A volume of 5oo ml of potassium sodium tartrate solution S1 of c1=0.21mol/l is to prepared. Determine the mass of hydrated potassium sodium tartrate of formula KNaC4H4O6.4H2O needed for this preparation .(molar atomic masses : H=1;C=12;O=16;Na=23;K=39)

To determine the mass of hydrated potassium sodium tartrate needed for the preparation, we can follow these steps:

1. Calculate the number of moles of potassium sodium tartrate needed:
Given concentration (C1) = 0.21 mol/l
Given volume (V) = 500 ml (which is 0.5 L)
Number of moles = concentration * volume
Number of moles = 0.21 mol/l * 0.5 L = 0.105 moles

2. Determine the molar mass of the hydrated potassium sodium tartrate:
The formula of hydrated potassium sodium tartrate is KNaC4H4O6 · 4H2O.
The molar mass of K = 39 g/mol
The molar mass of Na = 23 g/mol
The molar mass of C = 12 g/mol
The molar mass of H = 1 g/mol
The molar mass of O = 16 g/mol

To find the molar mass of KNaC4H4O6 · 4H2O, we add up the molar masses of all the elements:
Molar mass = (39 g/mol) + (23 g/mol) + (4 * 12 g/mol) + (4 * 1 g/mol) + (6 * 16 g/mol) + (4 * (2 * 1 g/mol + 16 g/mol))
Molar mass = 282 g/mol

3. Calculate the mass of hydrated potassium sodium tartrate needed:
Mass = number of moles * molar mass
Mass = 0.105 moles * 282 g/mol
Mass = 29.61 grams

Therefore, the mass of hydrated potassium sodium tartrate of formula KNaC4H4O6.4H2O needed for the preparation is 29.61 grams.