1.) A biochemistry student wants to make 4 liters of a phosphate solution using 48.6 g Na2HPO4 (FW=141.96) What is the concentration of this solution?
2. When she reaches the storeroom she finds that there is no Na2HPO4, however there is a bottle of hydrate Na2HPO4 * 7H20. (FW=268.07) how many grams of this salt should she use in order to make 4 liters with the same phosphate concentration as above?
I thought I worked this once. And you want me to go through it again? I'll be glad to help bur this could go on forever. Please post my response and show your work. Explain fully at which step you get stuck and we can go from there.
To find the concentration of the phosphate solution in question 1, we need to calculate the molarity. The molarity (M) is defined as the number of moles of solute per liter of solution.
First, we need to find the number of moles of Na2HPO4. We can use the formula:
moles = mass / molar mass
Given that the mass of Na2HPO4 is 48.6 g and the molar mass is 141.96 g/mol, we can substitute these values into the formula:
moles = 48.6 g / 141.96 g/mol = 0.342 mol
Next, we divide the number of moles by the volume of the solution to obtain the molarity:
Molarity = moles / volume
Since the volume of the solution is 4 liters, we substitute the values into the formula:
Molarity = 0.342 mol / 4 L = 0.0855 M
Therefore, the concentration of the phosphate solution is 0.0855 M.
Now, moving on to question 2. We need to find out how many grams of the Na2HPO4·7H2O hydrate should be used to achieve the same phosphate concentration as in question 1.
First, we need to find the number of moles of Na2HPO4 using the same formula as before. However, we need to account for the fact that Na2HPO4·7H2O has a higher molar mass due to the water molecules present. The molar mass of the hydrate is 268.07 g/mol.
moles = mass / molar mass
We do not have the mass of the hydrate, so let's denote it as x grams. Based on the molar mass, we can write the equation as:
moles = x g / 268.07 g/mol
Since the molar ratio between the anhydrous form and the hydrate is 1:1, the number of moles remains the same. Thus, we can write:
0.342 mol = x g / 268.07 g/mol
To solve for the mass of the hydrate, x:
x g = 0.342 mol * 268.07 g/mol
x g = 91.835 g
Therefore, she should use approximately 91.835 grams of the Na2HPO4·7H2O hydrate to make 4 liters of the solution with the same phosphate concentration as in question 1.