Photo AI
Explain how hard water is caused and how it wastes soap - Leaving Cert Chemistry - Question 7 - 2012
Question 7
Explain how hard water is caused and how it wastes soap. How can hard water be softened by ion exchange so that it is suitable for use as deionized water in the labo... show full transcript
Worked Solution & Example Answer:Explain how hard water is caused and how it wastes soap - Leaving Cert Chemistry - Question 7 - 2012
Step 1
Explain how hard water is caused and how it wastes soap.
Answer
Hard water is mainly caused by the presence of dissolved minerals, primarily calcium and magnesium ions. These minerals can come from various sources, such as limestone, chalk, or certain geological formations. When hard water is used with soap, it reacts with these ions to form insoluble compounds, which leads to the formation of soap scum. The chemical reaction can be represented as:
This interaction not only wastes soap but also reduces its effectiveness in cleaning.
Step 2
How can hard water be softened by ion exchange so that it is suitable for use as deionized water in the laboratory?
Answer
Hard water can be softened by ion exchange methods, which involve passing water through a resin that contains sodium ions. The resin exchanges sodium for the calcium and magnesium ions in hard water, effectively removing the hardness-causing elements. The basic process can be summarized as follows:
- The hard water flows through a column containing cation exchange resin.
- Calcium and magnesium ions are removed and replaced by sodium ions.
- The result is water that is free from hardness and suitable for laboratory use.
Step 3
In water treatment, what is the purpose of adding a flocculating agent?
Answer
A flocculating agent is added to help in the clumping together, or coagulation, of fine particles and impurities in the water. This process makes it easier to remove these particles during filtration, improving water clarity and quality.
Step 4
Step 5
Step 6
Step 7
Step 8
State the problem that would arise when each of two of these substances is added in excessive quantity.
Answer
If chlorine is added in excessive amounts, it can lead to the formation of harmful by-products, which may cause negative health effects. Additionally, adding too much calcium hydroxide can increase the water's hardness, leading to scaling and residue issues in plumbing systems.
Step 9
Why is water pollution by heavy metal ions, e.g. Hg²⁺ or Pb²⁺, a cause of concern?
Answer
Water pollution by heavy metal ions is a significant concern due to their toxic nature. Heavy metals such as mercury (Hg²⁺) and lead (Pb²⁺) can cause serious health issues, including neurological damage and developmental disorders. These ions can bioaccumulate in living organisms, leading to long-term ecological and health problems.
Step 10
Name an instrumental technique that could be used to detect and measure the concentration of a heavy metal ion in a water sample.
Answer
An effective instrumental technique for detecting and analyzing heavy metal ions in water is Atomic Absorption Spectrometry (AAS). This method allows for precise measurements of metal concentrations by measuring the absorption of light specific to the metal ions present in the sample.
Step 11
Explain how Hg²⁺ or Pb²⁺ ions can be removed from a water supply.
Answer
Hg²⁺ or Pb²⁺ ions can be removed from water using several techniques, such as:
-
Precipitation: Adding sulfides or phosphates can precipitate heavy metals from the water, allowing for easier removal through filtration.
-
Adsorption: Utilizing adsorbent materials like activated carbon can trap heavy metal ions.
-
Ion exchange: Specialized resins can replace heavy metal ions with less harmful ions, effectively decontaminating the water.
-
Reverse osmosis: This membrane process can filter out heavy metal ions along with other impurities, providing clean, safe water.