Nutshell: Bases and Alkalis

This is meant to be a simple explanation to differentiate base from alkali. This is a common question among students.

A base is usually a metal oxide. For example, sodium oxide, potassium oxide, calcium oxide.

If the base can be dissolved in water, we give them another term called alkali. For example, sodium oxide dissolves in water to form sodium hydroxide. Now we can call sodium hydroxide to be an alkali.

In general, any chemical name ending with the word hydroxide can be treated to be an alkali.

Nutshell: Sublimation

Sublimation is the process of changing a substance from the solid state directly into the gaseous state. It doesn’t form the liquid state before converting to the gaseous state.

For example, if you heat solid dry ice, it changes into the gaseous state.

Examples of substances that can undergo sublimation process are

1. Dry ice (solid carbon dioxide)
2. Ammonium chloride (it doesn’t really sublimes. Its a chemical reaction that is reversible upon heating)
3. Iodine
4. Napthalene
5. Camphor
6. Mercuric Chloride

Sublimation is also used to describe a method used to separate mixtures containing substances that sublimes.

For example, to separate a mixture of iodine and sand, we can use sublimation to separate the iodine from the salt. When we heat the mixture, the iodine sublimes and became gaseous state leaving the sand behind. To collect the iodine back in the form of solid, we can place a filter funnel above the mixture. The gaseous iodine when touches the filter funnel will change back to the solid state.

20130702-073259.jpg

Nutshell: Solutions and Suspensions

Solutions are mixtures. Solutions are formed when the solute dissolves in a solvent. The solutes are usually in the solid state and the solvent in the liquid state.(however that is not always the case). The solvent can also be in the form of a solid or a gas.

Water is commonly known as a universal solvent as it dissolves many substances. More substances are known to dissolve in water than in any other solvents.

However, water is a poor solvent for organic compounds thus we say organic compounds are insoluble in water.

Examples (solid and liquid mixture)

Format:
solute + solvent = solution

  • sugar + water = sugar solution
  • salt + water = salt solution
  • iodine + alcohol = iodine solution
  • Suspensions are mixtures too. However, the solute doesn’t dissolve in the solvent. In suspension, you will find that the solid is either floating around in the liquid or it sinks to the bottom of the liquid.

    List: Volatile Liquids

    Volatile liquids have low boiling point. As a result, they evaporate very easily at room temperature. Because of their low boiling points, volatile liquids convert to the gas phase at a lower temperature and the gas molecules can diffuse faster than the molecules of a non-volatile liquid. This is the reason why perfumes use volatile liquids so that their scent can disperse more quickly into the air.

    When volatile liquids come in contact with human skin, it gives us a cooling sensation.

    Some other examples of volatile liquids include acetone, ammonia, dichloromethane, and diethylether.

    Examples of volatile liquids:

  • alcohol
  • petrol
  • methylated spirits
  • acetone
  • chloroform
  • List: Substances that undergoes sublimation

    These are some common substances that undergo sublimation upon heating under the normal atmospheric pressure condition.

  • dry ice (solid carbon dioxide)
  • iodine crystals
  • napthalene (mothballs)
  • camphor
  • *ammonium chloride
  • *ammonium chloride doesn’t actually undergo sublimation upon heating. It decomposes and forms ammonia gas and hydrogen chloride gas. When they are in contact with cooler surfaces, they recombine to form back ammonium chloride. This gives a false impression that it has undergone sublimation.

    -decomposition of ammonium chloride-

    NH4Cl → NH3 + HCl

    Q&A: Condensation

    What is condensation and what are the conditions required for condensation to take place ?

    Condensation is a process where a gas changes state into the liquid state. This happens when the warmer gas is in contact with a cooler surface. The gas condenses on the surface and forms the liquid state.

    Examples
    -wait for further updates-