Module 2: Atoms and reactions Flashcards

(46 cards)

1
Q

What is relative atomic mass?

A

Relative atomic mass is the average mass per atom of the naturally occurring form of an element relative to 1/12th of the mass of a carbon-12 atom.

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2
Q

What is relative isotopic mass?

A

Relative isotopic mass is the mass of an atom of an isotope relative to 1/12th of the mass of a carbon-12 atom.

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3
Q

What is relative molecular mass?

A

Relative molecular mass is the sum of the relative atomic masses of the constituent atoms of a molecule relative to 1/12th of the mass of a carbon-12 atom.

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4
Q

What is the equation for calculating the relative atomic mass (Ar) of an isotope?

A

Ar = { ( abundance of isotope x isotopic mass of isotope ) /100

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5
Q

What is the equation linking molar mass, mass and number of moles?

A

number of moles = mass (g) / Mr (g/mol)

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6
Q

What is meant by the molar mass?

A

The mass per mole of a substance

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7
Q

What number represents Avogadro’s constant?

A

6.02 x 10*23

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8
Q

What is the empirical formula?

A

The empirical formula is the formula showing the simplest whole number ratio of atoms of each element present in a compound.

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9
Q

What is the molecular formula?

A

The molecular formula is the formula showing the actual number of atoms of each element in a molecule.

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10
Q

What is stated by Avogadro’s law?

A

At the same temperature and pressure, 1 mole of any gas will occupy the same volume.

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11
Q

What is standard temperature and pressure?

A

Pressure = 1 Atmosphere = 100,000Pa
Temperature = 25*C = 298 K

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12
Q

What is the equation for number of moles using volume (in dm cubed and cm cubed) at RTP?

A

moles = volume/molar volume

number of moles = volume (dm cubed) / 24

number of moles = volume (cm cubed) / 24000

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13
Q

What is the ideal gas equation?

A

PV = nRT

P = pressure in Pa
V = volume in m cubed
dm cubed / 103 = m cubed
cm cubed /10
6 = m cubed
n = number of moles
R = universal gas constant = 8.314 Jmol-1K-1
T = temperature in K
T(K) = T(*C) + 273

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14
Q

What does the % yield of a chemical reaction show?

A

The % yield of a chemical reaction shows how much product was actually made compared with the amount of product the was expected

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15
Q

What is the equation for % yield?

A

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

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16
Q

What are some reasons as to why yield is not often 100%?

A
  • the reaction may be incomplete
  • side reactions may occur, leading to by-products
  • reactants may not be pure
  • some reactants/products may be left behind in the apparatus
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17
Q

What is atom economy?

A

Atom economy is the % of reactants that end up as useful products

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18
Q

What is the equation for atom economy?

A

Atom economy = mass of wanted product (s) / total mass of all products x 100

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19
Q

What is the equation linking concentration, moles and volume?

A

Conc. (moles.dm-3) = moles / volume (dm3)

20
Q

What is concentration?

A

A measure of how much solute is dissolved per solvent.

21
Q

What is meant by hydrated?

A

Hydrated refers to a crystalline compound containing water molecules.

22
Q

What is meant by anhydrous?

A

Anhydrous refers to a substance that contains no water molecules.

23
Q

What is water of crystallisation?

A

Water molecules that are within the crystalline structure of the compound.

24
Q

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

A
  • chemical reactions involve electrons, and isotopes have the same number and arrangement of electrons
  • neutrons make no difference to chemical reactivity
25
What are the... 1. atomic numbers 2. mass numbers 3. no. of protons 4. no. of neutrons 5. no. of electrons in... a) 23 Na + 11 b) 35 Cl- 17
a) 1. 11 2. 23 3. 11 4. 12 5. 10 b) 1. 17 2. 35 3. 17 4. 18 5. 18
26
What does the contribution made by an isotope to the overall mass depend on?
- the percentage abundance of the isotope - the relative mass of the isotope
27
Why is the term relative formula mass used for some compounds, instead of relative molecular mass?
Compounds with giant structures don't exist as simple molecules - includes ionic compounds and covalent compounds
28
What can mass spectrometry be used for?
- identifying unknown compounds - finding the relative abundance of each isotope of an element - determining structural info. about molecules
29
How is a mass spectrometer used to determine the mass of a molecule/isotope?
It measures the mass-to-charge ratio of ions 1. it causes substances to become positive ions 2. positive ions are passed through the apparatus and separated depending on their mass and charge 3. a computer analyses the data on the ions present and produces a mass spectrum
30
Why do atoms of Be, B, C and Si not usually form ions?
It requires too much energy to transfer the outer shell electrons to form ions
31
What is the equation for converting moles to no. of particles?
No. of particles = n (moles) x Avogadro's constant (6.02x10^23)
32
Define Avogadro's constant
The number of atoms per mole of the carbon-12 isotope (6.02x10^23)
33
Define molar gas volume
The volume per mole of a gas - units are dm3/mol
34
What is the molar gas volume at RTP?
24.0 dm3/mol
35
What do chemists often use to measure gas volumes?
Gas syringe Alternatively could use a gas delivery tube leading into an upturned measuring cylinder in a water bath
36
What does the concentration of a solution tell us? What is the unit for concentration?
How much solute is dissolved in a given amount of solvent. The concentration of a solution is the amount of solute, in mol, dissolved per 1dm3 of solution Moldm-3
37
What is the equation for calculating the amount, in mol, of any volume of a solution of a known concentration?
n = cV
38
What is a standard solution and what are they often used for?
A standard solution is a solution of known concentration. Often used in titrations to determine unknown info about another substance
39
What piece of equipment is used to make up a standard solution?
A volumetric flask
40
How would you make up a standard solution?
1. weigh out the sol
41
Find the mass of potassium hydroxide required to prepare 250cm3 of a 0.200 moldm-3 solution
1. Find amount of KOH in mol required in the solution n = cV n = 0.200 x (250/1000) = 0.0500 mol 2. Convert moles into grams n = mass/Mr mass = n x Mr mass = 0.0500 x 56.1 = 2.805g
42
What is meant by… 1. Concentrated 2. Dilute
1. A large amount of solute per dm3 2. A small amount of solute per dm3
43
What do concentrated acids have a concentration greater than?
10 moldm-3
44
What is a species in chemistry?
A type of particle that takes part in a reaction A species could be an atom, ion, molecule, or empirical formula or electron
45
What are the 3 ways to work out an amount in moles?
From mass : n = mass/Mr From gas volumes : n = V (in dm3) / 24.0 n = V (in cm3) / 24000 From solutions : n = cV (V in dm3)
46
The empirical formula for hydrated magnesium chloride is MgCl2H10O5 Determine the dot formula
MgCl2.5H2O