In this experiment you will determine the value of y in the formula for hydrated barium chloride, BaCl2·yH2O - CIE - A-Level Chemistry - Question 2 - 2017 - Paper 1
Question 2
In this experiment you will determine the value of y in the formula for hydrated barium chloride, BaCl2·yH2O. You will do this by measuring the mass loss when a samp... show full transcript
Worked Solution & Example Answer:In this experiment you will determine the value of y in the formula for hydrated barium chloride, BaCl2·yH2O - CIE - A-Level Chemistry - Question 2 - 2017 - Paper 1
Step 1
Table of data
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Answer
Prepare a table to record the following data:
Mass of crucible (lid included)
Mass of crucible + FA 5
Mass of FA 5
Mass of crucible + contents after heating
Calculate the mass of FA 5 used by subtracting the mass of the crucible (with lid) from the mass of crucible + FA 5 recorded earlier.
Calculate the mass of the residue by taking the mass of the crucible with contents after heating and subtracting the mass of the crucible (with lid).
Calculate the mass of water lost by subtracting the mass of the residue from the mass of FA 5 used.
Step 2
(b)(i) Calculate the number of moles of barium chloride in the residue.
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Answer
To calculate the number of moles of barium chloride:
Use the formula:
moles=molar massmass
The molar mass of BaCl2 is approximately 208.3 g/mol.
Calculate:
moles of BaCl2=208.3mass of residue
Step 3
(b)(ii) Calculate the number of moles of water lost.
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To calculate the number of moles of water lost:
The molar mass of H2O is approximately 18 g/mol.
Use the formula:
moles of H2O lost=18mass of water lost
Step 4
(b)(iii) Calculate the value of y in BaCl2·yH2O.
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To find the value of y:
Use the moles of BaCl2 calculated previously and the moles of water lost:
The ratio can be defined as:
y=moles of BaCl2moles of H2O lost
Ensure y is presented as an integer.
Step 5
(c)(i) Explain fully what would happen to the value of y if BaCl2 were to decompose slightly during heating.
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If BaCl2 decomposes slightly during heating, it would produce additional products such as BaO or Cl2 gas. This would lead to a lower mass of BaCl2 remaining, resulting in an inaccurate calculation of moles. Consequently, the value of y calculated would be higher than the actual amount since there would be less barium chloride to correspond to the lost water, skewing the results.
Step 6
(c)(ii) Suggest how you could modify the experiment to determine more accurately the mass of water lost.
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To obtain a more accurate measurement of the mass of water lost, one could:
Use a more precise scale to determine the mass of the residue after heating.
Heat the sample gradually and slowly to avoid rapid loss of water or decomposition of the compound.
Employ a desiccator after heating to allow for cooling while preventing moisture absorption from the air.
