Standards are substances that contain a known quantity of a drug and can be used to calculate unknown quantities or calibrate analytical instruments. Primary and secondary standards are the two types of standards available. Primary standards are used to standardize secondary standard solutions, while secondary standards are used for certain types of analytical experiments.
In chemistry, a primary standard is a very pure reagent (99.9% accurate), easy to weigh, and offers an indicator of the number of moles in a molecule. A reagent is a material that is used to start a chemical reaction involving two or more components. To determine the amount of specific compounds in a sample solution, reagents are commonly used.
Characteristics of a good primary standard:
- It has a high degree of purity
- Has a non-toxic
- It has low reactivity and high stability
- Is affordable and easily available
- It has a high equivalent weight
- It has a high solubility
- In humid vs dry environments, it is unlikely to absorb moisture from the air to lessen mass fluctuations.
Frequently Asked Question (FAQ):
Is H2SO4 a primary standard?
H2SO4 is hygroscopic, its concentration in the air often changes, and hence it is not used as a primary standard. H2SO4, HNO3, HCl, NaOH, and NH4OH are not considered primary standard solutions.
Is NaOH a primary or secondary standard?
NaOH is used as a secondary standard rather than a primary standard because sodium hydroxide is hygroscopic which attracts carbon dioxide (CO2), sulfur dioxide (SO2), and hydrogen sulfide (H2S), from the air and are reacted quickly with it.
Why EDTA is not a primary standard?
EDTA is a secondary standard, due to water content ambiguity, the hydrated sodium salt of EDTA (Na2H2Y.2H2O) cannot be used as the primary standard for titrations. This allows one to calculate the reagent's average molar mass and water content, allowing it to be used to make EDTA standard solutions.
Why is HCl not used as a primary standard?
HCL is a secondary standard, HCl cannot be obtained in high purity, it is not a solid at normal temperature and pressure, and its molecular mass is low. These are the three main reasons why HCl is not used as a primary standard.
Why is K2Cr2O7 chosen as the primary standard?
Potassium dichromate (K2Cr2O7) is used as the primary standard since it has high purity, high solubility has a higher molecular mass, can be accurately weighed, is stable in the atmosphere, is not hygroscopic, and react rapidly during the titration.
Why is KIO3 a good primary standard?
Potassium iodate (KIO3) is an oxidizing agent and a good primary standard. It is mainly used in the titration of thiosulfate and sulfite solutions as a stable source of iodine, which is liberated in the presence of the iodide ion and acid. It is pure enough to serve as a standard against which other reagents can be measured.
Why is KMnO4 a self indicator?
Potassium permanganate is a flexible and potent oxidant used in redox titration as a self indicator. KMnO4 has a unique value in that it works as a self-indicator. Titration of permanganate must be done in a heavy acid solution.
Because KMnO4 is a redox indicator, Mn has a wide range of valencies. Mn's color varies when its valence state changes. As a result, no external indication is required potassium permanganate can serve as a self-indicator, indicating the endpoint of a reaction.
Why is NaCl a primary standard?
Sodium chloride is used as the primary standard because it is simple to obtain, has a high purity level, is inexpensive, has low reactivity (high stability), and does not decompose when heated. NaCl is used for silver nitrate (AgNO3) reaction as primary standards that meet all of the criteria of the primary standard. NaCl is hygroscopic, however when heated, it becomes stable, and it has high purity.
Why is nitric acid not used in titration?
Because nitric acid is a strong oxidizing agent it is not used in titration, in the redox titration, it will react with and consume some of the oxalate ions. As a result, less KMnO4 will be required to reach the endpoint in the presence of HNO3.
Why oxalic acid is used as the primary standard?
Oxalic acid is used as the primary standard as it is highly stable, pure, and does not change concentration due to environmental conditions. One issue with oxalic acid is that it can crystallize in two states: anhydric and dihydrate.
Why is sodium thiosulfate not a primary standard?
Because sodium thiosulfate (Na2S2O3) is hygroscopic, it is not used as a primary standard. When the humidity is high, the crystals absorb water, and when the humidity is low and the temperature is high, the water of crystallization is lost. As a result, we can't know a precise molecular weight without knowing the specific composition; hence a standard solution cannot be prepared without knowing the correct molecular weight.
Why is sodium oxalate a good primary standard?
Because of its high stability, non-toxicity, high molar mass, and readily available and inexpensive, disodium oxalate (Na2C2O4) can be used as a primary standard for standardizing potassium permanganate (KMnO4) solutions.
Why is sulphuric acid not used as a primary standard solution?
H2SO4 is not used as a primary standard solution because it doesn't fulfill the criteria for a primary standard as it absorbs moisture from the air. Sulphuric acid is available in the form of concentrated solutions that can be easily diluted; however, the concentration of the concentrated solution is unknown.
Why K2Cr2O7 cannot be used as a self indicator?
Because potassium dichromate can only work as an oxidizing agent in acidic media, it can't be employed as a self-indicator as its reduction product blocks the visual detection at the endpoint of the reaction.
Why KMnO4 is not a primary standard?
Potassium permanganate is secondary standard is not a primary standard because it is difficult to obtain the pure form as it is not free of MnO2. Furthermore, the color is so intense that it serves as its self indicator.
Why sodium carbonate is a primary standard?
Sodium carbonate is used as a primary standard in a different types of titrations, including acid-base titrimetry since anhydrous Na2CO3 is commercially available as an analytical reagent with a purity of 99.9% and is stable, so its strength does not fluctuate over time and its solution's molarity remains constant for a very long period.
What is titration in chemistry and its types?
Titration is a quantitative chemical analysis used to determine the concentration of a identified analyte. Titration is an important part of the study of chemistry. There are four types of titrations based on the chemical reaction that occurs between the titrant and the analyte: acid-base, redox, precipitation, and complexometric.
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