🔍 Key Concepts

• boiler water hardness is mainly caused by certain dissolved minerals in the feedwater (think calcium and magnesium salts) • difference between scale-forming salts and dissolved gases (like oxygen and CO₂) in terms of what problems they create • role of the de-aerating (DC) heater and what it is designed to remove from feedwater

💭 Think About

• Which of the answer choices actually adds or allows more hardness-causing minerals to remain in the water? • Do dissolved gases and zero alkalinity usually increase hardness, or do they cause different types of corrosion/chemistry issues? • What is the main job of a DC heater—does it remove hardness, gases, or something else—and how would its improper operation affect hardness?

✅ Before You Answer

• Be clear on what hardness means: it is related to calcium and magnesium salts, not gases. • Identify which option specifically involves scale-forming salts rather than corrosion or pH issues. • Ask yourself: does zero alkalinity create hardness, or does it just change the water’s acid/base balance?