7. (a) Define (i) acid, (ii) base - Leaving Cert Chemistry - Question 7 - 2014
Question 7
7. (a) Define (i) acid, (ii) base. What is meant by the term neutralisation?
(b) Define pH.
(c) How would you measure the pH of a dilute solution of hydrochloric a... show full transcript
Worked Solution & Example Answer:7. (a) Define (i) acid, (ii) base - Leaving Cert Chemistry - Question 7 - 2014
Step 1
Define (i) acid
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Answer
An acid is a substance that gives hydrogen (hydronium) ions (H⁺, H₃O⁺) in aqueous solution. It acts as a proton donor containing hydrogen that can be replaced by a metal.
Step 2
Define (ii) base
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A base is a substance that gives hydroxide ions (OH⁻) in aqueous solution. It acts as a proton acceptor.
Step 3
What is meant by the term neutralisation?
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Neutralisation is a chemical reaction between an acid and a base to form a salt and water. This process results in the pH moving towards neutral (pH 7).
Step 4
Define pH
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pH is defined as the negative logarithm of the concentration of hydrogen ions in a solution, represented mathematically as:
extpH=−extlog[extH+]
Step 5
How would you measure the pH of a dilute solution of hydrochloric acid (HCl)?
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You can measure the pH of a dilute solution of hydrochloric acid using pH paper, universal indicator solution, or a pH probe (meter) to obtain an accurate measure of acidity.
Step 6
Calculate the pH of (i) a 0.01 M solution of hydrochloric acid (HCl)
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To calculate the pH of a 0.01 M solution of hydrochloric acid:
extpH=−extlog[0.01]=2
Step 7
Calculate the pH of (ii) a 0.01 M solution of sodium hydroxide (NaOH)
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Answer
First, calculate the pOH:
extpOH=−extlog[0.01]=2
Then, find the pH:
extpH=14−extpOH=14−2=12
Step 8
Which of these substances (i) is neutral
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Answer
Pure water is neutral as it has a pH of 7.0.
Step 9
Which of these substances (ii) is basic?
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Answer
Saliva, with a pH of 7.4, is considered basic.
Step 10
If a large volume of pure water were added to the beer, would the pH of the diluted beer be higher or lower than 3.9, or would it remain at 3.9?
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If a large volume of pure water were added to the beer, the pH of the diluted beer would be higher than 3.9, as dilution reduces the concentration of acidic components and increases pH.
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