1.2 Chemical Calculations

*number are quickfire questions from WJEC book

HideShow resource information
  • 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
1 of 42
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
2 of 42
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
3 of 42
What is relative molecular mass?
The average mass of a molecule to one twelfth the mass of an atom of carbon-12
4 of 42
What is molar mass?
The mass of one mole of a substance
5 of 42
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
6 of 42
What unit is used for molar mass?
g mol-1
7 of 42
What does the mass spectrometer find?
The mass of the isotopes and their relative abundances
8 of 42
What can you work out from the results of the mass spectrometer?
The average mass of an atom
9 of 42
Name the basic processes that occur in the mass spectrometer
- Ionisation - Acceleration - Deflection - Detection
10 of 42
What does ionisation in the mass spectrometer indetail?
A gaseous example in bombarded with high energy electrons to from positive ions
11 of 42
What does acceleration in the mass spectrometer indetail?
An electric field accelerates the positive ions to high speed
12 of 42
What does deflection in the mass spectrometer indetail?
A magnetic field deflects ions according the their mass/charge ratio
13 of 42
Are heavier or lighter ions deflected more by the magnetic field in mass spectrometer
Lighter ions are deflected more
14 of 42
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.
15 of 42
*15 What is the relative molecular mass (Mr) of; (a) NH4NO3 (b) CuSO4.5H2O
(a) 80.02 (b) 249.7
16 of 42
*16 State why the space inside a mass spectrometer is connected to a vacuum pump
To prevent collisions between the sample and air molecules
17 of 42
*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
18 of 42
What does Ar stand for?
Relative atomic mass
19 of 42
What does Mr stand for?
Relative molecular mass
20 of 42
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
21 of 42
How do you work out the Ar from mass spec?
(abundance x mass/charge ratio) + same over 100
22 of 42
What is a molecular ion M+?
A positive ion formed in mass spectrometer when a molecule looses an electron
23 of 42
*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
24 of 42
What is empirical formula?
The simplest formula showing the whole number ratio of the amount of elements present
25 of 42
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
26 of 42
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
27 of 42
How do you work out the number of moles when given the mass?
moles (n) = mass (m) divided by Mr
28 of 42
What unit is normally used for concentration?
mol d-3
29 of 42
How do you work out the number of moles from concentration when volume is given in dm3?
Moles (n) = concentration (c) x volume (v)
30 of 42
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
31 of 42
*19 Calculate the mass of 0.50 mol of calcium hydroxide Ca(OH)2
37.06 g
32 of 42
*20 Calculate the concentration of 4.0g sodium hydroxide in 500 cm3 of solutoin
0.2 mol dm-3
33 of 42
What is stoichiometry?
The molar relationship between the amounts of reactants and products in a chemical reaction
34 of 42
What is molar volume? vm (little m)
The volume per mole of a gas
35 of 42
what does the equation mean n = v over vm
moles = volume divided by molar volume
36 of 42
*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
37 of 42
What is atom economy?
A value obtained from the chemical equation for the reaction
38 of 42
What is the formula for atom economy?
mass of required product divided by total mass of reactants x 100
39 of 42
What is percentage yield?
A value calculated from the mass of product actually obtained by experiment
40 of 42
What is the equation for percentage yield?
mass of product obtained divided by maximum theoretical mass x 100
41 of 42
A high atom economy means that the process is ____
Efficient
42 of 42

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
View more cards

Comments

No comments have yet been made

Similar Chemistry resources:

See all Chemistry resources »See all 1.2 resources »