COTW7

100.0 cm³ of a 0.50 mol dm^-3 solution of BaCl₂ is added to 50.0 cm³ of a 0.10 mol dm^-3 solution of Na₂SO₄.  A precipitate of BaSO₄ is formed according to the equation below:
BaCl₂(aq) + Na₂SO₄(aq) --> BaSO₄(s) + 2NaCl(aq)
What is the amount, in mol, of BaSO₄ produced?

• 0.0050
• 0.010
• 0.050
• 0.10

The diagram represents the emission spectrum of hydrogen.  Groups of arrows are labelled W, X, and Y.
Which statement is correct?

• The arrows represent the transition of electrons to different energy levels when heat is supplied.
• The arrows of W represent emission in the UV region.
• The smallest arrow of X represents a violet line in the emission spectrum.
• The arrows of Y represent emission of electromagnetic waves with higher energy than those represented by X and W.

Which electron configurations do not follow Hund's Rule?

• I and II only
• I and III only
• II and III only
• I, II, and III

The horizontal axis of the bar chart represents the elements of period 3 from sodium to chlorine (excluding silicon).  What could the vertical axis represent?

• Melting point of the element.
• Electronegativity of the bonded atom.
• Ionic radius of the most common ion.
• First ionization energy in the gaseous state.

Which statements about reactivity are correct?
I.  Potassium reacts more vigorously than sodium with chlorine.
II. Lithium reacts more vigorously than potassium with water.
III.  Fluorine reacts more vigorously than bromine with potassium iodide solution.

• I and II only
• I and III only
• II and III only
• I, II, and III

THIS IS A FREE RESPONSE, NOT MULTIPLE CHOICE! So answer all the questions.

A sample of magnesium contains three isotopes: magnesium-24, magnesium-25, and magnesium-26, with abundances of 77.44%, 10.00%, and 12.56% respectively.

a i) Calculate the relative atomic mass of this sample of magnesium correct to two decimal places.

a ii) Predict the relative atomic radii of the three magnesium isotopes, giving your reasons.

b i) A graph of the successive ionization energies of magnesium is shown in Graph B. Explain the increase in ionization energy values from the 3rd to the 8th electrons.

b ii) Explain the sharp increase in ionization energy values between the 10th and 11th electrons.

c i) Magnesium reacts with oxygen to form an ionic compound, magnesium oxide. Describe how the ions are formed, and the structure and bonding in magnesium oxide.

c ii) Carbon reacts with oxygen to form a covalent compound, carbon dioxide. Describe what is meant by a covalent bond.

c iii) State why magnesium and oxygen form an ionic compound while carbon and oxygen form a covalent compound.

d i) Predict the type of hybridization of the carbon and oxygen atoms in CO₂.

d ii) Sketch the orbitals of an oxygen atom in CO₂ on the energy level diagram provided in Image D including the electrons that occupy each orbital.

d iii) Define the term electronegativity.

d iv) Explain why oxygen has a larger electronegativity than carbon.

e i) The Graph E shows pressure and volume data collected for a sample of carbon dioxide gas at 330 K. Draw a best-fit curve for the data on the graph.

e ii) Use the data point labelled X on Graph E to determine the amount, in mol, of carbon dioxide gas in the sample.

f i) Most indicators are weak acids. Describe qualitatively how indicators work.

f ii) Identify a suitable indicator for a titration between a weak acid and a strong base, using Table 16 of the Data Booklet.

• I have answered ALL questions a-fii.

• I did NOT answer questions a-fii.