4. Compounds and Stoichiometry Flashcards by MIchael Smart

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

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

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What is the molar mass?

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

This is NOT the atomic number.

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

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

Pay attention to dimensional analysis.

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

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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What is the molar mass of NaBr?

113 g/mol

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What is the molar mass of SrCl₂?

157 g/mol

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What is the molar mass of C₆H₁₂O₆?

180g/mol

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

~.9 mol

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

~.6 mol

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

~.55 mol

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

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

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

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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What is the percent composition? What is the formula?

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

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

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

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

Find the atomic mass of each one.
Find the total atomic mass of the compound
Divide the atomic mass of each element by the total atomic mass

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(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?

Fe₂S₃O₁₂

What is a combination reaction?

occur when two or more reactants combine to form one product

2H₂ + O₂ -> 2 H₂O

What is a decomposition reaction?

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

What is a combustion reaction? What is the result?

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

What is a single or double displacement reaction?

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

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

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.

What type of reaction is a redox reaction?

Single displacement reaction.

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

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)

What is the most practical way to approach stoichiometry problems?

Convert from the given units to moles
Use the mole ratio
Convert moles to the desired units

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

22.4L

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

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.

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

**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

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

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

You use roman numerals Fe²⁺= Iron (II) Fe³⁺= Iron (III) Cu⁺= Copper (1) Cu²⁺= Copper (II)

What nomenclature do you use to describe a monoatomic anion?

You add (-ide) to the end H^- = Hydride F^-= Fluoride O^2-= Oxide S ^2-= Sulfide N^3-= Nitride P^3-= 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.

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

Hypo-= Fewest oxygens -ite = few oxygens -ate = more oxygens Per- =most oxygens ClO^-= hypochlorite ClO₂^-= chlorite ClO₃^-= Chlorate ClO₄^-= Perchlorate

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

One= bi- or just hydrogen Two= dihydrogen HCO₃^- = hydrogen carbonate or bicarbonate HSO₄^- = Hydrogen Sulfate or bisulfate H₂PO₄^-= dihydrogen phosphate

What are electrolytes?

contain equivalents of ions from molecules that dissociate in solution. The strength of an electrolyte depends on its degree of dissociation or solvation

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

**Strong Electrolytes**: dissolve completely **Weak Electrolytes**: hydrolyze incompletely