What is a base?
Define pH - Leaving Cert Chemistry - Question 7 - 2020
Question 7
What is a base?
Define pH.
Calculate the pH of a 0.05 M NaOH solution correct to one decimal place.
What is hard water?
The label on a bottle of mineral ... show full transcript
Worked Solution & Example Answer:What is a base?
Define pH - Leaving Cert Chemistry - Question 7 - 2020
Step 1
What is a base?
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Answer
A base is a substance that gives hydroxide ions (OH−) in aqueous solution (water) or it acts as a proton (H+) acceptor.
Step 2
Define pH.
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Answer
The pH is defined as:
pH=−extlog[H+]
where [H+] is the concentration of hydrogen ions in solution.
Step 3
Calculate the pH of a 0.05 M NaOH solution correct to one decimal place.
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Answer
To find the pH, we first calculate the pOH:
pOH=−extlog[OH−]
For a 0.05 M NaOH, which dissociates completely, [OH−] = 0.05 M:
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Answer
Hard water is water that contains dissolved minerals, particularly calcium (Ca) and magnesium (Mg) ions.
Step 5
Is the water at source acidic or basic?
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Answer
The water at source has a pH of 7.2, which indicates that it is basic.
Step 6
How does the label indicate that the water is hard?
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Answer
The label indicates that the water is hard by referencing the presence of calcium and magnesium ions.
Step 7
How does the label indicate that the water contains temporary hardness?
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Answer
The label indicates temporary hardness through the reference to bicarbonate (hydrogen carbonate) ions.
Step 8
Drops of barium chloride (BaCl$_2$) solution were added to a few cm$^3$ of the mineral water in a test-tube.
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The barium chloride will react with sulfate ions if present, leading to the formation of a white precipitate of barium sulfate, indicating the presence of sulfate ions.
Step 9
Give an advantage of drinking this water instead of tap-water.
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Answer
An advantage of drinking mineral water is that it tastes better and contains beneficial minerals like calcium, which are good for bones and teeth.
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