2.1 Atoms And Reactions Flashcards
Define Isotope
Atoms of the same element with different number of neutrons but same number of protons
Define relative isotopic mass
The mass of an isotope compared to 1/12th the mass of carbon-12
Define relative atomic mass
The weighted average mass of an atom compared to 1/12th the mass of carbon-12
What’s the relative mass of an electron?
1/2000
Ar formula?
((Isotope mass x %)+(isotope mass x %))/100
Number of particles formula?
Moles x avogadros constant
What does mass spectrometry tell us?
Determine the relative abundances of each isotope of an element
Identified unknown substances
Provide structural information about a molecule
How do you use mass spectra to work out relative atomic masses of different elements?
Step 1. Mulitply each relative isotopic mass by its relative isotopic abundance, and add up the results
Step 2. Divide by the sum of the isotopic abundances
(x * y) + (x * y) + (x * y)=z
(y + y + y=u)
z/u=answer
What’s the formula to finding the number of moles? when you have mass
no. of moles (mol) = mass (g) / Mr (g mol-1)
Why do different isotopes of the same element react in the same way?
- Chemical reactions involve ELECTRONS, and isotopes have the same number and arrangement of electrons.
- Neutrons make no difference to chemical reactivity.
What is the Avogadro’s constant?
The number of atoms per mole of the carbon-12 isotope (6.02 x 10^23 mol-1)
What are the steps to calculate the empirical formula?
- Find the moles of the element
- Divide the answer for each element by the smallest number
- If necessary, multiply the answer by a suitable value to make sure the ratio is in whole number only.
Define molecular formulae
Tells you the number of each type of atom that make up a molecule
What are the steps to calculate the molecular formulae?
Q.
A molecule has an empirical formula of
C4 H3 02, and a molecular mass 166g mol-1
Work out the its molecular formula
- Work out the empirical formula mass (same as relative formula mass) of the compound.
- Given molecular mass/the empirical formula mass= No. of empirical units in the molecule
- empirical formula x No.^
A.
(4 x 12)+(3 x 1.0)+(2x16.0)=83.0g/mol
166/83 = 2 empirical units in the molecule
so molecular formula is: C8H604
How do you write an ionic equation?
Q. What’s the ionic equation for the reaction of Nitric acid with sodium hydroxide
- Write out a full balanced equation
- Rewrite the equation showing all the ions that are in the reaction mixture (only aqueous compounds, leave solids and gasses as is)
- Cross out ions that appear on both side of the equation
A. HNO3 (aq) + NaOH(aq) –> NaNO3(aq) + H2O(l)
H+ + NO3- + Na+ OH- —> Na+ + NO3- + H2O
H+ + OH- —> H20
What’s the formula to finding the number of moles? when you have volume of gas
n=v/24
What’s the formula to finding the number of moles? when you have solution volume and concentration
n=C x V
what’s the ideal gas equation?
pV=nRT p in pa V in m^3 n is no. of moles R is gas constant 8.314 J/K/mol T is temperature in k
What’s the molar volume?
The molar volume is the volume per mole of gas. At room temperature and pressure it is
24.0 dm3/mol
What’s a hydrated salt?
A hydrated salt is one which contains water of crystallisation e.g. MgSO4·7H2O.
It is water that trapped inside the ionic lattice
What’s an anhydrous salt?
An anhydrous salt is one with no water of crystallisation e.g. MgSO4.
How do you work out the amount of water of crystallisation in a salt
Q. Heating 3.210g of hydrated magnesium sulfate, MgS04,XH20, Forms 1.567g of anhydrous magnesium sulfate. Find the value of X and write the formula of the hydrated salt.
-From the Mr
Find the Mr of the anhydrous salt and subtract it from the hydrated Mr then divide the remainder by the Mr
of water
-From experimental results
Find the moles of water lost when a hydrated salt is heated in a crucible and the number of moles of anhydrous salt left at the end
A.
Mass of water lost: 3.210-1.567=1.643g
Moles of water lost: 1.643/18 (ar of water) = 0.09127
Mr of MgSO4 is 120.4
no. of moles: 1.567/120.4=0.01301
0.01301 moles of salt : 0.09127 moles of water
1mol of salt: 0.09127/0.01301=7.015
SO ITS MgSO4.7H2O
What are acids?
Proton donors. They release h+ ions when mixed with water
What are bases?
Proton acceptors. They want to grab H+ ions in solution
Bases that are soluble in water are alkalis.
Name 4 common acids
HCL-Hydrochloric acid
H2SO4-Sulfuric acid
HN03-Nitric acid
CH3COOH-Ethanoic acid
Name 3 common bases
NaOH-Sodium hydroxide
KOH-Pottasium hydroxide
NH3-Ammonia
What is the diffrence between strong and weak acids?
and strong bases and weak bases?
Strong acids completely dissociate (give up H+ ions) in solution, weak acids only partially dissociate
Strong bases completely dissociate (give up OH- ions) in solution, weak bases only partially dissociate
What is produced in the neutralisation reaction between acids and alkalis?
Eg. HCL + KOH—>
Salt and water
HCL + KOH—> KCL + H20
Why is aqueous ammonia still an alkali despite not directly producing hydroxide ions?
HN3 + H20 –> NH4+ + OH-
The reaction between ammonia and water produces hyrdroxide ions. Ammonia accepts hyrdogen ions from water molecules, forming an ammonium ion and hydroxide ion. In this way ammonia can neutralise acids.
Metal + acid –>
metal salt + hydrogen
Metal oxide + acid –>
salt + water
Metal Hydroxide + acid –>
Salt + water
Metcal carbonate + acid –>
metal salt + carbon dioxide + water
Ammonia + acid –>
Ammonium salt
How do you carry out a titration calculation?
These allow you to find out exactly how much acid is needed to neutralize a quantity of alkali
• Measure alkali into a flask using a pipette
• Add indicator
• Fill burette with known quantity of acid
• Conduct a rough titration to approximate amount
○ Add acid from burette
○ Swirl flask
○ The alkali will be neutralized when the indicator changes colour
• Conduct accurate titration
○ Run acid within 2cm3 of the end point
○ Slowly add more and record the amount of acid used to neutralize the alkali
• Conduct experiment 2/3 times
• Take an average value
Methyl orange and phenolphthalein color change?
YELLOW->RED
PINK->COLOURLESS
How do you make a standard solution?
- Use precise balance to weigh solid on to a watch glass
- Transfer to beaker and use water to make sure it all transfers
- Add water to completely dissolve solid, stir with glass rod
- Transfer to volumetric flask. rinse beaker in to volumetric flask
- fill up volumetric flask with water up to graduation line. use pipett to be precise
- mix flask
Whats special about polyprotic acids?
They donate more then one proton
Percentage yield =
Why might it be low?
Percentage yield = actual yield/theoretical yield x 100
Percentage yield may be low due to the reaction not going to completion, impurities or side reactions
Atom economy =
Why might it be low?
Atom economy = Molar mass of desired product/molar mass of all products x 100
Atom economy will be low if more than one product is formed
Why is low atom economy bad?
How else can they make reactions more sustainable?
- Lots of waste to dispose of, so its costly and bad for environment
- reactant chemicals expensive, so its waste of money if theres less sueful products
- less sustainable, many raw materials are limited n supply
- Have lower energy costs to maintain (low pressure and temp)
- Raw materials can be from renewable rescources (plants, enzyme)
Whtas more sustaible addition or substituion reactions?
- Addition reaction have atom economies of 100%
* Substitution and elimination reactions have lower atom economies
Give an example of a sustaible reaction
Fermentation
What is the oxidation number of elemnts bonded to the same element?
0
Whats the oxidation number for:
Oxygen (O)
peroxides (02^2-)
molecular oxygen (O2)
Oxygen is -2
peroxides is -1
molecular oxygen (O2) is 0
Whats the oxidation number for:
Hydrogen (H)
hydrogen in Metal hydrides (MHx)
molecular Hydrogen (H2)
Hydrogen (H) is +1 Metal hydrides (MHx) is -1 molecular Hydrogen (H2) is 0
What is the formula of iron(III) sulfate?
What is the formula for iron (II) nitrate?
Iron has oxidation number of 3+ (due to III) , sulfate ion is SO4^2- so 2- charge overall.
So the forumla is Fe2(S02)3
Fe(NO3)2
What is the systematic name for ClO2 -1?
What is the systematic name for CR2(SO4)3?
Oxygen usually exist as -2. 2 oxygens means -4
the overall charge on the compound is -1. so Cl must be +3 as -4+3=-1 SO it’s Chlorate(III)
Chromium (III) Sulfate
Oxidation is…
Reduction is…
Oxidation is Loss of electrons but gain of oxygen
Reduction is gain of electrons but loss of oxygen
Reducing agent donates electrons so is oxidised
Oxidising agent accepts electrons so is reduced
OIL RIG
Identitfy the oxidising and reducing agent in:
4Fe + 3O2 —> 2Fe2O3
Iron has gone from oxidation number of 0 to +3
so its lost electrons so its a reducing agent
Oxygen has gone ffrom 0 to -2
so its gained lectrons so its an oxidising agent
Metals usually have positive oxidation numbers so are usually
When metals react with acids they produce salt and hydrogen gas.
why is this a redox reaction?
Metal atoms are oxidised as they from positive metal ions (in salts)
Hydrogen ions in solution are reduced , gaining electrons and forming hydrogen molecules.
Whats the equation for magnesium reacting with dilute hydrochloric acid? and what type of reaction is this?
Mg(s) + 2HCL –> MgCl2(aq) + H2
Redox reaction
Mg oxidation number increases from 0 to 2+ (OIL)
H Oxidation number decreased from +1 to 0 (RIG)
define mole
amount of substance that has as many particles as there are atoms in 12g of carbon-12
define empirical formula
the simplest whole number ratio of each element in a compound
percentage uncertainty?
equipment uncertainty x no. of uses/measured value x100
Give thermal decomposition of group 2 metal
MCO3 —> M0 + CO2
Define an alkali?
Relaeses OH- Ions (can’t just say proton pair acceptor)
