Question

Washing soda is

• A. \(\text{Na}_2\text{CO}_3\)
• B. \(\text{Na}_2\text{CO}_3.\text{H}_2\text{O}\)
• C. \(\text{Na}_2\text{CO}_3.10\text{H}_2\text{O}\)
• D. \(\text{NaHCO}_3\)

Hint:

Remember the prefixes used for hydrates in chemical formulas: hemi (1/2), mono (1), di (2), tri (3), tetra (4), penta (5), hexa (6), hepta (7), octa (8), nona (9), deca (10).

Answer 1

The Correct Option is C

Step 1: Recall the common names and chemical formulas of important sodium compounds.
In chemistry, several sodium compounds have common names that are frequently used. It's important to associate these common names with their correct chemical formulas. Some relevant compounds include:
Sodium carbonate (anhydrous): \(\text{Na}_2\text{CO}_3\)
Sodium carbonate monohydrate: \(\text{Na}_2\text{CO}_3.\text{H}_2\text{O}\) Sodium carbonate decahydrate (washing soda): \(\text{Na}_2\text{CO}_3.10\text{H}_2\text{O}\) Sodium bicarbonate (baking soda): \(\text{NaHCO}_3\) 
Step 2: Identify the chemical formula corresponding to the common name "washing soda".
Washing soda is the common name for sodium carbonate decahydrate. The term "decahydrate" indicates that ten water molecules are associated with each formula unit of sodium carbonate. Therefore, the chemical formula for washing soda is \(\text{Na}_2\text{CO}_3.10\text{H}_2\text{O}\).
Step 3: Evaluate the given options.
(1) \(\text{Na}_2\text{CO}_3\): This is the chemical formula for anhydrous sodium carbonate, also known as soda ash. It is related to washing soda but is not washing soda itself. (2) \(\text{Na}_2\text{CO}_3.\text{H}_2\text{O}\): This is the chemical formula for sodium carbonate monohydrate. It contains one water molecule per formula unit of sodium carbonate. (3) \(\text{Na}_2\text{CO}_3.10\text{H}_2\text{O}\): This is the chemical formula for sodium carbonate decahydrate, which is commonly known as washing soda. (4) \(\text{NaHCO}_3\): This is the chemical formula for sodium bicarbonate, also known as baking soda or sodium hydrogen carbonate. It has different properties and uses than washing soda. 
Step 4: Conclude the correct chemical formula for washing soda.
The correct chemical formula for washing soda is \(\text{Na}_2\text{CO}_3.10\text{H}_2\text{O}\).