Concept:Sodium chloride is an ionic lattice, so its fundamental particles are called "formula units". We find the total count by converting mass to moles, then multiplying by Avogadro's number.
Formula:$$ \text{Formula Units} = \left( \frac{m}{M} \right) \times N_A $$
Solution:- Determine the molar mass of NaCl: \( \text{Na (23)} + \text{Cl (35.5)} = 58.5 \text{ g/mol} \).
- Calculate moles: \( 117 \text{ g} / 58.5 \text{ g/mol} = 2.0 \text{ moles} \).
- Multiply by Avogadro's number: \( 2.0 \times (6.022 \times 10^{23}) \).
- Result: \( 12.044 \times 10^{23} \).
- To put this in proper scientific notation, shift the decimal one spot to the left and increase the exponent by one: \( 1.204 \times 10^{24} \text{ formula units} \).
Why other options are incorrect:- \( 1.204 \times 10^{23} \): Result of forgetting to multiply by the 2 moles (this is just the count for 0.2 moles).
- \( 12.04 \times 10^{22} \): Severe decimal point misplacement (equals \( 1.2 \times 10^{23} \)).
- \( 6023 \times 10^{23} \): Complete mangling of Avogadro's number and scientific notation.
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