Week 2 (Claire) Flashcards
(Claire)
What are the basic principles of a chemical equation?
1) Reactants
2) Products
3) Physical states (e.g. gas, liquid, solid, aqueous)
What law do balanced equations obey?
Balanced equations obey the law of Conservation of Mass (“Mass is neither created nor destroyed in chemical reactions”)
What is Stoichiometry?
Stoichiometry is the relationship between the number of reactant and product molecules in a chemical equation.
E.g. CaCO3(s) + 2HNO3(aq) —> Ca(NO3)2(aq) + CO2(g) + H2O(l)
[2HNO3 is the stoichiometry coefficient]
What are the steps to balancing a chemical equation?
1) Write an unbalanced equation with correct formulas for all substances.
2) Balance atoms of one of the elements;
i. start with the most complex molecule.
ii. change the stoichiometric coefficients.
iii. do NOT alter the chemical formulas.
3) Balance the remaining elements.
What types of chemical reactions are there?
1) Combination reactions.
2) Decomposition reactions.
3) Exchange reactions.
4) Precipitation reactions.
Explain Combination Reactions:
X + Z —> XZ
Element + Halogen/O2;
e.g. 2Mg(s) +O2(g) —> 2MgO(s)
Other types;
2SO2(g) + O2(g) —> 2SO3(g)
Explain Decomposition Reactions:
XZ —> X + Z
Often initiated by heat;
CaCO3(s) —[800-1000 degrees]—> CaO(s) + CO2(g)
Occasionally by shock;
4C3H5(NO3)3(l) —> 12CO2(g) + 10H2O(l) + 6N2(g) + O2(g)
Explain Exchange Reactions:
AD + XZ —> AZ + XD
AgNO3(aq) + HCl(aq) —> AgCl(s) + HNO3(aq)
What chemical species are soluble?
- All ammonium & Group 1A (Na+, K+, NH4+ salts)
- All nitrates (NO3-)
- Most chlorides, bromides, & iodides (exceptions; AgX, Hg2X2, PbX2).
- Most sulfates (SO42-) (exceptions; CaSO4, SrO4, BaSO4, Ag2SO4, PbSO4, & Hg2SO4).
- All chlorates (ClO3-)
- All percolates (ClO4-)
- All acetates (CH3COO-)
What chemical species are insoluble?
- All phosphates (PO43-) [exception; Group 1A, NH4+]
- All carbonates (CO32-) [exception; Group 1A, NH4+]
- All hydroxides (OH-) [exception; Group 1A, NH4+]
[Sr(OH)2, Ba(OH)2, & Ca(OH)2 are slightly soluble] - All oxalates (C2O42-) [exception; Group 1A, NH4+]
- All oxides (O2-) [exception; Group 1A]
- All sulfides (S2-) [exception; Group 1A, NH4+]
[Mgs, CaS, & BaS are slightly soluble]
Explain Precipitation Reactions:
- When mixing ionic solutions, a precipitate may form.
- However, not all ions react.
- A reaction occurs if a product is insoluble.
** Solubility rules help predict reactions **
What are the general writing rules for precipitation reactions?
1) Write a balanced equation.
2) Solubility?
3) Dissociate the soluble components.
4) Write the complete ionic equation.
5) Cancel the ions appearing on both sides (spectators).
6) Check the charges are balanced.
** this process gives you the net ionic equation **
Briefly explain REDOX reactions…
Oxidation is the process of adding oxygen.
Reduction is the process of reducing an ore to a metal (reverse of oxidation).
If something is oxidised something must be reduced.
Oxidation is a loss of electrons (+e-).
Reduction is a gain of electrons (-e-).
Name at least 2 general rules for oxidation numbers…
- Pure element =0.
- Monatomic ion = charge of ion.
- Some elements have the same oxidation number in almost all their compounds.
- The sum of the oxidation numbers of all atoms in any species = the charge of the species.
Give one example of a biological redo reaction…
- Hämoglobin transporting oxygen in the body.
- Iron containing protein (Fe2+ / Fe3+)
Find the oxidation number for all elements in SO3^2-…
O = -2 (not a peroxide, not bonded to hydrogen)
S - sum of oxidation numbers = charge = -2
(oxidation number for S) + 3(oxidation number for O) = -2
(ox. no. for S) + 3(-2) = -2
(ox. no. S) -6 = -2
Therefore S = +4
True or False?
Oxidation numbers always change during redox reactions?
True.
If an element reacts to form a compound, its a redox reaction.
What is an example of a biological redox reaction?
Haemoglobin transports oxugen in the body.
Fe containing protein (Fe^2+ / Fe^3+)
What is atomic mass (amu)?
Different chemicals have different weights.
amu = atomic mass units (same as gmol-1)
What is Avogadro’s number?
Avogadro’s number is one mole (1 mol) contains 6.022x10^23 entities.
What is molar mass? How do you calculate this?
The molar mass is 1 mole of an element, expressed in grams (g).
How to calculate:
1) Obtain the molar mass of each element.
2) Multiply each molar mass by the number of moles in the formula.
3) Calculate the molar mass by adding the masses of the elements together.
Explain empirical formula…
The empirical formula is the simplest formula for a compound that agrees with the elemental analysis and gives rise to the smallest set of whole numbers of atoms.
Explain molecular formula….
Molecular formula is the formula of the compound as it exists, it may be a multiple of the empirical formula.
What are some examples showing the empirical formula and molecular formulas…
Hydrogen Peroxide:
EF; HO
MF; H2O2
Borane:
EF; BH3
MF; BH3
Diborane:
EF; BH3
MF; B2H6
Octene:
EF;CH2
MF; C8H16
How do you determine both empirical and molecular formula?
First assume a 100.0 g sample (% becomes mass in grams).
Then divide each mass by its atomic mass (gives the number of moles of each in 100.0g).
Divide each by the smallest answer found (smallest whole number ratio is the empirical formula).
The molecular formula can be determined if the molecular mass is known.
