Answer :

Sure, let's work through each part of the problem step-by-step to convert the given amounts into moles.

### Step-by-Step Solution:

#### a) Converting 128.400 mg of Ag to moles

1. Convert milligrams to grams: Since 1 gram (g) is equal to 1000 milligrams (mg), we can convert 128.400 mg to grams:
[tex]\[
128.400 \, \text{mg} = \frac{128.400}{1000} = 0.1284 \, \text{g}
\][/tex]

2. Find the molar mass of silver (Ag): The molar mass of Ag (given) is 107.87 g/mol.

3. Calculate moles: Use the formula
[tex]\[
\text{moles} = \frac{\text{mass (g)}}{\text{molar mass (g/mol)}}
\][/tex]
[tex]\[
\text{moles of Ag} = \frac{0.1284 \, \text{g}}{107.87 \, \text{g/mol}} \approx 0.00119 \, \text{moles}
\][/tex]

#### b) Converting 0.74 kg of HNO₃ to moles

1. Convert kilograms to grams: Since 1 kilogram (kg) is equal to 1000 grams (g), we convert 0.74 kg to grams:
[tex]\[
0.74 \, \text{kg} = 0.74 \times 1000 = 740 \, \text{g}
\][/tex]

2. Find the molar mass of nitric acid (HNO₃): The molar mass of HNO₃ (given) is 63.01 g/mol.

3. Calculate moles: Use the formula
[tex]\[
\text{moles of HNO₃} = \frac{740 \, \text{g}}{63.01 \, \text{g/mol}} \approx 11.74 \, \text{moles}
\][/tex]

#### c) Converting 940 g of FeCl₃ to moles

1. Find the molar mass of iron(III) chloride (FeCl₃): The molar mass of FeCl₃ (given) is 162.2 g/mol.

2. Calculate moles:
[tex]\[
\text{moles of FeCl₃} = \frac{940 \, \text{g}}{162.2 \, \text{g/mol}} \approx 5.80 \, \text{moles}
\][/tex]

### Final Answers:
- 128.400 mg of Ag is approximately 0.00119 moles.
- 0.74 kg of HNO₃ is approximately 11.74 moles.
- 940 g of FeCl₃ is approximately 5.80 moles.

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