2.75g of a sample of dolomite containing CaCO3 and MgCO3 is dissolved in 80cm^3 1.00 mol/dm^3 HCl solution. The solution is then diluted to 250cm^3. 25.0 cm^3 of this solution requires 20.00cm^3 of 0.100 mol/dm^3 NaOH solution for complete neutralization. Calculate percentage composition of the sample.The answer is 52.4% CaCO3 and 47.6% MgCO3 but I do not know how to get this. I am also confused with the dissolving of the sample in HCl, is the chemical equation for this CaCO3 + MgCO3 + 4HCl --gt; CaCl2 + MgCl2 + 2 H2O + 2 CO2 or split up, CaCO3 + 2 HCl --gt; CaCl2 + H2O, MgCO3 + 2 HCl --gt; MgCl2 + H2O?
Mg 24, Ca 40, C 12, O 16 n number of moles M molarity V volume Neutralization : base + acid salt + water NaOH + HCl → NaCl + H?O for complete neutralization: 1 mole NaOH requires 1 mole HCl NaOH 0.100 mol/dm?, 20.00cm? and HCl 25.0cm? n MV n (0.100 mol/dm?)(20.00cm? x 1dm?/1000cm?) n 0.002 moles of NaOH ---------------------------------- moles of NaOH moles of HCl used in neutralization n 0.002 moles of HCl (used in neutralization) HCl 0.002 moles, 25cm? moles contained in 250cm? of HCl of the same solution if 25cm? of diluted solution of HCl is 0.002 moles HCl then 250cm? contains 0.002 moles (250cm? /25cm?) 0.02 moles of HCl that did not react with dolomite --------------------------- Initial number of moles HCl in 80cm? 1 mol/dm? total moles of HCl in 80cm? 1 mol/dm? HCl solution; n MV n (1 mol/dm?)(80.00cm? x 1dm?/1000cm?) n 0.080 moles of HCl ------------------------------- moles of HCl that reacted with dolomite n (total moles of HCl) - (moles of HCl that did not react with dolomite) n 0.08 - 0.02 n 0.06 moles of HCl used to react with dolomite ---------------------------- Dolomite reaction with HCl MgCO? + 2HCl → MgCl? + CO? + H?O CaCO? + 2HCl → CaCl? + CO? + H?O . same as MgCO? + CaCO? + 4HCl → MgCl? + 2CO? + H?O using 0.06 moles of HCl (in balancing the equation) MgCO? + CaCO? + 4HCl → MgCl? + 2CO? + H?O molar ratios if you start with 0.06 moles of HCl 0.015MgCO? + 0.015CaCO? + 0.06HCl → 0.015MgCl? + 0.030CO? + 0.015H?O mass moles x molar mass MgCO? mass 0.015(84) mass 1.26 g of MgCO? in the sample CaCO? mass 2.75 - mass of MgCO? mass 2.75 - 1.26 mass 1.49 % compositions: MgCO? : (mass/mass of sample)100% (1.26/2.75)100% 45.8% ------------- CaCO? : (mass/mass of sample)100% (1.49/2.75)100% 54.2% ------------
