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Calculate the number of Na+ ions present in 710 mg of Na2SO4 dissolved in aqueous solution. (NA = 6 × 10²³ mol⁻¹). If your answer is x × 10^y, find x (where x is a single digit integer).
- 3
- 6
- 9
- 12
Correct answer: 6
Solution
710 mg = 0.71 g of Na2SO4. Molar mass = 142 g/mol. Moles = 0.71/142 = 0.005 mol. Each Na2SO4 gives 2 Na+ ions, so moles of Na+ = 0.01 mol. Number of Na+ ions = 0.01 × 6×10²³ = 6×10²¹. Written as x × 10^y: x = 6, y = 21. Answer: x = 6.
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