Calculate the number of moles in 2.5 grams of potassium chloride. Show all the steps.
The correct Answer and Explanation is:
To calculate the number of moles of potassium chloride (KCl) in 2.5 grams, we follow these steps:
Step 1: Find the molar mass of potassium chloride (KCl).
- Potassium (K) has an atomic mass of approximately 39.10 g/mol.
- Chlorine (Cl) has an atomic mass of approximately 35.45 g/mol.
So, the molar mass of KCl is calculated by adding the atomic masses of potassium and chlorine:Molar mass of KCl=39.10 g/mol+35.45 g/mol=74.55 g/mol.\text{Molar mass of KCl} = 39.10 \, \text{g/mol} + 35.45 \, \text{g/mol} = 74.55 \, \text{g/mol}.Molar mass of KCl=39.10g/mol+35.45g/mol=74.55g/mol.
Step 2: Use the formula for calculating moles.
The formula for calculating moles is:Moles=MassMolar mass.\text{Moles} = \frac{\text{Mass}}{\text{Molar mass}}.Moles=Molar massMass.
We are given the mass of KCl as 2.5 grams and we just calculated the molar mass as 74.55 g/mol. Plug these values into the formula:Moles of KCl=2.5 g74.55 g/mol.\text{Moles of KCl} = \frac{2.5 \, \text{g}}{74.55 \, \text{g/mol}}.Moles of KCl=74.55g/mol2.5g.
Step 3: Perform the calculation.
Moles of KCl=0.0335 moles.\text{Moles of KCl} = 0.0335 \, \text{moles}.Moles of KCl=0.0335moles.
Thus, 2.5 grams of potassium chloride is approximately 0.0335 moles.
Explanation:
The concept of moles is fundamental in chemistry. A mole represents a specific quantity of particles, typically atoms or molecules, which is Avogadro’s number, 6.022×10236.022 \times 10^{23}6.022×1023. When we calculate moles from a given mass, we are determining how many sets of this specific number of particles (molecules of KCl in this case) are present in the sample.
The molar mass of a substance represents the mass of one mole of that substance, expressed in grams per mole. For potassium chloride, the molar mass is 74.55 g/mol, which means that 74.55 grams of KCl is equivalent to one mole.
In this problem, we only have 2.5 grams of KCl, which is a small fraction of the molar mass. To find the number of moles, we divided the mass by the molar mass, yielding 0.0335 moles. This calculation helps chemists understand the quantity of KCl present at the molecular level, which is important for reactions, stoichiometry, and solution preparations.