IB Chemistry HL S1.2 The nuclear atom questions

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Question 1

Multiple choiceMedium1 mark

A copper ion is represented by 2965Cu2+^{65}_{29}\mathrm{Cu}^{2+} What are its numbers of protons, neutrons and electrons, respectively?

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Answer: A. For a nuclide, the proton number is ZZ and the neutron number is A−ZA-Z a 2+2+ charge means two fewer electrons than protons. Thus p=29p=29 n=65−29=36n=65-29=36 and e=29−2=27e=29-2=27

B: adds 2 to the proton number when finding electrons, reversing the charge effect.
C: uses the electron count instead of the proton number in A−ZA-Z giving 38 neutrons.
D: assumes the ion has the same number of electrons as a neutral copper atom, ignoring its charge.

Remember: ion formation changes the number of electrons, not the nucleus.

Question 2

Paper 2Medium10 marks

A representative sample of natural boron is characterized for use in a neutron-absorbing material. It contains the isotopes ¹⁰₅B and ¹¹₅B. The relative isotopic masses and relative atomic mass of the sample are:

IsotopeRelative isotopic mass
¹⁰₅B10.0129
¹¹₅B11.0093

The relative atomic mass, Aᵣ, of the sample is 10.811.

(a)

For the ion ¹⁰₅B⁺, state the number of protons, neutrons and electrons.

[3]
(b)

Explain why ¹⁰₅B and ¹¹₅B are isotopes.

[2]
(c)

Assuming the sample contains only these two isotopes, determine the percentage abundance of ¹⁰₅B. Give your answer to three significant figures.

[3]
(d)

A student claims that ¹⁰₅B and ¹¹₅B must have identical physical properties because they have the same number of protons. Explain why this claim is not justified.

[2]

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