Cl2 + NaOH + As = H2O + NaCl + Na3AsO4

Cl_2 chlorine + NaOH sodium hydroxide + As gray arsenic ⟶ H_2O water + NaCl sodium chloride + AsNa_3O_4 arsenic acid, trisodium salt

Balance the chemical equation algebraically: Cl_2 + NaOH + As ⟶ H_2O + NaCl + AsNa_3O_4 Add stoichiometric coefficients, c_i, to the reactants and products: c_1 Cl_2 + c_2 NaOH + c_3 As ⟶ c_4 H_2O + c_5 NaCl + c_6 AsNa_3O_4 Set the number of atoms in the reactants equal to the number of atoms in the products for Cl, H, Na, O and As: Cl: | 2 c_1 = c_5 H: | c_2 = 2 c_4 Na: | c_2 = c_5 + 3 c_6 O: | c_2 = c_4 + 4 c_6 As: | c_3 = c_6 Since the coefficients are relative quantities and underdetermined, choose a coefficient to set arbitrarily. To keep the coefficients small, the arbitrary value is ordinarily one. For instance, set c_3 = 1 and solve the system of equations for the remaining coefficients: c_1 = 5/2 c_2 = 8 c_3 = 1 c_4 = 4 c_5 = 5 c_6 = 1 Multiply by the least common denominator, 2, to eliminate fractional coefficients: c_1 = 5 c_2 = 16 c_3 = 2 c_4 = 8 c_5 = 10 c_6 = 2 Substitute the coefficients into the chemical reaction to obtain the balanced equation: Answer: | | 5 Cl_2 + 16 NaOH + 2 As ⟶ 8 H_2O + 10 NaCl + 2 AsNa_3O_4

+ + ⟶ + +

chlorine + sodium hydroxide + gray arsenic ⟶ water + sodium chloride + arsenic acid, trisodium salt

Construct the equilibrium constant, K, expression for: Cl_2 + NaOH + As ⟶ H_2O + NaCl + AsNa_3O_4 Plan: • Balance the chemical equation. • Determine the stoichiometric numbers. • Assemble the activity expression for each chemical species. • Use the activity expressions to build the equilibrium constant expression. Write the balanced chemical equation: 5 Cl_2 + 16 NaOH + 2 As ⟶ 8 H_2O + 10 NaCl + 2 AsNa_3O_4 Assign stoichiometric numbers, ν_i, using the stoichiometric coefficients, c_i, from the balanced chemical equation in the following manner: ν_i = -c_i for reactants and ν_i = c_i for products: chemical species | c_i | ν_i Cl_2 | 5 | -5 NaOH | 16 | -16 As | 2 | -2 H_2O | 8 | 8 NaCl | 10 | 10 AsNa_3O_4 | 2 | 2 Assemble the activity expressions accounting for the state of matter and ν_i: chemical species | c_i | ν_i | activity expression Cl_2 | 5 | -5 | ([Cl2])^(-5) NaOH | 16 | -16 | ([NaOH])^(-16) As | 2 | -2 | ([As])^(-2) H_2O | 8 | 8 | ([H2O])^8 NaCl | 10 | 10 | ([NaCl])^10 AsNa_3O_4 | 2 | 2 | ([AsNa3O4])^2 The equilibrium constant symbol in the concentration basis is: K_c Mulitply the activity expressions to arrive at the K_c expression: Answer: | | K_c = ([Cl2])^(-5) ([NaOH])^(-16) ([As])^(-2) ([H2O])^8 ([NaCl])^10 ([AsNa3O4])^2 = (([H2O])^8 ([NaCl])^10 ([AsNa3O4])^2)/(([Cl2])^5 ([NaOH])^16 ([As])^2)

Construct the rate of reaction expression for: Cl_2 + NaOH + As ⟶ H_2O + NaCl + AsNa_3O_4 Plan: • Balance the chemical equation. • Determine the stoichiometric numbers. • Assemble the rate term for each chemical species. • Write the rate of reaction expression. Write the balanced chemical equation: 5 Cl_2 + 16 NaOH + 2 As ⟶ 8 H_2O + 10 NaCl + 2 AsNa_3O_4 Assign stoichiometric numbers, ν_i, using the stoichiometric coefficients, c_i, from the balanced chemical equation in the following manner: ν_i = -c_i for reactants and ν_i = c_i for products: chemical species | c_i | ν_i Cl_2 | 5 | -5 NaOH | 16 | -16 As | 2 | -2 H_2O | 8 | 8 NaCl | 10 | 10 AsNa_3O_4 | 2 | 2 The rate term for each chemical species, B_i, is 1/ν_i(Δ[B_i])/(Δt) where [B_i] is the amount concentration and t is time: chemical species | c_i | ν_i | rate term Cl_2 | 5 | -5 | -1/5 (Δ[Cl2])/(Δt) NaOH | 16 | -16 | -1/16 (Δ[NaOH])/(Δt) As | 2 | -2 | -1/2 (Δ[As])/(Δt) H_2O | 8 | 8 | 1/8 (Δ[H2O])/(Δt) NaCl | 10 | 10 | 1/10 (Δ[NaCl])/(Δt) AsNa_3O_4 | 2 | 2 | 1/2 (Δ[AsNa3O4])/(Δt) (for infinitesimal rate of change, replace Δ with d) Set the rate terms equal to each other to arrive at the rate expression: Answer: | | rate = -1/5 (Δ[Cl2])/(Δt) = -1/16 (Δ[NaOH])/(Δt) = -1/2 (Δ[As])/(Δt) = 1/8 (Δ[H2O])/(Δt) = 1/10 (Δ[NaCl])/(Δt) = 1/2 (Δ[AsNa3O4])/(Δt) (assuming constant volume and no accumulation of intermediates or side products)

| chlorine | sodium hydroxide | gray arsenic | water | sodium chloride | arsenic acid, trisodium salt formula | Cl_2 | NaOH | As | H_2O | NaCl | AsNa_3O_4 Hill formula | Cl_2 | HNaO | As | H_2O | ClNa | AsNa_3O_4 name | chlorine | sodium hydroxide | gray arsenic | water | sodium chloride | arsenic acid, trisodium salt IUPAC name | molecular chlorine | sodium hydroxide | arsenic | water | sodium chloride |

| chlorine | sodium hydroxide | gray arsenic | water | sodium chloride | arsenic acid, trisodium salt molar mass | 70.9 g/mol | 39.997 g/mol | 74.921595 g/mol | 18.015 g/mol | 58.44 g/mol | 207.887 g/mol phase | gas (at STP) | solid (at STP) | solid (at STP) | liquid (at STP) | solid (at STP) | solid (at STP) melting point | -101 °C | 323 °C | 817 °C | 0 °C | 801 °C | 1260 °C boiling point | -34 °C | 1390 °C | 616 °C | 99.9839 °C | 1413 °C | density | 0.003214 g/cm^3 (at 0 °C) | 2.13 g/cm^3 | 5.727 g/cm^3 | 1 g/cm^3 | 2.16 g/cm^3 | 2.81 g/cm^3 solubility in water | | soluble | insoluble | | soluble | surface tension | | 0.07435 N/m | | 0.0728 N/m | | dynamic viscosity | | 0.004 Pa s (at 350 °C) | | 8.9×10^-4 Pa s (at 25 °C) | | odor | | | odorless | odorless | odorless |