Calculate the amount of sodium chloride, NaCl, in 55.0cm3 solution with a concentration og 0.5mol/dm3
The amount in moles of a solute in a solution in a given volume of solution can be calculated if the concentration of the solution is also known. The equation for concentration is: Concentration in mol/dm3 = Amount of solute in mol/ Volume in dm3. The above equation can be rearranged to give amount of solute in mol = concentration in mol/dm3 × volume in dm3. Furthermore, the mass of a substance can be calculated using the equation Mass (g) = Moles x Relative molecular mass.1) Convert the volume from cm3 to dm3 , 55 cm3 = 55.0 ÷ 1000 = 0.055 dm3. (This is really important as a lot of people forget to do this) 2) Calculate the amount of NaCl in moles , Amount of NaOH in mol = concentration in mol/dm3 × volume in dm3 = 0.5 mol/dm3 × 0.055 dm3 = 0.0275 moles3) Calculate the mass of NaCl using the equation mass = moles x relative molecular mass = 0.0275 x 58.5 = 1.60875 = 1.61g ( Be careful when calculating Mr as this is also a common mistake that costs students marks)
