What mass of solid potassium sulfate, K2SO4, is used to make up exactly 100.0cm^3 of 0.100 mol/dm^3 SO4^2-?
This should be a very easy, 1-mark question but for some reason I can't wrap my head around it.
moles = mass/Mr, so all you gotta do is moles x molecular mass. Mr is 174.3, but I'm unsure about how to calculate moles. Thanks in advance for your help!
How many mols SO4^2- are in K2SO4; i.e., 1 mol K2SO4 contains 1 mol SO4^2-. Now how many mols K2SO4 do you need? That's mols = mols/dm^3 x dm^3 = 0.1 mol/dm^3 x 0.1 dm^3 = ?
Now convert to grams. grams - mols K2SO4 x molar mass K2SO4 = ?
To calculate the mass of solid potassium sulfate (K2SO4) needed to make up 100.0 cm^3 of 0.100 mol/dm^3 SO4^2-, you need to follow these steps:
Step 1: Determine the moles of SO4^2- ion.
Given the concentration of SO4^2- ion is 0.100 mol/dm^3, you can simply multiply the concentration by the volume in dm^3 to get the number of moles.
Moles of SO4^2- ion = Concentration × Volume
= 0.100 mol/dm^3 × 0.100 dm^3
= 0.010 mol
Step 2: Calculate the moles of potassium sulfate.
From the balanced chemical equation, you can see that one mole of K2SO4 produces one mole of SO4^2- ion. Therefore, the number of moles of K2SO4 is the same as the number of moles of SO4^2- ion.
Moles of K2SO4 = Moles of SO4^2-
= 0.010 mol
Step 3: Calculate the mass of potassium sulfate.
The molar mass of K2SO4 can be calculated by adding up the atomic masses of its constituent elements: potassium (K), sulfur (S), and oxygen (O).
Molar mass of K2SO4 = (2 × atomic mass of K) + atomic mass of S + (4 × atomic mass of O)
= (2 × 39.1 g/mol) + 32.1 g/mol + (4 × 16.0 g/mol)
= 174.3 g/mol
The mass of potassium sulfate can be obtained by multiplying the number of moles of K2SO4 by its molar mass.
Mass of K2SO4 = Moles of K2SO4 × Molar mass of K2SO4
= 0.010 mol × 174.3 g/mol
= 1.743 g
Therefore, the mass of solid potassium sulfate needed to make up exactly 100.0 cm^3 of 0.100 mol/dm^3 SO4^2- is 1.743 grams.