Titrating Weak Acid With Strong Base

Now, we are titrating weak acid with strong base. For example in this condition we use 50 mL of 0.1M CH3COOH as weak acid and 0.1M NaOH as strong base. Firstly, we must calculate NaOH required to reach the equivalent point. (see eq. 1)

On the condition where there aren’t NaOH , we must calculate the pH of the solution. Acetic acid is weak acid, so the reaction in solution is (see eq. 2)

So, from the result above, pH solution is 2.88. Then, NaOH beginning added to the solution, this makes some acetic acid converted to buffer or conjugate base. In this condition we must use special formula to calculate its pH, the formula used in this condition is Henderson-Hasselbalch equation, (see eq. 3)

From the reaction, there is unreacted acetic acid which causes from higher of constant for reaction. So, before equivalent point the concentration of acetic also must be calculated using equation , (see eq. 4-5)

Acetic acid dominate at the equivalent point than NaOH added, although the concentration of two reagent are similar. This is because the reaction is effectively proceeds to completion. Acetic ion is weak base, so it must be calculated using equation (see eq. 6-7)

After equivalent point reached, NaOH is excess in the solution. This condition calculated using normal equation such as titrating strong acid with weak base. The equation is (see eq. 8)

Titrating Strong Acids with Strong Bases

Titrating strong acids and strong bases means that the titrand is strong acid with known concentration and volume, moreover the analyte is strong bases. The reaction during titration is H3O+ + OH- <--> 2H2O. Firstly, we can now start to calculate strong bases(NaOH) volume required for titration. Titrand used for this example is HCl 0.1M and volume 50 mL. From the reaction, we can now that moles of HCl is equal to moles of NaOH, so it could be calculated easily. So, the formula is M1.V1=M2.V2. Which M1 is concentration of HCl and V1 is volume of HCl, also M2 is concentration of NaOH and V2 is volume of NaOH. So, The volume of NaOH required to reach the equivalent point is :

V2 = (M1.V1)/M2 = (0.1 M x 50 mL)/0.2 M = 25 mL

From beginning of titrant added, H+ from HCl is excess in the solution, so the pH level is function of H+. We can calculate it using formula of pH = -log[H3O+] = -log[HCl] = -log[0.1] = 1.
After adding the bases, solution has more NaOH, for example we add 10 mL of NaOH. So, the pH would be :

HCl = [(M1.V1)-(M2.V2)]/V1+V2 = [(0.1 x 50)-(0.2 x 10)]/(50+10) = 0.05 M
pH = -log[HCl] = -log[0.05] = 1.3

At equivalent point, HCl and NaOH has the same moles so it has value of pH same equal to Kw or 10^-7.
So, the value of pH is 7.

After the equivalent point, solution has excess of NaOH than HCl so the equation similar with above formula, just little modification, which in the case of added 30 mL of NaOH :

NaOH [OH-] = [(M2.V2)-(M2.V2)]/V1+V2 = [(0.2 x 30)-(0.1 x 50)]/(50+10) = 0.0125 M

pH is power of H+, so we must calculate of H+ in the solution using formula :
Kw = H+.OH-, H+ = Kw/OH- = 10^-14/0.0125 = 8 x 10^-3
pH = -log[H3O+] = -log[8x10^-3] = 12.10

if we calculate each 5 mL adding of NaOH, the result of curve is like picture above.

Acid Base Titration Curve

Now, we will discussed about Titration Curve that describe the availability of the analyte and also the character. Experimentally the equivalent point would result on changed of solution color. On acid base titration equivalent point is function from concentration of analyte and titrant and strength of acid and base characters. By visual equivalent point wouldn't be visible if we don't use a suitable indicator. During titration, pH level change by adding of just a little titrant. This will result understanding of equivalent and end point of titration.

Titration curve important for the use of determine the end and equivalent point. It's function of volume titrant that added to solution versus pH level of titrand. In the titration, we use titrant/titrator that placed on the top or burrete. Titrant must be standard solution and known of concentration. Titrand or analyte is placed in the erlenmeyer flask with unknown of concentration.

There's 5 types of neutralization with specific type of titrant or titrand :

* Titrating Strong Acids with Strong Bases
* Titrating Weak Acids with Strong Bases
* Titrating Weak Bases with Strong Acids
* Titrating Weak Acids with Weak Bases
* Titrating Polyprotic Acids with Strong Bases

Acid - Base

There is two character of solution depend on its pH, acidic and basic character. First, acidic is character of solution where excess of H+ . And on the contrary basic is leak of H+. Bronsted and Lowry defined acid as proton donor, and base as acceptor of proton. NormalBrønsted-Lowry equation: acid + base acid + base. For example: HNO2(aq) + H2O(aq) NO2-(aq)+ H3O+(aq). Each acid has a conjugate base and each base has a conjugate acid. These conjugate pairs only differ by a proton. In this example: NO2- is the conjugate base of the acid HNO2 and H3O+ is the conjugate acid of the base H2O. Lux-Flood also has its definition of acid-base. Lux-Flood declare acid-base on the melt oxide which base is donor of oxyde and acid is oxyde acceptor. Nevertheless, on solution system, acid is things that increase the character/concentration of its cation, and base is things that increase the anion characters/concentrations. Arrhenius defines acid: generates [H+] in solution, base: generates [OH-] in solution. Normal Arrhenius equation: acid + base salt + water. For example: HCl(aq) + NaOH(aq) NaCl(aq) + H2O(l). Lewis defines acid: accepts an electron pair, base: donates an electron pair. The advantage of this theory is that many more reactions can be considered acid-base reactions because they do not have to occur in solution.

Acidic and Basic Condition very influence the macroscopy and microscopy organism. The nature of organism just can live on the neutral condition where the pH of the environment is approximately 7. But there is organism that can live on the extreme condition where the acid or basic character is high. Organism like that has to adapt their physical part to hold up on the environment such that. Organism that can live on the extreme condition usually called as extrememophile.

In the chemical reaction, acidic and basic character also has important role. It's can regulate the result of the reaction. For example, there is reaction which just can react on the acid condition, and vice versa. And there is effect when the reaction must set to acidic condition but in the practice we use basic condition. Things such that will get the reaction unpredictable or wrong.

The Nature of Acid Base Titration

What is the definition of acid base titration ?

Here's the simple definition, acid base titration is titration which the titrant and analyte reacts as acid base reaction. On the early of 1800's there's limited reactant which acts asa acidic dan basic reagent. For acidic reagent is H2SO4, HCl, and HNO3. For basic reagent is K2CO3 and Na2CO3. The important thing of titration is indicator. More sensitive indicator is better than one not sensitive. The limit of reagent and indicator result in the accuracy of the result.

In the mid of 1800's NaOH firstly intoduced as base titrant. And the used of NaOH improve the result of titration. Later, discovery of phenolphthalein and methyl orange has improved the result of titration too.

Titration bases is conducted by added one solution to another solution until the equilibirium point reached. While the titration process occur, there's chemical reaction between titrant and the analyte. Titration must stop until the indicator 'says' that there's a lot of titrant on the solution on the erlenmeyer flask(usually). The indicator would change the color of solution depend on the indicator used. For example, phenolphthalein is indicator for acid base titration. In The acidic form it has colorless form, but in the basic form H+ from its structure released and has red color. Phenolphthalein is commonly indicator for titration.