7. (a) What is a base?
(b) Define pH - Leaving Cert Chemistry - Question 7 - 2020
Question 7
7.
(a) What is a base?
(b) Define pH.
(c) Calculate the pH of a 0.05 M NaOH solution correct to one decimal place.
(d) The label on a bottle of mineral water ... show full transcript
Worked Solution & Example Answer:7. (a) What is a base?
(b) 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 provides hydroxide ions (OH⁻) in an aqueous solution or acts as a proton (H⁺) acceptor.
Step 2
Define pH.
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Answer
pH is defined as the negative logarithm of the concentration of hydrogen ions in a solution:
pH = - ext{log} [ ext{H}^+]
Step 3
Calculate the pH of a 0.05 M NaOH solution correct to one decimal place.
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Answer
To calculate the pH of NaOH:
First, calculate the pOH:
extpOH=−extlog(0.05)=1.3
Then use the relationship between pH and pOH:
extpH=14−extpOHextpH=14−1.3=12.7
Thus, the pH is correctly calculated as 12.7.
Step 4
How does the label indicate that the water is hard?
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Answer
The label indicates that the water is hard because it contains dissolved minerals, particularly calcium (Ca) and magnesium (Mg) ions.
Step 5
How does the label indicate that the water contains temporary hardness?
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The label indicates the presence of bicarbonate ions (hydrogen carbonate) which are responsible for temporary hardness.
Step 6
Drops of barium chloride (BaCl₂) solution were added to a few cm³ of the mineral water in a test-tube.
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The addition of barium chloride to the mineral water will cause a precipitate to form if sulfate ions are present, indicating the presence of these ions in the water.
Step 7
Give an advantage of drinking this water instead of tap-water.
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An advantage of drinking this mineral water is that it may taste better and could contain beneficial minerals which are good for health, contrasting with tap water that may not have these minerals.
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