SAMPLE LAB REPORT

4.4. How to prepare 10 percent nitric acid solution?

Nitric Acid (HNO₃) is a clear, colorless to slightly yellow inorganic acid. It is a strong monobasic acid and a powerful oxidizing agent. Nitric acid with water forms a constant boiling mixture (azeotrope) which having 68 % HNO₃ and boils at 121 °C.

Problem: The label on a nitric acid bottle states that it is 68 % nitric acid by mass and has the density of 1.40 g/cm³. How will you prepare 1 L of 10 percent nitric acid solution?

                    == SolCalc - Laboratory Report ==
                        August 04, 2013  17:01:13

NITRIC ACID
w(HNO3) = 10 %
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To prepare 1 L of a 10 % solution of nitric acid we will need to dilute 110.762 mL 
of 68 % HNO3 to a final volume of 1 L with deionized (distilled) water.


SOURCE:
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    Name: Nitric acid  
    Formula: HNO3
    Formula weight: 63.013 g/mol
    CAS Number: 7697-37-2 
    NFPA: Health 4, Flammability 0, Instability 0, 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 = 1 L
    w0 = 10 % = 10 * 1/100 = 0.1
    d0 = 1.05445 g/mL * (1 g/L)/(0.001 g/mL) = 1054.45 g/L
    Source solutions:
    w1 = 68 % = 68 * 1/100 = 0.68
    d1 = 1.4 g/mL * (1 g/L)/(0.001 g/mL) = 1400 g/L
    --------------------------------

First, we calculate the concentration of the desired solution

    c0 = d(solution) * w(HNO3) / M(HNO3)
    c0 = 1054.45 g/L * 0.1 / 63.0128 g/mol
    c0 = 1.6734 mol/L

Then, we determine the concentration of the source (stock) solution

    c1 = d(HNO3) * w(HNO3) / M(HNO3)
    c1 = 1400 g/L * 0.68 / 63.0128 g/mol
    c1 = 15.108 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 = 1 L * 1.6734 mol/L / 15.108 mol/L
    V1 = 0.110762 L

To convert the result into a desired unit we will use dimensional analysis again

    V(68 % HNO3) = 0.110762 L * (1000 mL)/(1 L) = 110.762 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 °C). 
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:
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- 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.


DISCLAIMER:
-------------
Use SolCalc at your own risk! If you don't understand the results, DON'T use them.

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