Q: During the electrolysis of water, a total of 672 mL of gas is collected at STP. Using Faraday's Law, how much charge (in coulombs) was passed through the solution? ($$1\ \mathrm{mol}$$ electrons $$= 96,500\ \mathrm{C}$$; $$1\ \mathrm{mol}$$ gas at STP $$= 22.4\ \mathrm{L})$$

$$3.86 \times 10^3$\ \mathrm{C}$$

Question 1

Which of the following statements correctly describes the electron configuration of a sodium (Na) atom in its ground state?

Accepted Answer

Na has 1 electron in its M shell, corresponding to the configuration $$1s^2$$ $$2s^2$$ $$2p^6$$ $$3s^1$$

Question 2

Which of the following best explains why the ammonium ion ($$\mathrm{NH_4$^+}) $$forms four shared electron pairs?

Accepted Answer

Nitrogen forms four shared electron pairs: three standard covalent bonds and one coordinate covalent bond with a proton.

Question 3

According to VSEPR theory, what is the molecular geometry of ammonia ($$\mathrm{NH_3$}$$), and what causes this shape?

Accepted Answer

Trigonal pyramidal, due to three bonding pairs and one lone pair on nitrogen.

Question 4

Which of the following correctly matches each substance with its crystal type?

Accepted Answer

CO$$_2 ($$dry ice): molecular; SiO$$_2 ($$quartz): covalent network; CaO (quicklime): ionic

Question 5

A student reacts magnesium with hydrochloric acid. If the maximum mass of magnesium that can react is 0.048 g and the volume of HCl used is 50 mL, what is the required concentration of HCl to ensure complete reaction? (Mg: 24.0 g/mol)

Accepted Answer

$$1.0\ \mathrm{mol/L}$$

Question 6

A sample is completely vaporized at 25°C and 1 atm, producing 0.50 L of gas. Using the ideal gas law $$PV = nRT$$, which of the following is the correct calculation for the number of moles of gas produced? ($$R = 0.0821\ \mathrm{L\cdot atm\cdot $$mol^{-1}$$\cdot K$$^{-1}$$})$$

Accepted Answer

$$n = \dfrac{(1\ \mathrm{atm})(0.50\ \mathrm{L})}{0.0821\ \mathrm{L\cdot atm\cdot $$mol^{-1}$$\cdot K$$^{-1}$$} 	imes 298\ \mathrm{K}}$$

Question 7

Which of the following salts is formed from a weak diprotic acid and a strong monovalent base, and what is the expected pH of its aqueous solution?

Accepted Answer

Na$$_2CO$_3$$; basic

Question 8

In a redox titration, 30 mL of 0.200 M KMnO$$_4 is $$required to completely react with 50 mL of 0.300 M H$$_2O$_2. $$What is the stoichiometric ratio of KMnO$$_4 to H$_2O$_2 in $$the balanced equation?

Accepted Answer

2:5

Question 9

During the electrolysis of water, a total of 672 mL of gas is collected at STP. Using Faraday's Law, how much charge (in coulombs) was passed through the solution? ($$1\ \mathrm{mol}$$ electrons $$= 96,500\ \mathrm{C}$$; $$1\ \mathrm{mol}$$ gas at STP $$= 22.4\ \mathrm{L})$$

Accepted Answer

$$3.86 	imes 10^3$\ \mathrm{C}$$

Question 10

For the endothermic reaction $$\mathrm{H_2$(g) + I_2$(g) \rightleftharpoons 2HI(g)}$$, what will be the effect of lowering the temperature on the equilibrium position?

Accepted Answer

The equilibrium will shift toward the formation of HI.

Question 11

Which of the following metals will NOT react with dilute hydrochloric acid to produce hydrogen gas?

Accepted Answer

Copper (Cu)

Question 12

Which pair of procedures will result in no observable reaction due to the relative reactivity of the metals involved?

Accepted Answer

Ag + HCl and Pt + FeSO$$_4$$

Question 13

In which of the following reactions does water act as a Brønsted-Lowry acid?

Accepted Answer

b) NH$$_3 + H$_2O$$ $$\rightarrow NH$_4^+ + OH$^-$$ and c) 2Na + 2H$$_2O$$ $$\rightarrow 2$$NaOH + H$$_2$$

Question 14

Sulfur dioxide (SO$$_2) is $$used as a bleaching agent for delicate materials. What is the primary chemical mechanism by which SO$$_2$$ bleaches?

Accepted Answer

Reduction of colored compounds

Question 15

Which property distinguishes Zn$$^{2+}$$ ions in qualitative analysis?

Accepted Answer

Forms a white precipitate with NaOH that dissolves in excess NaOH or NH$$_3$$

Question 16

How many unsaturated isomers exist for C$$_3H$_5Br$$, and how many of these yield a product with an asymmetric carbon upon addition of Br$$_2$$?

Accepted Answer

4 isomers; 2 yield an asymmetric carbon

Question 17

Which of the following best describes the reaction of ethylene (C$$_2H$_4) $$with bromine water?

Accepted Answer

Ethylene decolorizes bromine water via an addition reaction.

Question 18

What is the main product when benzene is treated with a mixture of concentrated nitric acid and sulfuric acid?

Accepted Answer

Nitrobenzene

Question 19

Cyclohexadiene (C$$_6H$_8) $$reacts with 2 moles of Br$$_2. $$What is the molecular formula and molecular weight of the product?

Accepted Answer

C$$_6H$_8Br$_4$$, MW = 400

Question 20

Which of the following pairs of synthetic polymers both require formaldehyde as a key reactant in their synthesis?

Accepted Answer

Phenol resin and Vinylon

2021 EJU Chemistry Examination: Comprehensive Study Notes

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