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General Properties of Aqueous Solution


Solution is a homogeneous mixture of solute and solvent.  Solute is a substance or component present in smaller quantity or proportion, while solvent is a substance or component present in larger amount or proportion.  There are different types of solution, these are the solid solution, liquid solution and the gaseous solution.  Aqueous solution is a type of liquid solution where the solvent is water. Solutes can either be solid, liquid, or gas.  Example of aqueous solution is sugar dissolved in water, salt dissolved in water, alcohol in water and more.

Aqueous solution can be electrolyte and nonelectrolyte.  Electrolyte is a substance that when dissolve in water it conducts electricity while nonelectrolyte is a substance that does not conduct electricity when dissolve in water.  Electrolytes conduct electricity since the substances is completely breaks up into ions in water while nonelectrolytes, the substances do not dissociate in water.

Electrolytes can be classified into strong electrolytes and weak electrolytes:  Strong electrolytes are those substances that are completely or 100% dissociated in water, while weak electrolytes are substances not completely dissociated in water.  Below are examples of weak and strong electrolytes:

How can we determine if an electrolyte is a strong, weak and nonelectrolyte?

An electrical conductivity apparatus is used to determine if an electrolyte is weak, strong and nonelectrolye.  The two electrodes of electrical conductivity apparatus are placed in the solution, once the bulb light very bright it means that the solution is a strong electrolyte and if light dimly, solution is said to be weak electrolyte.  But if no light produced in the electrical conductivity apparatus then the solution is a nonelectrolyte.

Electrical Conductivity Setup

Difference between strong, weak and nonelectrolyte by means of light produced in an electrical conductivity apparatus.


The  first bulb don't show light which means that the first solution is a nonelectrolyte.  Second bulb lights dimly which indicates that the solution is weak electrolyte and the third bulb lights brightly which indicates that the solution is a strong electrolyte.


What happens when substances dissociate in water?

Water is a polar Substance, it can dissolve both ionic and polar substances. Being polar, water has two ends, the positive and negative.  The oxygen is the negative end  and the hydrogen is the positive end.  When an ionic substance such NaCl is dissolved in water, the three-dimensional structure of solid in NaCl is destroyed, and the Na+ and Cl- ions are separated from each other. In solution, each Na+ ion is surrounded by a number of several water molecules orienting their negative end towards the cation.  In the same manner, each Cl- ion is surrounded with several water molecules with their positive ends oriented towards the anion.     The process is called hydration.  A process where ions are surrounded by water molecules arranged in a specific manner.  It helps in the stabilization of the solution which prevents the cations to combine with anions.

Acids and bases are also electrolytes.  Some are 100% ionized in water (strong electrolytes) like HCl (hydrochloric acid)  and HNO3 (nitric acid) while other are just slightly ionized in water (weak electrolytes) like CH3COOH (acetic acid) and HF (hydrofluoric acid).  In water, HCl gas is ionized into H+ ions and Cl- ions completely as shown in the equation below:

Acetic acid (CH3COOH) in water is slightly ionized  in water as shown in the equation below:

The double arrow in the equation above shows that the reaction is reversible, meaning the reaction can be in the forward reaction and reverse reaction.  Initially, acetic acid is ionized to formed into CH3COO- ions and H+ ions,  As time goes on some of the CH3COO- ions recombine with H+ ions forming again CH3COOH molecules.  There comes a time when the rate of forward reaction equalizes the rate of backward reaction, in this point a state of chemical equilibrium is reached.


Note:
Dissociation is used for ionic substances dissolved in water.
Ionized is used for acids and bases dissolved in water.
 












This post first appeared on Science Concepts And Questions (K To 12), please read the originial post: here

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General Properties of Aqueous Solution

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