CHEM 101 Ch 3 - Molecules, Compounds, and Atoms

How many atoms of oxygen are in a 0.78 mol sample of CaCO 3 ?

1.4x10^24atoms

How many grams of carbon and how many grams of hydrogen are in the original sample from Question 64?

11.2 g C and 1.25 g H

By which integer should the number of moles of each element be multiplied in the unknown sample?

2 The value for C (6.497 mol) is within 0.50 of a whole number, so every number of moles needs to be multiplied by 2.

What is the mass percent of magnesium in magnesium chloride? Your answer should have the appropriate number of significant figures (use two decimal places in atomic masses). Only give the numeric value of your answer. Don't include the percent sign.

25.53 mass % magnesium = 24.31gMg / (2x35.45 + 24.31) gMgCl2 x 100 = 24.31gMg / 95.21gMgCl2 x 100 = 25.53%

Fructose has the same empirical formula as glucose. What is the molar mass of fructose's empirical formula (in units of g/mol)? Your answer should have the appropriate number of significant figures (use two decimal places in atomic masses). Only give the numeric value of your answer. Don't include the units.

30.03 The empirical formula for glucose is CH2O, so the molar mass is 12.01 g/mol C + 2 × 1.01 g/mol H + 16.00 g/mol O = 30.03 g/mol.

What is the result when the number of moles of H is divided by the smallest amount? Your answer should have the appropriate number of significant figures (use two decimal places in atomic masses).

8.93 8.67/0.9706 = 8.93

How many grams of carbon are in a 100 gram sample of decane? Your answer should have the appropriate number of significant figures (use two decimal places in atomic masses). Only give the numeric value of your answer. Don't include the units.

84.39 mass percent carbon% (10x12.01)gC/(10x12.01 + 22x1.01) g C10H22 x100 = 120.1 gC / 142.32 g C10H22 x100 = 84.39%

Which of the following is the formula for iron(II) chloride dihydrate?

FeCl2 • 2H2O Iron(II) chloride is FeCl2 because it takes two chloride ions (each with a −1 charge) to create a neutral compound with Fe2+. Dihydrate indicates that there are two water molecules associated with the compound.

What is the formula of carbonic acid?

H2CO3 ​CO32− is carbonate, so it requires two hydrogen atoms to form a neutral compound. The hydrogen atoms are listed first because it's an acid.

KBr (ionic or covalent)

Ionic

What is the formula of xenon trioxide?

XeO3 The lack of a prefix on xenon means there is only one xenon atom. The tri- prefix on oxide means there are three oxygen atoms. ​

he formula of a covalent compound contains

all the atoms connected by these covalent bond(s)

What is the name of NH4HCO3?

ammonium bicarbonate or ammonium hydrogen carbonate NH4+ is always named ammonium, whereas HCO3− is named either bicarbonate or hydrogen bicarbonate unless it is in a compound with sodium, when it is also called baking soda.

Covalent compounds,

are typically made of two or more nonmetals and characterized by the atoms sharing their electrons

Lithium is in Group 1, so it is a

metal

Fluorine is in Group 7A, so it is a

non metal

Examples of binary compounds

sodium chloride (NaCl) and calcium oxide (CaO).

elements in a compound are listed

most metallic to least metallic or most positive to least positive or left to right and lower to higher based on placement on periodic table

nonmetals have a positive or negative charge when they become ions?

negative - by gaining one or more electrons

C5H12 what is the systematic name

pentane The compounds are named based on the number of carbon atoms in their formula.

metals have a positive or negative charge when they become ions?

positive - by losing one or more electron

in binary compounds, the nonmetal (the negatively charged anion) keeps its original name or takes on an -ide ending

takes on an -ide ending

LiF is the smallest number of cations and anions that form a neutral ionic compound, so it is

the formula unit.

Ionic compounds

usually are composed of a metal and a nonmetal, where one or more electrons have been completely transferred away from the metal, making it a positively charged cation, and giving the electron(s) to the nonmetal, making it a negatively charged anion.

NaCl (ionic or covalent?)

ionic

If there are four fluorine atoms and one sulfur atom in a compound, what is its chemical formula?

SF4

What is the empirical formula for acetic acid, CH3COOH?

CH2O The formula for acetic acid contains 2 carbon atoms, 4 hydrogen atoms, and 2 oxygen atoms. The smallest whole number ratio of these values is 1:2:1

Li+ is a positively charged ion, so it is a

cation

H2S(g)

hydrogen sulfide

A student measures out 45.62 g of sodium chloride on a laboratory scale. How many moles of sodium chloride have they weighed? Your answer should have the appropriate number of significant figures (use two decimal places in atomic masses). Only give the numeric value of your answer. Don't include the units.

0.7806 The molar mass (58.44 g/mol) of NaCl is used as a conversion factor. moles of NaCl (mol) = 45.62g NaCl x 1mol/ 58.44g NaCl = 0.7806 mol NaCl

If an unknown sample burns to create 41.1 g CO2, then how many moles of carbon were present in the original sample? Your answer should have the appropriate number of significant figures (use two decimal places in atomic masses). Only give the numeric value of your answer. Don't include the units.

0.934

How many moles of O are in the sample? Your answer should have the appropriate number of significant figures (use two decimal places in atomic masses). Only give the numeric value of your answer. Don't include the units.

0.9706 moles of O (mol) = 15.53 gOx 1mol/16.oogO = 0.9706 molO

What is the formula of barium fluoride?

BaF2 Because barium is a Group 2 metal, it takes a +2 charge. There must be two fluoride anions (each with a −1 charge) to create a neutral compound. ​

HI(aq)

Binary Acid is aqueous and its formula begins with "H", so it is an acid. Because it only contains two elements it is a binary acid

Classify the compound HCl(aq).

Binary acid H is first in the formula and it doesn't contain an oxygen.

C4H10 what is the systematic name

Butane The compounds are named based on the number of carbon atoms in their formula.

What is the formula of cobalt(III) bromide?

CoBr3 Cobalt has the Roman numeral III, so it has a +3 charge. There must be three bromide anions (each with a −1 charge) to create a neutral compound. ​

Which of the following is the name for the compound KH2PO4?

Potassium dihydrogen phosphate The name of the metal is unchanged (potassium). H2PO4−is called dihydrogen phosphate.

Which of the following is the name for the compound K2O?

Potassium oxide The compound follows the pattern metalnonmetal-ide where the potassium is the metal and oxygen is the nonmetal with the -ide ending. The name doesn't depend on the number of potassium or oxygen atoms in the compound.

If there are three oxygen atoms and one sulfur atom in a compound, what is its chemical formula?

SO3 ​

Which of the following is the name for the compound SF6?

Sulfur hexafluoride The first element does not get the mono- prefix. Because there are six fluorine atoms, it gets a hexa- prefix.

Which of the following is the name for the compound ZnCl2•6H2O?

Zinc chloride hexahydrate ZnCl2 follows the naming pattern for ionic compounds. Because there are six water molecules, zinc chloride is followed by hexahydrate.

What is the name of the compound NH4NO3?

ammonium nitrate The polyatomic ion NH4+ is ammonium and the polyatomic ion NO3− is nitrate.

F- is a negatively charged ion, so it is

an anion

Hydrogen is often an exception; it is listed after elements like

boron (BH3), carbon (CH4), and nitrogen (NH3)

metal(charge) nonmetal-ide Exceptions:

cations that only take one charge (Groups 1 and 2, Group 3 cations like aluminum (Al3+), and certain transition metals like zinc (Zn2+)) do not use Roman numerals for their charges.

Binary compounds

compounds that contain two different kinds of elements. When the two elements in a compound are a metal and a nonmetal, the metal will be listed first and the nonmetal second (a reminder that, in general, elements are listed in the order they appear in the periodic table, as you move across from left to right). The names of these compounds follow the pattern: "metal nonmetal-ide"

For both ionic and covalent compounds, the subscripts within the formula can also be used as a

conversion factor between the moles of the compound and the moles of the element within the compound. For example, in one mole of water (H2O) there are two moles of hydrogen and one mole of oxygen.

C2H6

covalent

CO2

covalent

H20 (ionic or covalent?)

covalent

C10H22 what is the systematic name

decane The compounds are named based on the number of carbon atoms in their formula.

C2H6 what is the systematic name

ethane The compounds are named based on the number of carbon atoms in their formula.

SO3 -Sulfur is below oxygen on the periodic table, so it is listed (first or second)

first

. Common anions include

halogens in Group 7A (which take a −1 charge), where their -ine ending is dropped for the -ide ending. Group 6A elements like oxygen and sulfur (with a −2 charge), called oxides and sulfides, respectively

Na3PO4(aq)

ionic compound made up of Na+ and PO4^-3

FeO

ionic compound s made of a metal (Fe) and a nonmetal (O) so it is an ionic compound.

SF4 - Sulfur appears first because

it is to the left of fluorine on the periodic table (indicating that it is "more metallic")

in binary compounds, the metal (the positively charged cation) keeps its original name or takes on an -ide ending

keeps its original name

Right side of periodic table is (more metallic or less metallic)

less metallic

The formula unit for ionic compounds reflects the

minimum number of each atom necessary for the compound to have an overall neutral charge, that is, for its charge to be zero. ex: So while a pinch of table salt may have many sodium and chloride ions, its formula unit is simply NaCl because it only takes one of each ion to make the sum of their charges equal zero.

Covalent compounds are commonly referred to by the shorter term

molecules

left side of periodic table is (more metallic or less metallic)

more metallic

H2CO3(aq)

oxoacid - is aqueous and its formula begins with "H", so it is an acid. Because it contains a polyatomic ion that has oxygens, it's an oxoacid

Hydrogen is often an exception; it is listed before elements like

oxygen (H2O) and sulfur (H2S)

How many moles of iron(II) chloride are in 54.1 mg?

4.27x10 mol The formula for iron(II) chloride is FeCl2, which has a molar mass of 126.75g/mol. moles of FeCl2(mol) = 54.1mg FeCl 2 x 1g/1000mg x 1mol / 126.75g FeCl2 = 0.000427 mol FeCl2

If 29.9 g of the sample were originally burned, then how many moles of oxygen were present in the original sample from Question 64? Your answer should have the appropriate number of significant figures (use two decimal places in atomic masses). Only give the numeric value of your answer. Don't include the units.

1.09 29.9 total grams - (11.2 g C + 1.25 g H) = 17.4 g oxygen.

If the unknown sample from Question 64 burns to create 11.2 g H2O, then how many moles of hydrogen were present in the original sample? Your answer should have the appropriate number of significant figures (use two decimal places in atomic masses). Only give the numeric value of your answer. Don't include the units.

1.24

Potassium nitrate is used for a variety of applications, including fertilizer, rocket fuel, and fireworks. How many molecules of potassium nitrate are in a 25 g sample?

1.5×10^23 molecules molecules of KNO3 = 25gKNO3 x 1mol/101.11gKNO3 x 6.022x10^23 molecules/1mol = 1.5 x 10^23 molecules

How many grams of O are in a 100.0 g sample of the unknown? Your answer should have the appropriate number of significant figures. Only give the numeric value of your answer. Don't include the units.

15.53 If there are 100 g of the sample, then the mass percent is equal to the number of grams.

If a linear alkane has 12 carbon atoms, how many hydrogen atoms will it have?

26 (12 x 2) +2=26

What is the molar mass of carbon monoxide (in units of g/mol)? Your answer should have the appropriate number of significant figures (use two decimal places in atomic masses). Only give the numeric value of your answer. Don't include the units.

28.01 molar mass of CO(g/mol) = 12.01 g/molC + 16.00 g/mol O = 28.01 g/mol CO When the compound contains more than one atom of a given element, its mass must be taken into account for each occurrence.

Limestone is primarily a crystal form of CaCO 3 How many moles of oxygen are in a 1.25 mol sample of CaCO 3? Only include the numerical value in your answer. Do not include units.

3.75

What is the molar mass of carbon dioxide (in units of g/mol)? Your answer should have the appropriate number of significant figures (use two decimal places in atomic masses). Only give the numeric value of your answer. Don't include the units.

44.01 molar mass of CO2 (g/mol) = 12.01 g/mol + 2 x 16.00 g/mol O = 44.01 g/mol CO2 The molar mass of ionic compounds is referred to as the "formula mass" because ionic compounds are described by their formula unit.

What is the formula mass of sodium chloride (in units of g/mol)? Your answer should have the appropriate number of significant figures (use two decimal places in atomic masses). Only give the numeric value of your answer. Don't include the units.

58.44 molar mass of NaCl (g/mol) = 22.99 g/mol Na + 35.45 g/mol Cl = 58.44g/mol Na Cl

If the molar mass of fructose's chemical formula is 180.16 g/mol, then what is the whole number ratio of the mass of the chemical formula to the mass of the empirical formula?

6 180.16/30.03 = 5.999, which rounds to 6.

What is the result when the number of moles of C is divided by the smallest amount? Your answer should have the appropriate number of significant figures (use two decimal places in atomic masses).

6.497 6.306/0.9706 = 6.497

How many moles of H are in the sample? Your answer should have the appropriate number of significant figures (use two decimal places in atomic masses). Only give the numeric value of your answer. Don't include the units.

8.65 moles of H (mol) = 8.74gHx 1mol/1.01gH = 8.65molH

How many grams of H are in a 100 g sample of the unknown? Your answer should have the appropriate number of significant figures (use two decimal places in atomic masses). Only give the numeric value of your answer; don't include the units.

8.74 Explanation If there are 100 g of the sample, then the mass percent of the element is equal to the number of grams of the elements.

What is the empirical formula for the unknown sample? Give your answer in the form C#H#O#, where the number following the element's symbol corresponds to the subscript in the formula

C13H18O2 6.497 x2 = 13 mol C, 8.93 x2 = 18 mol H, and 1 x2 = 2 mol O.

What is the empirical formula of the compound in Question 64? Give your answer in the form C#H#O#, where the number following the element's symbol corresponds to the subscript in the formula. (Don't include a 1 subscript explicitly.) For example, the formula CH2O would be entered as CH2O.

C3H4O3 or C6H8O7

Based on the ratio determined in Question 60, what is the chemical formula for fructose? Give your answer in the form C#H#O#, where the number following the element's symbol corresponds to the subscript in the formula.

C6H12O6 Because the chemical formula is six times heavier than the empirical formula, each subscript must be multiplied by six.

What is the formula for carbon tetrafluoride? Give your answer in the form A#B#, where the number is the subscript (don't include a 1 subscript explicitly). For example, the formula MgCl2 would be entered as MgCl2.

CF4 The lack of a prefix on carbon means there is only one carbon atom. The tetra- prefix on the fluoride means there are four fluorine atoms.

A laboratory analysis of a sample finds it is composed of 38.8% carbon, 16.2% hydrogen, and 45.1% nitrogen. What is its empirical formula? Give your answer in the form C#H#N#, where the number following the element's symbol corresponds to the subscript in the formula (Don't include a 1 subscript explicitly). For example, the formula CH2O would be entered as CH2O.

CH5N 38.8%C -> 38.8gC X 1MOL/12.01gC = 3.23 molC 16.2% H -> 16.2 gHx 1mol/1.01 gH = 16 mol H 45.1%N -> 45.1 gN x 1mol/14.01 gN = 3.22 molN 3.23/3.22 = 1.003 -> 1molC 16.2/3.22 = 5.031 -> 5 mol H 3.22/3.22 = 1.000 -> 1molN

What is the formula of calcium nitrite?

Ca(NO2)2 Because calcium is a Group 2 metal, it takes a +2 charge. There must be two nitrite anions (each with a −1 charge) to create a neutral compound. Note that the subscript indicating there are two nitrite anions is outside the parentheses enclosing the nitrite.

Which of the following is the name for the compound Cr2O3 ?

Chromium(III) oxide Because there are three −2 anions, together the chromium ions must have a total charge of +6 and each chromium ion must be +3.

What is the formula for cobalt(II) chromate? Give your answer in the form A#B#, where the number is the subscript (don't include a 1 subscript explicitly). For example, the formula MgCl2 would be entered as MgCl2.

CoCrO4 Because cobalt has the Roman numeral II it has a +2 charge. Chromate, CrO4^2− , has a −2 charge. There must be one cobalt cation and one chromate polyatomic ion to create the neutral compound CoCrO4 ​ .

PCl3

Covalent Compound is made of two nonmetals, so it is covalent.

Classify the compound CCl4.

Covalent compound Both carbon and chloride are nonmetals.

What is the formula for copper(II) phosphide? Give your answer in the form A#B# where the number is the subscript.

Cu3P2 Copper has the Roman numeral II, so it has a +2 charge. Phosphide has a −3 charge. There must be three copper cations and two phosphide anions to create the neutral compound Cu3P2 ​ .

Which of the following is the name for the compound N2O4?

Dinitrogen tetraoxide. Because there are two nitrogen atoms, N gets a di- prefix. Because there are four oxygen atoms, O gets a tetra- prefix

A laboratory analysis of a 100 g sample finds it is composed of 1.8 g hydrogen, 56.1 g sulfur, and 42.1 g oxygen. What is its empirical formula? Give your answer in the form H#S#O#, where the number following the element's symbol corresponds to the subscript in the formula. (Don't include a 1 subscript explicitly.) For example, the formula CH2O would be entered as CH2O.

H2S2O3

What is the formula for acetic acid? Give your answer in the form A#B#, where the number is the subscript (don't include a 1 subscript explicitly). For example, the formula MgCl2 would be entered as MgCl2.

HC2H3O2 or HOOCCH3 C2H3O2− and - OOCCH3 are both ways of writing acetate. As an acid, the additional hydrogen atom is listed first.

What is the formula for hydrocyanic acid? Give your answer in the form A#B#, where the number is the subscript (don't include a 1 subscript explicitly). For example, the formula MgCl2 would be entered as MgCl2.

HCN or HCN(aq) The acidic form of cyanide (CN−) is named like a binary acid.

What is the formula of hydroiodic acid?

HI The hydro- prefix indicates the compound is a binary acid. Iodic is the -ic form of iodine (I).

Which of the following is the formula for nitrous acid?

HNO2 ​xplanation Because NO2 is nitrite, the acid takes the -ous ending

Which of the following is the name for molecular HF when it is dissolved in water?

Hydrofluoric acid Because the compound is a binary acid (as indicated by the hydrogen being first in the formula, and it being in aqueous solution), it takes the hydro- prefix and ends in acid.

H2Se(g)

Hydrogen selenide

H2Se(aq)

Hydroselenic acid

H2S(aq)

Hydrosulfuric acid

Na2O

Ionic

Classify the compound KNO3 ​

Ionic compound Potassium (K) is a metal while nitrate (NO3−) is a polyatomic ion

Which of the following is the name for the compound FeCl2?

Iron(II) chloride Because there are two −1 anions, the iron must have a +2 charge

What is the formula for lithium oxide? Give your answer in the form A#B#, where the number is the subscript (don't include a 1 subscript explicitly). For example, the formula MgCl 2 would be entered as MgCl2.

Li2O Because lithium is a Group 1 metal, it takes a +1 charge. Oxide has a −2 charge. There must be two lithium cations to create the neutral compound Li2O.

Which of the following is the name for the compound MgS?

Magnesium sulfide The compound follows the pattern metalnonmetal-ide, where the magnesium is the metal and sulfur is the non-metal with the -ide ending.

What ions do Mg and S form?

Mg 2+ , S2− Magnesium (Mg) is in Group 2, so it takes a +2 charge. Sulfur (S) is in Group 6A so it takes a −2 charge.

Which of the following is the formula for magnesium sulfate heptahydrate?

MgSO4•7H2O

C8H18 what is the systematic names

Octane The compounds are named based on the number of carbon atoms in their formula.

Which of the following is the name for the compound HClO4?

Perchloric acid Because ClO4− is perchlorate, the acid takes the -ic ending