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15240672380's Question
Chemistry
Posted 7 months ago

6.) Concentrated nitric acid is 70.0%HNO370.0 \% \mathrm{HNO}_{3} by mass, which is 15.9M15.9 \mathrm{M}. Calculate the density and molality of concentrated nitric acid.
a)
70%HNO315.9molL
70 \% \mathrm{HNO}_{3} 15.9 \frac{\mathrm{mol}}{\mathrm{L}}
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Answer from Sia
Posted 7 months ago
Solution
1
Calculate the mass of 1 liter of solution: Given that the solution is 70% HNO3\mathrm{HNO_3} by mass, we can assume a 100 g total mass for ease of calculation. This means we have 70 g of HNO3\mathrm{HNO_3}. Since the molarity (M) is 15.9 mol/L, we can calculate the mass of 1 liter of solution. The molar mass of HNO3\mathrm{HNO_3} is approximately 63.01 g/mol
2
Determine the mass of the solution: Using the molarity, we calculate the mass of HNO3\mathrm{HNO_3} in 1 liter of solution: 15.9 mol/L×63.01 g/mol=1002.259 g15.9 \, \text{mol/L} \times 63.01 \, \text{g/mol} = 1002.259 \, \text{g}. Since this is 70% of the total mass, we find the total mass by dividing by 0.70: 1002.259 g÷0.70=1431.7986 g1002.259 \, \text{g} \div 0.70 = 1431.7986 \, \text{g}
3
Calculate the density: The density (d) is the mass of the solution divided by its volume. We have the mass from step 2 and the volume is 1 liter (1000 mL), so d=1431.7986 g÷1000 mL=1.4318 g/mLd = 1431.7986 \, \text{g} \div 1000 \, \text{mL} = 1.4318 \, \text{g/mL}
4
Calculate the molality (m): Molality is moles of solute per kilogram of solvent. We already know there are 15.9 moles of HNO3\mathrm{HNO_3} in 1 liter of solution. The mass of the solvent (water) is the total mass minus the mass of HNO3\mathrm{HNO_3}: 1431.7986 g−1002.259 g=429.5396 g1431.7986 \, \text{g} - 1002.259 \, \text{g} = 429.5396 \, \text{g}, which is 0.4295 kg. The molality is then 15.9 mol÷0.4295 kg=37.02 mol/kg15.9 \, \text{mol} \div 0.4295 \, \text{kg} = 37.02 \, \text{mol/kg}
Answer
Density: 1.4318 g/mL
Molality: 37.02 mol/kg
Key Concept
Density and molality are physical properties that describe the concentration of a solution. Density is mass per unit volume, while molality is moles of solute per kilogram of solvent.
Explanation
The density was found by dividing the mass of the nitric acid solution by its volume. The molality was calculated using the number of moles of HNO3\mathrm{HNO_3} and the mass of the water (solvent) in kilograms.

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