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In this experiment you will determine x in the formula of hydrated sodium carbonate, Na2CO3⋅xH2O, by titration - CIE - A-Level Chemistry - Question 1 - 2018 - Paper 1
Question 1
In this experiment you will determine x in the formula of hydrated sodium carbonate, Na2CO3⋅xH2O, by titration. FA 1 is hydrated sodium carbonate, Na2CO3⋅xH2O. FA 2... show full transcript
Worked Solution & Example Answer:In this experiment you will determine x in the formula of hydrated sodium carbonate, Na2CO3⋅xH2O, by titration - CIE - A-Level Chemistry - Question 1 - 2018 - Paper 1
Step 1
Making a solution of FA 1
Answer
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Record all masses:
- Weigh the container holding FA 1, and note the mass.
- Add FA 1 to a 250 cm³ beaker and note its weight.
- Weigh the empty container again to find the mass of FA 1 used.
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Prepare solution:
- Add approximately 100 cm³ of distilled water to the beaker.
- Stir thoroughly to ensure FA 1 dissolves completely.
- Transfer the solution to a 250 cm³ volumetric flask.
- Rinse the beaker twice, with about 20 cm³ of distilled water each time, adding to the volumetric flask.
- Add distilled water to fill the volumetric flask up to the 250 cm³ mark and mix well.
- Label this solution as FA 3.
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Record mass of FA 1:
- Calculate and write down the mass of FA 1 used in preparing the solution FA 3.
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Titrations:
- Conduct multiple titrations to ensure consistent results, recording the volume of FA 2 used for each trial.
- Ensure all readings are accurate to the nearest 0.05 cm³, including initial and final values on the burette.
Step 2
From your accurate titration results, obtain a suitable value for the volume of FA 2 to be used in your calculations.
Answer
Calculate the average volume of FA 2 used from the accurate titrations recorded. Ensure to round to appropriate significant figures based on your measurements to derive a suitable value for FA 2, for example:
- If volumes recorded are 25.0 cm³ and 24.8 cm³, the average volume could be calculated as:
ext{Average volume} = rac{25.0 + 24.8}{2} = 24.9 ext{ cm³}
Step 3
Calculate the number of moles of sodium carbonate in 250.0 cm³ of FA 3.
Answer
To calculate the number of moles, you can use the following formula:
n = rac{C imes V}{1000}
where:
- n = number of moles,
- C = concentration of FA 2 (in mol/dm³), and
- V = volume of FA 3 used (in cm³).
Assuming the concentration of FA 2 is 0.110 mol/dm³ and the volume of FA 3 is 25.0 cm³:
n = rac{0.110 imes 25.0}{1000} = 0.00275 ext{ moles}
Step 4
Use this answer and your data to calculate the relative formula mass, M_r, of hydrated sodium carbonate, Na2CO3⋅xH2O.
Answer
To find the relative formula mass, use the equation involving moles:
M_r = rac{ ext{mass of Na2CO3 used}}{ ext{moles of Na2CO3}}
- Calculate the mass of the sodium carbonate used in the reaction from your data and apply the calculated moles from the previous question to find M_r.
Step 5
Calculate the value of x in Na2CO3⋅xH2O. Give your answer to the nearest whole number.
Answer
Using the formula mass calculated, you can relate it to the formula of the hydrated compound.
Rearranging gives:
x = rac{M_r - ext{mass of Na2CO3}}{ ext{mass of H2O}}
Based on the calculated values, solve for x and round to the nearest whole number.
For example, if the calculated M_r indicates a value leading to x = 10 after substitution, then x = 10.