Photo AI
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, in mol dm⁻³, of calcium chloride, CaCl₂, in this solution.
Answer
To calculate the concentration of calcium chloride in mol dm⁻³, we first need to determine the number of moles of CaCl₂.
-
Calculate Molar Mass:
The molar mass of CaCl₂ is calculated as follows:
-
Calculate Moles:
We use the formula:
Substituting the values, we get:
-
Calculate Concentration:
The total volume of the solution is 500 cm³, which is equivalent to 0.5 dm³. The concentration in mol dm⁻³ is calculated as follows:
Thus, the concentration of CaCl₂ in this solution is 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 solution of the alkali, follow these steps:
-
Rinse the Pipette:
First, rinse the pipette with the alkali solution to avoid contamination.
-
Fill the Pipette:
Use a pipette filler to draw the alkali solution into the pipette up to the 25.0 cm³ mark. Ensure to do this at eye level for accuracy.
-
Transfer the Solution:
After filling, carefully remove the pipette from the filler and place it into a conical flask. Release the liquid by pressing the pipette filler to transfer the solution into the flask.
Step 3
Step 4
Describe tests that you should carry out on each sample to identify the type of water in each sample.
Answer
To identify the type of water in each sample, carry out the following tests:
-
Soft Water:
- Add a small amount of soap solution to the sample and shake it well.
- Observe the formation of lather immediately, indicating that it is soft water.
-
Permanent Hard Water:
- Add the soap solution and shake.
- There will be little to no lather, and you may observe scum or precipitate.
- Boil the sample. If boiling does not change the results, it confirms permanent hardness.
-
Temporary Hard Water:
- Similarly, add soap and shake.
- There will be less lather than soft water, potentially forming scum.
- Boil the sample. After boiling, if you see a precipitate forming, it indicates temporary hardness.