# To see how the concentration of acid, reacting with potassium carbonate, affects the rate of reaction

Aim: To see how the concentration of acid, reacting with potassium carbonate, affects the rate of reaction.

Intro:

This is the reaction I am using in my coursework:

2HCl + K2CO3 CO2 + 2KCL + H2O

In order for substances to react together the particles in the substances must collide with each other and the collision must have enough energy. If there isn't enough energy, no reaction occurs. If there are lots of successful collisions then a lot of CO2 will be produced. The rate of a reaction depends on how many successful collisions there are in a given unit of time.

A reaction can be made to go slower or faster by changing the concentration of a reactant.

Acid particle Water molecule Potassium carbonate tablet

1 2

In dilute acid, there are not so many acid particles (see diagram 1). This means there is not much chance of acid particles hitting a potassium carbonate particle.

In a more concentrated solution of acid, there are more acid particles (see diagram 2). There is now more chance of a successful collision occurring.

Concentration is how much of a substance there is in a certain volume and is measured in Moles per litre of solution (M). The concentration of a solution is the amount of solute, in grams or Moles that is dissolved in a litre of solution.

That is what my coursework is mainly about.

I predict that on my graphs for the results I get directly from the experiment, the curves will bend from a vertical line to a horizontal line and the faster the reaction the steeper the curve will start and the quicker it will reach a horizontal line. This is because as the reaction starts it is very quick and as the chemicals continue to react the reaction produces less CO2 per 10 seconds so it slows down gradually resulting in a curve, This is because after some time there are fewer acid and potassium carbonate particles so the reaction slows down.

I predict that the reaction will go slower when the concentration of the acid decreases. This is because the rate of reaction increases with the concentration. If the concentration of the acid is increased the reaction goes faster. In dilute acid there are not so many acid particles, so the chance of an acid particle colliding with a potassium carbonate particle is not very high.

To go with this piece of research there is another prediction I have come up with: I also predict that when the concentration is halved the rate of reaction will halve as well.

Method:

In this experiment I (by myself) am reacting potassium carbonate and hydrochloric acid together and collect the gas given off called carbon dioxide (CO2). To measure the rate of reaction I will collect the carbon dioxide produced and record the time taken every 10 seconds. This will tell me the speed of the reaction because, e.g. if a small amount of gas is produced in a long time then I will know it is slow reaction.

During the different times of the week when I will be carrying out this experiment the air temperature might change rapidly because it is summer and hot days vary a lot from cooler days. To make this fair I will attempt to cool the acid down before carrying out my experiment if I think the temperature is significantly higher by keeping the acid in an ice bath before the experiment. I will not cool the acid down while carrying out the reaction because if the reaction generates or loses its heat it will be different to cooler days because the acid won't be cooled as it is reacting.

I will drop a circular tablet of potassium carbonate (which are all the same in all the tests so there is no need to measure surface area or mass) into a conical flask containing the acid and the CO2 produced will be pushed through a delivery tube and bubble into an upside down measuring cylinder therefore allowing me to record the amount of CO2 produced every 10 seconds.

To change the concentration of the hydrochloric acid in the conical flask, in each case I will use 20cm3 acid and add certain amounts of tap water each time. ...

#### Here's what a teacher thought of this essay

This is a good experiment with valid results and a suitable conclusion. It does, however, appear to be missing the graphs that are mentioned in the report. It covers a simple topic and would be suitable for a lower ability pupil to read. Overall, this piece of work would be 4 out of 5 stars.