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A solution is made by dissolving calcium chloride in water - Edexcel - GCSE Chemistry - Question 5 - 2015 - Paper 1

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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

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Answer

To find the concentration in mol dm⁻³, first calculate the number of moles of calcium chloride (CaCl₂).

  1. Calculate the molar mass of CaCl₂: extMolarmass=40.0+2imes35.5=111.0extg/mol ext{Molar mass} = 40.0 + 2 imes 35.5 = 111.0 ext{ g/mol}

  2. Calculate the number of moles: extMoles=11.1extg111.0extg/mol=0.1extmol ext{Moles} = \frac{11.1 ext{ g}}{111.0 ext{ g/mol}} = 0.1 ext{ mol}

  3. The volume of the solution in dm³ is: 500extcm3=0.500extdm3500 ext{ cm³} = 0.500 ext{ dm³}

  4. Finally, the concentration is calculated as follows: Concentration=0.1extmol0.5extdm3=0.2extmoldm−3\text{Concentration} = \frac{0.1 ext{ mol}}{0.5 ext{ dm³}} = 0.2 ext{ mol dm⁻³}

Step 2

Describe how you would measure out and transfer 25.0 cm³ of the solution of the alkali.

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Answer

  1. Use a clean pipette.
  2. Rinse the pipette with the alkali solution to avoid contamination.
  3. Draw the solution into the pipette up to the 25.0 cm³ mark, ensuring the bottom of the meniscus is at the line.
  4. Transfer the solution from the pipette into a conical flask by releasing it gently.
  5. Ensure all the liquid has been transferred, adjusting for any liquid left in the pipette tip.

Step 3

Complete the sentence about the volume of acid added

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Answer

The volume of acid added that should be used in the calculation is B 25.00 cm³.

Step 4

Describe tests to identify the type of water in each sample

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Answer

For each sample of water:

Soft Water

  • Add soap solution and shake.
  • Check for lather generation. If lather forms immediately, it is soft water.

Permanent Hard Water

  • Add soap solution and shake.
  • Observe for scum or precipitate formation.
  • Test a boiled sample; if it still forms scum, it is permanent hard water.

Temporary Hard Water

  • Add soap solution and shake.
  • Observe for scum formation.
  • Boil the sample; if it becomes soft after boiling, it is temporary hard water.

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