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The diagram shows three reagent bottles containing acids - HSC - SSCE Chemistry - Question 24 - 2004 - Paper 1
Question 24
The diagram shows three reagent bottles containing acids. pH = 3.38 0.01 mol L⁻¹ Acetic acid pH = 2.56 0.01 mol L⁻¹ Citric acid pH = 2.00 0.01 mol L⁻¹ Hydrochl... show full transcript
Worked Solution & Example Answer:The diagram shows three reagent bottles containing acids - HSC - SSCE Chemistry - Question 24 - 2004 - Paper 1
Step 1
Calculate the pH after 10.0 mL of 0.01 mol L⁻¹ hydrochloric acid solution is diluted by the addition of 90.0 mL of distilled water.
Answer
To calculate the new concentration of hydrochloric acid after dilution, use the dilution formula:
where:
- (initial concentration)
- (initial volume)
- (final volume)
Now, solving for :
Next, calculate the pH from the concentration of hydrochloric acid:
Step 2
Explain the use of acetic acid and citric acid as food additives.
Answer
Acetic acid and citric acid are commonly used as food additives for various reasons:
Acetic Acid
- Preservative: Increases the acidity of foods, which helps to inhibit the growth of spoilage microbes.
- Flavoring Agent: Adds a tangy flavor to foods, which enhances the overall taste and aroma.
- pH Control: Helps to regulate pH in a variety of products, making them stable and safe for consumption.
Citric Acid
- Natural Preservative: Effectively prevents oxidation, which can spoil food, thereby extending shelf life.
- Flavor Enhancer: Provides a sour taste that can improve the flavor profile of various products like candies and beverages.
- Antioxidant Properties: Helps to preserve color and quality in food products.
Step 3
Explain the difference in pH between the three acids in the diagram.
Answer
The differences in pH among the three acids can be attributed to their relative strengths and dissociation in aqueous solutions:
Hydrochloric Acid
- Strong Acid: Completely dissociates in water, leading to a low pH value (2.00).
Citric Acid
- Weak Acid: Partially dissociates, resulting in a moderate pH value (2.56). Citric acid has multiple acidic protons, which affects its overall acidity.
Acetic Acid
- Weaker Acid: Also partially dissociates but has a lower acidic strength compared to citric acid, leading to a higher pH value (3.38). The degree of dissociation is less than that of hydrochloric and citric acids, which reflects in its higher pH.