Describe how you would prepare 250.0 mL of a 0.1500 M NaCl solution given that the NaCl is supplied as a solid.
Describe how you would prepare 1.25 L of a 0.025 M sucrose solution from a stock solution with concentration of 5.00 M.
What is the benefit of adding salt to water when cooking rice or pasta? Explain your answer by discussing changes to vapour pressure.
#1. How many mols NaCl do you want? That's mols = M x L = ?
Then mols = grams/molar mass. You know mols and molar mass, solve for grams. To prepare the solution you place that many grams (the ? calculated above) in a 250 mL volumetric flask, add some water, swirl until all of the NaCl is dissolved, add water to the mark on the flask, stopper, mix thoroughly.
#2. Use the dilution formula of
L1 x M1 = L2 x M2
1.25L x 0.025M = L2 x 5.00 M. Solve for L2.
#3. Frankly, I don't think there is any advantage to adding NaCl to rice or pasta when cooking it. The addition of NaCl to water to lower vapor pressure thereby raising the boiling point of water, requires too much NaCl to be significant. Cooks will tell you to add NaCl when cooking (as opposed to adding it after cooking) is to "cook in" the salt/flavor. You will need to sort all of this out from what you've been told in class.
2.160692 x10 7 atm Is this the correct answer?
I meant
#1 0.00064168g/mol?
#2 0.006g/mol?
Q#2.use the formula Mi x Vi=Mf x Vf
0.025 x 1.25= 5 Vf.
once the final volume's been found,transfer the solution of that volume to an empty conical flask.then add distilled water to the required volume(in ths case,up to 1.25L or 1.25 cubic dm).
Shake the conical flask to ensure thorough mixing of the molecules
To prepare a 250.0 mL of a 0.1500 M NaCl solution from solid NaCl, you would need to follow these steps:
1. Calculate the amount of NaCl needed: Multiply the desired concentration (0.1500 M) by the desired volume (250.0 mL) to find the number of moles of NaCl needed. 0.1500 mol/L x 0.2500 L = 0.0375 moles.
2. Convert moles to grams: Use the molar mass of NaCl to convert moles to grams. The molar mass of NaCl is 58.44 g/mol. Thus, 0.0375 moles x 58.44 g/mol = 2.19 grams of NaCl.
3. Weigh the solid NaCl: Using an analytical balance, measure out precisely 2.19 grams of NaCl.
4. Dissolve the NaCl: Add the measured NaCl to a clean and dry 250.0 mL volumetric flask. Then, add distilled water to fill the flask up to the mark, ensuring that the NaCl fully dissolves.
To prepare 1.25 L of a 0.025 M sucrose solution from a stock solution with a concentration of 5.00 M, follow these steps:
1. Calculate the volume of stock solution required: Use the equation C1V1 = C2V2, where C1 and V1 are the concentration (5.00 M) and volume (unknown) of the stock solution, and C2 and V2 are the target concentration (0.025 M) and volume (1.25 L) of the final solution. Rearranging the equation, V1 = (C2 x V2) / C1. Plug in the values to find the required volume: (0.025 M x 1.25 L) / 5.00 M = 0.00625 L or 6.25 mL.
2. Measure the required volume: Use a graduated cylinder or pipette to measure precisely 6.25 mL of the stock solution.
3. Dilute the stock solution: Add the 6.25 mL of the stock solution to a clean and dry 1.25 L volumetric flask. Then, add distilled water to fill the flask up to the mark, ensuring complete mixing.
The addition of salt to water when cooking rice or pasta provides several benefits, including:
1. Improved flavor: Salt enhances the taste of the food, making it more enjoyable and flavorful.
2. Increased boiling point: The addition of salt to water raises its boiling point. This higher boiling point can result in increased cooking times, which can help to thoroughly cook the rice or pasta.
3. Decreased cooking time: Contrary to the previous point, adding salt to water can actually reduce the cooking time for rice or pasta. The higher boiling point allows for a faster transfer of heat to the food, speeding up the cooking process.
4. Altered vapor pressure: When salt is dissolved in water, it lowers the vapor pressure of the solution. In general, vapor pressure is the pressure exerted by the vapor molecules above a liquid. When salt is added, the salt ions disrupt the hydrogen bonding between water molecules, reducing the number of water molecules that can escape into the gas phase. This leads to a decrease in vapor pressure, resulting in lower evaporation and loss of water during cooking.
Overall, adding salt to water when cooking rice or pasta improves flavor, alters the boiling point, reduces cooking time, and decreases water loss through vaporization.