organic chemistry lab and why is water the first choice for recrystallization when all factors are equal?
This isn't my subject area; one of our chem teachers will probably repond within 12 hours.
organic chemistry lab and why is water the first choice for recrystallization when all factors are equal?
Not quite sure what you mean by "all factors are equal"
On the plus side:
water is cheap,
water can easily handled with out PPE,
pH is easily adjusted,
dissolves a wide range of materials,
can be handled in the open lab,
....you can probably come up with more
On the negative side
High latent heat means more expensive to evapotate.
Higher viscosity can mean more difficult to filter (especially on a large scale) than organic solvents.
Hot water is quite agressive and can cause some functional groups to hydrolyse (e.g. esters).
Last traces of water can be difficult to remove.
Can cause organic impurities to be entrained in the crystals if the water solution is not washed with an organic solvent.
....again you can come up with some more.
Water is often the first choice for recrystallization in organic chemistry labs due to several factors. Let's discuss why water is preferred and how you can arrive at this conclusion yourself.
Recrystallization is a purification technique commonly used in organic chemistry labs to obtain a pure crystalline compound from a mixture. The choice of solvent for recrystallization depends on various factors such as solubility, temperature, safety, and environmental considerations.
To determine the first choice solvent for recrystallization when all factors are equal, you need to consider the following steps:
1. Look at the solubility of the compound: One of the key considerations is solubility. The chosen solvent should dissolve the compound to be purified at high temperatures but have minimal solubility at lower temperatures, allowing the compound to crystallize out. You can gather solubility data from reference books or databases like the CRC Handbook of Chemistry and Physics.
2. Assess the boiling point: Since the recrystallization process usually involves dissolving the compound at high temperatures, it is important to choose a solvent with a boiling point lower than the compound's melting point. This ensures that the compound can be dissolved at an elevated temperature and subsequently recrystallized upon cooling.
3. Consider solvent safety and environmental impact: Safety is paramount in the lab, so choosing solvents with low toxicity and low flammability is ideal. Additionally, environmental concerns should be taken into account, favoring solvents that are readily available, inexpensive, and have minimal impact on the ecosystem.
When considering these factors, water often emerges as the first choice for recrystallization due to several advantages:
1. Universal solvent: Water is an excellent solvent for a wide range of organic and inorganic compounds due to its polar nature. It can dissolve many organic compounds, making it versatile for recrystallizing various substances.
2. High boiling point and low melting point: Water has a high boiling point (100°C at standard pressure) and a low melting point (0°C), making it suitable for dissolving compounds at high temperatures and recrystallizing them upon cooling.
3. Safety and availability: Water is non-toxic, non-flammable, and readily available, making it a safe and easy-to-use solvent in the lab. It is also environmentally friendly, as it is abundant and can be easily disposed of without causing harm.
In summary, water is often the first choice for recrystallization when all factors are equal due to its broad solubility, high boiling point, low melting point, safety, and availability. Considering these factors and researching the solubility and characteristics of the compound in question will help you determine the most suitable solvent for recrystallization.