Multiple Choice
What is the molarity of methanol in the solution prepared by dissolving 20.2 mL of methanol in 100.0 mL of water, given the final volume is 118 mL and the density of methanol is 0.782 g/mL?
6. Chemical Quantities & Aqueous Reactions
Molarity
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A stock solution of Pb(NO3)2 (315 mL, 2.5 M) contains how many Pb²⁺ ions and how many nitrate ions?
A
2.50 x 10^23 Pb²⁺ ions and 5.00 x 10^23 nitrate ions
B
4.73 x 10^23 Pb²⁺ ions and 9.46 x 10^23 nitrate ions
C
5.00 x 10^23 Pb²⁺ ions and 5.00 x 10^23 nitrate ions
D
3.00 x 10^23 Pb²⁺ ions and 6.00 x 10^23 nitrate ions
Verified step by step guidance1
First, determine the number of moles of Pb(NO3)2 in the solution. Use the formula: \( \text{moles} = \text{molarity} \times \text{volume in liters} \). Convert 315 mL to liters by dividing by 1000.
Calculate the moles of Pb(NO3)2 using the given molarity (2.5 M) and the volume in liters from the previous step.
Understand the dissociation of Pb(NO3)2 in water: \( \text{Pb(NO3)}_2 \rightarrow \text{Pb}^{2+} + 2\text{NO}_3^- \). This means each mole of Pb(NO3)2 produces one mole of Pb²⁺ ions and two moles of nitrate ions.
Calculate the number of moles of Pb²⁺ ions, which is equal to the moles of Pb(NO3)2, and the number of moles of nitrate ions, which is twice the moles of Pb(NO3)2.
Convert the moles of Pb²⁺ ions and nitrate ions to the number of ions using Avogadro's number (\(6.022 \times 10^{23}\) ions/mole). Multiply the moles of each ion by Avogadro's number to find the total number of ions.
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