a) $$ \mathrm{Na}_{2} \mathrm{CO}_{3}+\mathrm{HCl} \longrightarrow \mathrm{NaCl}+\mathrm{H}_{2} \mathrm{O}+\mathrm{CO}_{2} $$ b) $$ \mathrm{Ca}(\mathrm{OH})_{2}+\mathrm{H}_{3} \mathrm{PO}_{4} \longrightarrow \mathrm{Ca}_{3}\left(\mathrm{PO}_{4} ight)_{2}+\mathrm{H}_{2} \mathrm{O} $$ c) $$ \mathrm{C}_{6} \mathrm{H}_{12} \mathrm{O}_{6} \longrightarrow \mathrm{C}_{2} \mathrm{H}_{6} \mathrm{O}+\mathrm{CO}_{2} $$ d) $$ \mathrm{Fe}_{2}\left(\mathrm{CO}_{3} ight)_{3}+\mathrm{H}_{2} \mathrm{SO}_{4} \longrightarrow \mathrm{Fe}_{2}\left(\mathrm{SO}_{4} ight)_{3}+\mathrm{H}_{2} \mathrm{O}+\mathrm{CO}_{2} $$ e) $$ \mathrm{H}_{3} \mathrm{PO}_{4}+\mathrm{CaO} \longrightarrow \mathrm{Ca}_{3}\left(\mathrm{PO}_{4} ight)_{2}+\mathrm{H}_{2} \mathrm{O} $$ f) $$ \mathrm{FeS}_{2}+\mathrm{O}_{2} \longrightarrow \mathrm{Fe}_{2} \mathrm{O}_{3}+\mathrm{SO}_{2} $$ g) $$ \mathrm{NH}_{3}+\mathrm{O}_{2} \longrightarrow \mathrm{NO}+\mathrm{H}_{2} \mathrm{O} $$ 2) Considere a mistura de $$ 0,5 \mathrm{~mol}^{ ext {de }} \mathrm{CH}_{4} $$ e $$ 1,5 \mathrm{~mol} $$ de $$ \mathrm{C}_{2} \mathrm{H}_{6} $$, contidos num recipiente de 30,0 litros a 300 K . O número total de moléculas no sistema é (Dado: constante de Avogadro $$ =6 \cdot 10^{23} $$ ) a) 2,0 . c) $$ 6,0 \cdot 10^{23} $$ e) $$ 12 \cdot 10^{23} $$ b) $$ 2,0 \cdot 10^{23} $$ d) $$ 9,0 \cdot 10^{23} $$ 3) Se o cloreto representado pela fórmula XCl possui massa molecular 74,5 , espera-se que o fluoreto XF apresente massa molecular (Dados: $$ \mathrm{F}=19 ; \mathrm{Cl}=35,5 $$ ): a) 29,0 . b) 37,5 . c) 44,0 . d) 58,0 . e) 83,5 . 4) No rótulo de uma determinada embalagem de leite integral UHT, processo de tratamento térmico a alta temperatura, consta que um copo de 200 mL deste leite contém $$ 25 \% $$ da quantidade de cálcio recomendada diariamente $$ \left(2,4 imes 10^{-2} \mathrm{~mol} ight) $$. A massa, em mg , de cálcio (massa molar $$ 40 \mathrm{~g} / \mathrm{mol} $$ ) presente em 1 litro desse leite é: a) 1200 . b) 600 . c) 300 . d) 240 . e) 120 .

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a) $$ \mathrm{Na}_{2} \mathrm{CO}_{3}+\mathrm{HCl} \longrightarrow \mathrm{NaCl}+\mathrm{H}_{2} \mathrm{O}+\mathrm{CO}_{2} $$ b) $$ \mathrm{Ca}(\mathrm{OH})_{2}+\mathrm{H}_{3} \mathrm{PO}_{4} \longrightarrow \mathrm{Ca}_{3}\left(\mathrm{PO}_{4}ight)_{2}+\mathrm{H}_{2} \mathrm{O} $$ c) $$ \mathrm{C}_{6} \mathrm{H}_{12} \mathrm{O}_{6} \longrightarrow \mathrm{C}_{2} \mathrm{H}_{6} \mathrm{O}+\mathrm{CO}_{2} $$ d) $$ \mathrm{Fe}_{2}\left(\mathrm{CO}_{3}ight)_{3}+\mathrm{H}_{2} \mathrm{SO}_{4} \longrightarrow \mathrm{Fe}_{2}\left(\mathrm{SO}_{4}ight)_{3}+\mathrm{H}_{2} \mathrm{O}+\mathrm{CO}_{2} $$ e) $$ \mathrm{H}_{3} \mathrm{PO}_{4}+\mathrm{CaO} \longrightarrow \mathrm{Ca}_{3}\left(\mathrm{PO}_{4}ight)_{2}+\mathrm{H}_{2} \mathrm{O} $$ f) $$ \mathrm{FeS}_{2}+\mathrm{O}_{2} \longrightarrow \mathrm{Fe}_{2} \mathrm{O}_{3}+\mathrm{SO}_{2} $$ g) $$ \mathrm{NH}_{3}+\mathrm{O}_{2} \longrightarrow \mathrm{NO}+\mathrm{H}_{2} \mathrm{O} $$ 2) Considere a mistura de $$ 0,5 \mathrm{~mol}^{	ext {de }} \mathrm{CH}_{4} $$ e $$ 1,5 \mathrm{~mol} $$ de $$ \mathrm{C}_{2} \mathrm{H}_{6} $$, contidos num recipiente de 30,0 litros a 300 K . O número total de moléculas no sistema é (Dado: constante de Avogadro $$ =6 \cdot 10^{23} $$ ) a) 2,0 . c) $$ 6,0 \cdot 10^{23} $$ e) $$ 12 \cdot 10^{23} $$ b) $$ 2,0 \cdot 10^{23} $$ d) $$ 9,0 \cdot 10^{23} $$ 3) Se o cloreto representado pela fórmula XCl possui massa molecular 74,5 , espera-se que o fluoreto XF apresente massa molecular (Dados: $$ \mathrm{F}=19 ; \mathrm{Cl}=35,5 $$ ): a) 29,0 . b) 37,5 . c) 44,0 . d) 58,0 . e) 83,5 . 4) No rótulo de uma determinada embalagem de leite integral UHT, processo de tratamento térmico a alta temperatura, consta que um copo de 200 mL deste leite contém $$ 25 \% $$ da quantidade de cálcio recomendada diariamente $$ \left(2,4 	imes 10^{-2} \mathrm{~mol}ight) $$. A massa, em mg , de cálcio (massa molar $$ 40 \mathrm{~g} / \mathrm{mol} $$ ) presente em 1 litro desse leite é: a) 1200 . b) 600 . c) 300 . d) 240 . e) 120 .

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Let's solve the problems step by step.

### Problem 2: Total Number of Molecules

We have a mixture of $$0.5 \, \text{mol}$$ of $$ \text{CH}_4 $$ and $$1.5 \, \text{mol}$$ of $$ \text{C}_2\text{H}_6 $$.

1. **Calculate the total number of moles:**
   $$
   n_{\text{total}} = n_{\text{CH}_4} + n_{\text{C}_2\text{H}_6} = 0.5 + 1.5 = 2.0 \, \text{mol}
   $$

2. **Use Avogadro's number to find the total number of molecules:**
   $$
   N = n_{\text{total}} \times N_A = 2.0 \, \text{mol} \times 6 \times 10^{23} \, \text{molecules/mol}
   $$

Now, let's calculate $$N$$:
$$
N = 2.0 \times 6 \times 10^{23} = 12 \times 10^{23} \, \text{molecules}
$$

Thus, the answer is:
- **e) $$12 \cdot 10^{23}$$**

### Problem 3: Molecular Mass of Fluoride

Given that the molecular mass of $$XCl$$ is $$74.5$$ g/mol, we can find the mass of $$X$$ using the mass of chlorine.

1. **Calculate the mass of $$X$$:**
   $$
   \text{Mass of } X = 74.5 - 35.5 = 39.0 \, \text{g/mol}
   $$

2. **Now calculate the mass of $$XF$$:**
   $$
   \text{Mass of } XF = \text{Mass of } X + \text{Mass of } F = 39.0 + 19 = 58.0 \, \text{g/mol}
   $$

Thus, the answer is:
- **d) 58.0**

### Problem 4: Mass of Calcium in Milk

We know that a glass of $$200 \, \text{mL}$$ of milk contains $$25\%$$ of the daily recommended calcium, which is $$2.4 \times 10^{-2} \, \text{mol}$$.

1. **Calculate the amount of calcium in $$200 \, \text{mL}$$:**
   $$
   n_{\text{Ca}} = 0.25 \times 2.4 \times 10^{-2} = 6.0 \times 10^{-3} \, \text{mol}
   $$

2. **Convert this to mass:**
   $$
   m_{\text{Ca}} = n_{\text{Ca}} \times M_{\text{Ca}} = 6.0 \times 10^{-3} \, \text{mol} \times 40 \, \text{g/mol} = 0.24 \, \text{g}
   $$

3. **Convert grams to milligrams:**
   $$
   m_{\text{Ca}} = 0.24 \, \text{g} \times 1000 \, \text{mg/g} = 240 \, \text{mg}
   $$

Thus, the answer is:
- **d) 240**

### Summary of Answers
1. Problem 2: **e) $$12 \cdot 10^{23}$$**
2. Problem 3: **d) 58.0**
3. Problem 4: **d) 240**
- **Problem 2:** There are $$12 \times 10^{23}$$ molecules. - **Problem 3:** The molecular mass of $$XF$$ is 58.0 g/mol. - **Problem 4:** The mass of calcium in 1 liter of milk is 240 mg.

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