Effect of Concentration on the rate of reaction of magnesium ribbon in hydrochloric acid

Effect of concentration on rate of reaction of magnesium ribbon in hydrochloric acid

Aim / Objective: 

To investigate the effect of concentration on rate of reaction of magnesium ribbon in hydrochloric acid.

Abstract:  

The rate of reaction was determined by measuring the time required for a given amount of magnesium metal to be consumed by Hydrochloric acid (HCl) solution of varying concentrations.

Introduction: 

The rate of a chemical reaction is the time required for a given quantity of reactant(s) to be changed to product(s). The unit of time may be seconds, minutes, hours, days or years.

The rate is affected by several factors, some of which are listed as follows:

(1) Nature of the reactants, i.e., one metal may react vigorously with acid while another does not react.

(2) The particle size of the reactants, i.e., a lump of coal burns slowly but powdered coal may explode.

( 3 ) Temperature increases in general increase the rate of reaction, i.e., a 2O°C rise in temperature doubles the reaction rate.

( 4 ) Catalysts affect the rate by using or allowing a different pathway for the reaction to follow.

(5) Concentration affects the rate of reaction, i.e., if the concentration of one of the reactants is doubled and is an integral part of the reaction then rate increases appropriately.

Some reactions are fast and other reactions are slow. The rate of a specific reaction can be found only by experiment.

Apparatus/Materials:

Magnesium ribbon , ruler, scissors, analytical balance, sandpaper, hydrochloric acid, measuring cylinder, graduated cylinder, distilled water, glass stirring rod.

Method / Procedure:

  1. Clean a 25cm length magnesium ribbon lightly by using sandpaper to remove the surface oxide layer. Cut the clean ribbon into five equal pieces of 6cm using a ruler.
  2. Weigh the five pieces together and determine the mass of one piece assuming all six are the same.
  3. Make up 30mL of each of the following five solutions of hydrochloric acid (HCl) with water: 2.0M, 1.5M, 1.0M, 0.5M and 0.25M. To do this, calculate the volumes of 3.0 mol L-1 stock hydrochloric acid solution and water that must be mixed using the dilution equation: (number mL stock HCL solution) x [HCL]= (3.0mL diluted solution) x [HCL] diluted
  4. Measure the calculated volume of stock hydrochloric acid solution using 10mL graduated cylinder. Pour this acid into a 50-mL graduated cylinder and then dilute to the 30-mL mark by carefully adding water from a bottle.
  5. Make up the other for solutions in a similar way. Pour each diluted solution into a 50-mL beaker.
  6. Drop a piece of magnesium into the 2.0 mol L-1 acid solution and start timing the reaction. Stir gently at first using the glass stirring rod to make sure the metal does not stick to the sides of the beaker.
  7.  Measure the time elapsed when the reaction stops and record the time.
  8. Repeat the procedure with the other four acid solutions.
  9. **Your instructor may require you to plot a graph

Suggested Results:

Table showing the effect of varying concentration of HCl on rate of reaction of Magnesium ribbon

Table showing the effect of varying concentration of HCl on rate of reaction of Magnesium ribbon

Discussion:

Write a balanced equation for the reaction

>>> Mg(s) + 2HCl(aq)      =         MgCl2(aq)   + H2(g)

 

Write the ionic equation for the reaction

>>>Mg(s) + 2H+(aq)           =        Mg2+(aq)  + H2(g)

 

Identify the variables in the experiment

  • The manipulated variables were the HCl and the water
  • The responding variable was time
  • The controlled variable was the magnesium ribbon

Based on your experimental data, make a general statement about the effect of concentration of reactants on time and reaction rate

>>>Concentration affects the rate of reaction. Therefore over time as the concentration of HCl increased then the rate of the reaction also increased.

Source of Error/ Limitations/ Assumptions:

  •  Inaccurate timing. Time may be lost during the experiment between the times taken to notice the cross has disappeared to the actual stopping of the watch.
  • Inaccurate measurement of reactants will affect the overall rate of reaction.

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