1.2 Chemical Calculations

*number are quickfire questions from WJEC book

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  • Created by: Danielle
  • Created on: 15-12-13 20:21
What is one mole?
The amount of any substance that contains the same number of particles as there are atoms in exactly 12g of carbon-12
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What is relative atomic mass?
The average mass of one atom of the element relative to one twelfth the mass of one atom of carbon-12
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What is relative isotopic mass?
The mass of an atom of an isotope relative to one twelfth the mass of an atom of carbon-12
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What is relative molecular mass?
The average mass of a molecule to one twelfth the mass of an atom of carbon-12
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What is molar mass?
The mass of one mole of a substance
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What is the number or atoms in a mole and what is this called?
the Avogadro constant (L) 6.02 x 10 to the power of 23
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What unit is used for molar mass?
g mol-1
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What does the mass spectrometer find?
The mass of the isotopes and their relative abundances
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What can you work out from the results of the mass spectrometer?
The average mass of an atom
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Name the basic processes that occur in the mass spectrometer
- Ionisation - Acceleration - Deflection - Detection
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What does ionisation in the mass spectrometer indetail?
A gaseous example in bombarded with high energy electrons to from positive ions
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What does acceleration in the mass spectrometer indetail?
An electric field accelerates the positive ions to high speed
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What does deflection in the mass spectrometer indetail?
A magnetic field deflects ions according the their mass/charge ratio
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Are heavier or lighter ions deflected more by the magnetic field in mass spectrometer
Lighter ions are deflected more
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What does detection in the mass spectrometer indetail?
Ions with the correct mass/charge ratio mass through a slit and are detected by an instrument such an an electrometer.
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*15 What is the relative molecular mass (Mr) of; (a) NH4NO3 (b) CuSO4.5H2O
(a) 80.02 (b) 249.7
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*16 State why the space inside a mass spectrometer is connected to a vacuum pump
To prevent collisions between the sample and air molecules
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*17 A sample of strontium showed three peaks. First at m/z 86 with an abundance of 10%, second at m/z 87 with an abundance of 7%, third at m/z 88 with an abundance of 83%. Calculate the Ar to three s.f.
87.7
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What does Ar stand for?
Relative atomic mass
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What does Mr stand for?
Relative molecular mass
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Name three other uses of the mass spectrometer other than the average mass
- Identify unknown compounds - Identify tracing compounds in forensic science - Analysing molecules in space
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How do you work out the Ar from mass spec?
(abundance x mass/charge ratio) + same over 100
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What is a molecular ion M+?
A positive ion formed in mass spectrometer when a molecule looses an electron
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*18 In the mass spectrum of chlorine, explain why peaks due to chlorine atoms are present although chlorine gas contains only Cl2 molecules.
The molecular ion splits to give Cl+ ions
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What is empirical formula?
The simplest formula showing the whole number ratio of the amount of elements present
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What is molecular formula?
Shows the actual number of atoms of each element present in a molecule, can be simple multiplication on the empirical formula
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How do you work out an empirical formula?
1) ratio divided by Ar 2) divide all by the smallest number giving you the final ratio
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How do you work out the number of moles when given the mass?
moles (n) = mass (m) divided by Mr
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What unit is normally used for concentration?
mol d-3
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How do you work out the number of moles from concentration when volume is given in dm3?
Moles (n) = concentration (c) x volume (v)
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How do you work out the number of moles from concentration when volume is given in cm3?
Moles (n) = concentration (c) x volume (v) over 1000
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*19 Calculate the mass of 0.50 mol of calcium hydroxide Ca(OH)2
37.06 g
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*20 Calculate the concentration of 4.0g sodium hydroxide in 500 cm3 of solutoin
0.2 mol dm-3
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What is stoichiometry?
The molar relationship between the amounts of reactants and products in a chemical reaction
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What is molar volume? vm (little m)
The volume per mole of a gas
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what does the equation mean n = v over vm
moles = volume divided by molar volume
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*21 What amount, in mol, of gas molecules are there in 0.56 dm3 O2 at 0 degrees c and 1 atm? (occupies 22.4 cm3)
0.025
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What is atom economy?
A value obtained from the chemical equation for the reaction
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What is the formula for atom economy?
mass of required product divided by total mass of reactants x 100
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What is percentage yield?
A value calculated from the mass of product actually obtained by experiment
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What is the equation for percentage yield?
mass of product obtained divided by maximum theoretical mass x 100
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A high atom economy means that the process is ____
Efficient
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Other cards in this set

Card 2

Front

What is relative atomic mass?

Back

The average mass of one atom of the element relative to one twelfth the mass of one atom of carbon-12

Card 3

Front

What is relative isotopic mass?

Back

Preview of the front of card 3

Card 4

Front

What is relative molecular mass?

Back

Preview of the front of card 4

Card 5

Front

What is molar mass?

Back

Preview of the front of card 5
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