2.1 Sodium thiosulphate, [tex]Na_2S_2O_3[/tex] (s), reacts with [tex]200 \, \text{cm}^3[/tex] of hydrochloric acid solution, [tex]HCl[/tex] (aq), of concentration [tex]0.2 \, \text{mol/dm}^3[/tex] according to the following balanced equation:

[tex]\[
Na_2S_2O_3(s) + 2HCl(aq) \rightarrow 2NaCl(aq) + S(s) + SO_2(g)
\][/tex]

2.1.1 Define the term "concentration of a solution."



Answer :

The concentration of a solution refers to the amount of solute that is dissolved in a given quantity of solvent or solution. It is usually expressed in terms of moles of solute per liter of solution (mol/L), which is also known as molarity (M).

To further elaborate, here is a step-by-step breakdown:

1. Solute: This is the substance that is dissolved in a solvent. In this context, solute examples include substances like sodium thiosulphate ([tex]$Na_2S_2O_3$[/tex]) or hydrochloric acid ([tex]$HCl$[/tex]).

2. Solvent: This is the substance that dissolves the solute. Typically, in many solutions, water is used as the solvent.

3. Solution: When a solute is completely dispersed within a solvent, forming a homogeneous mixture, it is termed a solution.

4. Molarity (M): This is a key concept in concentration measurement, denoted as the number of moles of solute per liter of solution. It is given by the formula:
[tex]\[ \text{Molarity (M)} = \frac{\text{Number of moles of solute}}{\text{Volume of solution in liters}} \][/tex]

For example, if you have a [tex]$0.2\ \text{mol/dm}^3$[/tex] solution, it means that there are [tex]$0.2$[/tex] moles of solute (like [tex]$HCl$[/tex] in this case) in every [tex]$1$[/tex] liter (or [tex]$1\ dm^3$[/tex]) of solution.

Ultimately, concentration allows us to quantify and understand the ratio of solute to solvent, making it possible to conduct accurate and reproducible chemical reactions.