Experiment to investigate factors affecting the rate of reaction between magnesium ribbon and hydrochloric acid.

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Vicki Biggs 11KB 17th February 2003

Rates of Reaction: Investigation

Experiment to investigate factors affecting the rate of reaction between magnesium ribbon and hydrochloric acid.

Chemical reactions between substances are caused by the collision of particles. More collisions mean a quicker rate of reaction.

In the reaction between hydrochloric acid and magnesium ribbon, the chemical reaction takes place when the magnesium ribbon is dropped into the hydrochloric acid. The products are hydrogen gas and magnesium chloride.

The equation for this reaction is as follows:-

Magnesium + Hydrochloric acid Magnesium chloride + Hydrogen

Mg (s) + 2HCL (aq) MgCl2 (aq) + H2 (g)

Factors that affect the rate of reaction:-

* Temperature

* Mass of magnesium ribbon

* Concentration of hydrochloric acid

* Surface area of magnesium ribbon

I have chosen to use the concentration of hydrochloric acid as my independent variable. These different concentrations can be varied easily and made up accurately for the experiment.

Each experiment will be done four times so that an average reading can be calculated - ensuring an accurate and reliable conclusion. The measured variable will be the time taken for the same quantity of magnesium ribbon in each experiment to be used up in reaction. The constant variable will be the length of the magnesium ribbon used in each experiment.

Rate of reaction = Gradient of the line of a graph plotted with time taken to cease reacting against

concentration.

Concentration of a solution describes the number of active particles in a particular volume.

The unit of concentration is: mol.dm-3

Prediction

I predict that the higher the concentration of hydrochloric acid, the quicker the rate of reaction will become, so the graph of results will have a positive gradient. I predict this because of collision theory. There will be more particles in a solution of hydrochloric acid with a higher concentration than in a lower concentration, in the same volume of liquid. This means that particles in higher concentrations will collide with magnesium particles more frequently, therefore increasing rate of reaction i.e. a shorter time measured for the magnesium to be used up in reaction.

I can predict that rate of reaction will increase with concentration of acid. The quicker the rate of reaction, the less time the reaction will take to be completed.

Therefore:-

Rate of reaction 1 concentration of acid

time taken to react

So...

Rate of reaction concentration

time taken to react

Plan

I am intending to react a chosen length of magnesium ribbon with different concentrations of hydrochloric acid. I will measure the time taken for the magnesium ribbon to disappear (be used up in reaction) with a stop-clock. This will be switched on when the piece of magnesium ribbon is dropped into the hydrochloric acid & seen to be reacting with the acid i.e. producing bubbles of gas, and switched off when the magnesium is no longer visible & no more new bubbles are being produced.
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Results will be recorded in a results table, with 4 readings and an average time for each concentration value.

- I will conduct a preliminary experiment to investigate the optimum length of magnesium ribbon to be used in my experiments.

3cm, 2cm and 1cm of magnesium ribbon was dropped into separate beakers of 4cm3 of 2M hydrochloric acid. The time taken for the reaction to take place was measured with a stop-clock and recorded in the table below.

Any time values which take over 4 minutes to react are unacceptable, as 2M is ...

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