2.1 Atoms And Reactions

Question 1

Define Isotope

Answer 1

Atoms of the same element with different number of neutrons but same number of protons

Question 2

Define relative isotopic mass

Answer 2

The mass of an isotope compared to 1/12th the mass of carbon-12

Question 3

Define relative atomic mass

Answer 3

The weighted average mass of an atom compared to 1/12th the mass of carbon-12

Question 4

What’s the relative mass of an electron?

Answer 4

1/2000

Question 5

Ar formula?

Answer 5

((Isotope mass x %)+(isotope mass x %))/100

Question 6

Number of particles formula?

Answer 6

Moles x avogadros constant

Question 7

What does mass spectrometry tell us?

Answer 7

Determine the relative abundances of each isotope of an element

Identified unknown substances

Provide structural information about a molecule

Question 8

How do you use mass spectra to work out relative atomic masses of different elements?

Answer 8

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

Question 9

What’s the formula to finding the number of moles? when you have mass

Answer 9

no. of moles (mol) = mass (g) / Mr (g mol-1)

Question 10

Why do different isotopes of the same element react in the same way?

Answer 10

1. Chemical reactions involve ELECTRONS, and isotopes have the same number and arrangement of electrons.
2. Neutrons make no difference to chemical reactivity.

Question 11

What is the Avogadro’s constant?

Answer 11

The number of atoms per mole of the carbon-12 isotope (6.02 x 10^23 mol-1)

Question 12

What are the steps to calculate the empirical formula?

Answer 12

1. Find the moles of the element
2. Divide the answer for each element by the smallest number
3. If necessary, multiply the answer by a suitable value to make sure the ratio is in whole number only.

Question 13

Define molecular formulae

Answer 13

Tells you the number of each type of atom that make up a molecule

Question 14

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

Answer 14

1. Work out the empirical formula mass (same as relative formula mass) of the compound.
2. Given molecular mass/the empirical formula mass= No. of empirical units in the molecule
3. 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

Question 15

How do you write an ionic equation?

Q. What’s the ionic equation for the reaction of Nitric acid with sodium hydroxide

Answer 15

1. Write out a full balanced equation
2. Rewrite the equation showing all the ions that are in the reaction mixture (only aqueous compounds, leave solids and gasses as is)
3. 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

Question 16

What’s the formula to finding the number of moles? when you have volume of gas

Answer 16

n=v/24

Question 17

What’s the formula to finding the number of moles? when you have solution volume and concentration

Answer 17

n=C x V

Question 18

what’s the ideal gas equation?

Answer 18

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

Question 19

What’s the molar volume?

Answer 19

The molar volume is the volume per mole of gas. At room temperature and pressure it is
24.0 dm3/mol

Question 20

What’s a hydrated salt?

Answer 20

A hydrated salt is one which contains water of crystallisation e.g. MgSO4·7H2O.

It is water that trapped inside the ionic lattice

Question 21

What’s an anhydrous salt?

Answer 21

An anhydrous salt is one with no water of crystallisation e.g. MgSO4.

Question 22

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.

Answer 22

-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

Question 23

What are acids?

Answer 23

Proton donors. They release h+ ions when mixed with water

Question 24

What are bases?

Answer 24

Proton acceptors. They want to grab H+ ions in solution

Bases that are soluble in water are alkalis.

Question 25

Name 4 common acids

Answer 25

HCL-Hydrochloric acid H2SO4-Sulfuric acid HN03-Nitric acid CH3COOH-Ethanoic acid

Question 26

Name 3 common bases

Answer 26

NaOH-Sodium hydroxide KOH-Pottasium hydroxide NH3-Ammonia

Question 27

What is the diffrence between strong and weak acids? | and strong bases and weak bases?

Answer 27

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

Question 28

What is produced in the neutralisation reaction between acids and alkalis? Eg. HCL + KOH--->

Answer 28

Salt and water HCL + KOH---> KCL + H20

Question 29

Why is aqueous ammonia still an alkali despite not directly producing hydroxide ions? HN3 + H20 --> NH4+ + OH-

Answer 29

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.

Question 30

Metal + acid -->

Answer 30

metal salt + hydrogen

Question 31

Metal oxide + acid -->

Answer 31

salt + water

Question 32

Metal Hydroxide + acid -->

Answer 32

Salt + water

Question 33

Metcal carbonate + acid -->

Answer 33

metal salt + carbon dioxide + water

Question 34

Ammonia + acid -->

Answer 34

Ammonium salt

Question 35

How do you carry out a titration calculation?

Answer 35

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

Question 36

Methyl orange and phenolphthalein color change?

Answer 36

YELLOW->RED | PINK->COLOURLESS

Question 37

How do you make a standard solution?

Answer 37

* 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

Question 38

Whats special about polyprotic acids?

Answer 38

They donate more then one proton

Question 39

Percentage yield = Why might it be low?

Answer 39

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

Question 40

Atom economy = Why might it be low?

Answer 40

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

Question 41

Why is low atom economy bad? How else can they make reactions more sustainable?

Answer 41

* 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)

Question 42

Whtas more sustaible addition or substituion reactions?

Answer 42

* Addition reaction have atom economies of 100% | * Substitution and elimination reactions have lower atom economies

Question 43

Give an example of a sustaible reaction

Answer 43

Fermentation

Question 44

What is the oxidation number of elemnts bonded to the same element?

Answer 44

0

Question 45

Whats the oxidation number for: Oxygen (O) peroxides (02^2-) molecular oxygen (O2)

Answer 45

Oxygen is -2 peroxides is -1 molecular oxygen (O2) is 0

Question 46

Whats the oxidation number for: Hydrogen (H) hydrogen in Metal hydrides (MHx) molecular Hydrogen (H2)

Answer 46

``` Hydrogen (H) is +1 Metal hydrides (MHx) is -1 molecular Hydrogen (H2) is 0 ```

Question 47

What is the formula of iron(III) sulfate? What is the formula for iron (II) nitrate?

Answer 47

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

Question 48

What is the systematic name for ClO2 -1? What is the systematic name for CR2(SO4)3?

Answer 48

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

Question 49

Oxidation is... Reduction is...

Answer 49

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

Question 50

Identitfy the oxidising and reducing agent in: | 4Fe + 3O2 ---> 2Fe2O3

Answer 50

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

Question 51

When metals react with acids they produce salt and hydrogen gas. why is this a redox reaction?

Answer 51

Metal atoms are oxidised as they from positive metal ions (in salts) Hydrogen ions in solution are reduced , gaining electrons and forming hydrogen molecules.

Question 52

Whats the equation for magnesium reacting with dilute hydrochloric acid? and what type of reaction is this?

Answer 52

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)

Question 53

define mole

Answer 53

amount of substance that has as many particles as there are atoms in 12g of carbon-12

Question 54

define empirical formula

Answer 54

the simplest whole number ratio of each element in a compound

Question 55

percentage uncertainty?

Answer 55

equipment uncertainty x no. of uses/measured value x100

Question 56

Give thermal decomposition of group 2 metal

Answer 56

MCO3 ---> M0 + CO2

Question 57

Define an alkali?

Answer 57

Relaeses OH- Ions (can't just say proton pair acceptor)