# Exercise 3


Solutions, hints and answers can be found in the Solutions Page. It is strongly recommended that students do not look at the solutions until after completing or attempting to complete the problems. Going straight to the solutions will reduce the point of the exercises.

## 3.1

1. Write a balanced molecular equation for the dissociation of $$NaCl$$ in water.
2. Based on the equation in part a, is $$NaCl$$ a strong electrolyte or a weak electrolyte?
3. Hydrofluoric acid is a weak acid, and does not completely dissociate in water. Is it a strong electrolyte or a weak electrolyte?

## 3.2

Write the balanced, complete ionic, and net ionic equations for the following reactions :

1. $$CoCl_2 + NaCl \rightarrow$$
2. $$KSO_4 + Ba(NO_3)_2 \rightarrow$$
3. $$NaOH + CaCl_2 \rightarrow$$

## 3.3

What amount of 0.100 M $$KOH$$ is needed to neutralize 10.00 mL of 0.210 M $$HF$$?

## 3.4

A students has 97 mL of 0.80 M HCl which they would like to neutralize with 0.18M NaOH. What volume of NaOH should be used?

## 3.5

Below are a list of reactions. State whether each is an oxidation-reduction reaction and if it is an oxidation-reduction reaction, identify the reducing and oxidizing agents.

1. $$CO_2(g) + H_2(g) \rightarrow CO_{(g)} + H_2O_{(g)}$$
2. $$K_2SO_{4\, (aq)} + BaI2(aq) \rightarrow BaSO_{4\, (s)} + 2KI_{(aq)}$$
3. $$H_3PO_{4\,(aq)} + Se^{2-}_{(aq)} \rightarrow HPO_4^{2-}(aq) + H_2Se_{(aq)}$$
4. $$Zn (s) + CuSO_4 \rightarrow ZnSO_4(aq) + Cu(s)$$

## 3.6

Indicate the oxidation state of the element assigned in the compounds below:

1. $$C$$ in $$CO_2$$
2. $$S$$ in $$CaSO_4$$
3. $$Sn$$ in $$SnO_2$$
4. $$Cd$$ in $$Cd$$
5. $$Co$$ in $$CoCl_2$$

## 3.7

When titrating a 4.00 mL volume of the diprotic acid, $$H_2SO_4$$ of 0.645 M concentration, what volume of 0.493 M $$NaOH$$ is necessary?

## 3.8

Write down a balanced formula equation for an acid-base reaction that forms potassium nitrate.

## 3.9

Balance the following equations in both acidic and basic environments:

1. $$H_2(g) + O_2(g) \rightarrow H_2O(l)$$
2. $$Cr_2O_7^{2-}(aq) + C_2H_5OH (l) \rightarrow Cr^{3+}(aq) + CO_2(g)$$
3. $$Fe^{2+}(aq) + MnO_4^-(aq) \rightarrow Fe^{3+}(aq) + Mn^{2+}(aq)$$
4. $$Zn (s) + NO_3^-(aq) \rightarrow Zn^{2+}(aq) + NO(g)$$
5. $$Al (s) + H_2O (l) + O_2 (g) \rightarrow [Al(OH)_4]^-(aq)$$
6. Balance in only acidic Solutions
1. $$Mn^{2+} + BiO_3^- \rightarrow MnO4^- + Bi^{3+}$$
2. $$ClO_3^- + Cl - \rightarrow Cl_2 + ClO_2$$
7. Balance in only Basic Solution
1. $$Zn + NO_3^ - \rightarrow Zn(OH)_4^{2-} + NH_3$$
2. $$Al + OH^- \rightarrow AlO_2^- + H_2$$

## 3.10

Write the products of these acid-base reactions. Balance the complete reaction.

1. $$HClO_{4\; (aq)} + Mg(OH)_{2\; (aq)} \rightarrow$$
2. $$H_2S_{(aq)} + NaOH_{(aq)} \rightarrow$$

## 3.11

Write chemical reactions for the dissociation of the following compounds in water and determine if they are strong electrolytes or weak electrolytes: $$HCl$$, $$NaOH$$, $$MgCl_2$$, $$Al_2S_3$$.

## 3.12

Dichloromethane ($$CH_2Cl_2$$) is a useful solvent for many chemical processes in the organic chemistry lab. In the food industry, dichloromethane can be used to decaffeinated coffee and tea as well as to prepare extracts of hops and other flavorings.

Figure: Sample of dichloromethane. from Wikipedia.

Dichloromethane's vapor pressure at 25 °C is 57.3 kPa. Convert this pressure to the following pressure units.

1. atm
2. torr
3. psi
4. mm H
5. bar

## 3.13

An ideal gas is contained in a flask with a volume of 10 mL. If the volume of the container is increased to 50 mL, what is the final pressure, $$P_f$$ in the flask? Assume the original pressure is $$P_i$$ and the temperature is maintained constant.

## 3.14

A truck tire will blow out if its internal pressure increases to 2 atm. In a morning, a driver filled the tire will air to 1.50 atm at $$18 ^oC$$. Driving the truck at noon increases the temperature to $$32 ^oC$$. Assuming the volume of the tire is constant, what’s the final condition of the tire?

Figure: Overpressurizing a tire can result in catastrophic failure (i.e., "a blown tire").

## 3.15

Please calculate the density of nitrogen gas at STP (1 atm and 0 $$^\circ\rm C$$).

## 3.16

A chemist notices that one of many organic solvents is leaking from the hood. The rate of effusion of this organic gas is 2.866 mL/sec while the effusion of oxygen gas is 3.640 mL/sec. What is the molar mass of this organic solvent?

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