The diagram in Fig. 1 shows a water-treatment worker checking the concentration of a chlorine compound in a storage tank. A sample contains 0.0150 mol of so...
Question 1 Report
The diagram in Fig. 1 shows a water-treatment worker checking the concentration of a chlorine compound in a storage tank. A sample contains 0.0150 mol of sodium hypochlorite in 2.50 dm3 of water. Sodium hypochlorite is used to kill microorganisms, but a solution that is too concentrated could irritate skin. The worker has also written the formula for concentration on the clipboard.
(a) Write the unit for molar concentration. [1]
(b) Use the information to calculate the concentration of sodium hypochlorite. [2]
(c) Explain why a fixed volume of water is needed when preparing this disinfectant. [2]
Answer Details
(a) The unit of molar concentration is mol/dm3, also written as mol dm-3. [1]
(b) Use \(c=\frac{n}{V}\): \[c=\frac{0.0150\text{ mol}}{2.50\text{ dm}^3}=0.00600\text{ mol/dm}^3\] [2]
(c) Concentration depends on volume as well as amount of solute. Using a fixed volume of water ensures the stated amount of sodium hypochlorite gives a safe, repeatable concentration of active disinfectant. [2]
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