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A student investigated the mass of dissolved solids in 5 cm³ samples of water - AQA - GCSE Chemistry Combined Science - Question 3 - 2018 - Paper 2
Question 3
A student investigated the mass of dissolved solids in 5 cm³ samples of water. Figure 3 shows the apparatus. Table 2 shows the student's results. Type of water Wa... show full transcript
Worked Solution & Example Answer:A student investigated the mass of dissolved solids in 5 cm³ samples of water - AQA - GCSE Chemistry Combined Science - Question 3 - 2018 - Paper 2
Step 1
Calculate mass X in Table 2
Answer
To find the mass X of dissolved solids in river water, we can use the data from the sea water and rainwater samples. For sea water, the dissolved solids in 1000 cm³ of water is 28.00 g. Since the sample size is 5 cm³, we can set up a proportion:
ext{Dissolved solids in 5 cm³} = rac{ ext{Dissolved solids in 1000 cm³}}{1000} imes 5This gives:
For river water:
Thus, the value of X in Table 2 is 0.08 g.
Step 2
Give one advantage and one disadvantage of using a larger volume
Answer
Advantage: Using a larger volume of water can lead to more accurate results as it averages out potential anomalies.
Disadvantage: A larger volume requires more time and energy to heat up, making the process less efficient.
Step 3
Describe the difference between potable water and pure water
Answer
Pure water contains no dissolved solids or impurities, making it chemically H₂O. In contrast, potable water may contain dissolved solids and is safe for drinking. Potable water might also have chlorine or other chemicals added for disinfection.
Step 4
Describe how groundwater and sea water are treated to produce potable water
Answer
Groundwater is typically filtered and sterilized to remove any impurities and pathogens. In contrast, sea water is treated through processes like desalination or reverse osmosis to remove the salts and make it suitable for drinking.
Step 5
Calculate the mass of the dissolved solids
Answer
To find the mass of dissolved solids, we can use the percentage given: 2.2% of a 6.50 g sample.
The equation is:
ext{Mass of dissolved solids} = rac{2.2}{100} imes 6.50
Calculating this gives:
Thus, the mass of the dissolved solids is 0.143 g.