Investigation of the factors affecting the rate of reaction between a metal and an acid.

SAFETY

Below is a chart of possible dangers and ways of avoiding them when carrying out the investigation:

METHOD

We set up the apparatus, setting the water level in the burette to roughly 50cm3 and put it in the burette holder, with the open end in water (in an ice cream tub). This stopped the water from falling out the bottom. Before I did this, I made sure that the tap at the top end of the burette was closed. This meant that there was no space for air to get into the tube, therefore the water level stayed constant. Leading into the bottom of the burette was a thin bent glass tube and it lead to a bung in a conical flask. To start with I put 20cm3 of distilled water, and 20cm3 of hydrochloric acid. Then when all the apparatus was ready and the stop clock was set at zero, I dropped a 2cm strip of magnesium into the diluted hydrochloric acid. As I did this, I started the timer. Every 20 seconds I would take a reading of the water level in the burette. Then I would repeat this two more times. After repeating, I would change the concentration of the acid and then do the same experiment, repeating twice. I would continue with the same method until I had experimented with 5 different concentrations.

APPARATUS

Clamp Stand                Bent Glass tube

Ice cream tub                                        Stop clock

Burette holder                                        Pipette

Burette                                                Measuring cylinder

Conical flask                                                Hydrochloric acid

Distilled water                                        Tap water

DIAGRAM

PREDICTION

I predict that the higher the concentration of hydrochloric acid to water, the faster the rate of reaction. Therefore, the reaction will be completed quicker in the high concentration experiments than in the lower concentration experiments. This is because the more hydrochloric acid, the more energetic and quickly the particles move. The quicker they move, the more they collide with each other. The more energetically they move, the more successful the collisions are - no particles will bounce off each other; they will react with each other. As I said in my background knowledge, the more concentrated an acid is, the more readily it loses hydrogen atoms to water. The more diluted the acid is, the less readily it loses hydrogen atoms to water.

FAIR TESTING

Below is a table of factors that would affect the rate of reaction. I will make sure that I control these factors, as the only factor I am investigating is the concentration of acid.

The factor I am going to vary is the concentration of acid.

RESULTS

Once the magnesium strip is added to the diluted hydrochloric acid, I will start the timer and observe the burette. I will record the original water level before starting the experiment. Then, every 20 seconds I will record the water level again (for the higher concentration I will record the water level every 10 seconds). When the air has stopped travelling from the conical flask to the burette, I will stop timing the experiment and I will record the final time and water level. Instead of writing down the water level in my results, I need to find the volume of hydrogen so the amount that the water has dropped in volume will be the amount gained in hydrogen. I will repeat this method two times more. After repeating I will average out all the results of the repeats and plot it in a table and a graph. I will repeat this method with 4 other concentrations. The concentrations will be 1M, 0.65M 0.5M, 0.4M and 0.35M. The concentration of the acid is measured in molars. The formula for working out the concentration of the acid in molars is:

                            x                        x being the volume of water

                 x + y        and y being the volume of acid

So the concentrations will be:

20cm3  hydrochloric acid and 20cm3  water →    20

                                                                        20 + 20

27cm3  hydrochloric acid and 13cm3  water  →      13

                                                                          27 + 13

30cm3  hydrochloric acid and 10cm3  water→     10

                                                                         30 + 10

32cm3  water and 8cm3  hydrochloric acid →      8

                                                                          32 + 8

33cm3 hydrochloric acid and 7cm water3  →     7

                                                                       7 + 33

To keep results accurate:

I will make sure that all the measurements are done carefully

I will make sure that I read the measurements at exactly the correct time

I will read the water level to the nearest 0.1cm3

I will make sure the surrounding temperature is kept constant throughout by not moving around the room, i.e. near a window and then to shade.

I will make sure that when I rinse the conical flask, it will have no extra acid/water in it from last time's experiment.