Chemistry Exam 2

Determine if the following formulas represent ionic or molecular compounds a. Al2S3 B. P2O5 C. MgBr2 D. K2O

(a) Ionic (b) Molecular (c) Ionic (d) Ionic

Main group element

: any element labeled with letter A

The Periodic Table

: in which all known elements are arranged in columns and rows to emphasize periodic properties

How many moles of NaOH are in 1.85 L of a 0.250 M NaOH solution? A. 0.463 mols B.7.40 mols A.0.000460 mols B.463 mols

A

Approimately how much greater in mass is a D2 molecule than an H2 molecule

Deuterium, an isotope of hydrogen with 1 neutron and 1 proton, has a mass number of 2. A molecule of D2 has a mass of 4 amu and a molecule of H2 has a mass of 2 amu. Therefore, the mass of D2 is 2 amu greater (or two times greater) than the mass of H2.

Mass in grams to moles

Divide by molar mass

Ammonium

NH4+

Nitrate

NO3-

Hydroxide

OH-

Phosphate

PO4 3-

Naming Ionic Compounds

Roman numeral in a compound name represent the charge on the metal cation in an ionic compound Determining names for ionic compounds that contain metals that exhibit multiple charges: not a polyatomic ion name cation by stating the element name followed by the charge of the cation using Roman numerals then state the root of the element name for the anion and ade ide to the suffix Older method: suffix either ous or ic to the root of the original latin name for the metal, ous indicates lower of the two charges, ic indicates higher

Sulfate

SO4 2-

Naming different polyatomic ions

Start with the base name ending in "ate". •If one less oxygen change the name ending it "ite". or some of the polyatomics there are 4 variations based on the number of oxygens: ClO4- ClO- ClO3- ClO2- Chlorate Chlorite Perchlorate Hypochlorite

What is the approximate mass, in atomic mass units, of the folowing isotopes a. 2/1 H b. 238/92 U

The approximate mass of an isotope is equivalent to its mass number. This is true since most of the mass of an atom comes from the protons and neutrons in the nucleus. (a) 2 amu; (b) 238 amu

How do an atom and an ion of the same element differ?

They differ in the number of electrons. The identity of an atom or an ion is determined by the number of protons in the nucleus. However, ions have different numbers of electrons than protons. This is why ions are charged. For example, the ion N3- is similar to the N atom because it has 7 protons, but the ion has 10 electrons. The three "extra" electrons give the ion the 3- charge

How many atoms are in each of the following samples of carbon-12 a. 120 amu b. 12,000 amu c. 7.22 x 1024 amu

To calculate the number of carbon-12 atoms, we can convert amu to atoms using the atomic mass of carbon-12 (defined as exactly 12):Number of atoms = = atoms126 Catomsmassinamu12amux126C (a) 10. atoms; (b) 1.0 x 103 atoms; (c) 6.02 x 1023 atoms (see calculation below)1 26C126C126CNumber of atoms = = 6.02 x 1023 atoms

An unknown element (x) discovered on a planet in another galaxy was found to exist as two isotopes. What is the relative atomic mass of the element 22X mass: 21.995 Natural abundance %: 75 20X mass: 19.996 Natural abundance %: 25

To calculate the relative atomic mass we calculate the weighted average of the isotopes of X. Isotope mass x abundance = mass contribution from isotope21.995 amu x 0.7500 =16.50 amu22X 919.996 amu x 0.2500=5.00 amu20X21.50 amu (relative atomic mass of X

What forms when a Neutral atom undergoes each of the following changes a. gains one electron b. loses two electrons

When an atom gains one electron, an anion with a 1- charge is formed. For example, when a fluorine atom, with 9 protons and 9 electrons, gains 1 electron, there are 10 negative charges and 9 positive charges. This means that the resulting ion will have a 1- charge (F-). (b) When an atom loses two electrons, a cation with a 2+ charge is formed. For example, when a magnesium atom, with 12 protons and 12 electrons, loses 2 electrons, there are 12 positive charges and 10 negative charges. This means that the resulting ion will have a 2+ charge (Mg2+).

Based on their formulas which of the following compounds are ionic A. KCl B. CO2 C. CaO D. CCl4

a and c

Nomenclature

a system of naming

What forms when an ion with a 1+ charge undergoes each of the following changes a. it gains one electron b. it loses two electrons

a) The neutral atom is reformed.(b) A -1 anion is formed.

Molecular formula: tells us

actual number of atoms present in a single molecule of a compound

Dilution

adding more solvent to a solution to lower concentration of a solution, don't change moles

Monatomic ion

an ion of a single atom. The compound MgS consists of monatomic ions Anions are named as the first part of the element name with ide added as a suffice Cations are not given special endings to their root names, Na+ is a sodium ion

Transition metal

any element in any of the ten groups labeled with the letter B

Alkali

any member in group IA except hydrogen

What is the percent composition of potassium in potassium sulfate? A.28.9% B.44.8% C.32.8% D.24.7%

b Chemical formula: K2SO4Molar mass = 174.26 g/mol% K: 2 x 39.10 g/mol of K 174.26 g/mol of K2SO4x 100 = 44.8% K

Trivial

binary molecular compounds trivial names, such names often bear no direct relation to the compound's composition H20 is known as water

A 7.50 g sample of iron(II) sulfide contains 4.76 g of iron. How many grams of sulfur would be in a second sample of iron(II) sulfide with a mass of 85.0 g? A.53.9 g S B.43.7 g S C. 31.1 g S D. 20.7 g S

c Mass of sulfur: 7.50 - 4.76 = 2.74 gMass percent of sulfur: 2.74/7.50 x 100 = 36.5%36.5% of 85.0 g = 31.05 g 31.1 g S

Lithium carbonate, Li2CO3, is 18.8% by mass lithium. What mass of lithium is present in a 1.20-g sample of lithium carbonate? A.97.4 mg B.18.8 mg C.226 mg D.6.38 mg

c. .188 x 1.20 g = 0.2256 g0.2256 g => 225.6 mg

If a lab procedure requires 4.25 moles of calcium chloride (MM = 110.98 g/mol), what mass is needed?A.2.56 x 1024 g B.321 g C.472 g D.0.0383 g

c. 4.25 mol CaCl2 110.98 g CaCl2 1 mol CaCl2= 471.665 g 472 g

Organic (carbon-based):

compounds that contain the combination of atoms CO2H, called carboxylic acids

Ionic Compound

consists of oppositely charged cations and anions in proportions that give a net zero charge. Ionic compounds are easily identified because they usually consist of ions from a metal with ions from a nonmetal.

Polyatomic ion

containing two or more atoms, usually of more than one element

Mole

contains 6,022 X 10^23 atoms, molecules, ions, or formula unit

Concentrated solution:

contains a comparatively large amount of solute

Dilute solution

contains a relatively small amount of solute

Quartz, SiO2, is 46.7% silicon by mass. What mass of oxygen is present in 348 g SiO2? A. 7.45 g O B. 159 g OC. 163 g O D. 185 g O

d. ass percent of oxygen = 100% - 46.7% = 53.3%Mass oxy = 53.3% x 348 g = 0.533 x 348 g = 185.5 g O

Ionic Compounds

dissociate in water, crystalline solid, hard brittle solid, very high melting point, very high boiling point, high density, strong electrolyte in aqueous solution, electrical conductivity is good when compound is molten

Strong electrolyte

dissociates extensively in water, in conducts electricity well

Naming acids:

does the acid contain polyatomic no, use a hydro prefix, state teh root fo the element name for the non hydrogen element and add a ice suffix. End the name with the word acid. If yes, replace the -ate ending of a polyatomic ion with ic replace ite ending with ous, end the name with the word acid

atomic mass unit (amu)

equal to one-twelfth the mass of a carbon-12 atom There are three different naturally occurring isotopes of hydrogen each with a different mass

Empirical formula

expresses the simplest ratios of atoms in a compound, not always the same as a molecular formula

Empirical Formulas with Fraction Mole ratios

fractional values may correspond to ratios of small whole numbers, multiply each ratio by a small whole number to make all the subscripts whole numbers

Determining Empirical Formulas

from data on chemical composition of a compound. We have converted masses to numbers of moles and number of atoms. Either set can give us the formula. Need relative number of atoms divide number of moles of each element by number of moles of element present in the least amount. You can round if close to whole numbers

Molecular compounds

gas liquid or solid, soft solid, low melting point, low boiling point, low density, weak electrolyte or nonelectrolyte in aqueous solution, electrical conductivity poor in pure form

Period

horizontal row, have the same properties that tend to vary in a regular fashion

Avogadro's number

is the same as the number of atoms in exactly 12 grams of the isotope carbon-12

Percent composition by mass

it is an expression of the portion of the total mass contributed by each element %E=mass of E/mass of sample) X 100%

Percent by mass

mass solute divided by mass solution times 100%

Diatomic molecules

molecule consisting of two atoms

Greek Prefixes

mono di tri tetra penta hexa hepta octa nona deca

Moles to Number of formula units

multiply by avogadro's number

Moles to number of atoms

multiply by avogadro's number and the number of atoms in the formula of the element you are trying to determine it for

Naming molecular compounds

name of a molecular compound must communicate the specific number of atoms of each element in the molecule ex: CO2 carbon dioxide and CO carbon monoxide

Binary acids in solution

named with the prefix hydro followed by the stem of the name of the nonmetal with ic and the word acid Classify compound before naming it Determining which rules to apply in naming compounds Does the compound contain a metal or ammonium ion, yes ionic compound if no molecular compound or acid

Anion

negatively charged ion that contains more electrons than the number of protons in the nucleus.

Mass number

not actual mass, it is a count of the number of particles in the nucleus

Molecular compound

not composed of ions. It is composed of atoms from two or more different nonmetals.

Molarity

number of moles of solute dissolved in one liter of solution not solvent

Nonelectrolyte

one that stays intact and does not separate into ions such as sugar

Ionic compounds consist of

oppositely charged ions that have a strong force of attraction between them. It would take a lot more energy to break apart teh ions of KCL thant to separate CCl4

Oxoanion

polyatomic ions are anions that contain oxygen attached to some other element, typically with a nonmetal. If only two oxoanions of an element the one with the greater number of oxygen atoms is named by combining the root of the nonmetal element name and the ending ate The oxoanion with the lesser number of oxygen atoms uses the ending ite

Cation

positively charged ion that contains fewer electrons than the number of protons in the nucleus. The overall charge is represented as a superscript to the right of the element symbol

Concentration

relative amounts of solute and solvent in it

Metalloid

semimetal is an element that has physical properties resembling a metal but chemical reactivity more like that of a nonmetal

Group

similar properties vertical

Solvent

substance doing the dissolving

Electrolyte

substance like NaCl that separates into ions when dissolved in water, conducts

Solute

substance that is dissolved

Base

substance that reacts with an acid in aqueous solution to form water Most common bases either contain hydroxide ion OH- or can provide OH- ions in solution. Ex: NaOH and NH3

Acid

substance that when dissolved in water provides hydrogen ions H+

Weak electrolyte

such a substance does not conduct electricity well

SO2 sulfur listed first because

sulfur is farther to the left and farther down on periodic table

Stock System

systematic method used to name ionic compounds, it uses roman numeral in parentheses after the name of the metal to indicate charge

Molar Mass

term that describes the mass of one mol of a substance g/mol Molar mass of a molecular or ionic substance has the same value as the sum of the relative atomic masses of its component elements Molar masses of molecules are obtained by adding the molar masses of the component elements each weighed by the number of that atom in the molecule

Relative Atomic Mass

the average of the mass of the individual isotopes, taking in account the naturally occurring relative abundance of each (shown on periodic table)

Acids are compounds that

usually contain a hydrogen atom that can be removed as a H+ ion when dissolved in water

When writing formulas for acids

we generally place the hydrogen first and write aq after the formula to indicate that the compound is an acid when dissolved in water

Ionization

when a compound that is not ionic provides ions when dissolved in water

Ion

when an atom contains more or less electrons than protons

What is the formula and name of the acid that forms b A. HClO Hyperchlorous acid B. HClO2 Hypochlorous . HClO3 Perchloric acid D. HClO4 Perchloric acid

D

Formulas for Ionic Compounds

Charged cations and anions that make up an ionic compound are present in quantities that result in a net charge of zero. Total positive + total negative = zero net charge Formula unit: smallest repeating unit

Chlorate

ClO3-

If a compound is formed from the elements shown below, between which ion pair is expected to have the greatest attractive energy? A. Na and Cl B. Ca and FC. Li and ND. Mg and P

A. Na and Cl +1 and -1 B. Ca and F +2 and -1 C. Li and N +1 and -3 D. Mg and P +2 and -3 This is the answer

What is the name of (NH4)3PO4?

A.Ammonium phosphideB.Ammonium phosphateC.Triammonium phosphateD.Ammonium(I) phosphate

The carbonate ion is CO32-. Which of the following is the formula for carbonite?

A.CO3- B.CO22- C.HCO32-

How many C atoms are in 3.80 mol of C2H4? A.2.28 x 1024 C atoms B.4.58 x 1024C atoms C.1.26 x 10-23 C atoms D.3.01 x 1024 C atoms

B 3.80 mol C2H42 mol C 1 molC2H46.022 x 1023 atoms1 mol Cxx= 4.58 x 1024 C atoms

Which of the following compounds have the same empirical formula? C10H18O2 C6H12O6C5H9O A. I and II B. II and III C. I and III D. None of them

C

Cyanide

CN-

Carbonate

CO3 2-

The listed formulas are incorrect. Determine what is wrong with each and correct it. a. NaCl2 b. KSO4 C. Al3NO3

For each "compound" written, the charges do not balance so the compounds would have a net charge. In compounds, the sum of the positive and negative charges balances to zero (i.e. all compounds are neutral).(a) Sodium ion is Na+ and chloride ion is Cl-. In NaCl2 there are too many chloride ions. Only one chloride ion is needed to balance the charge of the sodium ion. The correct formula is NaCl. (b) Potassium ion is K+ and sulfate ion is SO42. In the formula KSO4 there are not enough potassium ions to balance the 2 charge on the sulfate ion. The correct formula is K2SO4.(c) Aluminum ion has a charge of 3+ and nitrate ion has a charge of 1. In the formula AlNO3there are not enough nitrate ions. Three nitrate ions are needed to balance the charge of one aluminum ion. The correct formula is Al(NO3)3.

Hydronium ion

H3O+

Naming and Writing Formulas for Molecular Compounds; Acids

Is a polyatomic ion present-yes- name the cation by simply stating the element name, uf the compound contains NH4+ state ammonium as the first word of the name-state the name of the polyatomic ion as the second word of teh compound name If no-name the cation by simply stating the element name-state the root of the element name for the anion and add an -ide suffix.