Fall Chemistry Final Answers

Which element has both metallic and nonmetallic properties?

Si The metalloids, those elements that have both metallic and nonmetallic properties, are found along the 'stairs' on the periodic table. Of the choices given, only Si is a metalloid.

2 AgNO3 + Ni --> Ni(NO3)2 + 2 Ag

Single replacement reaction

2 K + 2 H2O --> 2 KOH + H2

Single replacement reaction

Ca + 2 HCl --> CaCl2 + H2

Single replacement reaction

Which of these reactions is possible?

Sn + H2SO4 ==> SnSO4 + H2

What is the balanced equation for: ___ SnO2 + ___ H2 -------> ___ Sn + ___ H2O?

SnO2 + 2 H2--> Sn + 2H2O The first step is to notice that the Sn is already the same on both sides. The oxygen needs to balance, so you put a 2 in front of H2O on the product side. This causes a hydrogen imbalance,which is easily fixed by putting a 2 in front of the H2 on the reactants side. The count on both sides is now Sn = 1 O = 2 H = 4

2 C2H2 + 5 O2 --> 4 CO2 + 2 H2O

Synthesis reaction

8 Cu + S8 --> 8 CuS

Synthesis reaction

P4 + 5 O2 --> 2 P2O5

Synthesis reaction

Metals can be placed in order of reactivity. What is this order called?

The Activity Series

The density of gold is 19.30 g/cm3. What happens to the density of 38.6 g of gold?

The density will not change.

Which of the following statements is FALSE for the chemical equation given below in which nitrogen gas reacts with hydrogen gas to form ammonia gas assuming the reaction goes to completion? N2 + 3H2 ----> 2NH3

The reaction of three moles of hydrogen gas will produce 17 g of ammonia.

What is the information on the activity series used for?

To determine whether or not a single-replacement reaction will occur. The element would only replace (a reaction will occur) another element if the replacing element is higher on the activity series. In other words for AB + C --> AC + B to occur, C has to be higher on the activity series.

Which is true of the reaction shown below?

Two molecules of Substance Y will be left over when this reaction goes to completion.

Matter that is composed of two or more different elements chemically combined in a fixed proportion is classified as

a compound A compound is defined as the chemical combination of two or more elements in a fixed proportion. The idea of definite proportions was proposed by Dalton.

Which is an example of a chemical change?

a nail rusting

Which compound is soluble: magnesium hydroxide or ammonium hydroxide?

ammonium hydroxide

Which compound is soluble?

ammonium phosphate

You know that an expected ion exchange reaction has taken place if the products include

any of the above.

Which substance can NOT be broken down by a chemical reaction?

argon, Ar Only elements can NOT be broken down by a chemical reaction. Of the choices given, only argon is an element.

What determines the order of placement of the elements on the modern Periodic Table?

atomic number

Which halogens are gases at STP?

chlorine and fluorine Iodine is a solid and bromine is a liquid. The gaseous halogens are chlorine and fluorine.

2 C2H2 + 5 O2 --> 4 CO2 + 2 H2O

combustion reaction

2 C6H14 + 19 O2 --> 12 CO2 + 14 H2O

combustion reaction

C3H8 + 5 O2 --> 3 CO2 + 4 H2O

combustion reaction

2 NaClO3 --> 2 NaCl + 3 O2

decomposition reaction

BaCO3 --> BaO + CO2

decomposition reaction

H2CO3 --> H2O + CO2

decomposition reaction

Ca(C2H3O2)2 + Na2CO3 --> CaCO3 + 2 NaC2H3O2

double replacement reaction

Cu(OH)2 + 2 HC2H3O2 --> Cu(C2H3O2)2 + 2 H2O

double replacement reaction

All of the elements in Period 2 of the Periodic Table have the same number of

energy levels

Which of these elements has physical and chemical properties most similar to silicon (Si)?

germanium (Ge)

Which metal is less reactive than copper?

gold

A compound differs from a mixture in that a compound always has a

homogeneous composition By definition compounds are homogeneous. They cannot be separated by physical means. A mixture (salad for example) is not homogeneous.

Which two products are formed when magnesium reacts with hydrochloric acid?

magnesium chloride and hydrogen

Which gas is monatomic at standard room conditions?

neon The noble gases, group 8A, are the least reactive elements. Look up Neon on the periodic table and notice that it has a completely filled energy shell. When an energy shell is completely filled, the element does not form bonds with other atoms. It is inert or nonreactive. Thus Neon is a monatomic gas. Cl2, F2, and N2 are diatomic gases (bond with another atom. Di means two).

Which element is a solid at room temperature and a good conductor of electricity?

nickel Metals are good conductors of electricity. Both mercury and nickel are metals, but nickel is a solid at room temperature and mercury is a liquid.

According to the activity series for metals, adding metallic iron to a solution of aluminum chloride should result in

no metal replacement reaction.

An atom is electrically neutral because the

number of protons equals the number of electrons. Protons and electrons have equal but opposite charges, and neutrons have no charge. An atom is neutral because the number of protons equals the number of electrons.

Which is more reactive than magnesium?

potassium

Which compound is soluble: potassium sulfate or barium sulfate

potassium sulfate

Which two particles each have a mass approximately equal to one atomic mass unit?

proton and neutron

Which metal is most likely to be found in rocks as the metal itself and not combined with other elements like oxygen, because it has low reactivity?

silver Silver is lowest on the activity series of the metals listed.

At standard room conditions, which substance is the best conductor of electricity?

silver The best conductors of electricity are metals. Silver is a metal, the others are nonmetals.

2 AgNO3 + Ni --> Ni(NO3)2 + 2 Ag

single replacement reaction

Ca + 2 HCl --> CaCl2 + H2

single replacement reaction

Which element's ionic radius is smaller than its atomic radius?

sodium Elements that lose electrons form positive ions that are smaller than atoms of the same element. Therefore the ionic radius of these ions is smaller than its atomic radius. Only choice c, sodium, is a metal that will lose electrons. Neon is stable and will neither lose nor gain electrons. N and S will tend to gain electrons, each having a larger ionic radius than atomic radius.

Which elements belong in the same family or group?

sodium and potassium

The alkali metals lithium, potassium and sodium all react with cold water to produce a gas and an alkaline solution. What is their order of increasing reactivity?

sodium, potassium , lithium

Which of the following does NOT form a diatomic molecule in its elemental form?

sulfur The seven diatomic molecules which you must memorize are O2, H2, N2 ,F2, Cl2, Br2 ,I2.

4 Cr + 3 O2 --> 2 Cr2O3

synthesis reaction

8 Cu + S8 --> 8 CuS

synthesis reaction

P4 + 5 O2 --> 2 P2O5

synthesis reaction

All of the following involve chemical changes, except

the dissolving of a sugar cube in cup of coffee.

A balanced chemical equation has

the same number of each kind of atom on both sides of the equation.

Which products always are created in a combustion reaction?

water and carbon dioxide All combustion reactions start with fuel and oxygen, and result in carbon dioxide gas and water being created. Think about the products of cell respiration, which is a controlled combustion reaction. You burn calories in hydrocarbon food by combining it with oxygen that you breathe in. Your cells create water and carbon dioxide, which you breathe out as waste products.

The atomic mass of titanium is 47.88 atomic mass units. This atomic mass represents the

weighted average mass of all the naturally occurring isotopes of Ti

Which compound is insoluble: potassium carbonate or zinc carbonate?

zinc carbonate

The salt produced when zinc reacts with sulphuric acid is

zinc sulfate

Which measurement contains a total of three significant figures?

0.125 Try writing all the numbers in correct scientific notation. Zeros that are just to denote the power will drop out and not be considered 'significant'. Choice A has 2 sig figs, and choices C and D have four and five sig figs respectively.

Which quantity of heat is equal to 200. joules?

0.200 kJ Just use dimensional analysis (factor label method): (200. J) x (1 KJ/ 1E3J) = 0.200 J

What is the net charge on an ion that has 9 protons, 11 neutrons, and 10 electrons?

1- Each proton contributes a charge of 1+ , and each electron contributes a charge of 1-. Neutrons have no effect on the charge. The charge on the ion is (9+) + (10-) = 1-.

When the numbers 1.2 E2 and 3.4 E1 are added, the result, expressed in proper scientific notation, is

1.5 E2

How many grams are in 1.946 moles of NaCl?

113.8 g

Expressed to the correct number of significant figures, what is the sum of (3.04 g + 4.134 g + 6.1 g)?

13.3g The value with the lowest precision is 6.1 g, measured to the nearest tenth. Therefore, the answer can only be precise to the nearest tenth.

What is the gram formula mass of K2CO3?

138 g Find the formula mass in grams. K =39 x 2 = 78 g; C =12 x 1 = 12 g; O =16 x 3 = 48 g. Total is 78 + 12 + 48 or 138 g.

If 1.000 kg = 2.2046 lb, how much does a 72.0 kg person weigh in pounds?

159 lbs

Calcium carbide, CaC2, is an important preliminary chemical for industries producing synthetic fabrics and plastics. CaC2 may be produced by heating calcium oxide with coke, which is pure carbon: CaO + 3C ----> CaC2 + CO What is the amount of CaC2 which can be produced from the reaction of excess calcium oxide and 10.2 g of carbon? (Assume 100% efficiency of reaction for purposes of this problem.)

18.1 g

What is the total number of electrons in an atom of potassium?

19 An atom is a neutral particle that contains and equal number of protons and electrons. The atomic number of potassium, K, is 19. Therefore, an atom of potassium contains 19 protons and 19 electrons.

In the reaction 2CO(g) + O (g) 2CO (g), what is the ratio of moles of oxygen used to moles of CO2 produced?

1:2

Which is the correct mole ratio of K3PO4 to KNO3 in the BALANCED chemical reaction Mg(NO3)2 + K3PO4 Mg3(PO4)2 + KNO3 ?

1:3

A sample of an element has a mass of 34.261 grams and a volume of 3.8 cubic centimeters. To which number of significant figures should the calculated density of the sample be expressed?

2 When dividing two measured quantities, the answer should contain the same number of sig figs as the quantity with the smaller number of sig figs. The mass is expressed to 5 sig figs and the volume to 2. The answer must contain 2 sig figs.

What is the total number of carbon atoms in ethanoic (acetic) acid, (also known as vinegar), with a molecular formula CH3COOH?

2 Since subscripts apply to the symbol which comes BEFORE it, the little 3 goes with the hydrogen. There are only two carbons. By the way, the prefix 'eth' means 'two.'

Given the reaction CH4 + 202 --> C02 + 2H20, What amount of oxygen is needed to completely react with 1 mole of CH4?

2 moles The number of moles in a balanced equation is shown by the coefficients. Hint: when there is no coefficient (the number in front of the compound), the number 1 is understood. 1 mole of CH4 reacts with 2 moles of 02.

What are the coefficients for the balanced equation for: __ AgI + __ Na2S --> __ Ag2S + __ NaI

2, 1, 1, 2 Start with putting 2 in front of Ag to balance it. 2AgI + __ Na2S --> __ Ag2S + __ NaI Now the I is not balanced. Put a 2 in front of NaI. Is it balanced now? 2AgI + __ Na2S --> __ Ag2S + 2NaI Yes. Final count for both sides: Ag = 2; I = 2; Na = 2; S = 1.

The equation below shows the decomposition of lead nitrate. How many grams of oxygen are produced when 11.5 g NO2 is formed?

2.00 g

Expressed in proper scientific notation, the number 0.00213 is

2.13 E-3

A cube has a volume of 8.00 cubic centimeters and a mass of 21.6 grams. The density of the cube can best be expressed as

2.70 g/cm3

How many moles of Cu are needed to react with 5.8 moles of AgNO3? Cu + 2 AgNO3 Cu(NO3)2 + 2 Ag

2.9 moles

What is the correct reading of this buret? (Please notice the direction that the values change!)

20.38 mL Burets need to be read from the top down. You read the labeled value, then count DOWN the glassware markings, remembering to record the uncertain, estimated value as the last digit. This gives you the most precise measurement.

What is the total number of atoms represented in the formula CuSO4 . 5H2O?

21 Cu=1; S=1; O=4; H=10; O=5 for a total of 21 atoms.

Given that 1.00 miles = 1.61 kilometers (km), convert 65 mph to meters per second.

29 m/s (65 miles/1 hr) x (1.61 km/1.00 miles) x (1000m/1km) x (1 hour/60 min) x (1 min/60 sec) = 29 m/s

Convert 72°F to Kelvins. We know that °F = (9/5)(°C) + 32 AND °C = 5/9 (°F -32). We also know that K= 273 + °C.

295.2 K (72°F - 32) x 5/9 = 22.2 °C and then 22.2 °C + 273 = 295.2K

What is the balanced equation for: __ KNO3 + __ H2CO3--->__ K2CO3 + __ HNO3

2KNO3 + H2CO3---> K2CO3 +2 HNO3 First, you notice you want to put a 2 in front of the KNO3 to get the K to balance. That creates a problem for the NO3 unit. If you put a coefficient of 2 in front of HNO3 , that balances those NO3 atoms. Now we have to count hydrogens, and you can see we will have 2 on each side. Final count for each side: K = 2 NO3= 2 CO3 =1 H = 2

In the calculation 41.06 centimeters x 10.2 centimeters, how many significant figures should the product of the two values contain?

3

A temperature of 37°C is equivalent to a temperature of

310. K K = °C + 273 = 37°C + 273 = 310.K

How many grams of H2O will be produced if 750 grams of Fe are produced?

322 g

Which Kelvin temperature is equal to 56°C ?

392 K K = °C + 273 = 56°C + 273 = 329 K

When the numbers 4.2 E2 and 8.4 E 1 are multiplied, the exponent of the result, expressed in proper scientific notation is

4

What is the number of moles of beryllium atoms in 36 g of Be?

4.0 moles

How many millimeters are in 0.00436 cm?

4.36 E-2 mm Converting cm to mm is moving the decimal once to the right. Then, you put it into scientific notation.

What is the correct measurement on this meter stick to the correct precision?

4.98 cm If you look carefully, the left end of the screw is NOT on the zero mark. You measure the distance from one end to the other, and the screw is slightly less than 5 cm. I estimated 5.10cm - 0.12cm = 4.98 cm.

What is the correct reading of this graduated cylinder?

43.0 mL

When the number 602,000,000,000,000,000,000,000 is written in scientific notation, it is

6.02 E23

How many grams of NH3 can be prepared from 77.3 grams of N2 and 14.2 grams of H2? (Hint: Write and balance the equation first.)

79.7 g

The total number of atoms in one molecule of the compound K3PO4 is

8

Astatine is the rarest naturally occurring element in the universe. It's name comes from the Greek "astatos" meaning unstable. It was first found in the thyroid of a guinea pig, imitating its group member, iodine. What is astatine atomic number?

85 Using the reference tables, you can look up astatine, and find that its symbol is At, and on the periodic table it is number 85, found right below iodine. Would you expect it to be diatomic?

A substance has a density of 8.96 g/mL. Calculate the mass of this substance if the volume is 1.035 DaL.

9.27 E4 g First convert DaL to Liters then to mL. 1.035DaL x (10L/1DaL) x (1000 mL/1L) = 10,350mL Using the density, solve for mass in grams: (8.96 g)/ (1 mL) = X g/ (10,350 mL) = 92,736 grams, but to three significant figures it is 9.27E4 grams

A displacement reaction can be described as:

A more reactive metal replacing a less reactive metal in its compound.

Which of the following salts is insoluble?

AgCl

According to the solubility rules, which one of the following is soluble in water?

BaSO4

2 C6H14 + 19 O2 --> 12 CO2 + 14 H2O

Combustion reaction

C3H8 + 5 O2 --> 3 CO2 + 4 H2O

Combustion reaction

2 NaClO3 --> 2 NaCl + 3 O2

Decomposition reaction

H2CO3 --> H2O + CO2

Decomposition reaction

3 AgNO3 + K3PO4 --> Ag3PO4 + 3 KNO3

Double replacement reaction

Ca(C2H3O2)2 + Na2CO3 --> CaCO3 + 2 NaC2H3O2

Double replacement reaction

Which element is most chemically similar to chlorine?

F Elements within the same group (family) have similar chemical properties. Of the choices given, only F is in the same group as chlorine.

Which of these is NOT a reason reactions go forward and create more product?

Formation of a liquid. Formation of gas (which can leave the container and is no longer available to react), a precipitate (which settles out of solution and is no longer available to react), or water in an acid/base reaction all drive the reaction to happen.

Which element below is in the same column as the alkali metals, but is not a metal?

H

Which of the following net ionic equations best represents the reaction that takes place in aqueous solution, when sulfuric acid and sodium hydroxide solutions are mixed?

H+ + OH- --> H2O Letter A is not an ionic equation. Letter B is not even a full ionic equation because the H2SO4 should ionize in water. Letter C is not even a full ionic equation because the NaOH should ionize in water. Letter D is correct because it is the net ionic equation for the materials which drive the reaction forward.

Why doesn't gold tarnish in air?

It is relatively unreactive

Which set of elements contains a metalloid?

K, Mn, As, Ar Go to the Periodic Table and note the location of the stepped line dividing metals and nonmetals. Elements next to the left or right of this line are metalloids. As (Arsenic) is a metalloid.

Which statement describes a chemical property of the element magnesium?

Magnesium reacts with an acid. A chemical property is one in which the substance is changed when the property is investigated. In other words, a chemical reaction occurs. When magnesium atoms react with an acid, hydrogen gas and magnesium ions are formed. The other choices are all correct PHYSICAL properties of magnesium.

Which block has the smallest density? BLOCK:Mass (g)/Length(cm)/Width(cm)/Height(cm)

Mass (g) Length (cm) Width (cm) Height (cm) 6.0 4.0 2.0 1.5

When alpha particles are scattered by thin metal foils, which observation indicates a very high percentage of space in atoms?

Most pass through with little or no deflection.

Which symbols represent atoms that are isotopes?

O-16 and O-18 Isotopes are atoms of the same element (same atomic number) but with a different number of neutrons (different atomic mass). Only choice b is correct. Choice a: C and N are not the same elements. Choice c: both are the same element but there is no difference in mass. Therefore, they are not isotopes. Choice d: not the same elements.

Which atom contains exactly 15 protons?

P-32 An atom with 15 protons also has an atomic number of 15. Refer to the Periodic Table for element 15 (phosphorus).

Which element has a molar mass of 30.974?

Phosphorus

Which of the following is the correct order of decreasing reactivity?

Potassium, magnesium, iron, copper, gold

The limiting reagent in a chemical reaction is one that:

is consumed completely.

When combining with nonmetallic atoms, metallic atoms generally will

lose electrons and form positive ions Metals tend to lose electrons and form positive ions. A neutral atom of Li has 3 protons (+) and 3 electrons (-). If it loses an electron, the Li atom now has +3 and -2 or a net charge of +1. Later we will learn that metals also have low electronegativities and low ionization energies. That just means they lose electrons easily and it does not take much energy for them to give up their electrons.

An atom of carbon-12 and an atom of carbon-14 differ in

mass number

Which two particles make up most of the mass of a hydrogen-2 atom?

proton and neutron The nucleus contains most of the mass of an atom. The nucleus of a hydrogen-2 (mass number!) atom contains 1 proton and 1 neutron.

When the rules for significant figures are used, the sum of 0.027 gram and 0.0023 gram should be expressed as

0.029g In adding or subtracting, the value measured to the least precision (has the least number of places after the decimal place) limits the precision 'truth' of your final answer. You are not allowed to report a precision that is a misrepresentation of the true precision used in the lab.

Which measurement contains three significant figures?

0.0563g Write each number in correct scientific notation and the correct answer become clear!

Which is the equivalent of 750. joules?

0.750 kJ

How many moles of aluminum are needed to react completely with 1.2 moles of FeO? 2Al(s) + 3FeO(s) 3Fe(s) + Al O (s)

0.8 mol

Which temperature originally represented the fixed points on the Celsius scale?

0° and 100°

How many grams of H3PO4 are produced when 10.0 moles of water react with an excess of P4O10?

653 g

The atomic masses and the natural abundances of the two naturally occurring isotopes of lithium are shown in the table below. Which numerical setup can be used to determine the atomic mass of lithium?

(0.075)(6.02 u) + (0.925)(7.02 u)

A 100.00-gram sample of naturally occurring boron contains 19.78 grams of boron-10 (atomic mass = 10.01 atomic mass units) and 80.22 grams of boron-11 (atomic mass = 11.01 atomic mass units). Which numerical setup can be used to determine the atomic mass of naturally occurring boron?

(0.1978)(10.01) + (0.8022)(11.01)

What is the total charge of the nucleus of a carbon atom?

+6 The nucleus of Carbon (atomic number 6) has 6 protons, each of which has a positive charge. It also has neutrons, 6 on average, but they have no charge.

In a laboratory exercise to determine the density of a substance, a student found the mass of the substance to be 6.00 grams and the volume to be 2.0 milliliters. Expressed to the correct number of significant figures, the density of the substance is

3.0 g/mL When multiplying or dividing, you use the measured value with the least number of significant figures to determine the number of sig figs in your answer. It determines the limit of the precision of the measured value, and tells you the degree to which you can 'trust' the answer.

What is the balanced equation for: __ KOH + __ H3PO4 --> __ K3PO4 + __ H2O

3KOH + H3PO4 --->K3PO4 + 3 H2O Starting with K, you can see that you have one on the reactant side and three on the product side. You need to use a coefficient of 3 on the reactant side. If you look at the choices, only A and C have that. You can rule out A because there is yet another coefficient in front of the K on the product side. That leaves you with C for your choice. Double check the hydrogen and oxygen to confirm that using a coefficient of 3 in front of the H2O balances the entire equation. Total count: K = 3 O = 7 H= 6 P = 1

Silicon carbide, an abrasive, is made by the reaction of silicon dioxide with graphite. SiO2 +3C SiC + 2CO If 100 g of SiO2 and 100 g of C are reacted as far as possible, which one of the following statements will be correct?

40 g of C will be left over.

Which of the following shows 4657.847 reduced to four significant figures?

4658

Which is the mass of 8 moles of sodium chloride?

468 g

In the measurement using a graduated cylinder of 247.35 mL, which number represents an estimate?

5 The last value in any laboratory measurement is the estimated value. This assumes you know how to correctly use lab equipment to the correct precision.

An ion with 5 protons, 6 neutrons, and a charge of 3+ has an atomic number of

5 The number of protons is the same as the atomic number. There are 5 protons so the atomic number is also 5.

What mass of ZnCl2 can be prepared from the reaction of 3.27 grams of zinc with 3.30 grams of HCl? (This is basically a limiting reactant problem.) Zn +2HCl ZnCl2 + H2

6.17 g

What is the mass number of an atom which contains 28 protons, 28 electrons, and 34 neutrons?

62 Atomic mass is found by adding protons plus neutrons. 28 + 34 = 62. Electrons have a mass of nearly 0 so they are not counted in the formula for atomic mass.

A commercially valuable paint and adhesive stripper, dimethyl sulfoxide (DMSO), (CH3)2SO, can be prepared by the reaction of oxygen with dimethyl sulfide, (CH3)2S, using a ratio of one mole oxygen to two moles of the sulfide: O2 + 2(CH3)2S --------> 2(CH3)2SO If this process is 83% efficient, how many grams of DMSO could be produced from 65 g of dimethyl sulfide and excess O2?

68 g

Given the unbalanced equation: Al + O2 = Al2O3 When this equation is completely balanced using the smallest whole numbers, what is the sum of the coefficients?

9 4Al + 3O2 = 2Al2O3. Coefficients are the numbers in front of the element symbols. Add 4 + 3 + 2 to get 9.

Which two blocks may be made of the same material? BLOCK:Mass (g)/Length(cm)/Width(cm)/Height(cm)

A and C Mass (g) Length (cm) Width (cm) Height (cm) A 72. 4.0 3.0 2.0 C 30. 10. 1.0 1.0

What was concluded about the structure of the atom as the result of the gold foil experiment?

A positively charged nucleus is surrounded by mostly empty space. An English physicist, Ernest Rutherford, beamed alpha particles at thin gold foils. When he examined the scattering patterns of the alpha particles, he concluded that most of the volume of the atom was empty space and that most of the mass of the atom was concentrated in a dense, positively charged nucleus.

The net ionic equation for the reaction , if any, when aqueous solutions of silver nitrate and sodium chloride are mixed is:

Ag+ + Cl - --> AgCl Look at your solubility rules. You can see that AgCl is insoluble, so formation of that precipitate will drive the reaction forward. You need to look for the answer which shows the ions needed to form the AgCl, which is choice D.

Which statement describes a chemical property?

It reacts with hydrogen to form a gas. While all the answers are true for iodine, only choice d describes a chemical property. The other choices are physical properties.

What can be concluded if an ion of an element is smaller than an atom of the same element?

The ion is positively charged because it has fewer electrons than the atom. When an atom loses an electron, it becomes a positive ion (cation) and its radius decreases because the nucleus pulls on the remaining electrons more tightly.

Petroleum is classified chemically as

a mixture Petroleum is not listed on the Periodic Table so it cannot be an element. A compound is composed of two or more elements with a fixed composition: petroleum does not have a fixed composition. This eliminates b and c. A substance by definition is matter that has the same properties and composition throughout. Every molecule of oxygen is identical to every other oxygen molecule. Every water molecule has the same formula: H2O. Not true for air. Air is a mixture (not the same throughout). Tossed salad, a can of mixed nuts, and gravel are mixtures. Mixtures are made of two or more substances that do not combine chemically and do not have a fixed composition. Petroleum is a mixture.

Which of the following substances can be decomposed (broken down) by chemical means?

ammonia, NH3 Compounds can be decomposed by chemical means, but elements cannot. Only ammonia is a compound. Oxygen is a diatomic element.

A proton has a charge that is opposite the charge of

an electron A proton is positive. The electron is negative.

A sample composed only of atoms having the same atomic number is classified as

an element

Two solid samples each contain sulfur, oxygen, and sodium, only. These samples have the same color, melting point, density, and reaction with an aqueous barium chloride solution. It can be concluded that the two samples are the same

compound Compounds are characterized by their composition and by their physical and chemical properties. Since the two samples contain the same elements, have the same physical properties (color, melting point, and density), and the same chemical property (reaction with aqueous barium chloride), we can conclude that the samples are the same compound.