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A solution is made by dissolving calcium chloride in water - Edexcel - GCSE Chemistry - Question 5 - 2015 - Paper 1
Question 5
A solution is made by dissolving calcium chloride in water. 11.1 g of calcium chloride are dissolved in water. The volume of the solution is made up to 500 cm³. C... show full transcript
Worked Solution & Example Answer:A solution is made by dissolving calcium chloride in water - Edexcel - GCSE Chemistry - Question 5 - 2015 - Paper 1
Step 1
Calculate the concentration of calcium chloride in mol dm³
Answer
To find the concentration of calcium chloride (CaCl₂), start with the formula:
- Calculate the molar mass of CaCl₂:
- Ca = 40.0 g/mol
- Cl = 35.5 g/mol (2 Cl atoms)
- Molar mass of CaCl₂ = 40.0 + (2 * 35.5) = 111 g/mol
- Calculate the number of moles of calcium chloride:
- Moles = mass / molar mass
- Moles = 11.1 g / 111 g/mol = 0.1 mol
- Convert the volume from cm³ to dm³:
- 500 cm³ = 0.5 dm³
- Substitute the values into the concentration formula:
- Concentration = 0.1 mol / 0.5 dm³ = 0.2 mol dm⁻³
Step 2
Describe how you would measure out and transfer 25.0 cm³ of the solution of the alkali
Answer
To measure and transfer 25.0 cm³ of the alkali solution accurately:
- Rinse the pipette with the alkali solution to avoid contamination.
- Use a pipette filler to draw the solution into the pipette up to the 25.0 cm³ mark.
- Make sure to read the measurement at eye level to avoid parallax error.
- Carefully transfer the alkali into the conical flask, ensuring no liquid remains in the pipette tip.
Step 3
Complete the sentence with the volume of acid added
Answer
From the readings provided:
- For titration 1: Volume added = 25.15 cm³
- For titration 2: Volume added = 24.90 cm³
- For titration 3: Volume added = 25.25 cm³
The most appropriate volume of acid to use for the calculation is 25.00 cm³ (option B) as it is the average and closest to the mean of the three titrations.
Step 4
Describe tests that you should carry out on each sample to identify the type of water
Answer
To identify the type of water in each sample:
-
Soft Water Test:
- Add a few drops of soap solution and shake.
- If a lather forms immediately with no residue, it is soft water.
-
Permanent Hard Water Test:
- Add soap solution and shake.
- If there is little or no lather and a scum forms, it is permanent hard water. Heating will not change the results.
-
Temporary Hard Water Test:
- Add soap solution and shake.
- If the solution forms a lather initially, but then it disappears after boiling, it indicates temporary hard water.