Look at the reaction below.
[tex]H_2 SO_4(a q)+Ca(OH)_2(a q) \longrightarrow CaSO_4(a q)+2 H_2 O(l)[/tex]
Which substance is the base in the reaction?
A. [tex]2 H _2 O ( l )[/tex]
B. [tex]H _2 SO _4(a q)[/tex]
C. [tex]CaSO _4(a q)[/tex]
D. [tex]Ca ( OH )_2(a q)[/tex]
Answer (2)
A base is a substance that accepts protons or donates hydroxide ions.
Examine each option to determine if it donates hydroxide ions or accepts protons.
C a ( O H ) 2 dissociates into C a 2 + and 2 O H − , donating hydroxide ions.
The base in the reaction is C a ( O H ) 2 ( a q ) .
Explanation
Understanding the Reaction We are given the chemical reaction: H 2 S O 4 ( a q ) + C a ( O H ) 2 ( a q ) ⟶ C a S O 4 ( a q ) + 2 H 2 O ( l ) The question asks us to identify the base in this reaction from the given options.
Defining a Base A base is a substance that can accept protons ( H + ions) or donate hydroxide ions ( O H − ions) in a chemical reaction. In this reaction, we need to determine which substance fits this definition.
Analyzing the Options Let's examine the given options:
2 H 2 O ( l ) : Water can act as both an acid and a base, but in this specific reaction, it's a product, not a reactant acting as a base.
H 2 S O 4 ( a q ) : Sulfuric acid is a strong acid, meaning it donates protons ( H + ions). Therefore, it's an acid, not a base.
C a S O 4 ( a q ) : Calcium sulfate is a salt formed from the reaction of an acid and a base. It doesn't typically act as a base.
C a ( O H ) 2 ( a q ) : Calcium hydroxide dissociates in water to form calcium ions ( C a 2 + ) and hydroxide ions ( O H − ). The presence of hydroxide ions indicates that it is a base.
Identifying the Base Since C a ( O H ) 2 dissociates into C a 2 + and 2 O H − , it donates hydroxide ions in the reaction, thus acting as a base.
Final Answer Therefore, the base in the reaction is C a ( O H ) 2 ( a q ) .
Examples
In everyday life, understanding acids and bases is crucial. For example, antacids like calcium hydroxide, C a ( O H ) 2 , neutralize excess stomach acid ( H Cl ) to relieve heartburn. This neutralization reaction is similar to the one in the problem, where the base C a ( O H ) 2 reacts with an acid to form a salt and water. This principle is also used in agriculture to adjust soil pH levels for optimal plant growth.
In the reaction H 2 S O 4 ( a q ) + C a ( O H ) 2 ( a q ) ⟶ C a S O 4 ( a q ) + 2 H 2 O ( l ) , the base is C a ( O H ) 2 ( a q ) . A base is defined as a substance that can donate hydroxide ions, and C a ( O H ) 2 does so. Thus, the correct answer is D: C a ( O H ) 2 ( a q ) .
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