Correct answer: Seawater

Why?:

The pH is a logarithmic scale with base 10. It is calculated as pH = -log[H⁺]. One common definition of acidity is the ability of a substance to donate H⁺ ions to solution. So the more acidic the substance, the greater H⁺ concentration it produces, and the lower its pH (note the negative sign in the equation). Since the equation that defines pH is logarithmic, a factor of 100 in [H⁺] causes a change in pH level by 2. This means that an acid that is 100 times more acidic than milk of magnesia will have a pH that is 2 lower than the pH of milk of magnesia.

Answering this question:

Locate in the graph milk of magnesia and determine its pH. According to the graph, the pH of milk of magnesia is 10. Anything more acidic than milk of magnesia will have a pH that is lower than 10. Since we are looking for the mixture that is 100 times more acidic than pH 10, we will choose the mixture that has a pH that is lower than 10 by 2. The mixture we are looking for must have a pH of 8 since it is 2 pH values lower than 10. The mixture with a pH of 8 is seawater.

Therefore, seawater is the mixture that is 100 times more acidic than milk of magnesia.

Correct answer: Blue

Why?:

Thymol blue is a chemical indicator that is used to determine if a substance or a mixture is acidic or basic. This can also be used to determine the possible pH of a mixture. Thymol blue changes its color from red to yellow at pH 1.2-2.8. This means that if a solution is at pH below 1.2, thymol blue will impart a red color. If the pH of the solution reaches around 1.2, thymol blue will impart a yellow color. Thymol blue also changes color from yellow to blue at pH 8.0-9.6. This means that if a solution has a pH below 8, thymol blue will impart a yellow color in it. If the pH of the solution reaches 8.0, then thymol blue will impart a blue color in it. According to the graph, milk of magnesia has a pH of 10. With thymol blue, milk of magnesia will have a bluish color.

Answering this question:

Locate milk of magnesia in the graph. From the point corresponding to milk of magnesia, draw an imaginary line going to the left until it comes to the point corresponding to the pH of milk of magnesia. By doing this, it will be determined that the pH of milk of magnesia is 10. And since thymol blue changes color from yellow to blue at pH 8.0-9.6, then thymol blue will give milk of magnesia a blue color.

So the color of thymol blue in milk of magnesia is blue.

Correct answer: 1.0x10^-4 M

Why?:

The graph shows the relative hydronium ion concentration in the different mixtures. It can be observed from the table that tomato juice contains 1.0x10^-4 M of hydronium ion (H₃O⁺) and a corresponding pH of 4. The pH is a measure of the hydronium ion concentration in a mixture.

Answering this question:

Locate first tomato juice in the graph. From the point on the graph that corresponds to tomato juice, draw an imaginary line going down until it intersects a point corresponding to its hydronium ion concentration. By doing that, you will arrive at a point with hydronium ion concentration equal to 1.0x10^-4 M.

So the correct answer is 1.0x10^-4 M.

Correct answer: (3) HBr

Why?:

Acids turn blue litmus paper to red while bases turn red litmus paper to blue. When acids react with metals, they liberate hydrogen gas. This is evidenced by the formation of bubbles in the reaction mixture. Strong acids and bases are considered strong electrolytes as they generate ions into the solution. These ions carry with them electrical charges. They conduct electricity. Weak acids and bases however only partially ionize into the solution. Thus, they do not conduct electricity as well as the strong acids and bases. They are known as weak electrolytes.

Answering this question:

It is necessary to compare and contrast the substances in the choices based on the characteristics given by the problem. The characteristics given in the problem describe an acid. Among the choices, HBr is the only acid. Moreover, it is a strong acid so it is a strong electrolyte and conducts electricity. The presence of hydrogen in the beginning of the formula is a hint that it is an acid because most acids are written this way. Since it is an acid, it will turn blue litmus paper to red. It will also react with zinc metal to generate hydrogen gas.

So the correct answer is (3).

Correct answer: (3) H₂SO_4(aq) and Ca(OH)_2(aq)

Why?:

A neutralization reaction is the reaction of an acid with a base. The products are salt and water. A neutralization reaction can also fall under a kind of reaction called Double Replacement Reaction. In this kind of reaction, cations or anions "exchange partners". An example would be the following general reaction.

AB + CD ↔ AD + CB

Cations A and C exchanged partners to form AD and CB.

Answering this question:

Again, a neutralization reaction produces a salt and water. The salt here is CaSO₄. This means that the other product must be water. This also means that the reactants must contain the atoms H, O, S and Ca only. This will eliminate choices (1) and (2) as they contain the atoms Cl and N, respectively. Through examination of choice (3), it can be observed that "exchange of partners" will yield CaSO₄ and H₂O. This is already enough to conclude that (3) is the correct answer. With choice (4), there is no way to produce H₂O on the product side of the reaction as there is no hydrogen atom in the reactants. This is not a neutralization reaction.

So the correct answer is (3).

Correct answer: (1) 46 g

Why?:

Sodium nitrate or NaNO₃ is a soluble salt. This means that in water, it will ionize into Na⁺ and NO₃^- ions. However, like other salts, its solubility has a limit. The solubility of NaNO₃ in 100 g water is 125 g and 79 g at 60 and 10 degrees Celsius, respectively. Only 80 g of the initial 125 grams remains in solution at the lower temperature, and the difference must have precipitated or "settled out" of the original solution.

Answering this question:

Subtract the amount of salt that will dissolve in the lower temperature from that that will dissolve in a higher temperature. Their difference is the amount of the salt that did not dissolve. It is the amount that precipitated out of the solution.

Precipitate Mass = 125 g - 79 g = 46 g

The answer is choice (1) 46 g.

Correct answer: (4) hydroxide ion

Why?:

Svante Arrhenius defined acids as those substances that generate hydrogen cation, H+, into the solution. This is now called an Arrhenius acid. He defined bases as those substances that generate hydroxide ion, OH-, in the solution. This is the Arrhenius base.

Answering this question:

In the choices, it is clear that hydrogen ion and hydronium ion are not the answers because they both have positive charges. Besides, the two of them are just equivalent. Hydride ion is a negatively charged hydrogen ion, H^-. This is a base but this is not included in the definition of Arrhenius acids and bases. To answer this question, you need to have an idea on how acids and bases are defined by Arrhenius. Just remember the very famous NaOH. It is always used in the classroom as an example of a base. From it, you will have an idea that bases have OH^- or hydroxide ions in their formula. This could lead you to the correct answer.

So the correct answer is (4).

Correct answer: (4) KOH

Why?:

Electrolytes can be dissolved in solution to generate charged species that can carry charges. They either contain ions or generate ions. Substances that easily ionize into the solution are called strong electrolytes. Examples would be strong acids and bases, and most salts. There are also those substances that do not ionize into the solution as well as the strong electrolytes. They are called weak electrolytes. They conduct electricity only to a small extent. The answer choice (4) KOH is a strong base that generates K⁺ and OH^- ions in solution. It is the best choice. The remaining choices will only marginally conduct electricity.

Answering this question:

Among the choices, it is KOH that is ionic. This means that it is very much able to generate charged particles into the solution. These charged particles are then capable of conducting electricity. Moreover, KOH is a strong base. Hydroxides of the group IA and IIA of the periodic table are strong bases. Another example would be NaOH. Sodium and potassium both belong to group IA. Choices (1), (2), and (3) are made up of covalent bonds.  They do not readily form ions in the solution. Although they can undergo autoprotolysis and generate ions, it occurs only to a small extent. Thus they are considered weak electrolytes.

So the correct answer is (4).

Correct answer: (3) Pb⁺²

Why?:

There are four possible salts involved here. They are FeCl₂, MgCl₂, PbCl₂, and ZnCl₂. Among the four salts, it is PbCl₂ that has the highest solubility product constant, K_sp. The higher the K_sp value, the more insoluble is the salt in water. This means that among the four kinds of salts, PbCl₂ is the most insoluble.

Answering this question:

Without knowing that PbCl₂ has the highest K_sp value among the four salts, this can still be answered correctly by looking at the sizes of the cations involved. For any substance to be dissolved, it has to form a bond with the solvent. The solvent here is water. Oxygen in water contains lone pair of electrons. These are negative. The cations therefore should be attracted to the negative oxygen for dissolution to happen. Among the atoms Fe, Mg, Pb, and Zn, it is Pb that has the biggest atomic size. In the periodic table, it is located much below than the 3 atoms. And the trend in the atomic size is that as we go from top to bottom in the periodic table, size gets bigger. This means that the nucleus of Pb is farther from its surface compared to the tree other atoms. With this, we can deduce that it is harder for negatively charged particles to get attracted to the nucleus of the Pb atom since it is far. Therefore bonding is hindered. So Pb atoms cannot just easily be dissolved in water.

So this leaves us with (3) as the correct answer.