Determination of the Molar Mass of Magnesium by a Titrimetric Method

Experiment 2:            Determination of the Molar Mass of Magnesium by a Titrimetric Method

Student Name:                                                     Lab supervisor: –

Marking Criteria

There are 7 marks allocated for how well you do each of the titrations (HCl standardisation and mass of Mg titration).

Note this 1st part is most important.  If your titrations are poor you should do them again. It is better to have good work here than to answer the last few questions.

Note that you must get your work signed off and marked by demonstrators as you go.

Determination of the Molar Mass of Magnesium by a Titrimetric Method

             HCl  Mass of
AccuracyStandardisationMagnesium
Average titre value within 0.1 mL of the expected value4 marks 4 marks
                                     within 0.2 mL3 marks3 marks
                                     within 0.3 mL2 marks2 marks
Outside this range      Precision1 mark1 mark
Three values within 0.1 mL of each other3 marks3 marks
within 0.2 mL of each other2 marks2 marks
Outside this range     1 mark1 mark

NB: Burette readings, and therefore titres, are to be read to 2 decimal places. Make sure you have done this.

Calculations /4 marks
Timeline /2 marks
Total          /20 marks

Mass of magnesium used: ………0.0312……… (g)

Molarity of NaOH solution………….0.0481…………… mol L-1

HCl standardization: (Require 3 that agree no matter how many titrations it takes)

TitrationRough123
Final burette reading (mL) Initial burette reading (mL) Titre (mL)22.50   0.0043.21   22.5020.81   0.0041.72   20.81  

Average titration value ………………………………………………………………….. mL  

  1. Use your average titration volume to calculate the average number of moles of NaOH used in the titration.  You may wish to include or discard your rough titre volume.
  • Write a balanced equation for the reaction between HCl and NaOH, and the average number of moles of acid in a 20 mL sample.
  • Calculate the total amount of HCl in the 100mL volumetric flask.


Molar mass of magnesium titration: (Require 3 that agree no matter how many titrations it takes)

TitrationRough123
Final burette reading (mL) Initial burette reading (mL) Titre (mL)11.00   0.0021.00   11.0031.10   21.0041.30   31.10

Average titration value ………………………………………………………………….. mL

  • As for the standardization section calculate the amount of HCl in the 100 mL volumetric flask containing magnesium. 
  • Using your results from 3 and 4 calculate the number of moles of H+ consumed by the magnesium reaction.
  • What is the gas produced during this reaction?
  • With your answer to 6 in mind write a balanced reaction for magnesium dissolving in HCl.
  • Use this balanced reaction equation and your answer to 5 to calculate how many moles of magnesium have reacted.
  • Using the accurate weight of magnesium introduced at the beginning of the experiment, calculate the molar mass of magnesium. 
  1. Look up the average molar mass of Mg in the periodic table (last page of your lab manual). If your calculated molar mass for magnesium differs from that listed can you think of any reasons  

            that might explain this?

  1. Summarize, in your own words, how the measurements and calculations you have performed during this experiment were used achieve the stated outcome (‘Determination of the Molar Mass of Magnesium’).

 CHM001:  Laboratory Report Sheet

Experiment 2:            Determination of the Molar Mass of Magnesium by a Titrimetric Method

Student Name:                                                     Lab supervisor: –

Marking Criteria

There are 7 marks allocated for how well you do each of the titrations (HCl standardisation and mass of Mg titration).

Note this 1st part is most important.  If your titrations are poor you should do them again. It is better to have good work here than to answer the last few questions.

Note that you must get your work signed off and marked by demonstrators as you go.

             HCl  Mass of
AccuracyStandardisationMagnesium
Average titre value within 0.1 mL of the expected value4 marks 4 marks
                                     within 0.2 mL3 marks3 marks
                                     within 0.3 mL2 marks2 marks
Outside this range      Precision1 mark1 mark
Three values within 0.1 mL of each other3 marks3 marks
within 0.2 mL of each other2 marks2 marks
Outside this range     1 mark1 mark

NB: Burette readings, and therefore titres, are to be read to 2 decimal places. Make sure you have done this.

Calculations /4 marks
Timeline /2 marks
Total          /20 marks

Mass of magnesium used: ………0.0312……… (g)

Molarity of NaOH solution………….0.0481…………… mol L-1

HCl standardization: (Require 3 that agree no matter how many titrations it takes)

TitrationRough123
Final burette reading (mL) Initial burette reading (mL) Titre (mL)22.50   0.0043.21   22.5020.81   0.0041.72   20.81  

Average titration value ………………………………………………………………….. mL  

  1. Use your average titration volume to calculate the average number of moles of NaOH used in the titration.  You may wish to include or discard your rough titre volume.
  • Write a balanced equation for the reaction between HCl and NaOH, and the average number of moles of acid in a 20 mL sample.
  • Calculate the total amount of HCl in the 100mL volumetric flask.


Molar mass of magnesium titration: (Require 3 that agree no matter how many titrations it takes)

TitrationRough123
Final burette reading (mL) Initial burette reading (mL) Titre (mL)11.00   0.0021.00   11.0031.10   21.0041.30   31.10

Average titration value ………………………………………………………………….. mL

  • As for the standardization section calculate the amount of HCl in the 100 mL volumetric flask containing magnesium. 
  • Using your results from 3 and 4 calculate the number of moles of H+ consumed by the magnesium reaction.
  • What is the gas produced during this reaction?
  • With your answer to 6 in mind write a balanced reaction for magnesium dissolving in HCl.
  • Use this balanced reaction equation and your answer to 5 to calculate how many moles of magnesium have reacted.
  • Using the accurate weight of magnesium introduced at the beginning of the experiment, calculate the molar mass of magnesium. 
  1. Look up the average molar mass of Mg in the periodic table (last page of your lab manual). If your calculated molar mass for magnesium differs from that listed can you think of any reasons  

            that might explain this?

  1. Summarize, in your own words, how the measurements and calculations you have performed during this experiment were used achieve the stated outcome (‘Determination of the Molar Mass of Magnesium’).