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Standard solutions are chemical solutions with a precisely known concentration of a substance or an element. The concepts of molarity and molar concentration (mol/L) are used to determine the concentration of standard solutions. These solutions are commonly used to identify the unknown concentration of a substance in a solution.
When preparing a standard solution, the solute should meet the following criteria:
Upon preparing standard solutions, a known weight of the substance is dissolved in distilled water or purified water. Solutes can be categorized as liquid, powder, pellets, etc.
Example: Trizma acetate (pellets)
Type-wise, standard solutions are divided into two types as primary and secondary standard solutions. Primary solutions are pure and stable, and they do not change their properties upon reacting with other chemicals.
Examples: NaHCO3 (Sodium bicarbonate), KHP (Potassium hydrogen phthalate)
Secondary standard solutions are specifically made for a particular task, such as titration, by dissolving solute in small quantities and solvent in large quantities.
Secondary standard solutions are solutions with concentrations that we need to compare with a solution of a primary standard.
Example: HCl (Hydrochloric acid)
A buffer solution is an aqueous solution that maintains its pH value fairly constant even upon the addition of small amounts of acids or bases.
This feature is crucial for reactions or processes that require a specific and stable pH range. Buffer solutions have a working pH range and a capacity that dictate how much acid or base can be neutralized before pH changes.
There are acidic buffers and basic buffers in general:
Acidic buffers:
A weak acid with its conjugate base.
Example: CH3COOH (Acetic acid) and CH3COO- (Acetate ion)
Basic buffers:
A weak base and its conjugate acid.
Example: NH4OH (ammonium hydroxide) and NH4Cl (ammonium chloride)
How buffers work:
Buffers neutralize any added OH- and H+, making it a weaker acid or a weaker base, to maintain a moderate pH level.
When H+ is added, the base component of the buffer neutralizes the added H+, hence maintaining the pH level.
CH3COO- + H+ → CH3COOH + H2O
Similarly, when OH- is added, the acid component of the buffer neutralizes the OH- and maintains the pH level.
CH3COOH + OH- → CH3COO- + H2O
As the initial step, the mass of tris base needed was calculated. Then, the required mass was determined using the analytical balance. The procedure was as follows:
Mass of the tris base required to prepare a 100 ml solution of 0.001M tris buffer solution (Molecular Weight of Tris base: 121.14 g/mol)
Concentration (C) = Number of moles (n) ÷ Volume (V)
Number of moles (n) = Concentration (C) × Volume (V) / 1000
Number of moles (n) = 0.001 × 100 / 1000 = 0.0001 moles
Mass of tris base = 0.0001 moles × 121.14 g/mol = 0.01214 g
Approximately 0.0121 g of tris buffer was used for the experiment.
To prevent the mass of the watch glass from being calculated, the analytical balance's screen was reset to zero after placing the watch glass.
For a more accurate reading, the watch glass was placed inside the balance, and then, using both hands (spatula in one hand and tris bottle in the opposite hand), tris base was added.
After adding tris base, when it was time to get the final reading, the shutters of the analytical balance were closed to minimize errors caused by wind.
When transferring the watch glass full of tris out of the analytical balance, the watch glass was covered to prevent loss due to wind.
In conclusion, this experiment helped students become familiar with operating the analytical balance and preparing standard/buffer solutions. Specifically, a standard solution was prepared as a buffer solution.
Preparation of Standard Chemical Solutions and Buffers. (2024, Jan 03). Retrieved from https://studymoose.com/document/preparation-of-standard-chemical-solutions-and-buffers
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