a 500ml stock solution of NAOH has a purity of 70% and a density of 1.9g/ml.

calculate the concentration that would be in a 1L solution.
calculate the molarity.
What volume would we have to take to prepare 250ml of a solution of 0.1 mol/l

The problem isn't worded very well. Calculate the concn IN WHAT UNITS. BELOW IS THE COnCN IN M = mols/L

For part b
M NaOH in 1 L is:
1000 mL x 1.19 g/mL x 0.70 x 1/molar mass NaOH = ? approx 33 M

Then use the dilution formula for part C.
mL1 x M1 = mL2 x M2
250 x 0.1 = mL2 x approx 33.

To calculate the concentration in a 1L solution, you need to consider the purity and density of the stock solution. Here's how you can do it:

Step 1: Calculate the mass of NaOH present in the stock solution.
Mass = density * volume
The volume of the stock solution is 500 ml, and the density is 1.9 g/ml.
Mass = 1.9 g/ml * 500 ml = 950 g

Step 2: Calculate the mass of pure NaOH in the stock solution.
The purity of the stock solution is 70%, so we need to multiply the mass by the purity percentage.
Pure Mass of NaOH = Mass * purity
Pure Mass of NaOH = 950 g * 70% = 665 g

Step 3: Calculate the concentration in a 1L solution.
Concentration = Pure Mass of NaOH / Volume
The volume of the 1L solution is 1000 ml.
Concentration = 665 g / 1000 ml = 0.665 g/ml

To calculate the molarity, we need to know the molar mass of NaOH, which is:
Na (sodium) = 22.99 g/mol
O (oxygen) = 16.00 g/mol
H (hydrogen) = 1.01 g/mol
So, the molar mass of NaOH = 22.99 g/mol + 16.00 g/mol + 1.01 g/mol = 40.00 g/mol

Step 4: Calculate the molarity.
Molarity = Concentration / Molar mass
Molarity = 0.665 g/ml / 40.00 g/mol = 0.0166 mol/L or 0.0166 M

To determine the volume needed to prepare a 250 ml solution of 0.1 mol/L, we can use the formula:
Volume (in ml) = moles / concentration

Step 5: Calculate the volume required for a 0.1 mol/L solution.
Moles = Concentration * Volume
Concentration = 0.1 mol/L
Volume = 250 ml
Moles = 0.1 mol/L * 250 ml = 25 mol

Volume (in ml) = moles / concentration
Volume (in ml) = 25 mol / 0.1 mol/L = 250 ml

Therefore, to prepare a 250 ml solution of 0.1 mol/L, you would need to take 250 ml of the stock solution.