SNS - General Chemistry - Compounds And Stoichiometry

Question 1

Stoichiometry

Answer 1

Refers to the quantitative realtionships among compounds in a chemical reaction

Question 2

Stoichiometry

Law of constant composition

Answer 2

Any sample of a given compound will contain the same elements in an identical mass ratio, for example every sample of H2O will contain two atoms of hydrogen for every atom of oxygen, and one gram of hydrogen for every eight grams of oxygen

Question 3

Avogadro’s Number

Answer 3

6 x 10^23

Question 4

Stoichiometry Mole

Answer 4

The amount of substance that contains as many units as the number of atoms in 12 grams in 12g 12C. It is the central unit of measurement in chemistry.

Question 5

Stoichiometry

% Composition

Answer 5

= Mass of X in formula / formula weight of compound x 100%

Question 6

Stoichiometry Empirical Formula

Answer 6

Gives the smallest whole-number ratio of elements in a particular compound.

Question 7

Stoichiometry Empirical Formula Finding Empirical Formula From % Composition

Answer 7

1. Assume 100g sample 2. Find the number of moles of each element present in 100g sample by dividing % present by atomic mass 3. Divide numbers of moles by the smallest number of moles calculated to be present, eg, 4:6 = 1:1.5 - 2:3

Question 8

Stoichiometry Molecular Formula

Answer 8

Gives the actual number of aloms of each element present in a particular compound

Question 9

Types of Reaction

Answer 9

1. Combination 2. Decomposition 3. Single-replacement 4. Double-replacement 5. Combustion 6. Redox 7. Neutralisation

Question 10

Types of Reaction Combination

Answer 10

Involve the formation of one product by two or more substrates. Ofter called synthesis reactions If heat of formation is negative, the reaction proceeds spontaneously in order to acheive a lower eneergy state and is exothermic. With large negative values, the reaction proceeds rapidly and vice versa.

Question 11

Types of Reaction Decomposition

Answer 11

Involve the formation of two or more products from one substrate A very high positive value for the heat of formation indicates that a reaction will decompose explosively. A very high negative value indicates that the reaction is highly exothermic and will be difficult to decompose

Question 12

Types of Reaction Zn + S -> ZnS

Answer 12

Combination

Question 13

Types of Reaction 2HgO -> 2Hg + O2

Answer 13

Decomposition

Question 14

Types of Reaction Single Replacement

Answer 14

A single element reacts with a compound to produce a different element and a new compound

Question 15

Types of Reaction Double Replacement

Answer 15

Involve two compunds. The cations for the two compunds switch places

Question 16

Types of Reaction 2AgNO3 + Zn -> Zn(NO3)2 + 2Ag

Answer 16

Single Replacement

Question 17

Types of Reaction MgSO4 + BaCl2 -> MgCl2 + BaSO4

Answer 17

Double Replacement

Question 18

Types of Reaction Combustion

Answer 18

Start by combining an organic substance with oxygen to form carbon-dioxide and water If the original organic compound contains an element other that carbon, hydrogen or oxygen, these elements must be in their elemental state in the product

Question 19

Types of Reaction C5H12 + 8O2 -> 5CO2 + 6H2O

Answer 19

Combustion

Question 20

Types of Reaction Redox

Answer 20

Involve the transfer of electrons by a compund or ion. If electrons are on the right (product side), it is an oxidation reaction. If electrons are on the left (reactant) side, a reduction reaction has taken place. Thgese reactions are usually broken down into two half equations

Question 21

Types of Reaction I2 + 2Fe2+ -> 2Fe3+ + 2I-

Answer 21

Redox

Question 22

Types of Reaction I2 + 2e- -> 2I-

Answer 22

Reduction

Question 23

Types of Reaction 2Fe2+ -> 2Fe3+ + 2e-

Answer 23

Oxidation

Question 24

Types of Reaction Neutralisation

Answer 24

or Hydrolysis reactions A form of double replacement reaction using an acid and a base to form a salt and water

Question 25

Types of Reaction HCl + NaOH -> H2) + NaCl

Answer 25

Neutralisation/Hydrolysis

Question 26

Equivalents

Answer 26

For some substances it is useful to define a measure of reactive capacity, for example the ability of acids to donate protons. One mole HCl can donate one mole H+ while one mole H2SO4 can donate two moles H+. This difference is expressed using the term ‘equivalent’: One mole HCl contains one equivalent of H+, one mole H2SO4 contains two

By using equivalents, it is possible to say whether one equivalent will neutralise one equivalent of base - not necessarily true when dealing with moles

Question 27

Gram-Equivalent Weight

Answer 27

Used to determine the number of equivalents a compound contains:

Equivalents = weight of compound / gram equivalent weight

GEW = molar mass / n

where n = usually either the number of hydrogens used per molecule of acid in a reaction or the number of hydroxyl ions used per molecule of base in a reaction

Question 28

% Composition of Chromiun in K2Cr2O7

Answer 28

Mass of chromium in compound = 52 x 2 = 104

Formula mass = 104 + (39 x 2) + (16 x 7) = 294

% Composition = 104/294 x 100% = 35.4%

Question 29

Molecular and empirical formulae of a compound containing 40.9% carbon, 4.58% hydrogen, 54.52% oxygen with a molecular weight of 264 g/mol

Answer 29

1. Carbon: 40.9/12 = 3.41, Hydrogen: 4.58, Oxygen: 54.52/16 = 3.41
2. Carbon: 3.41/3.41 = 1, Hydrogen: 4.58/3.41 = 1.34, Oxygen = 3.41/3.41
3. Therefore 3C:4H:3O, empirical formula C3H4O3, mass = (36 + 4 + 48) = 88
4. = 264/88 = 3, Molecular formula = C9H12O9

Question 30

Balance the Equation:

C4H10 (l) + O2 → CO2 (g) + H2O (l)

Answer 30

2C4H10 + 13O2 → 8CO2 + 10H2O

Question 31

How many grams CaCl are needed to prepare 72g AgCl according to the following equation:

CaCl2 (aq) + 2AgNO3 (aq) → Ca(NO3)2 (aq) + 2AgCl (s)

Answer 31

1. =72/(144) = 0.5
2. =2/0.5 = 4
3. =(110) / 4 = 27.5g

Question 32

Percent Yield

Answer 32

= Actual Yield / Theoretical Yield x 100%