## Explanation

To convert 25 grams of HCl (hydrochloric acid) to moles, follow these steps:

### Step 1: Determine the Molar Mass of HCl

First, understand that the molar mass of a substance is the mass of one mole of that substance. The molar mass of HCl can be found by adding the atomic masses of hydrogen (H) and chlorine (Cl).

**Atomic mass of Hydrogen (H)**: approximately 1 g/mol**Atomic mass of Chlorine (Cl)**: approximately 35.5 g/mol

Therefore, the molar mass of HCl is:

$\text{Molar mass of HCl} = 1 \, \text{g/mol} + 35.5 \, \text{g/mol} = 36.5 \, \text{g/mol}$### Step 2: Use the Conversion Formula

The formula to convert grams to moles is:

$\text{Moles} = \frac{\text{Mass in grams}}{\text{Molar mass}}$### Step 3: Plug in the Values

Substitute the given mass and the molar mass into the formula:

$\text{Moles of HCl} = \frac{25 \, \text{grams}}{36.5 \, \text{g/mol}}$ $\text{Moles of HCl} = 0.685 \, \text{moles}$**Therefore, 25 grams of HCl is approximately 0.685 moles.**