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How can the percentage purity of sulphuric acid be calculated?
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Moham Abed
How can the percentage purity of sulphuric acid be calculated?
reaction :
This is a simple neutralization reaction:
H2SO4 + 2NaOH → Na2SO4 + 2H2O
Equivalence point of strong acid titration is usually listed as exactly 7.00. In the case of sulfuric acid second step of dissociation is not that strong, and end point is shifted up by tenths of the pH unit - but we are still very close to 7. Thus the best indicator of those listed on pH indicators preparation page is bromothymol blue. However, as we have discussed on the acid-base titration end point detection page, unless we are dealing with a diluted solution (in the range of 0.001 M) we can use almost any indicator that gives observable color change in the pH 4-10 range. In effect we can safely use the most popular phenolphthalein and titrate to the first visible color change.
phenolphthalein color change near titration end point
Color change of phenolphthalein during titration - on the left, colorless solution before end point, on the right - pink solution after end point. Note we have to end titration at first sight of color change, before color gets saturated.
procedure :
Pipette aliquot of sulfuric acid solution into 250mL Erlenmeyer flask.
Dilute with distilled water to about 100 mL.
Add 2-3 drops of phenolphthalein solution.
Titrate with NaOH solution till the first color change.
result calculation
According to the reaction equation
H2SO4 + 2NaOH → Na2SO4 + 2H2O
sulfuric acid reacts with sodium hydroxide on the 1:2 basis. That means number of moles of sulfuric acid is half that of number of moles of sodium hydroxide used.
Equivalence point of strong acid titration is usually listed as exactly 7.00. In the case of sulfuric acid second step of dissociation is not that strong, and end point is shifted up by tenths of the pH unit - but we are still very close to 7. Thus the best indicator of those listed on pH indicators preparation page is bromothymol blue. However, as we have discussed on the acid-base titration end point detection page, unless we are dealing with a diluted solution (in the range of 0.001 M) we can use almost any indicator that gives observable color change in the pH 4-10 range. In effect we can safely use the most popular phenolphthalein and titrate to the first visible color change.
phenolphthalein color change near titration end point
Color change of phenolphthalein during titration - on the left, colorless solution before end point, on the right - pink solution after end point. Note we have to end titration at first sight of color change, before color gets saturated.
procedure :
Pipette aliquot of sulfuric acid solution into 250mL Erlenmeyer flask.
Dilute with distilled water to about 100 mL.
Add 2-3 drops of phenolphthalein solution.
Titrate with NaOH solution till the first color change.
result calculation
According to the reaction equation
H2SO4 + 2NaOH → Na2SO4 + 2H2O
sulfuric acid reacts with sodium hydroxide on the 1:2 basis. That means number of moles of sulfuric acid is half that of number of moles of sodium hydroxide used.
Specific gravity would be a useful technique; perhaps not as accurate as titration. Weigh 50 mL of the unknown and check vs tables in the CRC Handbook.
Do a reaction: add weighed amounts of NaHCO3 (slowly, carefully) until the foaming stops. I think this will just neutralize 2 of the 3 acidic protons on H3PO4. Knowing how much NaHCO3 reacts, you can determine how much H3PO4 there was.
Evaporation to "dryness": in a porcelain dish, weigh a decent amount of the unknown and heat at about 110C for an hour or so. The liquid at the end will be highly concentrated, but perhaps not 100% H3PO4. Check with a known concentration of H3PO4.
If you can get the apparatus, you could check conductivity. You could even do it yourself (roughly) with a multimeter and stainless steel wire (of course, platinum wire is preferable).
You could try to determine viscosity; check vs known standards. Very rough for analysis.
Specific gravity would be a useful technique; perhaps not as accurate as titration. Weigh 50 mL of the unknown and check vs tables in the CRC Handbook.
Do a reaction: add weighed amounts of NaHCO3 (slowly, carefully) until the foaming stops. I think this will just neutralize 2 of the 3 acidic protons on H3PO4. Knowing how much NaHCO3 reacts, you can determine how much H3PO4 there was.
Evaporation to "dryness": in a porcelain dish, weigh a decent amount of the unknown and heat at about 110C for an hour or so. The liquid at the end will be highly concentrated, but perhaps not 100% H3PO4. Check with a known concentration of H3PO4.
If you can get the apparatus, you could check conductivity. You could even do it yourself (roughly) with a multimeter and stainless steel wire (of course, platinum wire is preferable).
You could try to determine viscosity; check vs known standards. Very rough for analysis.
reaction :
This is a simple neutralization reaction:
H2SO4 + 2NaOH → Na2SO4 + 2H2O
Equivalence point of strong acid titration is usually listed as exactly 7.00. In the case of sulfuric acid second step of dissociation is not that strong, and end point is shifted up by tenths of the pH unit - but we are still very close to 7. Thus the best indicator of those listed on pH indicators preparation page is bromothymol blue. However, as we have discussed on the acid-base titration end point detection page, unless we are dealing with a diluted solution (in the range of 0.001 M) we can use almost any indicator that gives observable color change in the pH 4-10 range. In effect we can safely use the most popular phenolphthalein and titrate to the first visible color change.
phenolphthalein color change near titration end point
Color change of phenolphthalein during titration - on the left, colorless solution before end point, on the right - pink solution after end point. Note we have to end titration at first sight of color change, before color gets saturated.
procedure :
Pipette aliquot of sulfuric acid solution into 250mL Erlenmeyer flask.
Dilute with distilled water to about 100 mL.
Add 2-3 drops of phenolphthalein solution.
Titrate with NaOH solution till the first color change.
result calculation
According to the reaction equation
H2SO4 + 2NaOH → Na2SO4 + 2H2O
sulfuric acid reacts with sodium hydroxide on the 1:2 basis. That means number of moles of sulfuric acid is half that of number of moles of sodium hydroxide used.
reaction :
This is a simple neutralization reaction:
H2SO4 + 2NaOH → Na2SO4 + 2H2O
Equivalence point of strong acid titration is usually listed as exactly 7.00. In the case of sulfuric acid second step of dissociation is not that strong, and end point is shifted up by tenths of the pH unit - but we are still very close to 7. Thus the best indicator of those listed on pH indicators preparation page is bromothymol blue. However, as we have discussed on the acid-base titration end point detection page, unless we are dealing with a diluted solution (in the range of 0.001 M) we can use almost any indicator that gives observable color change in the pH 4-10 range. In effect we can safely use the most popular phenolphthalein and titrate to the first visible color change.
phenolphthalein color change near titration end point
Color change of phenolphthalein during titration - on the left, colorless solution before end point, on the right - pink solution after end point. Note we have to end titration at first sight of color change, before color gets saturated.
procedure :
Pipette aliquot of sulfuric acid solution into 250mL Erlenmeyer flask.
Dilute with distilled water to about 100 mL.
Add 2-3 drops of phenolphthalein solution.
Titrate with NaOH solution till the first color change.
result calculation
According to the reaction equation
H2SO4 + 2NaOH → Na2SO4 + 2H2O
sulfuric acid reacts with sodium hydroxide on the 1:2 basis. That means number of moles of sulfuric acid is half that of number of moles of sodium hydroxide used.
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Specific gravity would be a useful technique; perhaps not as accurate as titration. Weigh 50 mL of the unknown and check vs tables in the CRC Handbook.
Do a reaction: add weighed amounts of NaHCO3 (slowly, carefully) until the foaming stops. I think this will just neutralize 2 of the 3 acidic protons on H3PO4. Knowing how much NaHCO3 reacts, you can determine how much H3PO4 there was.
Evaporation to "dryness": in a porcelain dish, weigh a decent amount of the unknown and heat at about 110C for an hour or so. The liquid at the end will be highly concentrated, but perhaps not 100% H3PO4. Check with a known concentration of H3PO4.
If you can get the apparatus, you could check conductivity. You could even do it yourself (roughly) with a multimeter and stainless steel wire (of course, platinum wire is preferable).
You could try to determine viscosity; check vs known standards. Very rough for analysis.
Specific gravity would be a useful technique; perhaps not as accurate as titration. Weigh 50 mL of the unknown and check vs tables in the CRC Handbook.
Do a reaction: add weighed amounts of NaHCO3 (slowly, carefully) until the foaming stops. I think this will just neutralize 2 of the 3 acidic protons on H3PO4. Knowing how much NaHCO3 reacts, you can determine how much H3PO4 there was.
Evaporation to "dryness": in a porcelain dish, weigh a decent amount of the unknown and heat at about 110C for an hour or so. The liquid at the end will be highly concentrated, but perhaps not 100% H3PO4. Check with a known concentration of H3PO4.
If you can get the apparatus, you could check conductivity. You could even do it yourself (roughly) with a multimeter and stainless steel wire (of course, platinum wire is preferable).
You could try to determine viscosity; check vs known standards. Very rough for analysis.
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