A standard sodium carbonate solution is prepared in a 250 cm^3 volumetric flask

during a titration,20 cm^3 of a 0,1 mol.dm^-3 nitric acid solution neutralises 25 cm^3 of the above standard solution according to the following balanced equation
2HNO3(aq) Na2CO3(aq)=>2NaNO3(aq) H20(l) CO2(g)

calculate the mass of sodium carbonate used to prepare the standard solution in the volumetric flask

2HNO3(aq) Na2CO3(aq)=>2NaNO3(aq) H20(l) CO2(g)

mols HNO3 = M x L = ?

Using the coefficients in the balanced equation, convert mols HNO3 to mols Na2CO3 (That will be 1/2 mols HNO3)

Then grams Na2CO3 = mols Na2CO3 x molar mass Na2CO3. This will be the grams in the 25 cc of the solution. That x (250/25) gives the grams in the 250 cc solution.

To calculate the mass of sodium carbonate used to prepare the standard solution in the volumetric flask, you will need to follow these steps:

Step 1: Determine the molar ratio
The balanced equation provided gives us the molar ratio between nitric acid (HNO3) and sodium carbonate (Na2CO3) as 2:1. This means that 2 moles of HNO3 react with 1 mole of Na2CO3.

Step 2: Calculate the moles of HNO3 used
Given that you used 20 cm^3 of a 0.1 mol.dm^-3 nitric acid solution, we can calculate the number of moles of HNO3 used by multiplying the volume (in liters) with the concentration (in mol.dm^-3):
Moles of HNO3 = volume (in liters) x concentration (in mol.dm^-3)
Moles of HNO3 = 0.02 L x 0.1 mol.dm^-3
Moles of HNO3 = 0.002 mol

Step 3: Calculate the moles of Na2CO3 used
Using the molar ratio from step 1, we can determine the moles of Na2CO3 used:
Moles of Na2CO3 = (2/1) x Moles of HNO3
Moles of Na2CO3 = (2/1) x 0.002 mol
Moles of Na2CO3 = 0.004 mol

Step 4: Calculate the molar mass of Na2CO3
The molar mass of Na2CO3 can be calculated by adding up the atomic masses of each element:
Molar mass of Na2CO3 = (2 x atomic mass of Na) + atomic mass of C + (3 x atomic mass of O)
Molar mass of Na2CO3 = (2 x 22.99 g/mol) + 12.01 g/mol + (3 x 16.00 g/mol)
Molar mass of Na2CO3 = 105.99 g/mol

Step 5: Calculate the mass of Na2CO3 used
The mass of Na2CO3 used can be calculated by multiplying the moles of Na2CO3 by its molar mass:
Mass of Na2CO3 = Moles of Na2CO3 x Molar mass of Na2CO3
Mass of Na2CO3 = 0.004 mol x 105.99 g/mol
Mass of Na2CO3 = 0.424 g

Therefore, the mass of sodium carbonate used to prepare the standard solution in the volumetric flask is 0.424 grams.