Correct Answer: (1) H⁺

Why:

The properties of an acid are often attributed to the properties of hydrogen. An arrhenius acid, particularly,  is a substance that increases the concentration of the Hydronium ion (H30+) when dissolved in water.  Chemists will often denote the denote this as H+(aq) but in reality the free hydrogen nucleus (essentially a proton) does not exist alone in water, it exists as a H3O+.

However, of the choices available here (1) is the best answer, as we know the arrhenius acid is an acid that increases the H+ activity in a solution.

Answering this question:

Even if you can not remember who Svante Arrhenius is and how he defined an acid this question is easily answerable.   We can remember that an Acid deals with the concentration of Hydrogen and the base deals with the concentration of OH.  Looking at the possible choices to this question our common sense can kick in as well.  They are all together on the periodic table, specifically in the same group (vertical line).  We know that this usually means that they will react and behave similar in chemical reactions.  So we're looking for which one is not like the others and more often than not, hydrogen is the exception to the rules, especially in periodic trends.  In conclusion, it is better to remember what defines an acid, however if you can't, it is still possible to get the correct answer with a little luck and common sense.

Neutralization involves the reaction of an acid and a base which yields water and an inorganic salt.

Answering the question:

H₂SO₄ is an acid while Ba(OH)₂ is a base.  When these two compounds react, the process is said to be a neutralization process.  Representing the said reaction in a chemical equation, we have:

H₂SO₄ + Ba(OH)₂ ®       BaSO₄ + 2H₂O

With water and an inorganic salt as the expected products of the neutralization reaction, we can therefore conclude from the chemical equation above that the inorganic salt is BaSO₄, which is option no. 4.

Options 1, 2 and 3 are eliminated.

Correct answer: (2)

A thymol blue indicator, also called thymolsulphonephthalein, serves as a pH indicator.  It is in crystalline powder form with its color ranging from brownish-green to reddish-brown.  At pH condition 1.2 to 2.8, it transitions from red to yellow and at pH 8.0 to 9.6, its color changes from yellow to blue.

Answering the question:

First, in order for thymol blue indicator to turn blue, the solution should be basic, as mentioned above, the color change to blue occurs at pH 8.0 to 9.6. We should be familiar with answers (3) and (4) as common acids that are used throughout the laboratory, this would immediately exclude them. Answer (1) known as ethanoic acid (vinegar) may not be as familiar but has the functional group RCOOH, this is the functional group for organic acids, which also have a low pH. Answer (2) is KOH which should also be a familiar base similar to NaOH. Although you may not know the exact pH range it is the only base in the group and therefore the best possible answer.

Correct answer:

When working on chemical equations, just like mathematical equations, both sides of the equation should be equal. For a chemical equation that means the number of moles of each reacting element must be equal to the number of moles for each element in the product. In order for this to occur it means that not all chemical reactions will occur in a one to one ratio.

Answering the Question:

When balancing a chemical equation it is important to know how electrons are transferred between reactants. An understanding of the trends in the periodic table and knowing the group that elements belong simplifies this process.

For the above equation knowing that Ca belongs to the alkali earth metals and is a part of group 2 of the periodic table is valuable knowledge. This means that Ca has two electrons in its valence orbital and is readily ionized forming Ca²⁺. However since a chemical equation is given it means the quantity of each elements on the left of the reaction should be equal to the quantity on the right. This means if you have 4 hydrogen atoms on the left of the equation then you should have 4 hydrogen atoms accounted for on the right.

Correct Answer: 6

The pH is a measure of the hydrogen ion (H⁺) concentration or acidity of a system. The equation below shows the relationship between pH and H⁺ concentration in moles. If the pH of a system is less than 7 it acidic, if it is greater than 7 then it is basic.

pH = -log[H⁺]

H⁺ = 10^-pH

Answering the Question:

Since the original pH of the soil was given as 4, the concentration of H⁺ can be calculated.

H⁺ = 10^-4

Therefore the concentration of H⁺ = 0.0001M or 1x10^-4M

This can be calculated using a scientific calculator by typing -4 and pressing the inv. Log or 2^nd func Log key.

After the addition of quicklime the H+ ion concentration fell 100 fold.

Therefore the new soil concentration is 0.0001/100 = 0.000001M or 1x10^-6

This mean our new soil pH would be:

pH = -log[1x10^-6]

pH = 6

The new pH of the soil sample is 6.

Correct Answer: 3.25x10^-3M

The above reaction is categorized as acid base reactions. This type of reaction is usually the result of an acid (H⁺ proton donor) reacting with a base (OH^- proton acceptor) to form products and water according to the equation;

Using the mole theory we know that 1 mole of H⁺ will react completely with 1 mole of OH^-. Based on this and the information in the question above, it is then possible to calculate the concentration of H+ ion in the acid rain.

Answering the question:

The molarity of the H+ in the acid rain can be determined by calculating the number of moles of NaOH used to neutralize it.

0.010M of NaOH contains 0.010 moles of NaOH in 1000ml

Therefore 1ml of solution would contain 0.010/1000 moles or 0.00001moles

This means 6.5ml would contain 6.5 x 0.00001 or 0.000065 moles or 6.5x10^-5 moles

Now based on the fact that 20ml of acid rain was neutralized by 6.5ml of NaOH, and the relationship of H+ and NaOH follows the ratio;

Thus 1 mole of H⁺ requires 1 mole of NaOH to completely react.

Therefore 20.0-milliliters of acid rain contains 6.5x10^-5 moles of H⁺ ions. The molarity of H+ is the number of moles in 1000ml is 1000/20 x 6.5x10^-5 moles which is equal to 0.00325M or 3.25x10^-3M

Giving an answer of 3.25x10^-3M