Chemistry, 31.08.2019 07:30 twil85459

Hard water often contains dissolved ca2+ and mg2+ ions. one way to soften water is to add phosphates. the phosphate ion forms insoluble precipitates with calcium and magnesium ions, removing them from solution. suppose that a solution is 5.5×10−2m in calcium chloride and 9.5×10−2m in magnesium nitrate.
what mass of sodium phosphate must be added to 2.0l of this solution to completely eliminate the hard water ions? assume complete reaction.
would anyone be able to explain to me how to approach this problem? not quite sure where to start. i just know they are asking for the mass of na3po4.

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Answer from: annamcveigh50

Answer is: mass of sodium phosphate must be added is 32.79 grams.

Balanced chemical reaction 1:

3CaCl₂(aq) + 2Na₃PO₄(aq) → Ca₃(PO₄)₃(s) + 6NaCl(aq).

Balanced chemical reaction 2:

3Mg(NO₃)₂(aq) + 2Na₃PO₄(aq) → Mg₃(PO₄)₃(s) + 6NaNO₃(aq).

c(CaCl₂) = 0.055 M; molarity of calcium chloride.

V(CaCl₂) = 2 L; volume of calcium chloride solution.

n(CaCl₂) = c(CaCl₂) · V(CaCl₂).

n(CaCl₂) = 0.055 mol/L · 2 L.

n(CaCl₂) = 0.11 mol; amount of calcium chloride.

From balanced chemical reaction 1: n(CaCl₂) : n(Na₃PO₄) = 3 : 2.

n₁(Na₃PO₄) = 2 · 0.11 mol ÷ 3.

n₁(Na₃PO₄) = 0.073 mol; amount of sodium phosphate in reaction 1.

2) c(Mg(NO₃)₂) = 0.095 M; amount of magnesium nitrate.

V(Mg(NO₃)₂) = 2 L; volume of magnesium nitrate solution.

n(Mg(NO₃)₂) = c(Mg(NO₃)₂) · V(Mg(NO₃)₂).

n(Mg(NO₃)₂) = 0.095 mol/L · 2 L.

n(Mg(NO₃)₂) = 0.19 mol; amount of magnesium nitrate.

From balanced chemical reaction 2: n(Mg(NO₃)₂) : n(Na₃PO₄) = 3 : 2.

n₂(Na₃PO₄) = 2 · 0.19 mol ÷ 3.

n₂(Na₃PO₄) = 0.126mol; amount of sodium phosphate in reaction 2.

3) n(Na₃PO₄) = n₁(Na₃PO₄) + n₂(Na₃PO₄).

n(Na₃PO₄) = 0.073 mol + 0.126 mol.

n(Na₃PO₄) = 0.2 mol; amount of sodium phosphate.

M(Na₃PO₄) = 3Ar(Na) + Ar(P) + 4Ar(O) · g/mol.

m(Na₃PO₄) = n(Na₃PO₄) · M(Na₃PO₄).

m(Na₃PO₄) = 0.2 mol · 163.94 g/mol.

n(Na₃PO₄) = 32.788 g; mass of sodium phosphate.

Answer from: Quest

it is to be noted that an alpha particle is an helium nucleus. so it contains 2 protons 2 neutrons and has a mass number of 4. when alpha decay particles are ejected from the nucleus it gets transformed into an atom which has atomic number less than 2 and a mass number less than 4.

an equation that could represent alpha decay is radium 226 decay of alpha particle forms radon 222.

$^{222}_{86} rn+ ^{4}_{2} he$ →

Answer from: Quest

They are all full and don't need any more electrons in there outer shell.

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Hard water often contains dissolved ca2+ and mg2+ ions. one way to soften water is to add phosphates...

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