Category: Chemistry

Osmosis vs. Diffusion 101: Definitions, Examples, and Practice Problems

Osmosis vs. diffusion is misleading as far as titles go. Both are kinds of passive transport. Passive transport is the gradual movement of molecules from one concentration to another until they are equalized, or at least that’s the shortest definition. Osmosis and diffusion are two ways to accomplish this equilibrium.

Both of these types of passive transport are meant to maintain equilibrium between things like gases, nutrients, water, and some wastes. This is the primary way cells maintain a balance between themselves and extracellular fluids. Both osmosis and diffusion cease once the concentration on both sides of a membrane, like a cell wall, are equalized.

What Exactly is O​​​​smosis?

normal osmosis

Osmosis is the movement of water, and some other liquids, across a semipermeable membrane such as a cell wall. Osmosis doesn’t require extra energy or pressure to occur. It’s one type of passive transport that allows some cells to move nutrients in or wastes out without using the body’s precious energy reserves. Osmosis moves down the concentration gradient.

Osmosis usually happens when water outside, or inside, a cell is more concentrated and helps move nutrients and wastes in and out of the cell. This is a crucial way cells are fed or grow. Osmosis isn’t just about feeding cells and helping them develop. It can occur between two compartments when the water level in one cell is higher, or a concentration of elements is suspended in water outside a cell.

In mammals, osmosis effects the number of nutrients, typically, inside or outside a cell. Through osmosis, cells maintain a steady flow of nutrients into the cavity for repairs or growth. It’s only the primary way cells get rid of wastes. In plants, osmosis is usually the only way water is absorbed from the ground and sent up the plant to feed cells. Osmosis does not work without water.

What isDiffusion?

Diffusion

Diffusion is the movement of particles from an area where the particles are dense to an area where the particles are less think. A great example of it is coffee creamer. At first, the creamer is localized to the spot where you poured it in, but after a few minutes, it invades every other part of your coffee cup. Another good example is muddy water mixing with clean water.

Diffusion typically occurs when gases or liquids are directly mixed in varying concentrations. If a membrane or other divider is removed allowing two vapors or liquids to mingle, diffusion is the result once the gas or liquid levels are balanced again. It is significant to body systems responsible for energy production.

Diffusion helps animals and plants maintain life and produce energy. When you breathe, you are using diffusion to keep oxygen flowing in and out of your body. It also helps regulate heat in animals that lack skin pores and sweat glands like dogs. it is essential to plants during their photosynthesis processes. It helps keep their upper levels watered as well.

Osmosis vs. Diffusion Methods

Thermodynamics

During Osmosis, water molecules pass freely through any semipermeable membrane. This process is spontaneous in both directions until the water concentration on both sides of the layer are equal. The sole purpose of osmosis in cells is to facilitate the movement of nutrients and wastes from outside to inside cells. It regulates the cells hydration during the process as a byproduct.

Anytime the area around the outside of a cell, or a neighboring cell, has a higher concentration of water, osmosis will spontaneously occur until the concentration of water matches on both sides of the cell wall membrane. The same is true if there is more water inside the cell than outside. Osmosis only occurs in the presence of water.

Osmosis also causes cells to swell or deflate based on the amount of water inside or outside the cell. If more water resides outside the cell wall, the cell loses water and tends to shrink. The opposite occurs if more water is outside the cell walls. If the concentration of water remains the same inside and outside, the cell stays the same size and osmosis does not happen. Osmosis always occurs from the lowest to the highest level.

Diffusion is spontaneous just like osmosis but does not require a membrane to pass through. Particles or molecules spread from high concentration areas to low concentration areas. Diffusion creates entropy because it’s random. There’s no measured transfer; it just happens until everything is mixed well. The mixtures that diffuse do become diluted in the process.

Diffusion follows the Second Law of Thermodynamics because it results in a less concentrated area of energy when it completes. It is the nature of diffusion to introduce randomness and reduce concentrations. It’s the process that allows us to breathe in oxygen and exhale carbon dioxide. The level of oxygen in the air outside our body is higher than it is in our lungs. Diffusion lets us equalize the two.

Osmosis plays a prominent role in the distribution of nutrients and wastes in plants and animals. It helps cells function by supplying them with water and nutrients while removing metabolic wastes from inside the cell. In plants, it takes on additional roles to help the plants get water and nutrients from the soil and move them up the plant.

Diffusion can happen through a semipermeable membrane just like osmosis, but it doesn’t require one to work. While osmosis primarily helps cells move nutrients and wastes around, diffusion helps other particles and molecules such as gases pass through cell walls. Both osmosis and diffusion are necessary to continue life.

The Different Types of Osmosis and Diffusion

types of osmosis

There are only two types of true osmosis, forward osmosis and reverse osmosis. Forward osmosis forces lower concentrated particles to move into higher concentrated areas. This is the primary version of osmosis used to filter things like water in nature. Where regular, or reverse, osmosis tends to push particles around, forward osmosis pulls them in. Forward and reverse osmosis are easy to get confused.

Reverse osmosis works off osmotic pressure. When the concentration of water outside, or inside, a membrane reaches a higher level than its neighbor, osmosis is triggered. If osmosis is possible, it usually prevents diffusion from taking place at the same time. Thus, reverse osmosis can be affected by volumetric and atmospheric pressure to force fluids through a membrane to create a forced filtering process.

There are several different types of diffusion:

  • Self-diffusion: measures how much diffusion will occur even with a chemical is at a neutral state.
  • Reverse diffusion: very similar to forward osmosis but relates to more particles such as gases.
  • Photon diffusion: the movement of light through an object and how the object scatters the light.
  • Momentum diffusion: the spread of liquids, mostly, based on the thickness of the liquid. Thicker liquids create higher momentum diffusion.
  • Gaseous diffusion: mainly used to enrich uranium for nuclear reactors and weapons.
  • Knudsen diffusion: a measure of how a particle reacts to a membrane based on the size of the membrane’s pores and the size of the particle.
  • Facilitated diffusion: the spontaneous movement of molecules through a cell membrane at times when osmosis and other forms of diffusion are inhibited.
  • Electron diffusion: the movement of electrons to create an electric current.
  • Effusion: occurs when a gas is filtered through small holes.
  • Surface diffusion: occurs when a dry, powdery substance falls onto the surface of a liquid.
  • Collective diffusion: the diffusion of large quantities of particles within a substance that aid each other in moving about the material.
  • Osmosis: actually just another form of diffusion.

Examples of Diffusion

example of diffusion

Diffusion happens all around and inside us all the time. If you drink tea or coffee, when you add sugar or creamer to them it diffuses until the whole cup is sweeter or creamier. The aroma from air fresheners or cooking food diffuses in the air and invades every room it can reach in your home. These are great examples of passive diffusion since no energy is needed to accomplish diffusion this way.

Plants and animals use diffusion to breathe. Animals draw air into their lungs where it diffuses with the air already in their lungs. This is how we get oxygen into our lungs, and it’s how we get rid of respiratory wastes like carbon dioxide. Carbon dioxide entering a plant’s stomata or oxygen leaving their stomata is how a plant uses diffusion to breathe.

Examples of Osmosis

example of osmosis

Probably one of the best examples of osmosis is water and nutrients entering a plant’s roots from the soil. Animals use osmosis in a similar way except we absorb nutrients and water throughout our digestive system. Unlike plants, animals eat or drink water and nutrients before they consume them for use by cells to grow and repair themselves.

Some Final Notes

The biggest differences between osmosis and diffusion are how plants and animals use these processes to sustain life. Most kinds of diffusion are similar, and osmosis is technically just another form of diffusion. We use diffusion and osmosis all the time, and most people don’t realize it. It occurs naturally, and it’s manufactured, but it’s necessary for life to exist.

Significant Figures Worksheet(Sig Figs): Definition, Examples, and Practice

Meta: Whether you’re relatively new to significant figures or are just looking for a refresher, you’ve come to the right place. Read on to learn more!

Significant Figures (Sig Figs): Definition, Examples, and Practice

Significant figures are a vital concept when you’re working in any field that requires precision; chemistry, for example. And while it feels like a complex subject, it’s fairly simple and straightforward. In this article, we’re answering your questions about significant figures and prepping you for significant figures worksheets with lots of examples.

Reason for Significant Figures

numbers and symbols

We can all agree that there’s nothing worse than complicated mathematics concepts that don’t seem to have anything to do with real life. Fortunately, that’s not the case with significant figures! The primary purpose for this somewhat abstract concept is precision.

The numbers we use in everyday life, as it turns, are not that precise. When you’re working in specialized fields, however, the precision of the data is everything. Significant figures help you communicate how precisely you’ve measured and help to ensure mistakes are made with the data.

Let’s Build a Tower

tower

Here’s an example: let’s say you’re building a tower. As you might imagine, precision matters hugely. You don’t want to get to the top of the tower only to realize your tower is taller–or shorter!–than you thought. Let’s say, then, that the steel manufacturer has measured its vertical beams to the nearest centimeter and is sending you three beams that are each 20.5 meters tall.

This measurement is precise to the centimeter, but the number doesn’t tell you anything about millimeters. This is a problem because the glass you’re cutting to cover the building in is measured to the nearest millimeter; in fact, the glass company is sending the glass to you in 15.75-meter sheets.

You know that your steel beams will stand end to end and that your finished tower will be (20.5*3) meters tall, or 61.5 meters tall. Three glass sheets will be 47.25 meters tall; too short. Four glass sheets will be 63 meters tall; too tall. You’ll need to lay three sheets of glass and cut the fourth to size. Now you need to figure out how much you should cut down that fourth sheet of glass.

The Problem With Imprecision

ruler

Here’s the problem: your steel is measured to the centimeter, but the glass cutter cuts to the millimeter. Each steel beam is 20.5 meters, which means it’s twenty meters and five centimeters; but how many millimeters is it?

We don’t know. It could be three millimeters (20.53 meters), or it could be seven millimeters (20.57 meters). Let’s say it’s the latter, and your three steel beams each have an extra seven millimeters that you don’t know about because they’ve only been measured to the nearest centimeter.

You think you’ve only got 61.5 meters of a tower (because 20.5*3 = 61.5) but you have 61.71 meters (because 20.57*3 = 61.71). That’s a difference of .21 meters, or a whopping two centimeters and one millimeter! If you cut your glass to 61.5 meters, you’ll get to the top of the tower to install it–only to realize you’re missing two centimeters and a millimeter of glass.

Oops!

This is an oversimplified example, but it helps to illustrate how important precision is–and now you know how significant figures work, even if you don’t know the concept by that name yet. That’s for the next section!

Rules for Significant Figures

The first thing you should remember is that significance doesn’t indicate whether a number is computed or not; it simply indicates the precision of measurement. We’ll explain; let’s start with the basic ground rules about significant figures, and then we’ll practice with some examples you might see on a significant figures worksheet:

  1. If it’s not a zero, the number is a significant figure (e.g., 1, 2, 3, 4, 5, 6, 7, 8, and 9 are all significant no matter where they are in the number)
  2. If a zero is between a non-zero digit, it is significant (e.g., the zeros in these numbers are significant: 507, 5007, 5000.07)
  3. Trailing zeros (the zeros at the end of a number) are only significant if the number has a decimal point (e.g., 5.0500 or 5.50); they are not significant if there are no decimal points (e.g., 500 or 50) (special note: in the latter case, significance can be indicated with a bar above or below the last measured figure)
  4. Leading zeros (zeros before non-zeros) are never significant (e.g., 005 or 0.005)

EXAMPLES

  • 51 has two significant figures (5 and 1; all numbers are non-zeros)
  • 1234.56 has six significant figures (1, 2, 3, 4, 5 and 6; all numbers are non-zeros)
  • 505.5505 has seven significant figures (5, 5, 0, 5, 5, 0, and 5; all non-zeros are significant, and all zeros between non-zeros are significant)
  • 0.0057 has two significant figures (5 and 7; the zeros are leading and are not significant)
  • 500 and 50 each have one significant figure (5 and 5; trailing zeros are not significant unless there is a decimal point)
  • 5.0500 has five significant figures (5, 0, 5, 0, and 0; the first zero is between two non-zeros and the trailing zeros are significant because the number contains a decimal)
  • 0.00050500 has five significant figures also (remember that leading zeros do not count)
  • 1300 has two significant figures (one and three) while 1300. has four significant figures (1, 3, 0, and 0) because the latter number has a decimal point

Multiplying, Dividing, Adding, and Subtracting with Significant Figures

Before we get into the mechanics of multiplying, dividing, adding, and subtracting with significant figures, you’ll first need to know how to round up significant figures. For example, if you have a number (let’s say 54.896) that has five significant figures, and you need to round it up to three significant figures, how do you do that?

Rounding Up

Here’s how:

  1. Identify the significant figures (in our example, there are five significant numbers: 5, 4, 8, 9, and 6)
  2. Identify the last of the desired significant figures (we know we need three significant figures, so eight, the third significant figure from the left, is the last significant figure)
  3. Look at the number to the right of the significant figure. If it is five or greater, add one to the last significant figure (in our example, eight is followed by nine; nine is greater than 5; therefore, eight is rounded up by 1 to 9 so that our new number is 54.9). If, however, the number is four or less, simply remove all the remaining numbers to the left (don’t replace them with zeros)

Here’s another example using 0.01234500:

If you want to round it to three significant figures, the answer would be 0.0123 (leading zeros are not significant; 4 is less than five, so 4 and all subsequent numbers are removed).

Special note: rounding significant figures is different than rounding decimals. For example, if you wanted to round our example number to three decimal places, the answer would be .012, which is a different number altogether from a precision standpoint.

Multiplying and Dividing

When you begin working seriously with multiplying and dividing, you’ll notice how quickly things can move from precise to imprecise. For example, let’s go back to our tower example and say we want to measure the area of our glass sheets. They are 15.75 meters tall and 2.5 meters wide.

A simple calculation (15.75*2.5=39.375) tells us the area is 39.375, but if you’re thinking, “wait! That measurement is more precise than what we measured!” you’d be right. To keep our quotients and products as precise as our initial measurements, we need to round up (or down).

The general rule is that the significant figures in the answer cannot be more than the smallest amount of significant figures used in the equation. In our glass sheets example, the two numbers we multiplied are 15.75 (which has four significant figures) and 2.5 (which has two significant figures). The smallest number of significant figures in either of these factors is two, so our answer can’t have more than two significant figures.

 

Our answer (39.375) has five significant figures, with 9 being the second significant figure. The number to the right of 9 is 3, which is less than 5, so we simply discard 3 and everything to its right. Our answer, then, is 40. (9 rolls to the 0 and the 3 becomes a 4; also note the use of the decimal!).

Adding and Subtracting

Adding and subtracting numbers with different amounts of significant digits is very similar to multiplying and dividing, except that the rounding up (or down) happens before the calculation.

Back to our tower example, let’s say you had one steel beam that was 20.5 meters and one that was 20.45 meters, you are dealing with two different levels of precision. The first beam has three significant figures and is less precise than the second beam, which has four significant figures.

If you add them together as is, it’s just messy. So, you need to round up the more precise number so that it matches the least precise number. That is, you would round up 20.45 to 20.5 and add both numbers (20.5 + 20.5 = 41.0; note that the answer is also precise to three significant figures).

Hopefully, significant figures are no longer mystifying, and you’re ready to tackle your significant figures worksheet; good luck!

Chemistry & Water

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Chemistry & Water
 

Multiple Choice
Identify the choice that best completes the statement or answers the question.
 1.
Which of these is an example of an organelle?
a.
chloroplast
b.
muscle
c.
epidermis
d.
intestine
e.
maple leaf
 2.
Which of these is a correct representation of the hierarchy of biological organization from least to most complex?
a.
organelle of a stomach cell, digestive system, large intestine, small intestine, intestinal tissue, organism
b.
organelle of an intestinal cell, digestive system, small intestine, large intestine, intestinal tissue, organism
c.
molecule, intestinal cell organelle, intestinal cell, intestinal tissue, digestive system, organism
d.
molecule, small intestine, large intestine, intestinal tissue, digestive system, organism
e.
molecule, digestive system, digestive cell organelle, small intestine, large intestine, intestinal cell, organism
 3.
As a result of photosynthesis, plants release ____ into the atmosphere.
a.
methane
b.
carbon dioxide
c.
water
d.
minerals
e.
oxygen
 4.
Which of the following types of cells utilize deoxyribonucleic acid (DNA) as their genetic material?
a.
animal
b.
plant
c.
archaea
d.
A and B only
e.
A, B, and C
 5.
There are approximately ____ identified and named species.
a.
1,800
b.
180,000
c.
1,800,000
d.
18,000,000
e.
180,000,000
 6.
Prokaryotic and eukaryotic cells generally have which of the following features in common?
a.
a membrane-bounded nucleus
b.
a cell wall made of cellulose
c.
ribosomes
d.
flagella or cilia that contain microtubules
e.
linear chromosomes made of DNA and protein
 7.
Which of the following are characteristics shared by members of both domain Bacteria and domain Archaea?
a.
cytosol
b.
nucleus
c.
DNA
d.
A and C only
e.
A, B, and C
 8.
Two species belonging to the same genus must also belong to the same
a.
kingdom.
b.
phylum.
c.
class.
d.
order.
e.
all of the above
 9.
Which of the following is (are) true of natural selection?
a.
requires genetic variation
b.
results in descent with modification
c.
involves differential reproductive success
d.
B and C only
e.
A, B, and C
 10.
Which of these individuals is most likely to be successful in an evolutionary sense?
a.
a reproductively sterile individual who never falls ill
b.
an organism that dies after 5 days of life but leaves 10 offspring, all of whom survive to reproduce
c.
a male who mates with 20 females and fathers 1 offspring
d.
an organism that lives 100 years and leaves 2 offspring, both of whom survive to reproduce
e.
a female who mates with 20 males and produces 1 offspring
 11.
In a hypothetical world, every 50 years people over 6 feet tall are eliminated from the population. Based on your knowledge of natural selection, you would predict that the average height of the human population will
a.
remain unchanged.
b.
gradually decline.
c.
rapidly decline.
d.
gradually increase.
e.
rapidly increase.
 12.
The statement “If you show your dog affection, then your dog will seek your company” is an example of
a.
a statement that can be tested.
b.
a statement derived from a hypothesis.
c.
a prediction.
d.
deductive reasoning.
e.
all of the above
 13.
Which of the following is not a theme that unifies biology?
a.
interaction with the environment
b.
emergent properties
c.
evolution
d.
reductionism
e.
structure and function
 14.
Calcium has an atomic number of 20 and an atomic mass of 40. Therefore, a calcium atom must have
a.
20 protons.
b.
40 electrons.
c.
40 neutrons.
d.
A and B only
e.
A, B, and C
 15.
The atomic number of carbon is 6. Carbon-14 is heavier than carbon-12 because the atomic nucleus of carbon-14 contains ____ neutrons.
a.
6
b.
7
c.
8
d.
12
e.
14
 16.
Electrons exist only at fixed levels of potential energy. However, if an atom absorbs sufficient energy, a possible result is that
a.
an electron may move to an electron shell farther out from the nucleus.
b.
an electron may move to an electron shell closer to the nucleus.
c.
the atom may become a radioactive isotope.
d.
the atom would become a positively charged ion, or cation.
e.
the atom would become a negatively charged ion, or anion.

Use the figure below to answer the following questions.

nar001-1.jpg

 17.
Which drawing depicts the electron configuration of nitrogen (N)?
a.
Drawing A
b.
Drawing B
c.
Drawing C
d.
Drawing D
e.
Drawing E
 18.
What does the reactivity of an atom depend on?
a.
number of valence shells in the atom
b.
number of orbitals found in the atom
c.
number of electrons in each orbital in the atom
d.
presence of unpaired electrons in the outer valence shell of the atom
e.
presence of hybridized orbitals in the atom

Use the information extracted from the periodic table in the figure below to answer the following questions.

nar002-1.jpg

 19.
How many electrons does phosphorus have in its valence shell?
a.
1
b.
2
c.
3
d.
4
e.
5
 20.
Nitrogen (N) is much more electronegative than hydrogen (H). Which of the following statements is correct about the atoms in ammonia (NH3)?
a.
Each hydrogen atom has a partial positive charge.
b.
The nitrogen atom has a strong positive charge.
c.
Each hydrogen atom has a slight negative charge.
d.
The nitrogen atom has a partial positive charge.
e.
There are covalent bonds between the hydrogen atoms.
 21.
What do the four elements most abundant in life-carbon, oxygen, hydrogen, and nitrogen-have in common?
a.
They all have the same number of valence electrons.
b.
Each element exists in only one isotopic form.
c.
They are equal in electronegativity.
d.
They are elements produced only by living cells.
e.
They all have unpaired electrons in their valence shells.

Use the figure below to answer the following questions. .

nar003-1.jpg

 22.
What results from the chemical reaction?
a.
a cation with a net charge of +1
b.
a cation with a net charge of -1
c.
an anion with a net charge of +1
d.
an anion with a net charge of -1
e.
A and D
 23.
The atomic number of chlorine is 17. The atomic number of magnesium is 12. What is the formula for magnesium chloride?
a.
MgCl
b.
MgCl2
c.
Mg2Cl
d.
Mg2Cl2
e.
MgCl3
 24.
Explains most specifically the attraction of water molecules to one another.
a.
nonpolar covalent bond
b.
polar covalent bond
c.
ionic bond
d.
hydrogen bond
e.
hydrophobic interaction
 25.
In a single molecule of water, the two hydrogen atoms are bonded to a single oxygen atom by
a.
hydrogen bonds.
b.
nonpolar covalent bonds.
c.
polar covalent bonds.
d.
ionic bonds.
e.
van der Waals interactions.
 26.
Which bonds must be broken for water to vaporize?
a.
ionic bonds
b.
nonpolar covalent bonds
c.
polar covalent bonds
d.
hydrogen bonds
e.
covalent bonds
 27.
The formation of ice during colder weather helps moderate the seasonal transition to winter. This is mainly because
a.
the breaking of hydrogen bonds absorbs heat.
b.
the formation of hydrogen bonds releases heat.
c.
the formation of hydrogen bonds absorbs heat.
d.
there is greater evaporative cooling of lakes.
e.
ice is denser than liquid water.
 28.
Recall that when sodium chloride (NaCl) is placed in water the component atoms of the NaCl crystal dissociate into individual sodium ions (Na+) and chloride ions (Cl-). In contrast, the atoms of covalently bonded molecules (e.g, glucose, sucrose, glycerol) do not generally dissociate when placed in aqueous solution. Which of the following solutions would be expected to contain the greatest concentration of particles (molecules or ions)?
a.
0.5 M NaCl
b.
0.5 M glucose
c.
1.0 M NaCl
d.
1.0 M glucose
e.
1.0 M MgCl2

Use the figure below to answer the following questions:

nar004-1.jpg

 29.
How many grams of the molecule in the figure above would be required to make 1 L of a 0.5 M solution of the molecule?
(Carbon = 12, Oxygen = 16, Hydrogen = 1)
a.
29
b.
30
c.
60
d.
150
e.
342
 30.
Which of the following ionizes completely in solution and is considered to be a strong acid?
a.
NaOH
b.
HCl
c.
NH3
d.
H2CO3
e.
CH3COOH
 31.
Which of the following statements is completely correct?
a.
H2CO3 is a weak acid, and NaOH is a weak base.
b.
H2CO3 is a strong acid, and NaOH is a strong base.
c.
NH3 is a weak base, and H2CO3 is a strong acid.
d.
NH3 is a weak base, and HCl is a strong acid.
e.
NH3 is a strong base, and HCl is a weak acid.
 32.
Buffers are substances that help resist shifts in pH by
a.
releasing H+ in acidic solutions.
b.
donating H+ to a solution when they have been depleted.
c.
releasing OH- in basic solutions.
d.
accepting H+ when the are in excess.
e.
both B and D
 33.

One of the buffers that contribute to pH stability in human blood is carbonic acid (H2CO3) Carbonic acid is a weak acid that dissociates into a bicarbonate ion (HCO3-) and a hydrogen ion (H+) Thus,

H2CO3 HCO3- + H+

If the pH of the blood drops, one would expect

a.
a decrease in the concentration of H2CO3 and an increase in the concentration of HCO3-.
b.
the concentration of hydroxide ion (OH-) to increase.
c.
the concentration of bicarbonate ion (HCO3-) to increase.
d.
the HCO3- to act as a base and remove excess H+ with the formation of H2CO3.
e.
the HCO3- to act as an acid and remove excess H+ with the formation of H2CO3.

 

         Start Over

Introduction and Chemistry

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Introduction and Chemistry
 

True/False
Indicate whether the statement is true or false.
 1.
The study of biology can help you better understand human reproduction.
 2.
Almost all organisms ultimately get their energy for survival from the sun.
 3.
All living things are composed of chemicals.
      nar001-1.jpg      nar001-2.jpg
 4.
Refer to the illustration above. Both species are multicellular.
 5.
Refer to the illustration above. Both species have DNA in their cells.
 6.
Refer to the illustration above. Reproduction ensures the ongoing success of both species.
 7.
Refer to the illustration above. The sand dollar and paramecium both show organization.
 8.
Refer to the illustration above. Unlike the sand dollar, the paramecium does not have to maintain a stable internal environment.
 9.
Scientists have not discovered any new species on Earth in more than 20 years.
 10.
A scientist who performs an experiment has no idea what the outcome of the experiment is going to be.
 11.
A theory is a hypothesis that has been proven true.
 12.
A theory is an assumption made by scientists and implies a lack of certainty.
 13.
Publication of the results of scientific investigations enables other scientists to verify these results.
 14.
Scientific investigations always follow a series of rigidly defined steps.
 15.
Resolution is a microscope’s power to increase an object’s apparent size.
 16.
The resolution power of an electron microscope is limited by the physical characteristics of light.
 17.
Units of time are not measured in metric units, so time measurements are not accepted for use with SI units.
 18.
The types of particles that are located in the nucleus of an atom are protons and neutrons, and the types of particles that are located in the energy levels surrounding the nucleus are electrons.
 19.
The atomic number of carbon is 6, so it must contain 12 electrons.
 20.
Most elements are stable if their outermost energy level contains an even number of electrons.
 21.
Atoms in a gas move more rapidly than atoms in a liquid or a solid do.
 22.
The products of an endergonic chemical reaction possess more energy than the reactants from which they are produced.
 23.
The amount of energy needed to cause a chemical reaction to start is called activation energy.
 24.
When an enzyme binds with its substrate, the activation energy needed for the chemical reaction to occur is raised.
 25.
Enzymes speed up a chemical reaction by increasing the activation energy of the reaction.
 26.
Without enzymes, chemical reactions necessary for life would not occur at a rate sufficient to sustain life.
 27.
Free hydrogen ions can react with water molecules and form a positively charged ion, the hydronium ion.
 28.
Bases tend to have a sour taste, while acids tend to have a bitter taste.
 29.
Buffers can neutralize acids, but they do not affect bases.
 

Multiple Choice
Identify the choice that best completes the statement or answers the question.
 30.
Biology is the study of
a.
minerals.
c.
the weather.
b.
life.
d.
energy.
 31.
Instructions for development that are passed from parents to offspring are known as
a.
a species plan.
c.
genes.
b.
organ codes.
d.
natural selections.
 32.
Homeostasis means
a.
a change over long periods of time.
c.
rapid change.
b.
keeping things the same.
d.
the same thing as evolution.
 33.
Which of the following is a means by which heterotrophs can obtain energy?
a.
using water, carbon dioxide, and energy from the sun to produce sugars
b.
using water and carbon dioxide to produce energy-rich compounds
c.
consuming autotrophs
d.
consuming simple chemicals from the environment and using them to assemble complex chemicals and structures needed by the organism
 34.
Which of the following is not necessarily a distinct property of living things?
a.
homeostasis
c.
complexity
b.
metabolism
d.
reproduction
 35.
All organisms are composed of
a.
diatoms.
c.
cells.
b.
cellulose.
d.
None of the above
 36.
Scientific hypotheses are most often tested by the process of
a.
communicating.
c.
experimenting.
b.
inferring.
d.
analyzing data.
 37.
A unifying explanation for a broad range of observations is a
a.
hypothesis.
c.
prediction.
b.
theory.
d.
controlled experiment.
 38.
Most typically, the order in which the steps of the scientific method are applied is
a.
observations, predictions, hypothesis, controlled testing, theory, verification.
b.
predictions, observations, hypothesis, theory, controlled testing, verification.
c.
observations, hypothesis, predictions, controlled testing, theory, verification.
d.
observations, hypothesis, predictions, controlled testing, verification, theory.
 39.
Atoms are composed of
a.
protons with a positive charge.
c.
electrons with a negative charge.
b.
neutrons with no charge.
d.
All of the above
 40.
Which of the following states of matter contain(s) particles that are tightly linked together in a definite shape?
a.
solid
c.
gas
b.
liquid
d.
solid and liquid
 41.
The bond formed when two atoms share a pair of electrons is called a
a.
hydrogen bond.
c.
covalent bond.
b.
nonpolar bond.
d.
water bond.
 42.
An atom that has gained or lost electrons is called a(n)
a.
molecule.
c.
ion.
b.
nucleon.
d.
element.
 43.
Which of the following statements most accurately describes the difference between an ionic bond and a covalent bond?
a.
Atoms held together by ionic bonds separate when placed in water while atoms held together by covalent bonds do not separate in water.
b.
Ionic bonds hold together atoms of two different types, while covalent bonds hold together atoms of the same type.
c.
Electrons are exchanged between atoms held together by an ionic bond, but they are shared between atoms held together by a covalent bond.
d.
Ionic bonds form between atoms that carry opposite charges, while covalent bonds form between uncharged atoms.
 44.
A reaction in which the products have less energy than the reactants is
a.
an endergonic reaction.
c.
a filamentous reaction.
b.
an exergonic reaction.
d.
impossible.
nar002-1.jpg
 45.
Refer to the graph above. Which of these statements is true regarding the graph?
a.
Reaction “2” occurs faster than Reaction “3” because Reaction “2” requires more energy than Reaction “3.”
b.
The difference in the graphs shown for Reaction “2” and Reaction “3” is due to a difference in the activation energy needed for these reactions.
c.
Reactant “A” contains more energy at the beginning of the reaction than Product “C” has after the reaction.
d.
All of the above
nar003-1.jpg
 46.
Refer to the graphs above. Which graph illustrates what happens during an exergonic reaction?
a.
Graph “A”
b.
Graph “B”
c.
Both graphs; they each show a different stage of an exergonic reaction.
d.
Neither graph shows an exergonic reaction.
 47.
Refer to the graphs above. Which graph illustrates a reaction during which reaction energy is released into the environment?
a.
Graph “A”
b.
Graph “B”
c.
Both graphs, since all chemical reactions release energy into the environment
d.
Neither graph, since chemical reactions do not involve energy
 48.
Enzymes
a.
are able to heat up molecules so that they can react.
b.
provide CO2 for chemical reactions.
c.
are biological catalysts.
d.
absorb excess heat so that reactions occur at low temperatures.
 49.
A neutral solution has an equal number of
a.
hydrogen and hydronium ions.
c.
hydrogen and hydroxide ions.
b.
hydroxide and hydronium ions.
d.
oxygen and hydrogen ions.
 50.
Buffers
a.
are of relatively little importance in living things.
b.
are formed when a large number of hydroxide ions are released in a solution.
c.
are formed when a large number of hydronium ions are released in a solution.
d.
tend to prevent great fluctuations in pH.

 

         Start Over

Chemistry Quiz

%CODE1%

Name: 

Chemistry

 

True/False
Indicate whether the sentence or statement is true or false.
1.
Two atoms having the same number of protons and electrons but different numbers of neutrons are called isotopes.
2.
The nucleus of an atom contains protons and electrons.
3.
A compound consists of atoms of two or more elements joined by chemical bonds.
4.
Energy can be converted from one form to another.
5.
The scale used for measuring the relative concentrations of hydrogen   ions and hydroxide ions in a solution is called the pH scale.
6.
Iron atoms and silver atoms have the same number of protons.
7.
An atom containing nine electrons can have three in its first energy level.
8.
Stable atoms need electrons to fill their outer energy levels.
9.
The types of particles that are located in the nucleus of an atom are protons and neutrons, and the types of particles that are located in the energy levels surrounding the nucleus are electrons.
10.
Buffers can neutralize acids, but they do not affect bases.
 

Multiple Choice
Identify the letter of the choice that best completes the statement or answers the question.
11.
A solution that contains equal concentrations of hydrogen ions and hydroxide ions is a(n):
a.
neutral solution
c.
base
b.
acid
d.
compound
12.
The type of bond formed when two atoms share electrons is a(n):
a.
covalent bond
c.
elemental bond
b.
ionic bond
d.
homogeneous bond
13.
Carbon has an atomic number of 6. The number of energy levels in carbon is:
a.
1
c.
3
b.
2
d.
6
14.
In most elements, how many electrons are in the outer energy level of stable atoms?
a.
3
c.
8
b.
5
d.
12
15.
A solution with a pH of 9 has:
a.
an equal concentration of hydrogen and hydroxide ions
b.
a greater concentration of hydroxide ions than hydrogen ions
c.
a greater concentration of hydrogen ions than hydroxide ions
d.
a greater concentration of hydroxide ions than a solution with a pH of 10
16.
Carbon 12 and carbon 14 have the same number of protons and electrons, but they differ in the number of neutrons.  Therefore, they are:
a.
isometric
c.
icicles
b.
isotopes
d.
two different elements
17.
How many protons are in an atom that has a mass number of 23 and an atomic number of 11?
a.
11
c.
23
b.
12
d.
34
18.
Which of the following is matter?
a.
oxygen
c.
heat
b.
light
d.
all of these
19.
The subscript ‘2’ in H2 represents the number of:
a.
electrons
c.
ions
b.
molecules
d.
atoms
20.
The smallest unit of a compound that still retains the compound’s unique chemical properties is the:
a.
sol
c.
atom
b.
bond
d.
molecule
21.
Which of the following best describes a compound?
a.
atoms of one element that are chemically combined
b.
two or more elements combined chemically in a definite proportion
c.
atoms of the same element that have different mass numbers
d.
two or more atoms that are not combined chemically
22.
In a covalent bond, electrons are:
a.
shared
c.
lost
b.
gained
d.
transferred
23.
Which of the following pH values represents the most acidic condition?
a.
3
c.
10
b.
6
d.
14
24.
The main difference between covalent bonds and ionic bonds is that electrons:
a.
are shared in covalent bonds, but not in ionic bonds
b.
are shared in ionic bonds, but not in covalent bonds
c.
are shared in both, but at different times
d.
are involved only in covalent bonds
25.
Which of the following is the most common solvent in organisms?
a.
alcohol
c.
water
b.
lipids
d.
amino acids
26.
The bond formed when two atoms share a pair of electrons is called a
a.
hydrogen bond.
c.
covalent bond.
b.
nonpolar bond.
d.
water bond.
27.
The smallest particle of matter that can retain the chemical properties of carbon is
a.
a carbon molecule.
c.
a carbon atom.
b.
a carbon macromolecule.
d.
an element.
28.
All matter in the universe is composed of
a.
cells.
c.
atoms.
b.
molecules.
d.
carbon.
29.
Which of the following statements most accurately describes the difference between an ionic bond and a covalent bond?
a.
Atoms held together by ionic bonds separate when placed in water while atoms held together by covalent bonds do not separate in water.
b.
Ionic bonds hold together atoms of two different types, while covalent bonds hold together atoms of the same type.
c.
Electrons are exchanged between atoms held together by an ionic bond, but they are shared between atoms held together by a covalent bond.
d.
Ionic bonds form between atoms that carry opposite charges, while covalent bonds form between uncharged atoms.
      chp2_files/i0320000.jpg
30.
Refer to the graph above. Reaction “3” in the graph
a.
probably occurred in the presence of a catalyst.
b.
requires a greater activation energy than Reaction “2.”
c.
is the same as Reaction “1,” but faster.
d.
takes longer than Reaction “2.”
31.
Changing the course or pathway of a chemical reaction so that it requires less activation energy
a.
is a violation of the laws of nature.
b.
requires higher temperatures than those found within cells.
c.
occurs only when reactants are quickly added to the reaction mixture.
d.
is accomplished by the action of catalysts on reactants.
32.
A cell contains
a.
thousands of different kinds of enzymes, each promoting a different chemical reaction.
b.
one kind of enzyme that promotes thousands of different chemical reactions.
c.
approximately 100 kinds of enzymes, each promoting a different chemical reaction.
d.
one enzyme that promotes photosynthesis and one enzyme that promotes cellular respiration.
33.
The terms base and alkaline refer to solutions that
a.
contain dissolved sodium hydroxide.
b.
contain more hydronium ions than hydroxide ions.
c.
contain more hydroxide ions than hydronium ions.
d.
contain more hydroxide ions than hydrogen ions.
34.
Acidic solutions have a pH that is
a.
less than 7.
c.
a negative number.
b.
between 0 and 14.
d.
more than 7.
35.
Buffers
a.
are of relatively little importance in living things.
b.
are formed when a large number of hydroxide ions are released in a solution.
c.
are formed when a large number of hydronium ions are released in a solution.
d.
tend to prevent great fluctuations in pH.

 

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