teas science 21 - chemistry - nurse cheung · 2019. 2. 24. · 2/21/19 1 ati teas science review...

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ATI TEAS SCIENCE REVIEW

CHEMISTRY

ATI TEAS SCIENCE – CHEMISTRY

Questions related to chemistry test your knowledge of chemicalproperties and processes. You may be asked questions about states ofmatter, properties of matter, phase changes, chemical bonds, chemicalsolutions, chemical reactions, and acids and bases. You may be asked tobalance chemical equations.

Let’s get started in understanding how chemistry is important on theATI TEAS.


UNDERSTANDING STATES OF MATTER

Matter is made up of microscopic particles that move different speedsdepending on the energy they are exposed to. We measure this energy

as temperature. The molecules can move either quickly and randomlyor hardly at all.

When the energy is high, matter take the form of a gas, in which

molecules are moving about quickly and are far apart. Gases have nofixed form. Molecules are free to move at random past each other, andthey tend to fill any container that holds them. If a gas is not contained,its molecules will disperse.

PHOTO CREDIT: LIVE SCIENCE


UNDERSTANDING STATES OF MATTER

Lower temperatures result in a liquid, in which molecules cohere butare fluid. Coherence means that the molecules remain close together,but they can change position by sliding over one another. In liquids,molecules move less freely than in a gaseous state, sliding past oneanother. They have a fixed volume but will flow freely unless they fill aportion of a container.

When the temperature is low, matter takes the form of a solid, in whichmolecules are packed closely together and retain their positions. Solidmatter is rigid, and molecules retain a uniform spacing. A solid has adefined form, which is brittle. It can be broken into pieces but tends tostay together.

A somewhat unusual state of matter is plasma, which is like a gas inmany of its properties but carries an electric charge.

The TEAS focus on solids, liquids, and gases.

PHOTO CREDIT: LIVE SCIENCE


UNDERSTANDING CHANGES IN STATE OF MATTER

The state of matter depends on temperature and pressure. Highertemperatures cause molecules to energize and move farther apart.Increasing pressure forces molecules closer together. Melting is thephase change from solid to liquid and boiling is the phase change fromliquid to gas. There is also a direct change from solid to gas known assublimation. The phase change from gas to liquid is condensation andthe change from liquid to solid is freezing. A direct change from gas tosolid is deposition.

PHOTO CREDIT: VECTORSTOCK


UNDERSTANDING PROPERTIES OF MATTER

All types of matter can be described in terms of the physicaland chemical properties each substance has. Physicalproperties are observable and there is an extensive list ofphysical properties that one could observe about a substance.A few examples are density, the temperatures at which the

substance undergoes phase changes, malleability,conductivity, specific heat capacity, mass, volume, color, andmany other properties. Physical properties are further divided

into intensive and extensive properties. An intensive propertydoes not depend on the size or amount of matter in theobject, while an extensive property does depend on theamount of matter in the object. For example, mass is

extensive because the measurement would change the size ofthe sample. Boiling point is intensive because thetemperature at which the object boils is not dependent on its

volume.

PHOTO CREDIT: THOUGHTCO

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Water is a polar inorganic compound that is transparent andnearly colorless. H2O is a covalent compound because oxygenand hydrogen are nonmetals. It has 8 total valence electrons(6 from oxygen and 1 from each hydrogen). Breaking thebonds requires a lot of energy, so water has a very highspecific heat and heat of vaporization. The molar mass ofwater is 18.02 g/mol. It commonly exists as solid, liquid, andgas.

PHOTO CREDIT: SLIDESHARE



The polarity of water allows it to exhibit both cohesive andadhesive properties. Cohesiveness allows water to travelthrough tiny capillaries and creates surface tension on thesurface of a body of water. Adhesiveness allows water to stickto other molecules and dissolve them, making it known as the“universal solvent.”

PHOTO CREDIT: BIONINJA



Water also has a unique property called osmosis, which is aspecific type of diffusion. Diffusion is a term used to describethe process of a substance moving from an area of highconcentration to an area of low concentration. Osmosis is atype of diffusion in which water moves passively through asemi-permeable membrane to equalize water concentrationon both sides of the membrane. This is how water movesthrough cell walls in the body. PHOTO CREDIT: BYJU


UNDERSTANDING CHEMICAL BONDS

A chemical compound is created when two or more atomsjoin to form a chemical bond that leaves the atoms in a lessexcited state than they were in before the bond. Such bondsform in two ways.

PHOTO CREDIT: SHUTTERSTOCK

ATI TEAS SCIENCE – CHEMISTRYUNDERSTANDING CHEMICAL BONDS

A covalent bond occurs when atoms share electrons between them. This type of bond iscommon between two atoms of the same element, as in hydrogen (H2) or in similarelements. When a molecule shares a pair of electrons in a stable state, it has formed acovalent bond. Alkanes, for example, share a single bond. In some compounds, one atomtakes the shared electron for more time, due to its structure, forming a polar covalentbond. This molecule is partly negatively charged and partly positively charged. Somemolecules form a double bond, sharing four electrons as opposed to two. These bondsare commonly represented in the alkenes, hydrocarbons with twice as many hydrogenmolecules as carbon molecules. It is possible to form triple bonds as seen in a group ofhydrocarbons called alkynes.

PHOTO CREDIT: BRITANNICA PHOTO CREDIT: QUORA

ATI TEAS SCIENCE – CHEMISTRYUNDERSTANDING CHEMICAL BONDS

An ionic bond is created between atoms when one atom gives an electron to the other.These bonds typically take place between metals and nonmetals due to the uniqueelectron configuration of metals, with the metal giving an electron to the nonmetal. Thistransfer creates a positive charge and a negative charge at the ends of the compound.The positive charge, or cation, is created by the giver of an electron. The negative charge,or anion, is located at the receiving end of the electron. The net charge of thecompounds remains balanced at zero.

PHOTO CREDIT: WIKIBOOKS

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UNDERSTANDING CHEMICAL SOLUTIONS

A chemical solution is a group of chemical compounds evenly distributed in a state ofmatter. The solution is a homogenous mixture where one chemical compound iscompletely dissolved in the others. This is most easily achieved in a liquid state. There aremixtures that are not solutions. A heterogeneous mixture maintains separation betweentwo substances, like oil and water.


UNDERSTANDING CHEMICAL SOLUTIONS

The solute is the compound dissolved in the solvent. Liquids make excellent solvents. The solubility of a solvent depends on the nature of the liquid as well as external factors like temperature. The concentration of the solution is the amount of solute in the solution. The mole is the unit of measurement for chemical reactions and refers to a compound’s molecular mass.

ATI TEAS SCIENCE – CHEMISTRYUNDERSTANDING CHEMICAL REACTIONS

To create a new chemical compound from other elements andcompounds, a chemical reaction is needed. Two or more reactants areadded together, often with an input of energy, creating one or moreproducts and by-products. Photosynthesis occurs, for instance, when aplant cell combines carbon dioxide and water. The sun’s rays providethe energy. The chemical reaction produces sugar and oxygen.

Chemical reactions are shown with equations and have a basicpattern: reactants go on the left and products go on the right, with thereaction sign (an arrow) showing the direction of the reaction in themiddle. Here is an example showing the direction of the reaction inthe middle. Here is an example showing the formation of watermolecules:

2"# + %# → 2"#%Equations for chemical reactions must be balanced; there must be thesame number of atoms of each element on both sides of the reaction.Notice in the equation above that there are four hydrogen atoms andtwo oxygen atoms on each side. Only their arrangement is changed.

PHOTO CREDIT: CHEMISTRY LIBRETEXTS

ATI TEAS SCIENCE – CHEMISTRYUNDERSTANDING CHEMICAL REACTIONS

There are five basic types of chemical reactions:

• Synthesis: two separate things joining together to form 1compound

• Decomposition: 1 compound breaks down into 2 or morecompounds

• Combustion: The use of fuel (combustible material) withoxygen to form carbon dioxide and water

• Single replacement: 1 element or compound replacesanother element or compound in a compound• For example: A + BC ⟹ AC + B

• Double replacement: 2 ionic compounds create two moreiconic compounds• For example: AB + CD ⟹ AD + CB

PHOTO CREDIT: CHEMISTRY LIBRETEXTS


UNDERSTANDING CHEMICAL REACTIONS

Reaction rates depend on the likelihood of collision between particles.The reaction rate can be altered by changing the following factors:

• Concentration – The more particles there are, the higher the chance ofcollisions.

• Temperature – Particles excite at higher temperatures, so morecollisions are likely andwill havemore energy.

• Pressure – Increased pressure forces particles together, so collisionsaremore likely

• Surface area – In a solid, only particles at the surface can collide. Thebigger the surface, the faster the reaction. Breaking up a sample intosmaller particles provides more surface area for collisions.

• Catalysts – A catalyst is a substance that changes the rate of a chemicalreaction but is chemically unchanged at the end of the reaction.


UNDERSTANDING CHEMICAL REACTIONS

Chemical reactions occur in nature and in the laboratory. A catalyst willspeed up the reaction by lowering the amount of energy needed tostart the reaction. Enzymes act as catalysts in cellular processes. Theyquicken the chemical reaction, turning a molecule, known as asubstrate, into a product without being altered themselves.

PHOTO CREDIT: BIONINJA

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ATI TEAS SCIENCE – CHEMISTRYUNDERSTANDING ACID BASE BALANCE

Many acids and bases can be understood from the perspective of thetheory developed by Arrhenius, a Swedish scientist. In this view, anacid is a substance that gives off hydrogen (H+) ions when it isdissolved in water. A base, or alkaline substance, is a substance thatgives off hydroxide (OH-) ions when it is dissolved in water. Acidicsolutions have higher concentrations of hydrogen ions, whereasalkaline solutions have lower concentrations of hydrogen ions.

The presence of acids and bases can be tested using tools known asindicators. One indicator in common use litmus paper. Litmus paperturns red in the presence of a base.



Here are some examples of acids and their chemical formulas.

ACID CHEMICAL FORMULA

• Acetic Acid !"#!$%#• Phosphoric Acid !$&%'• Citric Acid !$"(!)%*• Hydrochloric Acid HCL

• Sulfuric Acid !#+%'BASE CHEMICAL FORMULA

• Ammonium Hydroxide ,!'%!• Lithium Hydroxide LiOH

• Magnesium Hydroxide -.(%!)#• Potassium Hydroxide KOH

• Sodium Hydroxide NaOH

IMPORTANT NOTE: ACID = ACID; BASE = HYDROXIDE


The acidity or alkalinity of a solution is measured using a scale known as the pH scale.

\

Each step of the pH scale has 10 times the difference in concentration of hydrogen (!") ions as the step before or after it. So, a solution with a pH of 7 will have 10 times more hydrogen ions than a solution with a pH of 8 and 10 times fewer hydrogen ions than a solution with a pH of 6.



UNDERSTANDING BALANCING CHEMICAL EQUATIONS

The TEAS Science section may contain questions that ask you to balance chemical equations. We will outline the steps in this process later in this review.

One of the most important chemical equations for humans is the one that represents photosynthesis. Without the following equation, there would be no life on Earth:

!"# + %#" ⟹ !'%(#"' + "#This equation shows how green plant cells, with the help of the sun’s

energy, convert carbon dioxide (!"#) and water (%#") into glucose and oxygen ("#). The two reactants, carbon dioxide and water, are on the left side of the arrow. The arrow shows the direction of production. The two products, sugar and oxygen, are on the right side of the arrow.

ATI TEAS SCIENCE – CHEMISTRYUNDERSTANDING BALANCING CHEMICAL EQUATIONS

According to the Law of the Conversation of Mass, in a chemicalreaction, no energy is lost, but neither is mass destroyed. The amountof reactant must match the amount of products that are made, even ifthose products escape as a gas or a liquid.

In the photosynthesis equation, there is a difference in the number ofatoms on the right and left sides:

Element Reactants ProductsC 1 6H 2 12O 3 8

To produce sugar and oxygen requires more reactants than we haveon the left side. The solution is to balance the two sides.



We can multiply any molecule with a number, called a coefficient. Wecannot change the subscript, however, without changing the nature ofthe molecule. By adding coefficients to the reactants and products, wecan balance the equation in a few simple steps.

The best way to do this is by balancing each element in turn. Startwith the carbon. The right side has 6 carbon atoms, so the left sideneeds 6:

!"#$ + &$# ⟹ "(&)$#( + #$

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!"#$ + &$# ⟹ "(&)$#( + #$Here we have multiplied the "#$ by 6 to result in 6 carbon atoms onthe left side. When we multiply "#$ by 6, this also change the numberof oxygen atoms on the left side from 3 to 13. There are now 12oxygen atoms in the "#$ molecule, plus 1 in the &$# molecule, for atotal of 13. The 2 changed numbers are shown underlined in thefollowing table.


Now the carbon is equal, but the hydrogen remains unequal, and theoxygen has changed in number.



Next, we fix the hydrogen:

!"#$ + !&$# ⟹ "(&)$#( + #$Here we multiplied the &$# molecule by 6 to result in 12 hydrogen 2 atoms on the left side. When we multiple &$# by 6, the further changes the 2 number of the oxygen atoms on the left side from 13 to 18. There are now 12 oxygen atoms in the "#$ molecule, plus 6 in the &$# molecule, for a total of 18.




The last remaining imbalance rests with the oxygen. At this point, there is plenty of oxygen in the reactants. We can balance the equation by producing more !".

#$!" + #&"! � $'&("!' + #!"In this step, the !" molecule on the right side was multiplied by 6. This resulted in 18 oxygen atoms on the right side. The equation is now balanced. Each element has the same number of atoms on the left and right sides.


teas science 21 - chemistry - nurse cheung · 2019. 2. 24. · 2/21/19 1 ati teas science review...

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