Chapter 21 Science Final
When a chemical loses a hydrogen ion, is it behaving as an acid or a base?
A chemical that loses a hydrogen ion is behaving as an acid.
When can a solution of a weak base be more corrosive than a solution of a strong base?
A concentrated solution of a weak base could have more corrosive power than the dilute solution of a strong base.
Water is formed from the reaction between an acid and a base. Why is water not classified as a salt?
A salt is the ionic compound produced from the reaction of an acid and a base. Water is a covalent compound.
Why does a solution of a strong acid conduct electricity better than a solution of a weak acid having the same concentration?
A solution of a strong acid has more ions in solution and can conduct electricity better than a weak acid.
Show that the pH of a solution is 10 when the hydronium ion concentration of this solution is 1010 mole per liter. Is the solution acidic or basic? pH log [H3O] log (1010) (10) 10
A solution with a pH of 10 is basic. In such a solution, there are more hydroxide ions than hydronium ions.
Scientists have experimented with ways of enhancing the ocean's ability to absorb atmospheric carbon dioxide. Adding powdered iron to a small plot of the ocean, they found, has the effect of fostering the growth of microorganisms that enhance the rate at which carbon dioxide is absorbed. Might this be a solution to the problem of global warming? Why or why not?
Adding iron to the ocean to enhance its carbon dioxide absorbing power my help to lower the amount of carbon dioxide in the atmosphere. At the same time, however, it might drastically alter the ocean's ecology. For example, the excess carbon dioxide would lower the pH of the ocean. Shelled marine organism would die, which could affect the whole food chain. We would end up trading one problem for another.
What do the oxidation of zinc and the oxidation of aluminum have in common?
After oxidation, zinc and aluminum both form water-insoluble oxidized coats that prevent further oxidation.
Rank the following solutions in order of increasing concentration of hydronium ions, H3O. a) Hydrogen chloride, HCl (concentration 2 M) b) Acetic acid, CH3COOH (concentration 2 M) c) Ammonia, NH3 (concentration 2 M)
All of these solutions have the same concentration. The difference between them is their acid strength. As discussed in the text, hydrogen chloride is a strong acid, which means nearly all of the hydrogen chloride molecules donate hydrogen ions to form hydronium ions. Acetic acid is a weak acid, which means only a few of the acetic acid molecules in solution donate hydrogen ions to form hydronium ions. The ammonia behaves better as a base than an acid, which means that it contributes very, very few hydrogen ions. The ammonia solution, therefore, has the lowest concentration of hydronium ions. The acetic acid solution has more hydronium ions, but not as many as are found in the hydrogen chloride solution.
What is the difference between an oxidizing agent and a reducing agent?
An oxidizing agent causes another reactant to be oxidized (lose an electron), and a reducing agent causes another reactant to be reduced (gain an electron).
What happens to the pH of an acidic solution as pure water is added?
As water is added to an acidic solution, the hydronium ions (and anything else that is dissolved in this acidic solution) become more dilute, that is, less concentrated. Thus, the pH increases.
Pour vinegar onto beach sand from the Caribbean and the result is a lot of froth and bubbles. Pour vinegar onto beach sand from California, however, and nothing happens. Why?
Beach sand from the Caribbean and many other tropical climates is made primarily of the calcium carbonate remains of coral and shelled creatures. Vinegar is an acid and the calcium carbonate is a base. The reaction between the two results in the formation of carbon dioxide, which creates bubbles as it is formed. California beach sand primarily comes from the erosion of rocks and minerals, which are mostly made of inert silicon dioxide, SiO2.
When lightning strikes, nitrogen molecules, N2, and oxygen molecules, O2, in the air react to form nitrates, NO3, which come down in the rain to help fertilize the soil. Is this this an example of oxidation or reduction?
Both! The nitrogen is oxidized as it reacts with the oxygen while the oxygen is reduced. Remember, wherever there's an oxidation, there must be a reduction.
What are some differences between corrosion and combustion?
Corrosion is the deterioration of a metal by oxidation. Combustion is a redox reaction between a nonmetal and oxygen.
When an acid is dissolved in water, what ion does the water form?
Dissolving an acid in water causes the formation of a hydronium ion.
What is electrochemistry?
Electrochemistry is the study of electrical energy and chemical changes.
What is electrolysis, and how does it differ from what goes on inside a battery?
Electrolysis uses electrical energy to produce a chemical change whereas a battery uses a chemical change to produce electrical energy.
Identify the acid or base behavior of each substance in these reactions: a. H3O Cl H2O HCl b. H2PO4 H2O H3O HPO4
For (a) note that the H3O transforms into a water molecule. This means that the H3O loses a hydrogen ion, which is donated to the Cl. The H3O, therefore, is behaving as an acid while the Cl is behaving as a base in the reverse direction we see the H2O gaining a hydrogen ion (behaving as a base) to become H3O. It gets this hydrogen ion from the HCl, which in donating is behaving as an acid. You should be able make similar arguments for (b) to arrive at the following answers: a) acid, base, base, acid b) acid, base, acid, base
What is the prime difference between a battery and a fuel cell?
Fuel cells are very similar to batteries. Batteries, however, run down, while fuel cells can keep going indefinitely so long as fuel is supplied.
What gas, when provided in the in right concentration, has been shown to induce a state of suspended animation in mice?
Hydrogen sulfide, H2S, which is the same smelly stuff of rotten eggs!
What is true about the relative concentrations of hydronium and hydroxide ions in an acidic solution? How about a neutral solution? A basic solution?
If the hydronium ion concentration of a solution is higher than the hydroxide ion then the solution is acidic. If the opposite is true then the solution is basic.
How is suspended animation similar to death? How is it different?
In both suspended animation and death, the cells of the body are no longer working. Suspended animation is different from death, however, because the cells have the potential to start working again.
Assuming the technique of suspended animation was safe, which it currently isn't, what would be some of the disadvantages to putting yourself under suspended animation for a long period of time?
Of course there is the cost associated with maintaining your body for all those years. But perhaps, more significant is that you would be saying good-bye to all your loved ones.
Many of the smelly molecules of cooked fish are alkaline compounds. How might these smelly molecules be conveniently transformed into less smelly salts just prior to eating the fish?
Squeeze lemon juice upon the fish. The citric acid found in lemon juice reacts with these smelly alkaline compounds to form less smelly salts. The smell and taste of the lemon also helps to mask any additional undesirable fishy odors.
Are hydrogen sulfide, H2S, and oxygen, O2, molecules very different in size or about the same size?
Sulfur atoms are larger than oxygen atoms, but not larger than an oxygen molecule, O2. Add two hydrogens to the sulfur, however, and you have a hydrogen sulfide molecule, H2S, which is about the same size as an oxygen molecule, O2. The hydrogen sulfide is therefore thought work by mimicking molecular oxygen within the body. In other words, your cells will absorb hydrogen sulfide mistaking it for oxygen. But when the cell tries to use the hydrogen sulfide for oxygen, it doesn't work and the chemistry of the cell shuts down.
How do humans generate the air pollutant sulfur dioxide?
The burning of fossil fuels contributes to SO2 in the air.
What happens to the pH of water as you blow bubbles into it through a drinking straw?
The carbon dioxide in your breath reacts with the water to produce carbonic acid, which lowers the pH of the water. If you understand why rainwater is naturally acidic, you'll understand why your breath is naturally acidic as well.
When the pH of a solution is 1, the concentration of hydronium ions is 101 M 0.1 M. Assume that the volume of this solution is 500 mL. What is the pH after 500 mL of pure water is added? You will need a calculator with a logarithm function to answer this question.
The concentration of hydronium ions in the pH 1 solution is 0.1M. Doubling the volume of solution with pure water means that its concentration is cut in half. The new concentration of hydronium ions after the addition of 500 mL of water, therefore, is 0.05 M. To calculate for pH: pH log [H3O] log (0.05) (1.3) 1.3
Why do we use the pH scale to indicate the acidity of a solution rather than simply stating the concentration of hydronium ions?
The concentration of hydronium ions is typically so small it needs to be stated using scientific notation. The pH scale, therefore, is one of convenience.
What happens to the corrosive properties of an acid and a base after they neutralize each other? Why?
The corrosive properties are no longer present because the acid and base no longer exist. Instead they have chemically reacted with each other to form completely new substances—salt and water—that are not so corrosive.
Which elements have the greatest tendency to behave as oxidizing agents?
The elements in the upper right of the periodic table (except for noble gases) have the greatest tendency to behave as oxidizing agents.
What element is oxidized in the following equation and what element is reduced? I2 2Br 2I Br2
The iodine atoms, I, gain electrons and are reduced, while the bromine ions, Br, lose electrons and are oxidized.
Why aren't atmospheric levels of carbon dioxide rising as rapidly as might be expected based on the increased output of carbon dioxide resulting from human activities?
The ocean absorbs the CO2 where it is neutralized and is not re-released.
What happens to the polarity of oxygen atoms as they transform from molecular oxygen, O2, into water molecules, H2O?
The oxygen atoms become more negatively charged, which is to say they are gaining electron.
Water is 88.88 percent oxygen by mass. Oxygen is exactly what a fire needs to grow brighter and stronger. So why doesn't a fire grow brighter and stronger when water is added to it?
The oxygen is chemically bound to hydrogen atoms to make water, which is a completely different from oxygen, O2, which is what is required for combustion. Another way to phrase an answer to this question would be to say that the oxygen in water is already "reduced" in the sense that it has gained electrons from the hydrogen atoms to which it is attached. Being already reduced, this oxygen atom no longer has a great attraction for additional electrons.
When the hydronium ion concentration of a solution is 1 104 mole per liter, what is the pH of the solution? Is the solution acidic or basic?
The pH is of this solution is 4 and it is acidic.
What does the pH of a solution indicate?
The pH of a solution indicates the acidity of the solution as judged by the concentration of hydronium ions.
What is the product of the reaction between carbon dioxide and water?
The product of the reaction between CO2 and H2O is carbonic acid, H2CO3.
How might warmer oceans accelerate global warming?
The warmer the ocean, the lower the solubility of any dissolved gases such as carbon dioxide, CO2. Less CO2 would be absorbed and more of it would remain to perpetuate global warming.
Iron atoms have a greater tendency to oxidize than do copper atoms. Is this good news or bad news for a home in which much of the plumbing consists of iron and copper pipes connected together? Explain.
This is very bad news to have iron and copper pipes in contact with each other. The iron atoms will lose electrons to the copper atoms, which will pass those electrons onto oxygen atoms that are in contact with the surface.
Show that the pH of a solution is -0.301 when its hydronium ion concentration equals 2 moles per liter. Is the solution acidic or basic?
Use a calculator to find the log of 2 (it's 0.301) pH log [H3O] log (2) (0.301) 0.301 This a very acidic solution. Yes, pH can be negative!
Is water a strong acid or a weak acid?
Water is a weak acid.
As we digest and subsequently metabolize food, is the food gradually oxidized or reduced? What evidence do you have?
We exhale carbon dioxide and water vapor, which are the products of the oxidation of the food we eat.
What do we do to food molecules to obtain energy from them?
We oxidize food molecules with the oxygen we obtain from the air we breathe.
