In common household chemistry, washing soda is the popular name for which chemical compound?

Introduction / Context:
Many chemical compounds used in households and industry have common names that differ from their systematic chemical names. Washing soda is one such widely used substance, especially in cleaning and laundry. Identifying the correct chemical name for washing soda helps connect everyday language with chemical formulas and properties. This question asks you to choose which compound corresponds to washing soda.

Given Data / Assumptions:
- The options include sodium bicarbonate, calcium carbonate, sodium carbonate, and calcium bicarbonate. - Each option is a carbonate or bicarbonate salt of sodium or calcium. - Washing soda is typically used as a cleaning agent and water softener. - Baking soda is a different common substance with its own name and uses.

Concept / Approach:
Washing soda is the common name for sodium carbonate, usually in the form of sodium carbonate decahydrate, Na2CO3·10H2O. It is used in laundry detergents and for softening hard water by precipitating calcium and magnesium ions. Sodium bicarbonate NaHCO3 is known as baking soda and is used in cooking and as a mild antacid. Calcium carbonate CaCO3 is found in limestone and chalk, while calcium bicarbonate forms in hard water temporarily and is not a common solid household product. Therefore, the correct identification of washing soda is sodium carbonate.

Step-by-Step Solution:
Step 1: Recall that washing soda is used particularly in washing clothes and softening water. Step 2: Connect washing soda with sodium carbonate, usually written Na2CO3·10H2O, as described in school level chemistry texts. Step 3: Recognise that sodium bicarbonate NaHCO3 is instead called baking soda and is used in baking, cleaning, and neutralising acids. Step 4: Note that calcium carbonate CaCO3 is present in limestone, marble, and chalk but is not sold as washing soda. Step 5: Identify calcium bicarbonate as a dissolved form in temporary hard water rather than a common commercial product. Step 6: Therefore, the compound corresponding to washing soda is sodium carbonate.

Verification / Alternative check:
Textbooks on everyday chemistry explicitly state that washing soda is sodium carbonate decahydrate. Commercial boxes of washing soda also list sodium carbonate as the ingredient on their labels. In addition, water softening demonstrations often show washing soda precipitating calcium ions, consistent with sodium carbonate behaviour. Baking soda packets, in contrast, list sodium bicarbonate and are labelled differently. These clear distinctions confirm that sodium carbonate is the correct answer.

Why Other Options Are Wrong:
Option A (Sodium bicarbonate NaHCO3) is the common baking soda, not washing soda. Option B (Calcium carbonate CaCO3) is found in rocks and shells, used in cement and chalk, but is not washing soda. Option D (Calcium bicarbonate Ca(HCO3)2) exists mainly in solution in hard water and is not typically obtained as a solid product for washing.

Common Pitfalls:
Students often confuse washing soda with baking soda because both are white powders and have similar sounding names. Another pitfall is to assume that any carbonate could be washing soda. To avoid these mistakes, associate baking soda with sodium bicarbonate used in cakes, and washing soda with sodium carbonate used in laundry and water softening. Remembering their distinct uses and formulas helps keep them separate.

Final Answer:
The correct answer is: Sodium carbonate (Na2CO3).