TAKS Review Objective 4

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TAKS Review Objective 4

• Chemistry Review

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The next 7 slides are typical TAKS Chemistry
questions.

• If you miss the question, follow the directions
  to the slides that review that information.
• If you get it correct, you move on to the next
  question.
• If you get them all correct, you should be well
  on your way to doing well on the Objective 4
  section of the TAKS.

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• 1. Which of these would support the idea that
  mass is conserved in a reaction that produces a
  gas as a product?
• A Heating the reactants to ensure the reaction
  occurs in a gaseous state
• B Subtracting the mass of the gas from the mass
  of the solid and liquid products
• C Mixing the reactants and measuring their
  total mass
• D Trapping the gas and measuring its mass

Answer? D If you missed it, begin the review
on Slide 34
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• 2. Which set of coefficients balances the
  equation?
• F 3, 3, 1, 2
• G 6, 1, 1, 3
• H 3, 2, 1, 6
• J 6, 2, 1, 6

Answer? F If you missed it, begin the review
on Slide 36
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Answer? H If you missed it, begin the review
on Slide 14
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• 3. The table shows data from an investigation
  designed to find a liquid solution that is both
  an acid and a strong electrolyte. Based on the
  data, a solution that is both an acid and a
  strong electrolyte is
• A Solution 1
• B Solution 2
• C Solution 3
• D Solution 4

Answer? D If you missed it, begin the review
on Slide 43
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• 4. Portland cement is used to make concrete, a
  very common construction material. Which step in
  the production of portland cement causes a
  chemical change?
• A W
• B X
• C Y
• D Z

Answer? C If you missed it, begin the review on
Slide 30
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• 5. Which of these is the most appropriate unit
  of measure for reporting the density of a solid?
• F g/cm3
• G g/cm
• H g/L2
• J g/mm2

Answer? F If you missed it, begin the review on
Slide 34
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• 6. Which characteristic of water best explains
  its ability to dissolve a great variety of
  materials?
• A Its transparency in light
• B Its physical state of matter
• C Its electrical conductivity
• D Its molecular arrangement

Answer? D If you missed it, begin the review on
Slide 47
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• 7. Power plants that discharge warm water into
  rivers have a negative effect on aquatic life.
  This is because the higher water temperature
• A increases the pressure of the river water
• B increases the pH value of the river water
• C decreases sediment solubility in the
  riverwater
• D decreases the dissolved oxygen in the river
  water

Answer? D If you missed it, begin the review
on Slide 47
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And the answers are

1. D Mass conservation means the mass of all of
   the products mass of all reactants
2. H There are 3 Ca after the arrow, so put a 3 in
   front of Ca before the arrow. That makes 3 x 2
   of the C2H3O2 complex so put a 6 in front of the
   K C2H3O2 after the arrow.
3. D only solution 4 has High electrical and a low
   pH.
4. C This step the materials have oxygen added with
   heat, and produce new substances.
5. F Density is mass/volume and the volume of a
   solid is measured as length x width x height, or
   cm x cm x cm or cm3.
6. D Water is polar, which is a description of how
   the atoms are arranged.
7. D Warm dissolves more solids, and reduces gas
   dissolving.

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What good is the Periodic Table?

• What is an element?
• Basically elements are those substances listed
  anywhere on the periodic table (of the elements).
  
• If it is on the left side of the stair-step line
  it is a metal element, if it is on the right side
  it is a NONmetal element. (Hydrogen is the ONLY
  nonmetal to the left of the stairstep line.)
• Lets look . . .

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Where are the metal elements?
Left of the Stair-step line!
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Where are the nonmetals?
To the Right of the stair step line, and
Hydrogen!
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Nonmetals bonded to nonmetals form covalent bonds

• That means electrons are shared between the
  elements.
• The closer to Carbon the two elements are on the
  table, the more covalent, less ionic the bond is.
  
• The most equally shared electrons occur between 2
  atoms of the same element in a diatomic molecule.
  

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Diatomic Elements Nonmetals that come as
molecules

• 7 Elements are di- (2) atomic (atoms)
• The easy way to remember them is by the name
• Br2 I2 N2 Cl2 H2 O2 F2

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So, I can tell if its a metal or not, what else?

• Each column on the table is a group or family of
  elements that have similar chemical properties.
• They form the same types of compounds, in the
  same ratio.
• They have the SAME NUMBER OF OUTER SHELL
  (valence) electrons.
• Lets look . . .

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Group 18 is the family called Noble Gases
each one has 8 outer shell electrons (full shell)
so they dont form compounds.
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Group 1 is called the Alkalai Earth metals,
they have 1 valence electron, and will form 1
ions.

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For each group, they form compounds the same way,
for example. . .

• Beryllium forms a compound with Cl in the ratio
  of 12 or BeCl2
• Since Mg and Ca are in the same family or group,
  they will form the same type of compounds in the
  same ratio.
• MgCl2 and CaCl2
• This is what is meant when they have
• similar chemical properties

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Group 2 is called the Alkalai Earth Metals and
they have 2 valence electrons, which they will
give away to form 2 ions.
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Group 17 are the Halogens, they all have 7
electrons in their valence shell, and want to
have 1 more when they form compounds. They all
become -1 ions when they can.
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The center elements on the table are called the
transition metals. Many of them have more than 1
way they will give away electrons, so they
change, or transition, ion charges. The charge
these metals use are given by a roman numeral in
the name. (Iron (II) chloride)
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The Rare Earth Metals are radioactive and form
the bottom 2 rows, also called the Lanthanide and
Actinide Series.
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When metals and nonmetals form compounds . . .

• Metals tend to actually give away their outer
  shell valence electrons to the nonmetal ion or
  group.
• This gives the metal a positive charge (caion)
  so it is listed first in names and formulas.
• The electrons are accepted by the nonmetal or
  group, giving it a negative charge, and since
• Opposite charges attract, ionic bonds are very
  strong and make these compounds have high melting
  points.

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Each square also tells us information about each
element.

• The 1 or 2 letters that represent the element are
  its symbol.
• The number at the top of the square is the atomic
  number.
• The numbers at the bottom of the square is the
  average atomic mass.

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What do the numbers mean?
This is the atomic number. It is the number of
protons in a single atom of this element. By the
way, its also of electrons.
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Na
The symbol for this element.
This is the atomic mass, it is the number of
protons neutrons, or the mass of the nucleus of
an atom.
22.990 sodium
This is the name of the element.
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How can you tell which element is represented?

• Count the number of protons.
• Protons are positive and found in the nucleus.
  
• There are 4, so this is the 4th element on the
  Periodic Table Be
• Answer C

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Atoms are. . .

• The smallest part of a single element.
• The basis of all matter. Word was first used by
  Democritus.
• Made of mostly empty space, and have a positive
  core or nucleus. (Rutherford)
• Have electrons in orbit in energy levels.
  (Dalton)

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Changes Physical or Chemical?

• Physical changes are changes in the state of
  matter. They do not change the substance.
  (Melting, boiling, condensing, freezing, cutting)
  
• Chemical changes are reactions that result in new
  products with new properties.

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Changes Physical, Chemical or Nuclear?

• Physical changes do not change the substance.
  The state of the matter may change, but it keeps
  its own properties.
• Cutting a piece of wood does not change the wood,
  it is simply smaller.

• Chemical changes are also called chemical
  reactions.
• When a different substance is produced than what
  was present at the start, a chemical change has
  occurred.

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• 39 Which of these describes a chemical change?
• F Frost disappears from a window in the morning.
• G A decrease in temperature reduces the volume of
  a gas.
• H Soot is formed as a candle burns.
• J A cup of hot tea cools down.

F, G and J are simply temperature changes
affecting the state of matter, so H is correct.
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• 27 Which process best demonstrates a chemical
  change in distilled water?
• A Freezing the water
• B Separating the water into its elements
• C Calculating the waters density
• D Dissolving sugar in the water

Only when new substances are produced is a
chemical change, A, C and D still have water,
only B has elements instead of a compound.
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Density Mass / Volume THIS IS FROM THE FORMULA
PAGE

• 25 A block of maple wood with a volume of
• 405 cubic centimeters and a density of
• 0.67 g/cm3 is sawed in half. The density
• of the two smaller blocks is now
• A one-fourth the original density
• B one-half the original density
• C two times the original density
• D the same as the original density

If the block is cut in half, you cut the mass in
half AND you cut the volume in half, so Mass/2
or Volume/2 Mass x 2
(which is really 1) so . . . . Volume 2
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20 A sample of an element has a volume of 78.0 mL
and a density of 1.85 g/mL. What is the mass in
grams of the sample? Record and bubble in your
answer to the nearest tenth on the answer
document.
Use the formula page, D M/V
1.85 g/mL
Multiply both sides by 78.0 mL and you get
144.3 g Grid it in!
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Law of Conservation of Matter

• Matter can not be created or destroyed.
• The total mass of the substances before they are
  mixed is equal to the total mass as a mixture.
• Mass is conserved in a chemical reaction also.

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Chemical Reactions

• Since matter can not be created or destroyed,
  chemical reactions must be balanced in terms of
  mass.
• The amount of mass you start with must be equal
  to the mass of the products.

• Reactants ? Products
• 100g total 100g total

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39 According to the law of conservation of mass,
how much zinc was present in the zinc carbonate?
Since matter can not be created or destroyed in
chemical reactions, the mass on both sides of the
arrow must be equal. So 64g 192g 256g and
152 g Zinc 256g There must be 104g of Zinc.
Answer C.

• A 40 g B 88 g C 104 g D 256 g

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Chemical Equations

• Whole numbers written in front of formulas are
  called coefficients. For example, 4 C6H12O6
  indicates that there are 4 molecules of glucose
  sugar.
• To determine how many total atoms of each element
  are present, multiply the coefficients by the
  subscripts for each element.
• 4 C6H12O6 would contain 24 atoms of carbon
• (4 x 6), 48 atoms of hydrogen (4 x 12), and 24
  atoms of oxygen (4 x 6).

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To balance equations

• The number of atoms of each type of element on
  the reactant side (left of the arrow) must be
  equal those on the product side (right side of
  the arrow).
• 2 H2 O2 2 H2O
• There are 4 hydrogen atoms on the left (2 H2) and
  4 hydrogen atoms on the right (2 H2O)
• There are 2 atoms of oxygen (O2) on the left and
  2 atoms of oxygen on the right (2 H2O). When a
  subscript or coefficient is missing, it is
  understood to be 1. On TAKS coefficients of 1
  are written in blanks.

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K H2O ? KOH H2
HOH
2
2
2

• 19 What is the coefficient for H2O when the above
  equation is balanced?
• A 1
• B 2
• C 3
• D 4

To balance this equation, make water HOH, then
you will see that you need 2 H and get 2 OH
groups. That means the KOH gets a coefficient
of 2, the K gets a coefficient of 2 and The
water must also get a coefficient of 2.
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Balance the equation below, the boxes should get
the coefficients.
2
2
Which element does not have the same number of
atoms on both sides? Oxygen. It has 2 on the
reactant side and 3 on the product side. If we
put a coefficient of 2 in front of PbO, we will
now have 4 O and 2 Pb on the right. By placing
a coefficient of 2 in front of the reactant, we
have 2 Pb and 2 x 2 O. That means it is
balanced! Answer?
C
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Names of Acids and Bases

• Bases end in the hydroxide anion OH-
• They are named with the metal and hydroxide.
• NaOH is sodium hydroxide

• Acids that are two elements are named
  Hydro-nonmetal ic Acid such as
• HCl hydrochloric acid
• Group -ate becomes ic and -ite becomes ous.
• H2SO3 sulfurous acid
• H2SO4 sulfuric acid

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Properties of Acids and Bases

• Acids taste sour, are corrosive to metals, are
  electrolytes and have a low pH.
• Bases taste bitter, feel slippery, are
  electrolytes and have a high pH.
• Acids are red with litmus and bases are blue
  with litmus
• As pH changes one number, it is ten times
  stronger or weaker

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pH is a measure of the Strength of Acids Bases

• Acids have 0-6.99 pH
• Bases have 7.01-14 pH
• Remember because A begins the alphabet and zero
  begins numbers
• Litmus turns red in acids and blue in bases
• Phenothalein turns pink in a base and stays clear
  in acids.

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Higher pH levels means?

• 33 Two clear solutions are placed in separate
• beakers. The first solution has a pH of 4, and
  the pH of the second solution is unknown. If
• the two solutions are mixed and the resulting
• pH is 5, the second solution must have
• A fewer suspended solids
• B a lower temperature
• C more dissolved salt (NaCl) particles
• D a higher concentration of OH ions

Solutions are homogeneous and have no suspended
solids.
Nothing is mentioned about temperature so B is
invalid.
NaCl solutions are neutral so have no effect on
pH.
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Water called the universal solvent

• Water is composed of 1 oxygen and 2 hydrogens.
  H2O
• Although the electrons are shared, they are not
  shared equally.
• This makes water POLAR, it has a positive side
  (hydrogens) and a negative side (oxygen).
• LIKE DISSOLVES LIKE, so almost all ionics, and
  polar covalents will dissolve in water.

2-
1 1
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Solubility Factors What will dissolve?

• Solubility Rules
• 1. All sodium, potassium, and ammonium salts are
  soluble.
• 2. All silver, lead, and mercury salts are
  insoluble.
• 3. All carbonates, sulfides, and hydroxides are
  insoluble.
• 4. All nitrates and sulfates are soluble except
  calcium sulfate and barium sulfate.

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How much solute will dissolve?

• A solubility curve shows the amount of each
  solute that will dissolve in 100g H20 at each
  temperature.
• Saturated is on the line.
• Unsaturated is below the line.
• Supersaturated is above the line.

Grams solute/100 g H2O
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Concentrated or Dilute?

• A concentrated solution has as little solvent as
  possible.
• A dilute solution has added solvent.
• After adding more solvent, there is still the
  same mass of solute that you started with, but it
  has been diluted.

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Now lets try again . . .

• Answer the next 6 questions correctly, and you
  are ready for Objective 4. Please review any
  section you needed to review today at least 2
  more times before the test.

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• 1 Which of the following elements will most
  easily lose its electrons to fluorine to form a
  salt?
• A Na
• B Al
• C S
• D Ar
• 2 Which of the following is the best evidence
  that digestion involves chemical change?
• A Time is required to accomplish results.
• B The products mass equals the reactants mass.
• C Different compounds are involved.
• D New substances are produced.
• C Fe2O3 ? Fe CO
• 3 What is the coefficient for CO when the
  equation above is balanced?
• A 1
• B 2

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4 An element is discovered that has an atomic
number of 118 and 8 valence electrons. The
element is most likely A a noble gas B an
alkali metal C a halogen D a transition metal

• 5 In which diagram is a chemical change
  occurring?
• A Diagram 1
• B Diagram 2
• C Diagram 3
• D Diagram 4
• 6 Which diagram best demonstrates the law of
  conservation of mass?

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Check your answers If you are still missing
some of these, come back and ask for additional
help on a specific topic. . .

1. A
2. D
3. C
4. A
5. C
6. B