder. Add solvent until exactly
the required volume is reached, Bring To
2. Normal Solutions
• Normality is defined as the gram Eq.Wt. of the solute
per L of the solvent.
1N sol. = 1 EW solute / 1L of sol.
• Conc. Of acids and alkalis are usually expressed in
• gram Eq.Wt. is the M.W divided by the no. of H+ or
OH- ions released from 1 molecule of the acid or
base, respectively in solutions.
Eq. Wt. = MW of the substance / replaceable no. of H+ or OH15
1N Sulphuric Acid
M.W of H2SO4 = 98 g
Each molecule of acid releases 2 H+ ions in solutions.
Eq. Wt. = 98/2
So, 1L of 1N H2SO4 solution contains 49 g of H2SO4
1N of solution contains
3. Molal solutions
• Molality expresses the no. of moles per 1000 g or
1 Kg of solvent.
• It is dependent on the density of solvent.
• It is different from Molarity as the later refers to
volume of the solution, which is temperature
• Molal solutions are not usually used in
4. Percent solution
• Mass percent solutions are defined based on the grams of solute
per 100 grams of solution.
Example: 20 g of sodium chloride in 100 g of solution is a 20% by
• Volume percent solutions are defined as ml of solute per 100 mL
Example: 10 mL of ethyl alcohol + 90 ml of H2O (making approx.
100 mL of solution) is a 10% by volume solution.
• Mass-volume percent solutions are also very common. These
solutions are indicated by w/v % & are defined as the grams of
solute per 100 mL of solution.
Example: 1 g of phenolphthalein in 100 mL of 95% ethyl alcohol
is a 1 w/v % solution.
5. PPM and PPB
ppm: The number
of parts of solute
per 1 million parts
of total solution.
ppb: The number
of parts of solute
per billion parts of
5 ppm chlorine = 5 g of chlorine
in 1 million g of
5 mg chlorine in 1 million mg of
5 pounds of chlorine in 1 million
pounds of solution
To convert ppm or ppb to simple weight per
5 ppm chlorine = 5 g chlorine =
106 g water
5 g chlorine
106 mL water
= 5 mg/1 L water
= 5 X 10-6 g chlorine/ 1 mL water
= 5 micrograms/mL
A COMPARISON OF METHODS OF EXPRESSING THE CONCENTRATION OF A
CONCENTRATION OF SOLUTE
(Na2 SO4 )
AMOUNT OF SOLUTE
AMOUNT OF WATER
142.04 g Na2SO4
BTV 1 L with water
142.04 g Na2SO4
Add 1.00 kg of water
71.02 g Na2SO4
BTV 1 L with water
10 g Na2SO4
BTV 1 L with water
BTV 1 L
PREPARING DILUTE SOLUTIONS
FROM CONCENTRATED ONES
• Concentrated solution = stock solution
• Use this equation to decide how much stock
solution you will need:
Where, C1 = concentration of stock solution
C2 = concentration you want your dilute solution to be
V1 = how much stock solution you will need
V2 = how much of the dilute solution you want to make
• How would you prepare 1000
mL of a 1 M solution of Tris
buffer from a 3 M stock of
– The concentrated solution is 3
M, and is C1.
– The volume of stock needed is
unknown, ?, and is V1.
– The final concentration required
1 M, and is C2.
SUBSTITUTING INTO THE
C1 V1 = C2 V2
3 M (?) 1 M (1000 mL)
? = 333.33 mL
So, take 333.33 mL of the
concentrated stock solution
and BTV 1 L.
– The final volume required is
1000 mL and is V2.
Preparation of exact 1N HCL
• Dilute 100 ml of HCl with water to 1 L. Mix well.
• Prepare exact 1N sol. Of Na2CO3 by dissolving 5.30g
anhydrous Na2CO3 in 100 ml H2O.
• Phenolphthalein indicator
– Dissolve 250 mg indicator in 50 ml of 50% alcohol.
– Take 10ml of acid sol & 10ml H2O in a small beaker
– Add 2-3 drops of indicator
– Titrate with Na2CO3 sol from a 25ml burette till a faint red
colour is obtained
– Note the vol.(x ml) of base consumed at the end point
• Calculate the exact normality of the acid by
– Normality of base X vol. of base = normality of
acid X vol. of acid
– So, the normality of HCl = 1x X/10
– Normality of base is 1 vol of base is x ml.
• After calculating the exact normality of the
acid, it is proportionately diluted with water to
obtain to exact 1 normal sol.
Exact 1N NaOH solution
• Eq. Wt. Of NaOH is 40g
So 40g dissolved in 1L of H2O fo approx. 1N sol. & used.
• But for exact normality it is titrated against Oxalic acid
sol.(6.3g in 100ml water)
• Take 10ml oxalic acid + 10ml water in a beaker, add 2-3
drops of phenolpthalein indicator. Titrate against the NaOH
from a burette till a faint red colour is obtained.
• Calculate exact normality of sodium hydroxide sol as in
case of acid & dilute proportionately with water to obtain
exact 1N sol.
• Do not use chemicals
• Do not place labels on
top of one another.
• Label chemicals clearly
You make it- you label it
1. identity of contents
3. your name
4. date of preparation
5.Hazard alert (if applicable)
An unlabeled container will become
× eat, drink or smoke in the
× pipette by mouth
× leave equipment using
water, gas or electricity on
× Never add water to conc.
Keep your working area clean
wear a lab coat & appropriate
Open bottles near window
where ventilation is available.
wash hands after using any
substances hazardous to health,
on leaving the laboratory.
Handle conc. Acids & liquor
Ammonia with care.
label containers & solutions.
keep broken glassware & sharps
separate from other waste &
dispose of in the appropriate
secure the tops of reagent
bottles immediately after use
Know the solutions & different conc. to
Documentation, labeling & recording what
SOPs & SPs
Maintenance and calibration of instruments
Stability and expiration date recorded
Gallagher Sean R.; A.Wiley Emily; Current
protocols, essential laboratory techniques; 2nd
Ed. ; Wiley-Blackwell a John Wiley & sons, Inc.