Answer:
- Your questions only require for the explanations and not the calculations. All the explanations are below.
Explanation:
<em>Question 1: Explain how you would determine the number of grams of </em><em>Cu(NO₃)₂</em><em> that would be needed to make 1052 mL of a 2.50 M solution of </em><em>Cu(NO₃)₂</em>
<u>1. Use the molarity (2.50M) and the volume in liters (1052mL = 1.052 liter) to calculate the number of moles of Cu(NO₃)₂, using the formula:</u>
- Molarity = number of moles of solute / volume of solution in liters
⇒ number of moles = molarity × volume in liters
<u>2. Use the molar mass of Cu(NO₃)₂ to calculate the mass in grams using the formula:</u>
- mass in grams = number of moles × molar mass.
<em>Question 2: Explain how you would determine the mass of Na (s) needed to completely react with 25 mL of the </em><em>Cu(NO₃)₂</em><em> solution created in #1, given the unbalanced equation below: </em>
- <em>__ </em><em>Cu(NO₃)₂ (aq) + __ Na → __ NaNO₃ (aq) + ___ Cu (s)</em>
<u>1. Balance the equation, which yields:</u>
- Cu(NO₃)₂ (aq) + 2 Na → 2 NaNO₃ (aq) + Cu (s)
<u>2. Calculate the number of moles of Cu(NO₃)₂ in 25 mL of solution, using the formula of molarity:</u>
- number of moles = molarity × volume in liters
Subsititute with:
- molarity = 2.50M
- volume = 25 mL × 1 liter/1,000mL = 0.025liter
<u>3. Use the theoretical mole ratio to calculate the number of moles of Na:</u>
- 2 mol Na / 1 mol Cu(NO₃)₂ × number of moles of Cu(NO₃)₂
<u>4. Use the atomic mass of Na to convert the number of moles into mass with the formula:</u>
- mass in grams = number of moles × atomic mass.
<em>Question 3. Explain how you would determine the new concentration of </em>Cu(NO₃)₂<em> if 410 mL of distilled water was added to the solution of </em>Cu(NO₃)₂ <em>created in #1?</em>
<u>1. Use the number of moles in the 1052 mL of solution,</u> which was calculated in the first step of the question 1.
<u>2. Add the two volumes:</u> 410 mL + 1052 mL. This is the new volume of solution.
<u>3. Use the formula of molarity:</u>
- molarity = number of moles / volume of solution in liters.
<u>Q</u><em><u>uestion 4. Explain how you would determine the freezing point of the solution created in #1, if the kf of water is 1.853 °C/m. Assume the density of the solution is 1.00 g/mL</u></em>
<u>1. Use the formula for the depression of the freezing point (a colligative property):</u>
- ΔTf = Kf × i × m
<u>2. Kf is given: 1.853°C/m. </u>
<u>3. i is the van't Hoff factor. </u>
This is used when the solute is ionic. It is the number of ions produced per mole of solute. For Cu(NO₃)₂ is its 3, because each mole of Cu(NO₃)₂ produces one mole of Cu⁺ and two moles of NO₃⁻.
<u>4. m is the molality.</u>
You must calculate the molality using the molarity and the density of the solution.
- Assume 1 liter of solution
- Multiply by the density to convert to kg of solution
- Convert the number of moles of solute in one liter of solution (2.50 moles for the 2.50M solution) into mass in grams (using the molar mass).
- Find the mass of solvent by subtracting the mass of solute from the total mass of solution.
- Use the formula of molality:
m = number of moles of solute / kg of solvent.
Now that you have m, i, and Kf, just subsitute in the formula:
- ΔTf = Kf × m × i
The freezing point of the solution created is the normal freezing point of water, 0ºC, less the depression of the freezing point of the solvent, ΔTf.
Therefore, you are done.