chem1013: exam 2 (end of chapter 3, chapter 4, chapter 5, chapter 6)

What is mass percent composition?

each element’s percentage of total compound’s mass

We find the empirical and molecular formulas of a compound if what two things are known?

mass percent composition and molar mass

What is the formula of mass percent of an element?

[(mass of the element in 1 mol of compound) / (total mass of one mole of the compound)] x100

Calculate the mass percent composition of Cl in CCl2F2.

To calculate the mass percent composition of Cl in CCl2F2, divide the mass of Cl in one mole of CCl2F2 by the total mass of one mole of CCl2F2, then multiply by 100.

2(molar mass Cl)
_______________  X 100
molar mass CCl2F2

=[2(35.453 g/mol)] / [12.011 + 2(35.453) + 2(18.998)] X 100
= [70.906] / [120.911] X 100 = 58.7%

How can we use mass percent as a conversion factor?

since mass percent = per hundred, there are (mass percent in grams) per 100 grams of compound

ie: Cl is 58.7% mass of CCl2F2 → 58.7 g Cl : 100g CCl2F2
This allows us to convert between grams of an element and grams of the compound.

What do conversion factors tell us of an element in a compound?

ie: 1 mol CCl2F2 has 2 mol Cl atoms, thus, 1 mol CCl2F2 : 2 mol Cl
This means that for every mole of the compound, there are a specified number of moles of the element, allowing for stoichiometric calculations.

If you want to use the chemical formula as a conversion factor, what must you do first?

convert from grams to moles; the chemical formula indicates mol→ mol ratios, not mass;
therefore, you need to know the molar mass of the compound to make the conversion.

If we do not know the chemical formula of a compound, but know the percent mass of each element in the compound from experimental data, what can we determine?

empirical formula

What are the steps to calculate the empirical formula?

1. Convert the percent composition of each element to grams.

2. Convert grams to moles for each element.

3. Divide the moles of each element by the smallest number of moles to find the simplest ratio.

4. If necessary, multiply the ratio by a whole number to get integer subscripts.

What are the steps to calculate the molecular formula?

1. Determine the empirical formula.

2. Calculate the molar mass of the empirical formula.

3. Divide the molar mass of the compound by the molar mass of the empirical formula.

4. Multiply the subscripts in the empirical formula by this ratio to find the molecular formula.

molar mass= molar mass of empirical formula x n
find n
multiply subscripts in empirical formula by n

What is combustion analysis and it is used to find what kind of empirical formulas?

the unknown compound undergoes combustion in the presence of pure oxygen to produce carbon dioxide and water, allowing for the determination of the empirical formula by measuring the amounts of these products.

What are organic compounds?

composed of carbon, hydrogen, and a few other elements such as nitrogen, oxygen, and sulfur

What are hydrocarbons?

compounds composed of carbon and hydrogen only

What are alkanes?

single bonds

What are alkenes?

double bonds

What are alkynes?

triple bonds

All other organic compounds can be thought of as hydrocarbons with 1 or more ______— characteristic atoms or groups of atoms

functional groups

What is the prefix 1 for hydrocarbons?

meth-

What is the prefix 2 for hydrocarbons?

eth-

What is the prefix 3 for hydrocarbons?

prop-

What is the prefix 4 for hydrocarbons?

but-

What is the prefix 5 for hydrocarbons?

pent-

What is the prefix 6 for hydrocarbons?

hex-

What is the prefix 7 for hydrocarbons?

hept-

What is the prefix 8 for hydrocarbons?

oct-

What is the prefix 9 for hydrocarbons?

non-

What is the prefix 10 for hydrocarbons?

dec-

What is the affix for single bonds of hydrocarbons?

-ane

What is the affix for double bonds of hydrocarbons?

-ene

What is the affix for triple bonds of hydrocarbons?

-yne

How do you name simple, straight-chain hydrocarbons?

identifying the number of carbon atoms and adding the appropriate suffix (-ane, -ene, or -yne) based on the bonding type.

carboxylic acid

amine

alcohol

ketone

What is a chemical reaction?

1+ substances are converted to 1+ different ones, represented by a chemical equation

What must a chemical equation be, according to the law of conservation of mass?

balanced, with equal numbers of each type of atom on both sides

How are states specified using abbreviations in parentheses?

States are specified as (s) for solid, (l) for liquid, (g) for gas, and (aq) for aqueous.

What can you change and what can you not change when balancing equations?

You can change the coefficients in front of compounds, but you cannot change the subscripts within a chemical formula.

What are the steps to balance chemical equations?

1. write a skeletal equation (unbalanced)

2. count # atoms on each side of the arrow

3. use whole number coefficients to balance 

*start with the most complex compound and leave the pure for last

4. check for lowest whole number coefficients

What is reaction stoichiometry?

numerical relationships between reactants and products in a balanced chemical equation

What does reaction stoichiometry help us predict?

The amount of product formed from a given amount of reactant, or how much of 1 reactant is required to react with a given amount of another, in a chemical reaction.

What do coefficients specify?

relative amounts in moles of each substance

What is theoretical yield?

amount of product that can be made based on the limiting reagent

What is limiting reagent?

reactant that is completely consumed; limits product amount

What is excess reagent?

reactant still left over after reaction is complete

What is actual yield?

amount of product actually produced

What is the percent yield formula?

Percent yield = (actual yield / theoretical yield) x 100% 

What are the steps to find theoretical yield, limiting reactant, excess reactant(s), and percent yield?

1. convert reactants to grams of the product asked in the equation

2. theoretical yield= grams of product formed based on limiting reactant

3. Limiting reactant= least amount of grams of product

4. Excess reactant= the reactant that remains after the reaction in complete

5. Find the percent yield by:

   1. dividing actual yield (usually given in problem) by theoretical yield calculated

   2. multiply by 100%

In this experiment, 28.6kg of C reacted with 88.2kg of TiO2, and 42.8kg of Ti was produced. What is the theoretical yield (in kg) of Ti, and what is the percent yield for this reaction? Also, identify the limiting and excess reagents.

To determine the theoretical yield of titanium (Ti), convert the masses of carbon (C) and titanium dioxide (TiO2) to Ti using stoichiometry based on the balanced reaction equation. The limiting reactant will be the one that produces the least amount of Ti, while the excess reagent is the one that remains after the reaction is complete. Percent yield is calculated by dividing the actual yield (42.8 kg) by the theoretical yield and multiplying by 100%.

What is a solution?

homogeneous, uniform mixture of 2 substances

What is a solvent?

majority component (often water)

What is a solute?

minority component

What is an aqueous solution?

solvent is water

What is a dilute solution?

small amount of solute relative to the solvent

What is a concentrated solution?

large amount solute relative to solvent

What can solution concentration be expressed as?

Molarity (M)

What is the formula for molarity (M)?

M = moles of solute / liters of solution

What is the molarity of a solution with 25.5 g KBr dissolved in enough water to make 1.75 L of solution?

To find the molarity, first calculate the moles of KBr by using its molar mass (119.00 g/mol). Molarity (M) is then calculated as moles of solute divided by the volume of solution in liters. Therefore, M = (25.5 g / 119.00 g/mol) / 1.75 L = 0.123 M.

What volume (in mL) of a 0.155 M KCl contains 2.55 g KCl?

To determine the volume in milliliters, first calculate the moles of KCl using its molar mass (74.55 g/mol). Then, apply the molarity formula (M = moles of solute / liters of solution) to find the volume in liters, and convert to milliliters. Thus, volume = (2.55 g / 74.55 g/mol) / 0.155 M = 220 mL.

What are stock solutions?

concentrated forms of solutions

How do we use stock solutions for our experiments?

we add solvent (usually water) to increase the volume and decrease the concentration (amount of solute stays the same); simple, we are diluting the stock solution to the desired concentration for use in experiments.

What equation do we use for dilutions, and what are the rules for this formula?

M₁V₁ = M₂V₂
M₁ = initial concentration (stock)

V₁ = initital volume

M₂ = final concentration

V₂ = final volume

• volume units must match

• concentration units must match

A lab procedure calls for 3.00 L of a 0.5 M CaCl2 solution. How should we prep this solution from a 10.0 M stock solution?

To prepare 3.00 L of a 0.5 M CaCl₂ solution from a 10.0 M stock solution, use the dilution formula M₁V₁ = M₂V₂. Calculate V₁ as follows: V₁ = (M₂V₂) / M₁. = (0.5 M)(3.00 L) / 10.0 M = 0.150 L (150 mL) of stock solution.

What is the concentration of a solution prepared by diluting 56.6 mL of a 2.25 M stock solution with enough water to make 1.05 L of solution?

To find the concentration, use the dilution formula M₁V₁ = M₂V₂. Here, M₁ = 2.25 M, V₁ = 56.6 mL (0.0566 L), and V₂ = 1.05 L. Solving for M₂, we find M₂ = (M₁V₁)/V₂ = (2.25 M)(0.0566 L)/(1.05 L) = 0.121 M.

What can we calculate with the volume and concentration of a reactant or product?

its number of moles— using the formula: moles = concentration × volume.
* to convert between species, we use molar ratios from the equation

When ionic solutes form a solution with water, what do ions undergo?

hydration (water molecules surround each ion)

What is dissociation?

solute ions break their attraction to each other and are attracted to the water molecules and disperse into the water (solvent)

ie: NaCl (s) → Na⁺ (aq) + Cl^- (aq)

What happens to molecular solutes when they form solutions with solvents?

molecular solutes can also form solutions with solvents, but molecules only separate from each other (no dissociation, no bonds breaking)

ie: CH₃OH (l) → CH₃OH (aq)

What are electrolytes?

Substances that dissociate into ions in solution, conducting electricity.

What are strong electrolytes?

completely dissociate into ions when dissolved in water

mostly ionic compounds

ie: NaCl

What are non electrolytes?

do not dissociate into ions when dissolved in water

do not conduct electricity

mostly molecular compounds

ie: C₁₂H₂₂O₁₁

*not acids

Explain how sugar dissolves and how that differs from a sodium chloride solution?

sugar dissolves because the attraction between sugar and water molecules overcome the attraction of sugar molecules to each other. So, unlike a sodium chloride solution (which breaks up into Na⁺ and Cl^- ions), a sugar solution contains intact C₁₂H₁₂O₁₁ molecules homogeneously mixed with water molecules

What is a strong acid?

completely ionize in solution, strong electrolytes, single →
ie: HCl → H⁺ + Cl^-

What is a weak acid?

do not completely ionize in water, weak electrolytes, use double arrow (⇌) in equations, eg: CH₃COOH ⇌ H⁺ + CH₃COO⁻

What is solubility?

grams solute that can be dissolved in 100 g solvent (water) at a temperature in Celsius, to be said simpler: whether something dissolves or not

What does it mean if something is soluble?

dissolves in water

What does it mean if something is insoluble?

does not dissolve in water

How do you determine solubility?

look at the given paper and see the rules and exceptions

What are precipitation reactions?

a solid (precipitate) forms when two solutions mix

*only insoluble compounds form precipitates

*if both possible products are soluble, no reaction occurs and no precipitate forms

What do you do when no reaction occurs?

write “no reaction,” cross out the arrow, and do not write the products

How do you write a precipitate reaction?

1. write formulas of two compounds as reactants

2. write products that could form by combining cations and anions

3. use solubility rules to determine if products are insoluble (s)

4. if all possibly products are soluble, write no reaction; if soluble, write (aq), if insoluble, write (s)

   1. balance

What is a molecular equation?

complete neutral formulas for each compound

In actual solutions of soluble ionic compounds, how are dissolved substances presented?

as free ions, not as intact compounds

What is the complete ionic equation?

all of ions present (reactants and products) and shows states for each

ie: shows all soluble ions separated, indicating their participation in the reaction.

strong electrolytes are represented as their component ions in ionic equations— weak electrolytes are not
*liquids and solids do not break up, only aqueous

Write an example complete ionic equation for the reaction between lead (II) nitrate and potassium chloride.

The complete ionic equation shows the dissociation of lead (II) nitrate and potassium chloride in aqueous solution, resulting in lead (II) ions, potassium ions, and chloride ions, while maintaining the solid state of lead (II) chloride. It can be represented as: Pb^{2+} (aq) + 2 K^{+} (aq) + 2 Cl^{-} (aq) → PbCl_{2} (s) + 2 K^{+} (aq).

What are spectator ions?

do not participate in the reaction (same on both sides of the arrow)

What is the net ionic equation?

only species that actually change during the reaction and exclude spectator ions.

Write the net ionic equation for the  reaction between lead (II) nitrate and potassium chloride.

The net ionic equation is Pb^{2+} (aq) + 2 Cl^{-} (aq) → PbCl_{2} (s).

What is an acid-base reaction?

“neutralization reaction,” acid reacts with base and they neutralize each other, producing water (sometimes weak electrolyte)

What is a gas-evolution reaction?

gas forms, bubbling (many are acid-base reactions)

What is the Arrhenius definition of an acid?

produces H⁺ (or H₃O⁺) in an aqueous solution

What is the Arrhenius definition of a base?

produces OH^- in an aqueous solution

What are strong acids?

dissociate completely, single arrow

What are weak acids?

do not dissociate completely, double arrow

What are polyprotic acids?

have more than 1 ionizable proton, release them sequentially

ie: H₂SO₄ → H⁺ + HSO₄^-

HSO₄^- → H⁺ + SO₄^2-

What happens when you mix acids and bases (weak or strong)?

H⁺ (aq) from the acid combines with OH^- (aq) form the base to form H₂O (l) and usually an ionic compound, called a salt

What are the six strong acids?

The six strong acids are

H₂SO₄, HI, HBr, HNO₃, HCl, HClO₄

They completely dissociate in water.

What is a way to remember the six strong acids?

One mnemonic is "So I Brought No Clean Clothes" which stands for: HCl, HBr, HI, HNO₃, HClO₄, and H₂SO₄.

Any acids that are not the six strong acid list are considered what?

weak acids