Question

25mL of an unknown sodium carbonate and sodium hydroxide mixture reacted with 10mL of .5M SrCl2 is titrated with 1M HCl

Using the following endpoints determine (a) the number of moles of NaOH and (b) the number of moles of Na2CO3. (Show work)

Endpoint 1: 13.2mL HCl used

Endpoint 2: 12.9mL HCl used

To the first endpoint: (1) HCI(aq) + NaOH (aq) NaCl(aq) + H20(0) Between the first and second endpoints: (2) 2 HCl(aq) + SrC03(s)SrCl2(aq) + H20() + CO2(aq) UCLinvarod from the

Answer 1

(a)

The number of moles of NaOH present = number of moles of HCl used till first end point

= 13.2×10^-3L× 1mol/L

= 1.32×10^-2 mol. (Answer)

(b)

SrCO₃ + 2HCl $\rightarrow$ SrCl₂ + H₂O + CO₂

Or

Na₂CO₃ + 2 HCl $\rightarrow$ 2 NaCl + H₂O + CO₂

the number of moles of SrCO₃ formed = 0.5mol/L×10×10^-3 L

= 5×10^-3 mol

Number of moles of carbonates = number of moles of HCl ÷ 2

= 12.9×10^-3L × 1mol/L ÷ 2

= 6.45×10^-3 mol (Answer)