Planning experimental procedures.

Skill Area P : Planning experimental procedures:

Information:

Word equation: Hydrochloric acid (s) + Calcium carbonate (aq) ⇒ Carbon dioxide (g) + Calcium Chloride (aq) + Water (l)

Chemical equation: 2HCl (s) + CaCO3 (aq) ⇒ CO2 (g) + CaCl2 (aq) + H2O (l)

Ratio: 2 : 1 ⇒ 1 : 1 : 1

Molar ratio in thousandths: 0.002 : 0.001 ⇒ 0.001 : 0.001 : 0.001

The above equation shows when two moles of hydrochloric acid are added to one mole of calcium carbonate the products made are one mole of carbon dioxide, one mole of calcium chloride and one mole of water.

Introduction:

In a chemical reaction, the starting materials are called the reactants, and the finishing materials are called the products. If the reactants take a short time to change into products the reaction is a fast reaction. If the reaction takes a long time to change into the products the reaction is a slow reaction. The factors which can alter the reaction are:

Temperature because as the temperature is increased, the ions in the reactants gain more kinetic energy, and so move faster leading to a higher rate of reaction. Thus, there is a greater frequency of collisions and with a greater force i.e. they move more vigorously. So, there is a greater chance the reactants will react and they will then react faster.

Concentration of the reactants because if you increase the concentration of the reactants, there would be more molecules in the same volume and so the molecules would collide more often. So, the energy of the collisions will remain the same (as long as the temperature is kept constant), but the molecules will collide more often (as there are more of them) and so there is a greater chance of them reacting. Therefore increasing the concentration of the reactants would increase the rate of reaction.

Presence of a catalyst, because a catalyst is a substance which increases the speed of a chemical reaction, without being used up in the reaction. So, if the mass of a catalyst is increased up to a point, the speed of the chemical reaction will increase, and so the rate of the reaction will increase.

Stirring as if there is increased stirring, more kinetic energy would be given to the ions causing them to bump into each other more frequently and with greater force. This would lead to an increased rate of reaction.

The surface area of reactants because if the surface area of the reactants is increased by having the same mass of calcium carbonate in a powdered form rather than as just one large chip there would be a greater frequency of collisions, and consequently the rate of reaction is increased.

The presence of light because some chemical reactions absorb light as they take place and this leads to an increased rate of reaction.

The size of the particles of a solid reaction as smaller particles have a greater surface area leading to a faster rate of reaction.

Skill Area P : Planning experimental procedures:

The nature of the reactants.

Preliminary work:

When adding 50cm3 of 40g / dm3 of sodium thiosulphate solution to hydrochloric acid the time the reaction took was noted down to see when the cross at the bottom of the conical flask disappeared. This step was repeated four times using different concentrations of sodium thiosulphate solution. To dilute the molar solutions of sodium thiosulphate solution distilled water was used. Below a table is drawn to show the preliminary work’s results:

Table of results:

Graph of results:

Conclusion:

Skill Area P : Planning experimental procedures:

The rate of reaction is directionally proportionate to the concentration of sodium thiosulphate solution . Also, the higher the concentration of sodium thiosulphate solution, the higher the rate of reaction therefore a faster rate of reaction.

Apparatus: