Periodic Table and the Atom Answers

Periodic Table and the Atom Answers

Complete the table. There is enough information given for each element to determine all missing numbers.

Symbol / Atomic Number / Mass Number / Number of Protons / Number of Electrons / Number of Neutrons
23Na / 11 / 23 / 11 / 11 / 12
K / 19 / 40 / 19 / 19 / 21
Sr / 38 / 90 / 38 / 38 / 52
F / 9 / 19 / 9 / 9 / 10
Ca2+ / 20 / 41 / 20 / 18 / 21
Sn / 50 / 22 / 50 / 50 / 72
131I / 53 / 131 / 53 / 53 / 78
26Mg / 12 / 26 / 12 / 12 / 14

Review:

An element's or isotope's atomic number tells you ___ how many protons are in its atoms.______.
An element's or isotope's mass number tells you __ how many protons and neutrons in its atoms.__.
The heaviest part of an atom is the __nucleus______, which contains both ____protons____ and ___neutrons______. The _____electrons______are found in a cloud surrounding the nucleus.
If an atom was a penny inside a football stadium, the penny would represent the ______nucleus______and the football stadium would represent __the atom or electron cloud____.
Which has a higher atomic number?Helium or Hydrogen ____Helium______

Magnesium or Manganese _____Manganese______

6. Which has a lower atomic mass?Carbon or Calcium _____Calcium______

Xenon or Radon ______Radon______.

7. Generally speaking, how does atomic mass change throughout the periodic table? ___atomic mass______increases as you go across and down on the periodic table.______

The Groups and Periodic Trends Practice Problem Answers

Identify the following elements as metal, nonmetals, or metalloid.

1) Boron Metalloid

2) CarbonNonmetal

3) GoldMetal

4) LeadMetal

5) Hydrogen Nonmetal

Identify the following elements by which group they belong to on the periodic table.

6) Flourinehalogen

7) Argonnoble gas

8) Calcium alkaline earth metal

9) Potassiumalkali metal

10) Carbonnonmetal

11) Which of these elements has the largest atomic radius?

a) aluminum

b) calcium

c) fluorine

d) potassium

e) sulfur

12) Which of these elements has the smallest atomic radius?

a) potassium

b) iron

c) arsenic

d) bromine

e) krypton

13) Which of these elements has the highest first ionization energy?

a) oxygen

b) oxygen

c) fluorine

d) carbon

e) boron

14) Which of these elements has the highest electronegativity?

a) lithium

b) nitrogen

c) potassium

d) arsenic

e) beryllium

Lewis Dot Structure Practice Problem Answers

1)PBr3

2)N2H2

3)CH3OH

4)NO2-1

5)C2H4

6)BSF

7)HBr

8)C2H5OH (ethanol)

9)N2F4

10)SF6

Chemical Bonding Practice Problem Answers

1) How are ionic bonds and covalent bonds different?

Ionic bonds result from the transfer of electrons from one atom to another; Covalent bonds result from two atoms sharing electrons.

2) Describe the relationship between the length of a bond and the strength of that bond.

Strength of a bond increases as the bond gets shorter (inverse relationship)

3) Identify the type(s) of bond(s) found in the following molecules:

CCl4___covalent______
Li2O ___ionic______
NF3___covalent______
CaSO4___ionic and covalent______
SO2___covalent______

f. Mg(OH)2___ionic and covalent______

4) Determine if the bond between atoms in each example below is nonpolar covalent, polar covalent, or ionic.

a. H2___npc______

PCl___pc______

F2 ___npc______

NaBr___ionic______

NF __pc______

MgO__ionic______

CH __npc______

HCl__pc______

5) Proteins are large biological molecules. What type of bonds do they form? covalent

6) Carbohydrates are large biological molecules. What type of bonds do they form? covalent

7) Lipids are large biological molecules. What type of bonds do they form? covalent

8) Sugarsare large biological molecules. What type of bonds do they form? covalent

Types of Intermolecular Forces Practice Problem Solutions

What is the strongest intermolecular force present for each of the following compounds?

1)water hydrogen bonding

2)carbon tetrachloride London dispersion forces

3)ammonia hydrogen bonding

4)carbon dioxide London dispersion forces

5)phosphorus trichloride dipole-dipole forces

6)nitrogen London dispersion forces

7)ethane (C2H6) London dispersion forces

8)acetone (CH2O) dipole-dipole forces

9)methanol (CH3OH) hydrogen bonding

10)borane (BH3) dipole-dipole forces

For each of the following compounds, determine the main intermolecular force. You may find it useful to draw Lewis structures for some of these molecules:

11)nitrogen – Van der Waals forces

12)carbon tetrachloride – Van der Waals forces

13)H2S – dipole-dipole forces

14)sulfur monoxide – dipole-dipole forces

15)N2H2 – hydrogen bonding

16)boron trihydride – Van der Waals forces

17)CH4O – hydrogen bonding

18)SiH2O – dipole-dipole forces

Balancing Chemical Equations – Answer Key

Balance the equations below:

1)1 N2 + 3 H22 NH3

2)2 KClO32 KCl + 3 O2

3)2 NaCl + 1 F22 NaF + 1 Cl2

4)2 H2 + 1 O22 H2O

5)1 Pb(OH)2 + 2 HCl 2 H2O + 1 PbCl2

6)2 AlBr3 + 3 K2SO46 KBr + 1 Al2(SO4)3

7)1 CH4 + 2 O21 CO2 + 2 H2O

8)1 C3H8 + 5 O23 CO2 + 4 H2O

9)2 C8H18 + 25 O216 CO2 + 18 H2O

10)1 FeCl3 + 3 NaOH 1 Fe(OH)3 + 3 NaCl

11)4 P + 5 O22 P2O5

12)2 Na + 2 H2O 2 NaOH + 1 H2

13)2 Ag2O 4 Ag + 1 O2

14)1 S8 + 12 O28 SO3

15)6 CO2 + 6 H2O 1 C6H12O6 + 6 O2

16)1 K + 1 MgBr 1 KBr + 1 Mg

17)2 HCl + 1 CaCO31 CaCl2 + 1 H2O + 1 CO2

18)1 HNO3 + 1 NaHCO31 NaNO3 + 1 H2O + 1 CO2

19)2 H2O + 1 O22 H2O2

20)2 NaBr + 1 CaF22 NaF + 1 CaBr2

21)1 H2SO4 + 2 NaNO22 HNO2 + 1 Na2SO4

Mole Problems Answers

Question 1

How many moles of copper are in 6,000,000 atoms of copper? 9.96 x 1019 moles of copper

Question 2

How many atoms are in 5 moles of silver? 3.01 x 1024 atoms of silver

Question 3

How many atoms of gold are in 1 gram of gold? 3.06 x 1021 atoms of gold

Question 4

How many moles of sulfur are in 53.7 grams of sulfur? 1.67 moles of sulfur

Question 5

How many grams is a sample containing 2.71 x 1024 atoms of iron? 251.33 grams of iron.

Question 6

How many moles of lithium (Li) are in 1 mole of lithium hydride (LiH)? 1 mole of lithium

Question 7

How many moles of oxygen (O) are in 1 mole of calcium carbonate (CaCO3)? 3 moles of oxygen

Question 8

How many atoms of hydrogen are in 1 mole of water (H20)? 1.20 x 1024 atoms of hydrogen

Question 9

How many atoms of oxygen are in 2 moles of O2? 2.41 x 1024 atoms of oxygen

Question 10

How many moles of oxygen are in 2.71 x 1025 molecules of carbon dioxide (CO2) 90 moles

Question 11

Predict the mass of a mole of magnesium atoms. 24.3 grams

Question 12

Calculate the molecular weights of carbon dioxide (CO2) and sugar (C12H22O11) and the mass of a mole of each compound. 44 g CO2, 324 g C12H22O11

Question 13

Describe the difference between the mass of a mole of oxygen atoms and a mole of O2 molecules. The mass of a mole of oxygen (O) is only 16 grams, while the mass of the diatomic oxygen (O2) is twice that, or 32 grams because each molecule contains two oxygen atoms.

Question 14 Calculate the mass in grams of a single 12-C atom. 12 grams

Moles, Molecules, and Grams Worksheet – Answer Key

1)How many molecules are there in 24 grams of FeF3? 1.28 x 1023 molecules

2)How many molecules are there in 450 grams of Na2SO4? 1.91 x 1024molecules

3)How many grams are there in 2.3 x 1024 atoms of silver? 421 grams

4)How many grams are there in 7.4 x 1023 molecules of AgNO3? 209 grams

5)How many grams are there in 7.5 x 1023 molecules of H2SO4? 122 grams

6)How many molecules are there in 122 grams of Cu(NO3)2? 3.92 x 1023 molecules

7)How many grams are there in 9.4 x 1025 molecules of H2? 312 grams

8)How many molecules are there in 230 grams of CoCl2? 1.07 x 1024 molecules

9)How many molecules are there in 2.3 grams of NH4SO2? 1.69 x 1022 molecules

10)How many grams are there in 3.3 x 1023 molecules of N2I6? 430 grams

11)How many molecules are there in 200 grams of CCl4? 7.82 x 1023 molecules

12)How many grams are there in 1 x 1024 molecules of BCl3? 195 grams

13)How many grams are there in 4.5 x 1022 molecules of Ba(NO2)2? 17.1 grams

14)How many moles are in 15 grams of lithium? 0.46 moles

15)How many grams are in 2.4 moles of sulfur? 77.0 grams

16)How many moles are in 22 grams of argon? 0.55 moles

17)How many grams are in 88.1 moles of magnesium? 2141 grams

18)How many moles are in 2.3 grams of phosphorus? 0.074 moles

19)How many grams are in 11.9 moles of chromium? 618.8 grams

20)How many moles are in 9.8 grams of calcium? 0.24 moles

21)How many grams are in 238 moles of arsenic? 17,826 grams

Solutions for the Stoichiometry Practice Worksheet:

For both of the problems on this worksheet, the method for solving them can be found elsewhere in the “Mr. Guch’s Helpdesk” section of my website ( If you’re having problems with stoichiometry problems, I would highly suggest consulting this section of the site before answering these questions.

When doing stoichiometry problems, people are frequently worried by statements such as “if you have an excess of (compound X)”. This statement shouldn’t worry you… what it really means is that this isn’t a limiting reagent problem, so you can totally ignore whatever reagent you have an excess of. Don’t even give it a second thought, because if you do, you’ll run into trouble.

1)355.3 grams of Na2SO4

2)313.6 grams of LiNO3

3) Write the balanced equation for the reaction of acetic acid with aluminum hydroxide to form water and aluminum acetate:

3 C2H3O2H + Al(OH)3 Al(C2H3O2)3 + 3 H2O

4)Using the equation from problem #1, determine the mass of aluminum acetate that can be made if I do this reaction with 125 grams of acetic acid and 275 grams of aluminum hydroxide.

Two calculations are required. One determines the quantity of aluminum acetate that can be made with 125 grams of acetic acid and the other determines the quantity of aluminum acetate that can be made using 275 grams of aluminum hydroxide. The smaller of these two answers is correct, and the reagent that leads to this answer is the limiting reagent. Both calculations are shown below – the correct answer is circled.

5)What is the limiting reagent in problem #2? Acetic acid.

6)How much of the excess reagent will be left over after the reaction is complete?

Pressure and Diffusion Practice Problem Answers

1) Simple diffusion is defined as

a) molecules from areas of higher concentration to areas of lower concentration.

b) molecules from areas of lower concentration to areas of higher concentration.

c) water molecules across a membrane.

d) gas molecules across a membrane.

e) water or gas molecules across a membrane.

2) When sugar is mixed with water, equilibrium is reached when

a) molecules of sugar stop moving.

b) water and sugar molecules are moving at the same speed.

c) the dissolved sugar molecules are evenly distributed throughout the solution.

d) there are the same number of water molecules as dissolved sugar molecules.

e) two tablespoons of coffee are added.

3) The rate of diffusion is affected by which of the following?

a) temperature

b) size of molecules

c) steepness of the concentration gradient

d) A and B

e) A, B, and C

4) The molecules in a solid lump of sugar do not move.

a) True

b) False

5) Which of the following is the best explanation of why a decrease in volume causes an increase in pressure?

a) At a smaller volume the atoms will move faster and hit the sides more often.

b) At a smaller volume the atoms will slow down and so they will have more contact with the walls

of the container.

c) At a smaller volume the atoms will have less room to move around, so they will collide with the sides more often.

d) The initial statement is false. Gas pressures do not increase when the volume is decreased.

6) What are the five assumptions we make about an ideal gas?

All gas particles are in constant, random motion.

All collisions between gas particles are perfectly elastic (meaning that the kinetic energy of the system is conserved).

The volume of the gas molecules in a gas is negligible.

Gases have no intermolecular attractive or repulsive forces.

The average kinetic energy of the gas is directly proportional to its Kelvin temperature and is the same for all gases at a specified temperature.

Gas Laws Practice Problem Answers

Use Boyles’ Law to answer the following questions:

1)1.00 L of a gas at standard temperature and pressure is compressed to 473 mL. What is the new pressure of the gas? 2.11 atm

2)In a thermonuclear device, the pressure of 0.050 liters of gas within the bomb casing reaches 4.0 x 106 atm. When the bomb casing is destroyed by the explosion, the gas is released into the atmosphere where it reaches a pressure of 1.00 atm. What is the volume of the gas after the explosion?

2.0 x 105 L

3)The temperature inside my refrigerator is about 40 Celsius. If I place a balloon in my fridge that initially has a temperature of 220 C and a volume of 0.5 liters, what will be the volume of the balloon when it is fully cooled by my refrigerator? 0.47 L

4)A man heats a balloon in the oven. If the balloon initially has a volume of 0.4 liters and a temperature of 20 0C, what will the volume of the balloon be after he heats it to a temperature of 250 0C? 0.71 L

5)If I have 4 moles of a gas at a pressure of 5.6 atm and a volume of 12 liters, what is the temperature? 205 K

6)If I have an unknown quantity of gas at a pressure of 1.2 atm, a volume of 31 liters, and a temperature of 87 0C, how many moles of gas do I have?

1.26 moles

Convert the following temperatures into the unit required. 7) 100 K into C -173 C

8) 323 K into C50 C

9) 100 C into K373 K

10) 25 C into K298 K

pH Scale Practice Problem Answers

1) Five solutions A, B, C, D, E when tested with universal indicator showed a pH of 4, 1, 11, 7, and 9 respectively.

a) Which solution is (i) neutral, (ii) strongly alkaline, (iii) strongly acidic, (iv) weakly acidic, and (v) weakly alkaline?

b) Arrange the pH in increasing order of hydrogen ion comcentration.

2) Define the term "pH"; what does" pH" stand for?

Answer: The term "pH" is defined as the negative logarithm of H+ ion concentration of a given solution; the concentration being expressed as moles per litre. Mathematically pH = - log [H+] 'pH' stands for: Power of hydrogen ion concentration, 'p' for power and 'H' for H+ ion concentration.

3) What is 'pH' scale? Explain briefly.

Answer: The strength of an acid or a base is expressed in terms of hydronium ion concentration. This is expressed on a scale known as 'pH' scale. It is a 14 point scale; i.e., it has values ranging from 0 to 14, indicating the value of negative logs of H+ ion concentration of the solution. Some important benchmark values in the pH scale are: pH = 7 indicates neutral solutions e.g., aqueous solutions. pH > 7 to 14 indicates alkaline solutions and pH < 7 to 0 indicate acidic solutions

4) What is the 'pH' of pure water and that of rain water? Explain the difference.

Answer: The pH of pure water is seven. Rain water is slightly acidic because as rain drop fall, the carbon dioxide in the air dissolves with drops to form very weak carbonic acid. Accordingly, rain water has a pH that is slightly below 7.

5) What is the pH of solution 'A' which liberates CO2 gas with a carbonate salt? Give the reason?

Answer: The pH of solution 'A' is lesser than 7. Carbonates salts react with acids (A) to liberate CO2 gas.

6) What is the pH of solution 'B' which liberates NH3 gas with an ammonium salt? Give reason?

Answer: The pH of solution 'B' is lesser than 7 because 'B' is an alkali as it liberates NH3 gas.

7) How do you increase or decrease the pH of pure water?

Answer: By adding a few drops of alkali to pure water, it's pH increases; and by adding a few drops of an acid decreases the pH of pure water.

8) What are indicators?

Answer: Indicators are chemicals that show whether the given solution is acidic or basic, by the sudden change of color.

Types of Acids and BasesPractice Problem Answers

1) What is the pH of the solution with a hydronium concentration [H3O+] 1.47 x 10-4?

What is the pOH of this solution?

pH = 3.83

pOH = 10.17

2) What is the pOH of the solution with a hydroxyl concentration [OH-] 2.98 x 10-2?

What is the hydronium concentration [H3O+] of this solution?

pOH = 1.53 hydronium concentration [H3O+] = 3.37 x 10-13 OR pH = 12.47

hydronium concentration [H3O+] = 3.38 x 10-13

3) What is the hydronium concentration [H3O+] of a solution with a pH of 7.84?

What is the hydroxyl concentration [OH-] of this solution?

hydronium concentration [H3O+] = 1.45 x 10-8

hydroxyl concentration [OH-] = 6.90 x 10- OR pOH = 6.16hydroxyl concentration [OH-] = 6.9 x 10-7

4) What is the hydroxyl concentration [OH-] of a solution with a pH of 3.76?

hydroxyl concentration [OH-] = 5.75 x 10-11

5) What is the hydronium concentration [H3O+] of a solution with a pOH of 2.47?

hydronium concentration [H3O+] = 2.95 x 10-12

Identify the following compounds as a strong acid, weak acid, strong base, or a weak base.

NaOH strong acid

HClstrong acid

H2CO3weak acid

KOHstrong base

H2SO4strong acid

LiOH strong base

NH3weak base

Solute, Solvent/ Dissolving Process Practice Problem

Answers

Distinguish in the following examples between the solute and the solvent.

nail polish (solute) acetone (solvent)
glue (solute) acetone (solvent)
eggshells (solute) vinegar (solvent)

iodine (solute) hexane (solvent)
chromium (solute) hydrochloric acid (solvent)

Kool Aid (solute) water (solvent)

Describe the difference between unsaturated, saturated, and supersaturated solutions.

At the maximum solubility the solution is saturated and in dynamicequilibrium with the insoluble part of solute. Such a solution is called saturated. Solution with less concentration is call unsaturated.

NaCl(s) <==> Na+(aq) + Cl(aq)

If there is more solute dissolved than saturation allows, the solution is said to be supersaturated.

Draw a picture showing a salt crystal.

Now draw how that salt crustal dissolves in a water solution.

Dissolving and Solution Concentration Answers

1)How many grams of beryllium chloride are needed to make 125 mL of a 0.050 M solution?

0.50 grams

2)How many grams of beryllium chloride would you need to add to 125 mL of water to make a 0.050 molal solution?

0.50 grams

3)The density of ethanol is 0.789 g/mL. How many grams of ethanol should be mixed with 225 mL of water to make a 4.5% (v/v) mixture?

7.99 grams

4)Explain how to make at least one liter of a 1.25 molal ammonium hydroxide solution.

Dissolve 43.8 grams (1.25 moles) of ammonium hydroxide in 1 L H2O.

5)What is the molarity of a solution in which 0.45 grams of sodium nitrate are dissolved in 265 mL of solution.

0.020 M

6)What is the mole fraction of sulfuric acid in a solution made by adding 3.4 grams of sulfuric acid to 3,500 mL of water?

1.8 x 10-4

7)What will the volume of a 0.50 M solution be if it contains 25 grams of calcium hydroxide?

680 mL

8)How many grams of ammonia are present in 5.0 L of a 0.050 M solution?

4.3 grams

Endothermic and Exothermic Practice Problem Answers

1) What type of chemical reaction absorbs energy and requires energy for the reaction to occur?

a. endothermic

b. exothermic

c. synthesis

d. both A and B

2) What type of reaction releases energy and does not require initial energy to occur?

a. endothermic

b. exothermic

c. decomposition

d. both A and B

3) Which of the following are examples of an exothermic chemical reaction? Check all that apply.

a. photosynthesis

b. burning a piece of wood

c. freezing ice into water

d. none of the above

4) Which type of reactions cannot occur spontaneously?

a. endothermic

b. exothermic

c. neither

5) Any type of reaction that involves burning (combustion) can be classified as which of the following types of reactions?

a. synthesis

b. endothermic

c. exothermic

d. all of the above

6) Burning sugar is an exothermic process.

a. True

b. False

7) What is enthalpy?

a. heat content

b. absolute amount of energy is a chemical system

c. the reactants of the chemical reaction

d. none of the above

8) A 100 g sample of water at 25 oC and 1 atm. of pressure _?_ than 100 g of water that has recently been heated to 100 oC from 0 oC and then cooled to 25 oC at 1 atm. of pressure.

a. has more internal energy than

b. has less internal energy than

c. has the same internal energy as

9) Water has a specific heat of 4.184 J/g deg while glass (Pyrex) has a specific heat of 0.780 J/g deg. If 10.0 J of heat is added to 1.00 g of each of these, which will experience the larger increase of temperature?

a. glass

b. water

c. They both will experience the same change in temperature since only the amount of a substance relates to the increase in temperature.

Specific Heat Practice Problem Answers

1) cp = 0.0042 J/gC

2) final temperature of metal and water is 76C

3) final temperature of metal and water is 97C

4) 8.8 x 105 J 5) 3.2 x 104 J 6 a) 5.52 ºC b) 10.1 ºC

Changing the Rate of a Reaction Problem Answers

1. A

The activation energy is the energy that must be overcome for the reaction to proceed. Also remember that for a reaction to occur, the collisions between molecules must be sufficiently energetic and of the proper geometric orientation.

2. C

The energy change for the overall reaction is simply the difference between the energies of the products and reactants, and this is indicated by the letter C on the diagram.