Hardness in groundwater is due to the presence of metal ions, primarily mg2+ and ca2+ . hardness is generally reported as ppm caco3 . to measure water hardness, a sample of groundwater is titrated with edta, a chelating agent, in the presence of the indicator eriochrome black t, symbolized as in. eriochrome black t, a weaker chelating agent than edta, is red in the presence of ca2+ and turns blue when ca2+ is removed. red blue ca(in)2+ + edta ⟶ ca(edta)2+ + in a 50.00 ml sample of groundwater is titrated with 0.0450 m edta . if 13.70 ml of edta is required to titrate the 50.00 ml sample, what is the hardness of the groundwater in molarity and in parts per million of caco3 by mass? assume that ca2+ accounts for all of the hardness in the groundwater.
[Ca⁺²] = 0.0123 M
1234 ppm of CaCO₃
Ca(In)²⁺ + EDTA ⟶ Ca(EDTA)²⁺ + In
To solve this problem we need to keep in mind the definition of Molarity (moles/L) and parts per million (mg CaCO₃ / L water). First we calculate the moles of EDTA:0.0450 M * 13.70 mL = 0.6165 mmol EDTA
Looking at the reaction we see that one mol of EDTA reacts with one mol of Ca(In)²⁺, so we have as well 0.6165 mmol Ca(In)²⁺ (which for this case is the same as Ca⁺²). We calculate the molarity of Ca⁺²:[Ca⁺²] = 0.6165 mmol / 50 mL = 0.0123 M
For calculating the concentration in ppm, we use the moles of Ca⁺² and the molecular weight of CaCO₃ (100.09 g/mol):0.6165 mmol Ca⁺² * * 100.09 mg/mmol = 61.70 mg CaCO₃
That is the mass of CaCO₃ present in 50 mL (or 0.05 L) of water, so the concentration in ppm is:61.70 mg / 0.05 L = 1234 ppm
the reaction mixture contains some ammonia, plus a lot of unreacted nitrogen and hydrogen. the mixture is cooled and compressed, causing the ammonia gas to condense into a liquid. the liquefied ammonia is separated and removed. the unreacted nitrogen and hydrogen are then recycled back into the reactor .
there is none because earth is stationary and flat.