To determine the molecular mass of an unknown alkali metal carbonate, X2CO3.

Authors Avatar by pahuadignity123gmailcom (student)

Candidate Name:

Candidate Number:                Page |  

International Baccalaureate Diploma Program (IBDP)

Session: May 2015

Chemistry HL Lab Report

Lab Report Title: To determine the molecular mass of an unknown alkali metal carbonate, X2CO3.

Criteria Assessed:

  • Data Collection and Processing (DCP)
  • Conclusion and Evaluation (CE)

Candidate Name:

Candidate Number:

International School, Singapore

AIM: To determine the molecular mass of an unknown alkali metal carbonate X2CO3 using titration.


Since substance Z is an alkali metal carbonate, it can safely be hypothesized that the compound is most likely to be the carbonate of Lithium, Sodium or Potassium since these are the only three alkali metal carbonates which are stable and safe to use in a school laboratory.

Alkali metal carbonates are basic in nature and dissolve in water hence forming basic solutions. These basic solutions can readily react with strong acids such as HCl to form a salt and water. Therefore, in order to determine the molecular mass of substance Z, its ability to form alkali solutions was exploited and hence, aqueous samples of substance Z was titrated against 0.1 molarity solutions of HCl.

Substance Z reacts with HCl according to the following balanced chemical equation:

X2CO3 (aq.) + 2HCl (aq.)  2XCl (aq.) + CO2 (g) + H2O (l)


Independent Variables:

  1. Mass of substance Z – The same digital balance was used to weigh out all the nine samples.
  2. Volume of substance Z solution – 25.0cm3 of substance Z solution was used for each of the nine trial.

Dependent Variables:

  1. Volume of 0.1M HCl required to neutralize 25.0cm3 of substance Z – The end-point was determined only when the methyl orange indicator completely changed color from yellow to orange.  

Controlled Variables:

  1. Molarity of HCl – It was 0.1M for all trials.
  2. Drops of Phenolphthalein – For all trials, only three drops were used to prevent any misinterpretation of the reaction’s end point.
  3. Volume of water used to dissolve all samples of substance Z – For all trials, only 250cm3 of distilled water was used.
  4. Room temperature - All trials were performed in more or less, the same conditions.


Join now!


  1. The 50cm3 beaker was placed on the digital balance and the balance was calibrated to 0.  
  2. Using the metal spoon, slowly and carefully, 1.5g of substance Z was weighed out into the 50cm3 beaker.
  3. Distilled water was added to completely dissolve the solid mass of substance Z.
  4. The solution was poured into the 250cm3 volumetric flask making sure no solid or solution was left behind in the 50cm3 beaker.
  5. Enough distilled water was added to make a 250cm3 solution in the 250cm3 volumetric flask.
  6. The ...

This is a preview of the whole essay