In the lime-soda ash softening process, smaller plants find that ______ is less expensive to purchase; regardless of size, ______ needs to be mixed long enough because it dissolves slowly.

In the lime-soda ash softening process, smaller plants find that ______ is less expensive to purchase; regardless of size, ______ needs to be mixed long enough because it dissolves slowly.

• A. calcium oxide, lime
• B. calcium hydroxide, lime
• C. sodium carbonate, soda ash
• D. sodium bicarbonate, soda ash

Answer: (B)

In lime-soda ash softening, the cheaper-to-buy chemical is calcium hydroxide, which is the proper chemical name for lime. However, calcium hydroxide dissolves slowly in water, so it must be mixed for a longer time to fully dissolve and provide the necessary alkalinity for the subsequent reaction with soda ash. This slower dissolution is true regardless of plant size, which is why longer mixing is required for lime to do its job effectively. Soda ash dissolves more readily, so its mixing time is less of a concern.

In lime-soda ash softening, the cheaper-to-buy chemical is calcium hydroxide, which is the proper chemical name for lime. However, calcium hydroxide dissolves slowly in water, so it must be mixed for a longer time to fully dissolve and provide the necessary alkalinity for the subsequent reaction with soda ash. This slower dissolution is true regardless of plant size, which is why longer mixing is required for lime to do its job effectively. Soda ash dissolves more readily, so its mixing time is less of a concern.