Question

section 2 review
key ideas

1. identify which of the following is a complete and balanced chemical equation:

a. h₂o → h₂ + o₂
b. nacl + h₂o
c. fe + s → fes
d. caco₃

1. determine balanced chemical equations for the following chemical reactions:

a. koh + hcl → kcl + h₂o
b. nahco₃ → h₂o + co₂ + na₂co₃
c. pb(no₃)₂ + ki → kno₃ + pbi₂

1. explain why balancing an equation requires changing the coefficients in front of chemical formulas rather than the subscripts within chemical formulas.
2. describe the information needed to calculate the mass of a reactant or product for the following balanced equation: fes + 2hcl → h₂s + fecl₂

critical thinking

1. applying concepts chlorine gas is produced by the electrolysis of sodium chloride in water in the following reaction: 2nacl + 2h₂o → cl₂ + h₂+ 2naoh. what mass of sodium chloride is needed to make 71 g of chlorine gas?

Explanation:

Step1: Identify the molar - mass of chlorine gas

The molar mass of $Cl_2$ is $M_{Cl_2}=2\times35.5\ g/mol = 71\ g/mol$.

Step2: Determine the mole ratio from the balanced equation

From the balanced equation $2NaCl + 2H_2O
ightarrow Cl_2+H_2 + 2NaOH$, the mole ratio of $NaCl$ to $Cl_2$ is $n_{NaCl}:n_{Cl_2}=2:1$.

Step3: Calculate the moles of $Cl_2$

Given the mass of $Cl_2$ is $m_{Cl_2} = 71\ g$. Using the formula $n=\frac{m}{M}$, the number of moles of $Cl_2$ is $n_{Cl_2}=\frac{m_{Cl_2}}{M_{Cl_2}}=\frac{71\ g}{71\ g/mol}=1\ mol$.

Step4: Calculate the moles of $NaCl$

Since $n_{NaCl}:n_{Cl_2}=2:1$, when $n_{Cl_2} = 1\ mol$, $n_{NaCl}=2\ mol$.

Step5: Calculate the mass of $NaCl$

The molar mass of $NaCl$ is $M_{NaCl}=23 + 35.5=58.5\ g/mol$. Using the formula $m = n\times M$, the mass of $NaCl$ is $m_{NaCl}=n_{NaCl}\times M_{NaCl}=2\ mol\times58.5\ g/mol = 117\ g$.

Answer:

117 g