a) What is a base?
6
(b) Define pH - Leaving Cert Chemistry - Question 7 - 2020
Question 7
a) What is a base?
6
(b) Define pH.
Calculate the pH of a 0.05 M NaOH solution correct to one decimal place.
12
(c) What is hard water?
6
(... show full transcript
Worked Solution & Example Answer:a) What is a base?
6
(b) Define pH - Leaving Cert Chemistry - Question 7 - 2020
Step 1
What is a base?
96%
114 rated
Only available for registered users.
Sign up now to view full answer, or log in if you already have an account!
Answer
A base is a substance that gives hydroxyl (hydroxide) ions (OH⁻) in aqueous solution (water) or acts as a proton (hydrogen ion, H⁺) acceptor. This means bases can react with acids to form salts and water and typically have a pH value above 7.
Step 2
Define pH.
99%
104 rated
Only available for registered users.
Sign up now to view full answer, or log in if you already have an account!
Answer
The term pH is defined as:
pH=−extlog[H+]
or equivalently,
pH=14−pOH
where [H⁺] is the concentration of hydrogen ions in the solution.
Step 3
Calculate the pH of a 0.05 M NaOH solution correct to one decimal place.
96%
101 rated
Only available for registered users.
Sign up now to view full answer, or log in if you already have an account!
Answer
To calculate the pH of a 0.05 M NaOH solution:
Determine the pOH:
pOH=−extlog(0.05)=1.3
Calculate the pH using the relation:
pH=14−pOH=14−1.3=12.7
Thus, the pH is 12.7.
Step 4
What is hard water?
98%
120 rated
Only available for registered users.
Sign up now to view full answer, or log in if you already have an account!
Answer
Hard water is defined as water that lathers poorly with soap and is characterized by the presence of dissolved minerals, specifically calcium (Ca²⁺) and magnesium (Mg²⁺) ions.
Step 5
Is the water at source acidic or basic?
97%
117 rated
Only available for registered users.
Sign up now to view full answer, or log in if you already have an account!
Answer
The water is basic since the pH at the source is 7.2.
Step 6
How does the label indicate that the water is hard?
97%
121 rated
Only available for registered users.
Sign up now to view full answer, or log in if you already have an account!
Answer
The label indicates that the water is hard by referencing high concentrations of calcium and magnesium ions, which are typically present in hard water.
Step 7
How does the label indicate that the water contains temporary hardness?
96%
114 rated
Only available for registered users.
Sign up now to view full answer, or log in if you already have an account!
Answer
The label indicates the presence of temporary hardness by noting the levels of bicarbonates, such as hydrogen carbonate (243 mg/l), which can precipitate upon boiling.
Step 8
What observation confirms the presence of sulfate ions in the mineral water?
99%
104 rated
Only available for registered users.
Sign up now to view full answer, or log in if you already have an account!
Answer
The addition of barium chloride (BaCl₂) solution to the mineral water would produce a white precipitate (barium sulfate), confirming the presence of sulfate ions.
Step 9
Give an advantage of drinking this water instead of tap-water.
96%
101 rated
Only available for registered users.
Sign up now to view full answer, or log in if you already have an account!
Answer
One advantage of drinking this mineral water instead of tap water is that it contains essential minerals such as calcium and magnesium, which are beneficial for bone health.
Join the Leaving Cert students using SimpleStudy...
