HYDROGEN PEROXIDE
c(H2O2) = 1 mol/L
=======================
To prepare 100 mL of a 1 mol/L solution of hydrogen peroxide we will need to
dilute 5.68513 mL of 50 % H2O2 to a final volume of 100 mL with deionized
(distilled) water.
SOURCE:
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Name: Hydrogen peroxide
Formula: H2O2
Formula weight: 34.015 g/mol
CAS Number: 7722-84-1
NFPA: Health 3, Flammability 0, Instability 1, Special OX
CALCULATION:
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The key concept is that the amount of solute in the desired solution must be
equal to the amount of solute in the source solution. Remember, the
concentration is the amount of a solute divided by the volume of the solution.
Before we make any calculations we have to make sure that we only use one
system and one unit of measurement. DO NOT mix measurement systems and units.
Desired solution:
V0 = 100 mL * (1 L)/(1000 mL) = 0.1 L
c0 = 1 mol/L
Source solutions:
w1 = 50 % = 50 * 1/100 = 0.5
d1 = 1.19662 kg/L * (1 g/L)/(0.001 kg/L) = 1196.62 g/L
--------------------------------
Then, we determine the concentration of the source (stock) solution
c1 = d(H2O2) * w(H2O2) / M(H2O2)
c1 = 1196.62 g/L * 0.5 / 34.0147 g/mol
c1 = 17.5897 mol/L
Since the total amount of solute is the same before and after dilution, the
volume of stock solution needed is
V1 = V0 * c0 / c1
V1 = 0.1 L * 1 mol/L / 17.5897 mol/L
V1 = 0.00568513 L
To convert the result into a desired unit we will use dimensional analysis again
V(50 % H2O2) = 0.00568513 L * (1000 mL)/(1 L) = 5.68513 mL
PROCEDURE:
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First of all, fill the volumetric flask about halfway with deionized water to
avoid violent reactions. NEVER add water to concentrated acid.
Choose a clean pipette of suitable size and transfer the liquid to the
volumetric flask. When the whole solution has been drained, touch the tip of
the pipette to the side of the volumetric flask to allow the last of the liquid
to drain out. DO NOT blow out the remaining solution.
Allow the solution to reach room temperature because a volumetric flask is only
accurate at the temperature at which it has been calibrated (usually 20 癈).
Very carefully fill the flask to the mark on the neck of the flask, using a
dropping pipette to add the last few milliliters of liquid. Mix your solution
thoroughly, by inverting the flask and shaking. NEVER hold large volumetric
flasks by the neck alone - provide support at the bottom.
Transfer the prepared solution to a clean, dry storage bottle and label it.
NEVER store solutions in a volumetric flask.
SAFETY NOTES:
-------------
- When making chemical solutions, always use the appropriate safety equipment.
- As a general rule, always add the more concentrated solution to the less
concentrated solution.
- All chemicals that you are unfamiliar with should be treated with extreme
care and assumed to be highly flammable and toxic.
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