ミ☆ chemistry unit 5

what is the definition of a physical change from this video

changes in a substance that do not involve a change in the identity of the chemical makeup of that substance. all changes in state of matter are physical changes, and all physical changes are not necessarily accompanied by a chemical change.

write down the examples of physical change in this video.

grinding peanuts to become peanut butter, folding paper to be a paper airplane, bending copper to be a copper wire, melting ice to become water.

what is the definition of a chemical change from this video?

a change in a substance that involves a change in the identity of chemical makeup of that substance. all chemical changes are accompanied by physical changes.

write down the examples of chemical changes in this video.

fermenting sugar to alcohol, combusting logs to burning wood, oxidzing an iron nail to a rusty nail, and doing electrolysis to water to create h2 and o2 gas.

for the 8 examples, write down if they are classified as physical or chemical change and why the video creator classifies them in this way.

condensing water vapor - physical because it is a change in state

combustion of gasoline - chemical because the gasoline is reacting with oxygen to produce new substances.

turning water into h2 and o2 gas - chemical because the molecules are rearranging to become different molecules.

milk souring - chemical because milk is being turned into different substances by bacteria.

sublimation of dry ice - physical because it is a change in state

turning copper into wire - physical because the copper is only changing in shape.

fermentation of sugar into alcohol - chemical because the bacteria changes the sugar molecules into the substances that make up alcohol.

evaporating water - physical because it is a change in state.

write down the signs of chemical change indicated at the beginning of this video

bubbles of gas are released, heat is released or absorbed, light is given off, a precipitate (a solid) is formed from the solutions (a mixture of two subtances), a smell is produced, a change of color occurs, the chemical’s identity changes

record each example given, then write the sign(s) that indicate chemical change has occurred.

acidic acid and sodium bicorbonate produce bubbles of gas.

burning paper makes heat release and light to be produced.

silver nitrate (agno3) and sodium chloride (nacl) make a precipitate form.

sulfuric acid to water and phenolphthalein indicator make the water turn from clear to pink.

sour milk produces a foul smell.

iron and oxygen changes the identity of the chemical.

how do you name monatomic cations (representative elements)

as a cation, the magnesium 2+ ion would be called: magnesium ion, a rubidium cation (+1) would be called:, rubidium ion.

how would you name transition metals

if i had a gold (au) ion with a +2 charge, it would be named:, gold (ii) ion, if you had a lead (pb) ion with a +4 charge, it would be called:, lead (iv) ion

how do you name monatomic anions

name the nitrogen anion: nitride ion what is the name of the iodine anion? iodide ion

what are the names of certain polyatomic ions?

co3 2- carbonate ion, nh4 +ammonium ion, oh- hydroxide ion

write a step-by-step process for writing ionic compound formulas from names. included in your process should be explanations for: how to balance the charges, what the subscripts mean, and when subscripts and superscripts should be written.

for lithium oxide, find the elements on the periodic table (lithium and oxygen).

find out the charge they have based on the position on the periodic table (lithium has a +1 charge, oxygen has a -2 charge)

check to see if it is balanced, and change it if necessary (the +1 charge and the -2 charge do not balance out, so to balance it, add a lithium for the charges to be +2 and -2, effectively balancing out).

write out the chemical formula (li2o).

subscript refers to the amount of atoms, located on the lower right. the superscript is the electrical charge, located on the upper right.

outline the 2 common mistakes tyler points out at the end of the video, and why they are wrong.

do not write the subscript as 1, because a blank subscript already implies 1. do not add the charges to the elements because the charges already cancel out.

go back to your step by step process from the “writing ionic compounds video” (#2a) and add the information you need to keep in mind if you have a transition metal in the formula.

for chromium (ii) iodide, find the elements on the periodic table (chromium and iodine)

find out the charge they have based on the position on the periodic table (chromium has a +2 charge, indicated for the roman numeral, iodine has a -1 charge)

check to see if it is balanced, and change it if necessary (the +1 charge and the -2 charge do not balance out, so to balance it, add a lithium for the charges to be +2 and -2, effectively balancing out).,

write out the chemical formula (cr2i).

write a note for yourself about the big mistake tyler warns you about during the chromium (ii) iodide example.

the roman numerals indicate the positive charge, not the number of atoms in that compound.

write the examples for chromium (ii) iodide and manganese (iii) oxide.

cri2, mn2o3

steps for writing ionic formulas with polyatomic ions

identify elements, determine charges, balance charges, write formula with cation first and parentheses for multiple polyatomic ions

what is a polyatomic ion?

a group of two or more atoms that carry a charge

when to use parentheses in formulas

use parentheses when more than one polyatomic ion is present, do not use them if only one is present

why memorize common polyatomic ions?

so you can recognize them and know they are not on the periodic table

nitride vs nitrite vs nitrate formulas and naming clues

nitride = n3-, nitrite = no2-, nitrate = no3-, -ide = monatomic, -ite/-ate = polyatomic

how to tell ionic vs molecular compounds

ionic = metal + nonmetal, molecular = two nonmetals

steps for naming molecular compounds

name first element, name second with -ide, use prefixes, no mono- on first element, drop extra vowels (ao/oo → o)

prefix table

mono 1, di 2, tri 3, tetra 4, penta 5, hexa 6, hepta 7, octa 8, nona 9, deca 10

examples of molecular compound names

tetraphosphorus decasulfide = p4s10, carbon monoxide = co

flow chart for naming any compound

decide ionic vs covalent → ionic: check if metal needs roman numeral, name cation then anion (-ide) → covalent: name elements and add prefixes

flow chart for writing formulas from names

decide ionic vs covalent → ionic: identify ions, determine charges, balance to simplest ratio → covalent: use prefixes to determine subscripts

definition of a mole and how it is similar to a dozen

a mole describes a certain number of things (602 hexillion), similar to how a dozen means 12

avogadro’s number in scientific notation

6.02 x 10^23

why a mole is useful for atoms but not jelly beans

atoms are too small to count individually so a large unit is helpful, but jelly beans are large enough to count without using moles

relationship between moles, molar mass, and periodic table

the periodic table lists molar mass, which tells how many grams are in one mole of an element

examples of how much a mole of different substances weigh

sulfur: 32.07 g, carbon: 12.01 g, zinc: 65.38 g

moles in 31.87 grams of carbon

1 mol c = 12.01 g c, so 2.654 mol c = 31.87 g c

atoms in 31.87 grams of carbon

1 mol c = 6.02 x 10^23 atoms, so 2.654 mol c ≈ 1.6 x 10^24 atoms

definition of molar mass

the mass in grams of one mole of a substance

how to calculate molar mass of a compound

list each element, count atoms, multiply each by its atomic mass, then add all masses together

example molar mass problem

so2 has one sulfur and two oxygen: 1(32.07 g) + 2(16.00 g) = 64.07 g/mol

what are the traditional names of the ions for lead

lead (pb), plumbous = +2, plumbic = +4

what are the traditional names of the ions for iron

iron (fe), ferrous = +2, ferric = +3

what are the traditional names of the ions for copper

copper (cu), cuprous = +1, cupric = +2

what are the traditional names of the ions for mercury

mercury (hg), mercurous = +1, mercuric = +2

what are the traditional names of the ions for tin

tin (sn), stannous = +2, stannic = +4

how to name an acid where it ends in -ate

root + ic + acid (for example, hno3 = nitric acid)

how to name an acid where it ends in -ite

root + ous + acid (for example, hno2 = nitrous acid)

how to name an acid where it ends in -ide

hydro + root + ic + acid (for example, hcl = hydrochloric acid)

how can you tell if you have a 1-step or 2-step conversion

it depends on what you start with and what you end with. if you start with moles or end with moles, it is one step. if neither applies, it is two step

first example problem explanation

how many atoms of lithium are in 18.2 g of lithium? this is two step because you do not start or end with moles

first example dimensional analysis

18.2 g li × 1 mol li / 6.941 g li × 6.02×10^23 atoms li / 1 mol li = 1.58×10^24 atoms li

how she knew what to write in each factor (example 1)

start with given, convert grams to moles by canceling grams, then convert moles to atoms by canceling moles

second example problem explanation

how many liters of lithium are in 2.31×10^20 molecules? this is two step because you do not start or end with moles

second example dimensional analysis

2.31×10^20 particles li × 1 mol / 6.02×10^23 particles × 22.4 l / 1 mol = 0.00860 l

how she knew what to write in each factor (example 2)

start with given, convert particles to moles by canceling particles, then convert moles to liters by canceling moles

how to know if you have a scientific notation error

extremely large answers like 10^40 indicate a mistake, usually from missing parentheses

dimensional analysis example converting pounds to grams

5.0 lb × 16 oz / 1 lb × 28.35 g / 1 oz = 2268 g (units cancel: lb → oz → g)

how to convert between grams and moles

use molar mass from the periodic table: 1 mol = molar mass in grams

how to convert between moles and atoms

use avogadro’s number: 1 mol = 6.02×10^23 particles

how to convert between moles and liters

for gases at stp use 1 mol = 22.4 l

how to convert grams to atoms

convert grams to moles using molar mass, then moles to atoms using avogadro’s number

how to convert atoms to grams

convert atoms to moles using avogadro’s number, then moles to grams using molar mass

how to convert liters to grams

convert liters to moles using 22.4 l/mol, then moles to grams using molar mass

how to write dimensional analysis charts

start with the given value and multiply by fractions that cancel units until you reach the desired unit

law of conservation of mass

mass cannot be created or destroyed, so reactants and products must have equal mass

how new substances are formed

atoms rearrange and combine in new ways but the original elements still exist in the mixture

synthesis reaction definition

two or more simple substances combine to form one compound

synthesis reaction general form

a + b → ab

synthesis reaction example

c(s) + o2(g) → co2(g)

decomposition reaction definition

one compound breaks down into simpler substances or elements

decomposition reaction general form

ab → a + b

decomposition reaction example

h2o(l) → h2(g) + o2(g)

combustion reaction definition

a hydrocarbon reacts with oxygen to produce carbon dioxide and water

combustion reaction general form

cxhy (or cxhyoz) + o2 → co2 + h2o

combustion reaction example

ch4 + o2 → co2 + h2o

single replacement reaction definition

one element replaces another element in a compound

single replacement reaction general form

a + bc → b + ac

single replacement reaction example

fe + cucl2 → cu + fecl2

double replacement reaction definition

ions in two compounds switch partners to form two new compounds

double replacement reaction general form

ab + cd → ad + bc

double replacement reaction example

bacl2 + na2so4 → baso4 + nacl. notice how the na is different between the reactants and the products because of the need to balance charges.

how many moles of o2 are in 6.2 mol h2o? (2h2o → 2h2 + o2)

recipe method: multiply the reaction by 3.1 to get 6.2 h2o → 6.2 h2 + 3.1 o2. conversion factor: 6.2 mol h2o × 1 mol o2 / 2 mol h2o = 3.1 mol o2

how many moles of h2o are needed to make 19.2 mol o2? (2h2o → 2h2 + o2)

recipe method: multiply the reaction by 19.2 to get 38.4 h2o → 38.4 h2 + 19.2 o2. conversion factor: 19.2 mol o2 × 2 mol h2o / 1 mol o2 = 38.4 mol h2o

how many moles of o2 are needed to react with 8.4 mol h2s? (2h2s + 3o2 → 2so2 + 2h2o)

recipe method: multiply the reaction by 4.2 to get 8.4 h2s + 12.6 o2 → 8.4 so2 + 8.4 h2o. conversion factor: 8.4 mol h2s × 3 mol o2 / 2 mol h2s = 12.6 mol o2

recipe method for mole ratios

keep the same ratio of reactants and products by multiplying the entire reaction like doubling a recipe

conversion factor method explanation

multiply the given amount by a fraction with the undesired unit on the bottom and the desired unit on top to cancel units

where conversion factor numbers come from

the coefficients in the balanced chemical equation

how to balance chemical equations

adjust coefficients so each element has the same number of atoms on both sides of the equation

balancing equation strategy

start with elements that appear once on each side, leave hydrogen and oxygen for last, and only change coefficients not subscripts

balancing equation example

h2 + o2 → h2o

cheeseburger analogy for limiting and excess reactant

in a recipe of 1 bun + 1 cheese + 1 meat = 1 cheeseburger, meat is the limiting reactant because it runs out first when you have 4 buns, 9 cheese, and 3 meat. the excess reactants are the leftover buns and cheese.

concept of limiting reactant

the limiting reactant is the first reactant that gets completely used up in a reaction, stopping the reaction because no more product can form.

concept of excess reactant

the excess reactant is the substance left over after the limiting reactant is used up and the reaction stops.

maximum nh3 from 3.2 mol n2 and 5.4 mol h2 (n2 + 3h2 → 2nh3)

checking n2: multiply reaction by 3.2 to get 3.2 n2 + 9.6 h2. checking h2: 5.4 h2 × 1 mol n2 / 3 mol h2 = 1.8 n2. then 5.4 h2 × 2 mol nh3 / 3 mol h2 = 3.6 mol nh3. maximum nh3 = 3.6 mol.

limiting reactant in the nh3 problem

h2 is limiting because it runs out first when reacting with 3.2 mol n2.

excess reactant in the nh3 problem

n2 is in excess because some remains after h2 is used up. 3.2 mol n2 − 1.8 mol n2 = 1.4 mol n2 excess.

stoichiometry plan for the hydrogen peroxide problem (2h2o2 → o2 + 2h2o)

given 48.64 g h2o, find grams h2o2. convert grams h2o → moles h2o using molar mass, then moles h2o → moles h2o2 using mole ratio, then moles h2o2 → grams h2o2 using molar mass. answer: 91.83 g h2o2.

stoichiometry plan for the carbon monoxide problem (2co + o2 → 2co2)

given 174 g co, find molecules co2. convert grams co → moles co using molar mass, then moles co → moles co2 using mole ratio, then moles co2 → molecules co2 using avogadro’s number. answer: 2.74 × 10^24 molecules co2.

when polyatomic ions are involved in ionic compounds

treat the entire polyatomic ion as a single unit and do not change its subscripts unless you need parentheses to show multiple copies

which metals have variable charges

most transition metals have variable charges and require roman numerals, except zinc (zn2+), cadmium (cd2+), silver (ag+), and aluminum (al3+) which have fixed charges

what charge do solutions have

the total positive charge and total negative charge must cancel out so the compound is electrically neutral

relationship between net charge and aqueous solutions

in aqueous solutions ions separate and float individually, but the overall solution remains electrically neutral because total positive and negative charges still balance

relationship between net charge and solids

in solid ionic compounds ions are locked in a crystal lattice where positive and negative ions alternate to maintain zero net charge