OCS A Level Chemistry A 2023 Exam Synthesis and
Analytical Techniques Version 2 Top Prediction 100%
define isotopes - ANSWER: atoms with the same number of protons and electrons
but different number of neutrons
FOR ATOMS
Find the number of protons, neutrons, electrons - ANSWER: protons = atomic
number
neutrons = mass number - atomic number
electrons = atomic number
FOR IONS
Find the number of protons, neutrons, electrons - ANSWER: protons = atomic
number
neutrons = mass number - atomic number
electrons = atomic number - charge
Why do different isotopes of an element have the same chemical properties -
ANSWER: They have the same number of electrons in their outer shell
neutrons make no difference to chemical reactivity
State the similarities and differences between the atomic structure of isotopes of the
same element - ANSWER: similarities: number of protons and electrons
differences: number of neutrons
Explain why the same product would be formed when both carbon-12 and carbon-13
are combusted in oxygen - ANSWER: they have the same number of electrons in
their outer shell
number of neutrons make no difference to chemical reactivity
define relative atomic mass - ANSWER: the weighted mean mass of an atom
compared with the 1/12th mass of carbon-12
a sample of antimony, Ar=121.8, was analysed and was found to consist of 60%
121Sb and one other isotope.
determine the mass number of the other isotope in the sample of antimony -
ANSWER: (0.6*121)+(0.4x)=121.8
72.6+0.4x=121.8
0.4x=49.2
x=123
- 28Si 92.23%
- 29Si 4.68%
- 30Si 3.06%
, Calculate the relative atomic mass of silicon - ANSWER:
(28x92.23)+(29x4.68)+(30x3.06)/100 = 28.099
one coin has a mass of 5g and contains 84% of copper
calculate the number of copper atoms in one coin - ANSWER: n=m/M = 5/63.5 = 0.07
mol Cu
0.07*84/100 = 0.066 copper atoms
a salt used as a fertilizer has the empirical formula of H4N203
suggest the formulae of the ions present in this salt - ANSWER: NH4, N03
whats the formula of chromium (III) sulfate - ANSWER: take the charges and criss
cross method
Cr2(SO4)3
predict the formula of the compound formes when bromine reacts with aluminum -
ANSWER: take the charges and criss cross method
AlBr3
predict the formula of the gallium ion - ANSWER: Ga is in group 3, looses 3 electrons
so
Ga3+
zinc carbonate, ZnCO3 reacts with an excess of dilute hydrochloric acid in a test tube.
describe what the student would see during this reaction. - ANSWER: fizzing,
bubbling
whats the formula of ammonium sulfide - ANSWER: take the charges and criss cross
method
(NH4)2S
the electronic configuration of element X is: 1s2 2s2 2p6 3s2 3p4
whats the formula of a compound formed when sodium reacts with element X -
ANSWER: electronic configuration = 16
element X is sulfur
charges: Na+1 S-2
criss cross methos
Na2X
calculate the amount, in mol, of nitrogen atoms in 5.117x10^20 nitrogen molecules -
ANSWER: 5.177x10^20/6.022x10^20 = 8.5x10^-4
Nitrogen exists as N2 so
8.5x10^-4*2 = 1.7x10^-3
PBr3 can be prepared by heating bromine with phosporus, P4
write an equation for this reaction - ANSWER: P4 + 6Br2 = 4PBr3
Analytical Techniques Version 2 Top Prediction 100%
define isotopes - ANSWER: atoms with the same number of protons and electrons
but different number of neutrons
FOR ATOMS
Find the number of protons, neutrons, electrons - ANSWER: protons = atomic
number
neutrons = mass number - atomic number
electrons = atomic number
FOR IONS
Find the number of protons, neutrons, electrons - ANSWER: protons = atomic
number
neutrons = mass number - atomic number
electrons = atomic number - charge
Why do different isotopes of an element have the same chemical properties -
ANSWER: They have the same number of electrons in their outer shell
neutrons make no difference to chemical reactivity
State the similarities and differences between the atomic structure of isotopes of the
same element - ANSWER: similarities: number of protons and electrons
differences: number of neutrons
Explain why the same product would be formed when both carbon-12 and carbon-13
are combusted in oxygen - ANSWER: they have the same number of electrons in
their outer shell
number of neutrons make no difference to chemical reactivity
define relative atomic mass - ANSWER: the weighted mean mass of an atom
compared with the 1/12th mass of carbon-12
a sample of antimony, Ar=121.8, was analysed and was found to consist of 60%
121Sb and one other isotope.
determine the mass number of the other isotope in the sample of antimony -
ANSWER: (0.6*121)+(0.4x)=121.8
72.6+0.4x=121.8
0.4x=49.2
x=123
- 28Si 92.23%
- 29Si 4.68%
- 30Si 3.06%
, Calculate the relative atomic mass of silicon - ANSWER:
(28x92.23)+(29x4.68)+(30x3.06)/100 = 28.099
one coin has a mass of 5g and contains 84% of copper
calculate the number of copper atoms in one coin - ANSWER: n=m/M = 5/63.5 = 0.07
mol Cu
0.07*84/100 = 0.066 copper atoms
a salt used as a fertilizer has the empirical formula of H4N203
suggest the formulae of the ions present in this salt - ANSWER: NH4, N03
whats the formula of chromium (III) sulfate - ANSWER: take the charges and criss
cross method
Cr2(SO4)3
predict the formula of the compound formes when bromine reacts with aluminum -
ANSWER: take the charges and criss cross method
AlBr3
predict the formula of the gallium ion - ANSWER: Ga is in group 3, looses 3 electrons
so
Ga3+
zinc carbonate, ZnCO3 reacts with an excess of dilute hydrochloric acid in a test tube.
describe what the student would see during this reaction. - ANSWER: fizzing,
bubbling
whats the formula of ammonium sulfide - ANSWER: take the charges and criss cross
method
(NH4)2S
the electronic configuration of element X is: 1s2 2s2 2p6 3s2 3p4
whats the formula of a compound formed when sodium reacts with element X -
ANSWER: electronic configuration = 16
element X is sulfur
charges: Na+1 S-2
criss cross methos
Na2X
calculate the amount, in mol, of nitrogen atoms in 5.117x10^20 nitrogen molecules -
ANSWER: 5.177x10^20/6.022x10^20 = 8.5x10^-4
Nitrogen exists as N2 so
8.5x10^-4*2 = 1.7x10^-3
PBr3 can be prepared by heating bromine with phosporus, P4
write an equation for this reaction - ANSWER: P4 + 6Br2 = 4PBr3
