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Common Mistakes Chemistry Students Make and How to Avoid Them

by May 11, 2017Chemistry

Chemistry is the detailed study of how matter is formed, how they react with other materials and their unique properties. The importance of the subject is well acknowledged by schools all around the world by implementing it in their curriculum from the primary level itself. Yet, for a student, learning all about the plethora of chemical equations and the properties of elements can lead to confusion more often than not.

There are many common errors that students commit inadvertently, mostly because of their resemblance to a different chemical property, element or equation or incorrect sequence of radicals. This post highlights some of these common misconceptions and how to avoid them:

  1. Determining Bond Energy in Chemical Equations

Almost every chemical reaction is accompanied by either a release or absorption of heat energy, depending on whether atoms gained or lost electrons during the reaction. The energy released is denoted by -∆H, while the energy gained/absorbed is +∆H.

The sum of energy gained and energy released is termed as entropy, denoted simply by ∆H. Students usually mix up the + and – signs while showing the heat energy conversion in chemical equations. A simple way to remember is:

  • Energy release > Energy is lost > Hence ‘-‘ sign
  • Energy gained > Increase in energy > Hence ‘+’ sign
  1. Difference between Ionic and Covalent Bond

One of the most storied examples of common mistakes in chemistry is the difference between ionic and covalent bond. Frankly speaking, it is fairly easy to mistake covalent for ionic bond and vice versa, mainly because of how identical they sound; both the bonds involve sharing of electrons.

But what makes them different is the way electrons are shared.

In Ionic Bonds, valence electrons are transferred from one atom to another depending on the requirements of the host and donor atom. The electrons are shared in such a way that the metal/non-metal involved in the transfer is in a more stable state after the gaining/losing electrons.

Whereas in Covalent Bonds, electron pairs are involved in the transfer between atoms. These electrons are also known as shared pair/bonding pairs, unlike singular electrons in ionic bonds.

  • Ionic Bond – Single electron transfer
  • Covalent Bond – Electron pair transfer
  1. Difference between Real Gas and Ideal Gas

Gases are one of the three states of matter, along with solids and liquids. But the factor that makes them different from the last two is the calculation of gaseous equations taking the ‘ideal’ form, i.e. gas in its perfect theoretical state.  Although notable assumptions keep ideal gases different from real gases, students tend to improperly assume real gas in place of ideal gas and vice versa while solving chemistry problems involving gases.

  • Ideal Gases do not occupy any volume as the point mass of particles is assumed to be zero. They can be compressed indefinitely and the collision between gaseous particles is completely elastic.
  • Real Gases occupy some volume as the particles have point mass. They turn into liquid at some point when compressed and the collision between gaseous particles is inelastic.

Most chemical problems usually mention whether to use real gas or ideal gas during problem solving. If not mentioned, one has to look for hints. If the question states the point mass of the gas or any similar data, real gas equations apply. If no data about the gas is provided, then ideal gas equation comes into effect.

  1. Difference between Ions and Ionic Equation

The main point of focus here is the difference in writing an ion and its ionic equation. Often confused for the same thing, they are starkly difference in its written representation.

Taking a sample ion CaF2 as example:

  • The ionic equation of CaF2 is written as Ca2+ + 2F as both the Caions and F ions are written separately.
  • While CaF2 is simply the Calcium Fluoride ion in its written form.
  1. Wrong Usage of The ‘n’ in the Equation PV = nRT

In the above equation, ‘n’ is the number of moles of gas used in the chemical reaction. It can be used only in case of ideal gases, not real gases. In case of real gases, n can be calculated by estimating the stoichiometric relationship between the substance in its original state and the final state.

  1. Improper labeling of Diagrams

Chemical laboratories come up with its fair share of diagrams which represent the pictorial representation of individual chemical experiments and reactions. All the apparatus used must be properly labeled.

But many students tend to mix up the labeling with varying consequences, mostly cumulating in a less than desirable grade in the classroom. One way to avoid such mistakes is to memorize the individual components commonly used in chemistry labs, such as burners and flasks. It can be very helpful as many experiments use same apparatus, making them easy to spot.

  1. Improper Rounding Off of Decimal Places

Often the answer to a chemistry problem ends up as a number along with decimal places. Now, students sometimes tend to ignore the decimal rules while rounding up to the nearest digit, which can have disastrous consequences if the value is to be further used in a different equation.

Basic rules of rounding off a numerical value:

  • All the non-zero digits are significant, i.e. in 146, there are 3 significant figures and in 146.348, there are 6.
  • All zeroes present between two non-zero digits are significant, i.e. in 107. There are 3 significant digits and in 107.35, there are 5 significant digits.
  • All the zeroes present after the decimal point are significant, i.e. in 205.000, there are 6 significant digits.
  • All zeroes in the extreme left end side of the number are insignificant, i.e. in 000245.000 there are 6 significant digits.

In spite of the considerable length of the list, there are many other common mistakes that chemistry students make other than the ones stated above, but with enough practice, these can be slowly avoided with time.

 After all, practice makes a man perfect!