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Cat Chemistry > 4. Compounds and Stoichiometry > Flashcards

4. Compounds and Stoichiometry Flashcards

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1
Q

What is a molecule and what type of bond must it have?

A

A combination of two or more atoms held together by a covalent bond.

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2
Q

What is the molar mass?

A

It is the mass of one mole of a compound, usually grams per mole.

This is NOT the atomic number.

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3
Q

How would you determine the number of moles in a given amount (g) of H20?

A
  1. Calculate the molar mass of one H2O atom ( 1+1+16 g/mol)
  2. Divide the grams given by the molar mass (xxx g) * (mol/16g)
  3. Answer in the number of moles

Pay attention to dimensional analysis.

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4
Q

What are equivalents and how are they calculated? How are they related to molarity?

A

They are moles of a species of interest ( in essence).
For example, when thinking about equivalents, don’t think too hard.

For example, to create a 1 N solution of HCl, we would need 1 mole of HCl, because HCl can donate 1 hydrogen.

However, to create a 1 N solution of H2CO3, we would need .5 mole of HCl, because H2CO3 can donate 2 hydrogens.

This is more important for redox reactions.

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5
Q

What is the molar mass of NaBr?

A

113 g/mol

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6
Q

What is the molar mass of SrCl2?

A

157 g/mol

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7
Q

What is the molar mass of C6H12O6?

A

180g/mol

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8
Q

What is the number of moles in 100 g of NaBr?

A

~.9 mol

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9
Q

What is the number of moles in 100 g of SrCl2?

A

~.6 mol

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10
Q

What is the number of moles in 100 g of C6H12O6?

A

~.55 mol

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11
Q

How do the number of molecules in 18g of H20 compare to the number of formula units in 58.5 g of NaCl?

A

They are the same. Each one is the atomic mass (g/mol). So each one represents one mole.

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12
Q

What is the difference between the empirical formula or the molecular formula?

A

Empirical Formula: gives the simplest whole-number ratio of the elements of the compound

Molecular formula: gives the exact number of atoms of each element in the compound and isa multiple of the empirical formula.

It’s important to note that the molecular formula is either the same as the empirical formula or a multiple of it.

Empirical Formula: HO
Molecular Formula: H2O2

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13
Q

What is the percent composition? What is the formula?

A

Percent Composition: the percent of specific compound (mass) that is made up of a given element.

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14
Q

What are some similarities and differences between molecular and empirical formulas?

A

Similarities: Contain the same elements in the same ratios
Differences: Molecular formula gives the actual number of atoms in each element in the compound; but the empirical formulas only give the ratio and therefore may or may not give the actual number of atoms.

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15
Q

(Chem 4.2) Find the percent composition (by mass) of sodium, carbon, and oxygen, in sodium carbonate (Na2CO3)

A

Sodium: 46/106= 45%
Carbon: 12/106= 9%
Oxygen: 48/106= 46%

  1. Find the atomic mass of each one.
  2. Find the total atomic mass of the compound
  3. Divide the atomic mass of each element by the total atomic mass
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16
Q

(Chem 4.2) Experimental data from the combustion of an unknown compound indicates that it is 28.5% iron, 24% sulfur, and 49.7% oxygen by mass. What is the empirical formula?

A

Fe2S3O12

17
Q

What is a combination reaction?

A

occur when two or more reactants combine to form one product

2H2 + O2 -> 2 H2O

18
Q

What is a decomposition reaction?

A

Occur when one reactant is chemically broken down into two or more products

This typically occurs as a result of heating, high-frequency radiation, or electrolysis. (you need energy to break a bond)

2 H2O –> 2H2 + O2

19
Q

What is a combustion reaction? What is the result?

A

occur when a fuel and an oxidant (typically oxygen) react, forming the products of water and CO2 (if the fuel is a hydrocarbon)

20
Q

What is a single or double displacement reaction?

A

occurs when an ion of one compound is displaced with another element

21
Q

What is a neutralization reaction?
What type of compounds are the two reagents?
What subtype of reaction is it categorized under.

A

specific types of double displacement reaction are those in which an acid reacts with a base to form a salt (and usually water)

So if you see a salt, it’s probably a neutralization reaction.

22
Q

What type of reaction is a redox reaction?

A

Single displacement reaction.

23
Q

Describe in word what occurs when Zn(NO3)2 is dissolved in (NH4)2S

A

The ammonium cations swap places with (or displace) the zinc cations yielding ammonium nitrate and zinc (II) sulfide.

Zinc (II) sulfide then precipitates out of solution as a solid salt. (Neutralization reaction)

24
Q

What is the most practical way to approach stoichiometry problems?

A
  1. Convert from the given units to moles
  2. Use the mole ratio
  3. Convert moles to the desired units
25
Q

What is the volume of one mole of a gas at Standard Temperature and Pressure?

A

22.4L

26
Q

What is the best way to approach or solve limiting reagent/excess reagent problems?

A
  1. All comparisons of reactants must be done in units of moles. Gram-to-gram comparisons will be useless and may even be misleading
  2. It is not the absolute mole quantities of the reactants that determine which reactant is the limiting reagent. Rather, the rate at which the reactants are consumed (the stoichiometric ratios of the reactants) combined with the absolute mole quantities determines which reactant is the limiting reactant.
27
Q

What is the difference between the theoretical yield and the actual yield?

A

Theoretical Yield: the maximum amount of product that can be generated as predicted from the balanced equation, assuming that all of the limiting reactant is consumed, no side reactions have occurred, and the entire product has been collected. This is rarely ever accomplished
Actual Yield: The amount of product one actually obtains during the reaction

28
Q

What is the equation to calculate the percent yield of the a substance?

A
29
Q

How do you denote ionic charge in non-representative elements?

A

You use roman numerals

Fe2+= Iron (II)
Fe3+= Iron (III)
Cu+= Copper (1)
Cu2+= Copper (II)

30
Q

What nomenclature do you use to describe a monoatomic anion?

A

You add (-ide) to the end

H- = Hydride
F-= Fluoride
O2-= Oxide
S 2-= Sulfide
N3-= Nitride
P3-= Phosphide

A trend here is that all of these are just one atom, that have taken up the right number of hydrogens to fill their outer shell.

31
Q

What nomenclature do you use to describe oxyanion series? (x2)

A

Hypo-= Fewest oxygens
-ite = few oxygens
-ate = more oxygens
Per- =most oxygens

ClO-= hypochlorite
ClO2-= chlorite
ClO3-= Chlorate
ClO4-= Perchlorate

32
Q

What nomenclature do you use to denote the number of hydrogen ions?

A

One= bi- or just hydrogen
Two= dihydrogen

HCO3- = hydrogen carbonate or bicarbonate
HSO4- = Hydrogen Sulfate or bisulfate
H2PO4-= dihydrogen phosphate

33
Q

What are electrolytes?

A

contain equivalents of ions from molecules that dissociate in solution.

The strength of an electrolyte depends on its degree of dissociation or solvation

34
Q

Do strong electrolytes dissolve completely?
Do weak electrolytes dissolve completely?

A

Strong Electrolytes: dissolve completely
Weak Electrolytes: hydrolyze incompletely

Cat Chemistry (13 decks)

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