purpose:
This lab's purpose was to determine the unknown concentration of the NaOH solution using an already known concentration of an acid, HCl, required to perform the titration.
Procedure:
Data table:
calculations:
Titration curve (ph curve):
conclusion:
10 mL of HCl were used in the titration between HCl and NaOH in order to determine the concentration of NaOH. A burrette was used to drip amounts of NaOH into the HCl solution and continued at a moderate until solution became a faint pink. Four trial were taken to determine at what point the solution was neutralized and the amount of NaOH reacted in each trial was taken. Their average was then calculated. (first one was excluded because it was considered an outlier).The molarity of NaOH, based on the equation used for titration (M1V1/n1 = M2V2/n2) was found to be 1.3. The pH of HCl when no NaOH was present was -.18 because HCl was a strong acid and dissociated almost to completion; therefore, because H+ and Cl- had the same mole to mole ratio , the pH of HCl was calculated by taking the negative log of the concentration of H+(biggest effect on pH). When four milliliters of NaOH were added to the solution of HCl it dissociated almost completion. The solution consisted of Na+, OH-, H+, and Cl-, ions and H2O . The OH- (limiting reactant) then reacted to completion with H+, leaving 9.8 milllimoles (mmol) -milliliters times molarity- of H+ still unreacted: of the ions still present after the reaction(Na+, H+, Cl-,)and water , H+ contributed the most and was the most effect when calculating pH. The concentration of H+ was then found and using the process above was converted into a pH of .15. When 7.5 milliliters were added to the solution , the OH- again reacted to completion with H+. As a result 5.25 mmol of H+ were left unreacted and because it has the biggest effect on pH it was used to calculate a pH of .52(process same as above). Then 11.5 mL of NaOH were reacted and again was reacted to completion with HCl. However when reacted to completion , both the H+ and OH- reacted to completion(equivalence point), leaving Na+ and Cl- ions and H2O unreacted. Of those choices H2O is the only source of H+ and the pH of plain, distilled water is always 7.Then 14mL of 1.3M NaOH was poured into10mL of 1.5 mL HCl. In this case it was the H+ that reacted to completion with the OH-. The result was the ions Na+, Cl-, OH- and water. Of those choices OH- would be the most significant contributor to pH. The pOH(.89) was found using the concentration of OH- found using the same process as with H+. The equation pH + pOH=14 was then used to produce a pH of 13.11.Finally 18 mL of NaOH were reacted with HCl. It reacted much like the previous, but because more NaOH was used it became a slightly stronger base with pH of 13.34.
discussion of theory:
A buffered solution is one that resist a change in pH when added either OH- or H+. It can be a weak acid and a salt or a weak acid and its conjugate, both are equivalent. Or a buffer can be a weak base and its salt or conjugate. When H+ is added to a solution it reacts to completion with the weak base present. When OH- is added to a buffer solution it reacts to completion with a weak acid. If either thing is added the buffer solution causes it to be consumed completely preventing it from significantly affecting the pH. How much a buffer can absorb without changing the pH is determined by the amounts of concentration of a weak acid and its conjugate. A good buffer is one that occurs when the concentrations of the acid and its conjugate have a one to one ratio.
A titration is a process that involves a solution of a known concentration, known as the tyrant, delivered from burette into the unknown concentration of another solution until the unknown solution reacts completely, or is completely consumed. Before this process an indicator is placed inside the solution with a known concentration and it serves as a visual representation of when the unknown concentration is completely consumed. A good indicator is selected based on the equivalence point of the titration (strong acids/strong base pH interval between 5 and 9: for weak base strong acid pH interval higher than the 5 to 9: for weak bases strong acids interval below the 5to9). Although the equivalence point and the endpoint are not the same a good indicator will these values equivalent. Most common indicators are complex molecules that are weak acids and are represented by HIn., they turn one color when a proton is attached to them and one when it is not. For the experiment phenolphthalein, commonly used indicator, was used. However caution needs to be taken because color changes for indicators are very sharp. An indicator marks the endpoint of a titration by changing color. The indicator used was clear in its acid form and pink in its basic form.
The process of a titration is then modeled with a pH curve also known as a titration curve. It plots the pH of the titration according to the given
amount of unknown solution added. For titrations involving a strong base and strong acid because both sources of H+ are consumed and the only remaining one is H2O the pH of said solution is relatively close to seven . For titrations with strong bases and weak acids, the titration becomes a stoichiometric problem in which the molarity of the remaining acid and its conjugate base formed are calculated or a equilibrium problem in which the position of the weak acid is calculated. The pH of this titration is always greater than seven the stronger the base the higher the pH. For weak bases and strong acid the same process is taken as the previous one but the pH is always lower than seven.
In solutions of acids or bases containing a common ion equilibrium shifts away from added component. Equilibrium occurs when a solution is saturated. Based on the common ion effect if a solution already contains ions common to the solid the solubility is lowered. If the conjugate of a weak acid is effective it will increase the solubility in an acidic solution.
A titration is a process that involves a solution of a known concentration, known as the tyrant, delivered from burette into the unknown concentration of another solution until the unknown solution reacts completely, or is completely consumed. Before this process an indicator is placed inside the solution with a known concentration and it serves as a visual representation of when the unknown concentration is completely consumed. A good indicator is selected based on the equivalence point of the titration (strong acids/strong base pH interval between 5 and 9: for weak base strong acid pH interval higher than the 5 to 9: for weak bases strong acids interval below the 5to9). Although the equivalence point and the endpoint are not the same a good indicator will these values equivalent. Most common indicators are complex molecules that are weak acids and are represented by HIn., they turn one color when a proton is attached to them and one when it is not. For the experiment phenolphthalein, commonly used indicator, was used. However caution needs to be taken because color changes for indicators are very sharp. An indicator marks the endpoint of a titration by changing color. The indicator used was clear in its acid form and pink in its basic form.
The process of a titration is then modeled with a pH curve also known as a titration curve. It plots the pH of the titration according to the given
amount of unknown solution added. For titrations involving a strong base and strong acid because both sources of H+ are consumed and the only remaining one is H2O the pH of said solution is relatively close to seven . For titrations with strong bases and weak acids, the titration becomes a stoichiometric problem in which the molarity of the remaining acid and its conjugate base formed are calculated or a equilibrium problem in which the position of the weak acid is calculated. The pH of this titration is always greater than seven the stronger the base the higher the pH. For weak bases and strong acid the same process is taken as the previous one but the pH is always lower than seven.
In solutions of acids or bases containing a common ion equilibrium shifts away from added component. Equilibrium occurs when a solution is saturated. Based on the common ion effect if a solution already contains ions common to the solid the solubility is lowered. If the conjugate of a weak acid is effective it will increase the solubility in an acidic solution.
questions:
1. The purpose of a titration is to determine the concentration of a solution with unknown molarity using the controlled addition of a solution with a concentration.
2. An indicator is the substance which undergoes a color change when the titration has reached the equivalence point(if the correct indicator has been chosen), has become neutralized. It serves as a visual representation of when the equivalence point is reached, this point is known as the endpoint.
3. Suitable indicators must be selected based on the equivalence point. If the titration is a strong acid and strong base one indicators with endpoints as far as pH=5 and pH=9 can be used. Titration of weak acids or weak bases requires a different selection of indicator with the appropriate interval. Such as a weak acid solution indicators with higher pH and weak base solutions with indicators with a lower pH.
4. The equivalence point is the point at which the reaction between the solution of a known concentration and that one of the unknown concentration has been completed. The endpoint is the point in the titration when the indicator changes color. If the appropriate indicator is used and the titration is a good one these two points would be equivalent.
5. A strong base and strong acid titration would have an equivalence point and endpoint near the middle of the graph, or approximately have a pH of 7 and would be completely neutral. A weak acid strong base titration would always have an endpoint above7, making the solution slightly more basic. The higher the base ion the higher the pH value the titration produces. Graph below.
6. A strong acid and strong base titration without a buffer would be sharper and faster when added a buffer the pH curve will smooth out.Gaph below.
7. A buffer is a weak acid and is conjugate or a salt. A buffer solution is a solution that resists a change in its pH when hydroxide ions or protons such as hydrogen ions are added. In the buffer solution of a weak acid and its conjugate when a hydroxide ion is added it reacts with the weak acid forming the acid conjugate and water. Hydroxide ions are replaced by the conjugate. If H+ were added to the solution it would react with the conjugate forming a weak acid. If the concentration of the acid and its conjugate are bigger than the concentration of the hydrogen ion than the pH would not change significantly.
8. Potential sources of error:
a. N.If there was a small amount of distilled water in the flask before the titration occurred
b. L.If HCl in glass before titration continued it would increase the amount of acid making each pH more acidic due to the larger amount of millimoles.
c. N.If three drops of phenolphthalein was added I do not think it would affect the pH because phenolphthalein just serves as an indicator as to when the titration is complete.
d. N.If an air bubble was in the NaOH burret but stayed in, it would not affect the milliliters reacted because whether or not the air bubble was there the same amount would be recorded.
e. H.If the air bubble were present but came out during the titration we would have recorder a larger amount than necessary using the equation an higher millimole value would have resulted for NaOH.
f. L. If excess NaOH were already in the beaker the solution would have produced i higher concnetration for NaOH because the titration would have happened sooner producing a titration with a lower pH value.
g. L. If you forgot to calculate the phenolphthalein you would never have figured out how many actual milliliters it took to perform the titration so a large value would be assumed making the concentration of NaOH. significantly smaller.
2. An indicator is the substance which undergoes a color change when the titration has reached the equivalence point(if the correct indicator has been chosen), has become neutralized. It serves as a visual representation of when the equivalence point is reached, this point is known as the endpoint.
3. Suitable indicators must be selected based on the equivalence point. If the titration is a strong acid and strong base one indicators with endpoints as far as pH=5 and pH=9 can be used. Titration of weak acids or weak bases requires a different selection of indicator with the appropriate interval. Such as a weak acid solution indicators with higher pH and weak base solutions with indicators with a lower pH.
4. The equivalence point is the point at which the reaction between the solution of a known concentration and that one of the unknown concentration has been completed. The endpoint is the point in the titration when the indicator changes color. If the appropriate indicator is used and the titration is a good one these two points would be equivalent.
5. A strong base and strong acid titration would have an equivalence point and endpoint near the middle of the graph, or approximately have a pH of 7 and would be completely neutral. A weak acid strong base titration would always have an endpoint above7, making the solution slightly more basic. The higher the base ion the higher the pH value the titration produces. Graph below.
6. A strong acid and strong base titration without a buffer would be sharper and faster when added a buffer the pH curve will smooth out.Gaph below.
7. A buffer is a weak acid and is conjugate or a salt. A buffer solution is a solution that resists a change in its pH when hydroxide ions or protons such as hydrogen ions are added. In the buffer solution of a weak acid and its conjugate when a hydroxide ion is added it reacts with the weak acid forming the acid conjugate and water. Hydroxide ions are replaced by the conjugate. If H+ were added to the solution it would react with the conjugate forming a weak acid. If the concentration of the acid and its conjugate are bigger than the concentration of the hydrogen ion than the pH would not change significantly.
8. Potential sources of error:
a. N.If there was a small amount of distilled water in the flask before the titration occurred
b. L.If HCl in glass before titration continued it would increase the amount of acid making each pH more acidic due to the larger amount of millimoles.
c. N.If three drops of phenolphthalein was added I do not think it would affect the pH because phenolphthalein just serves as an indicator as to when the titration is complete.
d. N.If an air bubble was in the NaOH burret but stayed in, it would not affect the milliliters reacted because whether or not the air bubble was there the same amount would be recorded.
e. H.If the air bubble were present but came out during the titration we would have recorder a larger amount than necessary using the equation an higher millimole value would have resulted for NaOH.
f. L. If excess NaOH were already in the beaker the solution would have produced i higher concnetration for NaOH because the titration would have happened sooner producing a titration with a lower pH value.
g. L. If you forgot to calculate the phenolphthalein you would never have figured out how many actual milliliters it took to perform the titration so a large value would be assumed making the concentration of NaOH. significantly smaller.