 CHEMISTRY : Quantitative Analysis

Finding the Concentration of SULPHURIC ACID

 PROJECT CODE: 1.32 SECTION: QUANTITATIVE ANALYSIS PROJECT TITLE: Finding the Concentration of SULPHURIC ACID [Concentrated solution] RELEASE DATE: 1997 LAST UPDATE: 1 Sep 2009 VERSION HISTORY: 1.0 - First release 1.1 - Revision of text and formatting. 1.2 - Added new examples (retested samples in Aug 2009)

## PRINCIPLE:

##### Molarity [M]
###### The Principle of this test is to dilute the acid and find the titrate volume of known molarity of NaOH required to neutralize the Acid dilution. The reaction is follows:

ACID (aq) + ALKALI (s) --- > SALT (aq) + WATER (l)

H2SO4 (aq) + 2NaOH (aq) --- > Na2SO4 (aq) + 2H2O (l)

## SPECIFIC GRAVITY

#### Procedure

###### Tare an empty dry 100mL beaker over a balance Transfer carefully 10ml (or 25ml) of Acid solution using a volumetric pipette into the beaker. Note the volume used and weight read out. Repeat this for 2 more times to have 3 weight readings and average out the result. One can tare the weight after the previous reading and simply add over the next aliquot volume of acid and take the new weight.

 Specific Gravity (g / mL) = Mass (g) Volume (mL)

#### Calculations

##### Example 1 : Solution S - General Purpose Conc. H2S04 [98%] (tested in 1997)
###### In 1997 a solution of conc H2SO4 [98%] (labelled in this document as Sol S) provided the following results:
Reading Sol S Volume (mL) Weight (g) Specific Gravity (m/Vol)
1 25 45.67 1.827
2 10 45.60 1.824
3 10 45.75 1.830
4 50 90.85 1.817
Average Specific Gravity of Solution S is 1.82g/mL

##### Example 2 : Solution S2 - General Purpose Conc. H2S04 [98%] (Solution S tested in 2009)
###### In 2009 (12 years Later) the same solution S was tested and labelled here as Solution S2 . The following results were obtained:
Reading Sol. S2 Volume (mL) Weight (g) Specific Gravity (m/Vol)
1 10 17.5 1.75
2 25 44.30 1.77
3 50 88.71 1.77
Average Specific Gravity of Solution S is 1.77g/mL

##### Example 3 : Solution T - General Purpose Conc. H2SO4
###### Another old container with Conc H2SO4 (Concentration not stated) was tested and is given in this document the label name Sol.T
Reading Sol. T Volume (mL) Weight (g) Specific Gravity (m/Vol)
1 25 40.2 1.608
2 25 40.36 1.614
3 50 80.76 1.615
Average Specific Gravity of Solution T is 1.61g/mL

##### Example 4 :Solution U - 90% H2SO4 for Milk Testing (2.5L stock) from 1995
###### Another stock solution with Conc H2SO4 Analar labelled 90-91% for milk testing (from 1995 c.) is given in this document the name Sol.U and tested.
Reading Sol. U Volume (mL) Weight (g) Specific Gravity (m/Vol)
1 25 44.81 1.792
2 25 44.7 1.782
3 50 89.12 1.788
Average Specific Gravity of Solution U is 1.79g/mL

## Molarity [M]

#### Calculations

##### Example 1 : Solution S - General Purpose Conc. H2S04 [98%] (tested in 1997)
###### The calculation of the Molarity of H2SO4 is given using an example of Sol S with the following data: Molarity of NaOH used [M-NaOH] = 0.5M Dilution factor of H2SO4 [Dil] = 20 (5mL in 100mL)) Volume of Acid used in Titration [V-H2SO4] = 20mL Volume of NaOH required to neutralise H2SO4 [V-NaOH] = 72.8mL (average of 3 runs) The reaction equation of this Acid-Alkali neutralisation is

2NaOH (aq) + H2SO4 (aq) --- > Na2SO4 (aq) + 2H2O (l)

###### From the equatoion above: 2 mole NaOH : 1 mole H2SO4 0.0364 moles NaOH : 0.0182 moles H2SO4 0.0182 moles H2SO4 are present in 20mL volume ? moles of H2SO4 present in 1000mL are (0.0182 x 1000) / 20 = 0.91M H2SO4 However, there was a dilution factor of 20 and so the molarity of the concentrated H2SO4 is 0.91 x 20 = 18.2M The following formula can be used:

 Molarity H2SO4 = [M-NaOH] x [V-NaOH] x Dil 2 x [V-H2SO4]

## Percentage Concentration [%]

###### The percentage of Acid present should theoretically be worked out by the ratio of the weight of actual H2SO4 molecules present in 1000mL and the actual weight of 1000mL Concentrated H2SO4 using the specific gravity index.

 % Acid Conc. = [ Weight of Acid molecules in 1000mL ] x 100 Weight of 1000mL Acid
 % Acid Conc. = = [ RMM of Acid x Molarity] x 100 [Specific Gravity x 1000mL]