2.2 Group 2, the Alkaline Earth Metals

Magnesium reacts very slowly with water to form magnesium hydroxide and hydrogen. 

A student suggests that when magnesium reacts with steam, it should just produce magnesium hydroxide and hydrogen but at a quicker rate.

Write a balanced symbol equation to demonstrate the thermal instability of one of the student’s suggested products. You are not required to write the correct equation for the reaction of magnesium with steam.

Samples of magnesium, calcium, strontium and barium are reacted with water to form their hydroxides. The resulting solutions are then filtered to collect the precipitates.

State the trend in the expected mass for the precipitates.

Explain how the following trends of Group 2 metal hydroxides, from Mg - Ba, are connected:

• Solubility in water
• Strength as a base

Table 1 shows the solubility data for the Group 2 metal hydroxides.

Table 1

A student determined that a 50 cm³ solution of an unknown Group 2 metal hydroxide contained 802 mg of the metal hydroxide.

Identify the metal hydroxide in the unknown sample.

A student is asked to determine the identity of an impure Group (II) metal sample.

The impure sample was known to contain only sulfate-based chemicals. It appeared to be a white solid which formed a white precipitate in a pale blue solution when dissolved in
25.0 cm³ of water.

Suggest the identity of the impurity in the unknown sample.

Table 1 shows the solubility of the Group 2 metal sulfates at 20 C.

Table 1

Use the information in Table 1 to explain which Group (II) metal sulfate cannot be the unknown metal sulfate in the sample from part (a).

The student analysed a 2.50 g sample of the impure Group 2 metal sulfate.

They found the sample to be 94.4 % pure and that 0.12 % of the Group 2 metal sulfate had dissolved in 25.0 cm³ of water.

Use this information and Table 1 in part (b) to identify the Group 2 metal sulfate.

The uncertainty of the balance that the student used to measure the mass of the pure Group 2 metal sulfate was ± 0.0005 g.

Evaluate the effect that this uncertainty has on the identity of the Group 2 metal sulfate identified in part (c). 

Figure 1 shows the melting points of the Group 2 elements. 

Figure 1

Magnesium does not follow the general trend of the Group 2 metals. The actual melting point of magnesium is around 72.6 % of the expected value. 

Plot the actual melting point of magnesium on Figure 1.

The Kroll process is used to extract titanium from its ores, commonly rutile (TiO₂). The Kroll process involves, first, reacting rutile with chlorine and then reacting the product with magnesium at a temperature of 800 - 900 C. The reaction with magnesium is
exothermic, releasing around 412 kJ mol^-1. The final product is a titanium “sponge” which predominantly contains titanium and magnesium chloride.

Milk of magnesia, Mg(OH)₂, can be taken to relieve constipation and, as an antacid, to neutralise excess acid in the gut. It is used because magnesium hydroxide is only sparingly soluble in water so it is not absorbed into the body.

Suggest another property of milk of magnesia that makes it suitable for use in the human body.

Many of the Group 2 metal compounds are used to neutralise acid. Calcium hydroxide is used in agriculture to neutralise acidic soil, while magnesium hydroxide is used in medicine to neutralise excess stomach acid.

Write a balanced symbol equation, including state symbols, to represent these reactions.

Burning fossil fuels releases acidic pollutants into the atmosphere. These acidic gases can be removed from flue gases by a process called wet scrubbing. In wet scrubbing, a slurry is made by mixing powdered lime or limestone with water. This slurry is then sprayed on to the flue gases. One acidic gas reacts with the alkaline slurry to form solid calcium sulfite.

Write two balanced symbol equations, including state symbols, to show the reaction of this acidic gas with the lime slurry and the limestone slurry.

Barium sulfate is used to diagnose problems within the digestive tract. Patients are advised to not eat or drink for 8 - 12 hours before a barium swallow and can be described as nil-by-mouth. One reason for not eating before the barium swallow is so
that the barium sulfate doesn’t coat any food substances and give a false image of a blockage.

Suggest one reason for not drinking before the barium swallow.

A technician found a bottle of clear liquid, X, with only part of the label still on the bottle. From the label, the technician determined that liquid X is a solution containing a sodium salt. The technician added barium chloride solution to a small portion of liquid X and
observed a white precipitate. The technician concluded that the solution was sodium sulfate.

Give the full electron configuration for a magnesium ion, Mg²⁺.

Identify the element in Group 2 from magnesium to barium which has the lowest first ionisation energy.

Explain your answer. 

A group of students completed two experiments. In experiment 1, they added magnesium metal to nitric acid and in experiment 2, they added calcium metal to sulfuric acid. The students then compared the two reactions and found that a white solid had been produced in experiment 2.

The concentration of each acid was kept the same and the mass of each Group 2 metal used was also kept the same.

Predict and explain which reaction would finish first, and name the white solid formed.

Write equations for the reactions taking place in Experiment 1 and Experiment 2. 

Magnesium, calcium and barium are some of the Group 2 elements of the Periodic Table. 

State and explain the trend in atomic radius of the Group 2 elements from magnesium to barium.

Magnesium is frequently used in fireworks. It burns rapidly in oxygen, and it adds sparks which generally improves the appearance and brilliance of the firework.

Write an equation to represent the reaction which takes place when a strip of magnesium is burned in oxygen and state an observation which would be made.

Group 2 compounds, such as the hydroxides of magnesium and calcium, have a number of other uses. 

Group 2 elements will react with water.

A student added 20cm³ of water to two boiling tubes. To one of the boiling tubes they added a small piece of calcium and to the other they added a small piece of barium.

State two observations that the student would make and how the observations would differ between the two boiling tubes.

Barium is a Group 2 element whose compounds have a number of uses. Barium chloride solution is used to test for sulfate ions, but it must be acidified before it can be used.

Name the type of reaction taking place in part (a) and give a use of the product formed from this reaction. 

The solubility of compounds of Group 2 elements vary down the group.

State the trends in solubility of the Group 2 sulfates and the Group 2 hydroxides as you descend the group. 

Compare the reactivity of barium with the reactivity of magnesium. Explain your answer.

This question is about Group 1 and Group 2 metals of the Periodic Table.

Give the electron configuration of the s block metal which has the highest first ionisation energy.

Explain why the first ionisation energy of the element in part (a) is higher than the first ionisation energy of calcium.

A student has completed a number of simple test tube reactions to determine the identity of some unlabelled solutions.

The student has only two solutions left which they need to identify. One of the solutions is sodium nitrate and the other is sodium sulfate.

Magnesium is another Group 2 element which undergoes a number of chemical reactions.

A teacher is completing a demonstration for class, reacting magnesium ribbon with steam.

State two observations that the students would make during the demonstration and provide an equation, with state symbols, for the reaction which is taking place.