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Group 2

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Chemistry

In 2020, the Spitzer Space Telescope was retired by NASA after 17 years of service. It had observed the universe's infrared activity, providing us with a unique insight into previously hidden areas of space. It carried instruments that could detect wavelengths all the way from just 3.6 μm up to 160 μm in length, and used a mirror almost 1 metre in diameter to focus and reflect light. This mirror was cooled to a chilly 5.5 K - that's -268 °C!

But that's not the reason why it catches our interest. No, we care more about what it was built from. The mirror was made of beryllium, an example of a group 2 element.

Group 2 metals

Group 2 is a group of metals in the periodic table. They are also known as the alkaline earth metals.

  • This article is about group 2 in inorganic chemistry.
  • We'll start by providing an overview of the elements found in group 2.
  • We'll then look at the properties of group 2 elements, including their atomic radius and first ionisation energy.
  • After that, we'll explore how they react.
  • Finally, we'll go over how to test for group 2 elements.

Group 2 elements

Take a look at the periodic table below. The column in pink shows you one particular group, group 2.

Group 2, periodic table elements, StudySmarterGroup 2 in the periodic table. Olive, StudySmarter Originals

Group 2 contains six elements:

  • Beryllium (Be)
  • Magnesium (Mg)
  • Calcium (Ca)
  • Strontium (Sr)
  • Barium (Ba)
  • Radium (Ra)

These elements all appear in nature, although barium is never found on its own due to its high reactivity. Likewise, radium is extremely radioactive, and only occurs as part of the decay chains of heavier elements such as thorium and uranium.

Almost all of the naturally-occurring radium in the environment is 226Ra, an isotope with a half-life of 1600 years. However, it's not very common. One kilogram of the Earth's crust contains just 900 picograms of radium - that's grams!

Radium's only current commercial applications are its uses in nuclear medicine, where it can be used to treat certain types of cancers. However, in the early twentieth century, it rose to fame as a source of radiation for radioactive quackery. This is a pseudoscience that improperly promotes radiation as a cure for many illnesses. To this day, you can still find spas that proudly advertise their radium-containing waters as a treatment for all manner of ills and ailments.

In contrast, the group 2 metal calcium is the fifth most common element in the Earth's crust. It has many applications, such as in the production of soaps and cement. However, its most important function is arguably in the body. Calcium is an essential element for many organisms. For example, calcium ions help regulate muscle contraction and nerve function in animals. Our bones act as stores of these ions. A calcium deficiency can lead to osteoporosis. Calcium ions also play a structural role in plants, helping form the cell wall, cell membrane, and middle lamella.

You can find out more about the effect of calcium ions in Sliding Filament Theory.

Properties of group 2

Group 2 elements are fairly similar. Physically, they are all soft, shiny, silvery-white metals, with relatively low melting and boiling points and densities. Let's take a look at some of their other properties in more detail.

Group 2 structure and bonding

All group 2 elements have two electrons in their outer shell. These electrons are found in an outer s-orbital.

Not sure what we're talking about? Check out Electron Configuration to find out more about different electron orbitals.

Group 2, electron configuration of magnesium, StudySmarterThe electron configuration of magnesium. Created using images from commons.wikimedia.org

When they react, group 2 elements lose their two outer electrons to form cations with a charge of 2+, and an oxidation state of +2. This means that group 2 elements form ionic compounds.

There's one exception to the rule - beryllium. This element actually forms covalent molecules, not ionic compounds. We'll look at why this is so when we move on to group 2's trend in electronegativity.

Group 2 atomic radius

If you've read Periodic Trends, you should be able to predict how the atomic radius of group 2 elements varies as you move down the group. As you can see in the graph below, atomic radius increases moving down the group. This is because each subsequent element has more electrons, with more electron shells.

Group 2, atomic radius of group 2 elements, StudySmarterThe atomic radius of group 2 elements. Anna Brewer, StudySmarter Originals

We've already seen the electronic structure of magnesium: it has 12 electrons found in three electron shells. The next element in the group, calcium, has 20 electrons found in four electron shells. It, therefore, has a larger atomic radius.

Group 2, magnesium and calcium, StudySmarterMagnesium and calcium. Created using images from commons.wikimedia.org

Group 2 melting points

In general, the melting points of group 2 elements decrease as you move down the group. As solids, metals form metallic lattices consisting of positive metal cations surrounded by a sea of negative delocalised electrons, as shown below.

Group 2, calcium lattice, StudySmarterCalcium's metallic lattice. Anna Brewer, StudySmarter Originals

This lattice is held together by strong electrostatic attraction between the negative electrons and the nuclei of the positive cations. Remember that atomic radius increases as you move down the group. This means that the nuclei are further away from the delocalised electrons. Therefore, the electrostatic attraction is weaker. So, less energy is needed to overcome it and melt the solid.

Group 2, melting points of group 2 elements, StudySmarterThe melting points of group 2 elements. Anna Brewer, StudySmarter Originals

You'll notice that magnesium's melting point doesn't fit the overall trend. Unfortunately, there's no simple explanation for this. Likewise, the boiling points of group 2 metals don't show a clear trend either. Once again, there's no simple explanation. Yes, we know - deeply annoying!

Need more information on metallic lattices? Metallic Bonding has got you covered!

Group 2 first ionisation energy

We'll now move on to looking at the first ionisation energies of group 2 elements.

First ionisation energy is the energy needed to remove one mole of the most loosely held electrons from one mole of gaseous atoms. Each atom forms a cation with a charge of +1.

Can you guess the trend?

First ionisation energy decreases as you go down group 2. Once again, this is due to increasing atomic radius. As you move down the group, the outermost electron is further away from the nucleus. This means that the attraction between the nucleus and the electron is weaker, hence easier to overcome.

Group 2, first ionisation energy, StudySmarterThe first ionisation energy of group 2 elements. Anna Brewer, StudySmarter Originals

This topic is covered in much more depth in Trends in Ionisation Energy.

Group 2 electronegativity

Now let's look at electronegativity.

Electronegativity is an atom's ability to attract a bonding pair of electrons.

Once again, there is much more detail in Polarity. But the basic principles of electronegativity apply here too. Electronegativity decreases as you go down the group in the periodic table. As we know, atomic radius increases as you move down the group. This means that any bonded electrons are further from the nucleus, so the attraction between them is weaker.

You might also remember from Polarity that electronegativity is affected by nuclear charge - the number of protons in an atom's nucleus. As you go down the group, nuclear charge increases, so you might think that electronegativity would increase as well.

To explain this, go back to the structures of magnesium and calcium. Magnesium, with an atomic number of 12, has 12 protons in its nucleus. Calcium, on the other hand, has 20. However, magnesium has 10 inner shell electrons that shield the charge of 10 of these protons. In contrast, calcium has 18 inner shell electrons that shield the charge of its protons. In both elements, any bonding pair would therefore only feel the attraction of the two remaining unshielded protons. The effective nuclear charge is the same. But because calcium has a larger atomic radius, it has a lower electronegativity.

Remember that we mentioned that beryllium acts a bit strangely? It forms covalent molecules instead of ionic compounds. This is because it is such a small atom; thus, it has a higher electronegativity than all the other members of the group.

For example, take beryllium chloride and magnesium chloride. Chlorine is much more electronegative than magnesium, and a large difference in electronegativity causes an ionic bond. Chlorine atoms attract magnesium's electrons so strongly that magnesium gives them up completely. Both elements form ions.

Group 2, magnesium chloride, StudySmarter

Magnesium chloride. Anna Brewer, StudySmarter Originals

On the other hand, beryllium's electronegativity is high enough that it doesn't want to lose its electrons. Instead, it hangs on to them and shares them with chlorine in a covalent bond. This is why beryllium forms covalent molecules instead of ionic compounds.

Group 2, beryllium chloride, StudySmarterBeryllium chloride. Anna Brewer, StudySmarter Originals

Group 2 solubility

Like all metals, group 2 elements are insoluble in water. However, their compounds have varying solubilities. (You can find out more in Group 2 Compounds.)

Group 2 reactivity

The final property we'll look at is reactivity. Like most metals, group 2 elements are fairly reactive. Their reactivity increases as you go down the group. As we explored earlier, group 2 elements (apart from beryllium) always react to form ions with a charge of 2+. This requires removing two outer shell electrons - in other words, the processes of first and second ionisation. Ionisation energy decreases as you go down the group, so it is easier to remove these electrons. Therefore, reactivity increases.

Reactions of group 2

Now that we've learnt about the properties of group 2, we can take a look at some of their reactions.

All reactions involving group 2 are redox reactions.

Redox reactions are reactions involving both oxidation and reduction. Oxidation is the loss of electrons, whilst reduction is the gain of electrons. (See Redox for more details.)

The group 2 element loses two electrons to form a cation with a charge of 2+, and an oxidation state of +2. It is oxidised. On the other hand, the other elements involved gain electrons. They are reduced. Don't worry - we'll practice showing this below.

Let's now explore the reactions of group 2 with water, oxygen, chlorine, and acids.

We're ignoring beryllium in all of the following examples - it doesn't form ions, as we saw earlier. What a tricky exception to the rule!

Group 2 elements' reaction with water

Have you ever wondered why group 2 are called the alkaline metals? It's because they react with water to produce alkaline metal hydroxides and hydrogen gas. This is a great example of the trend in reactivity of group 2 elements. Here, M represents the group 2 metal:

Although we've shown the metal hydroxide as aqueous, this might not always be the case. The solubility of group 2 metal hydroxides actually varies, increasing as you move down the group. In fact, magnesium hydroxide is essentially insoluble, whilst calcium hydroxide is only sparingly soluble. Strontium and barium hydroxide are both extremely soluble in water.

As with all reactions involving group 2 elements (apart from that sneaky beryllium), the reaction between a group 2 metal and water is a redox reaction. The group 2 metal is oxidised and loses electrons, whilst the hydrogen in water is reduced and gains an electron. The oxygen doesn't take part in the redox reaction - it is just a spectator species. We can show this using oxidation states.

Group 2, oxidation states in magnesium hydroxide, StudySmarterThe oxidation states in magnesium hydroxide. Anna Brewer, StudySmarter Originals

Head over to Redox for more.

The reaction between a group 2 metal and water gets more vigorous as you go down the group. For example, magnesium reacts extremely slowly with water, producing just a few bubbles. You'd be hard-pressed to see any reaction at all. However, calcium fizzes gently when you add it to water, whilst strontium and barium bubble violently. Overall, their reactivity increases as you move down the group. Once again, this is because their ionisation energies decrease as you go down the group. Lower ionisation energies mean that it is easier to lose electrons, so reactivity increases.

Group 2 elements' reaction with oxygen

We'll now focus on the reaction between group 2 elements and oxygen. Burning a group 2 element in oxygen produces a metal oxide. Here's the equation:

The same reaction happens if you leave a group 2 metal exposed to air. A metal oxide rapidly builds up on the surface of the metal, producing a thin coating that stops any further reaction.

Strontium and barium also burn in oxygen to produce a peroxide, . However, beryllium, magnesium, and calcium don't. This has to do with the smaller size of these metal ions. Since they are smaller, they have a much higher charge density, attracting the oxygen molecules differently.

Metal peroxides are formed when the peroxide ion, O22-, reacts with a metal ion. The peroxide ion consists of two oxygen ions, each with a negative charge or 1-, covalently bonded together.

All elements in group 2 form ions with a charge of 2+. However, beryllium, magnesium, and calcium form smaller ions than strontium and barium. This means that they have a higher charge density. The charge density is so large that it is able to pull some of the electrons in the peroxide ion over to one of the oxygen atoms involved, breaking the covalent bond between them. This results in a neutral oxygen atom and an O2- ion, which bonds with the metal ion.

However, strontium and barium are larger ions. This means that they have a lower charge density. Their charge density isn't great enough to disrupt the covalent bonding in the peroxide ion. The peroxide ion remains intact when it bonds to the metal, so strontium and barium are able to form peroxides.

Magnesium also reacts with steam to produce the same product, magnesium oxide. The reaction initially forms magnesium hydroxide, but this splits up upon heating to produce the oxide and hydrogen gas. Overall:

Group 2 elements' reaction with chlorine

Group 2 metals react with chlorine to produce metal chlorides. In fact, they react in a similar way with all halides. Once again, reactivity increases as you go down the group. Here's the general equation:

Group 2 elements' reaction with acids

Finally, we'll turn our attention to the reactions of group 2 with acids. These vary depending on the type of acid used.

Hydrochloric acid

This is the simplest case - the group 2 element reacts with hydrochloric acid to give a metal chloride and hydrogen gas. For example, mixing magnesium with hydrochloric acid gives magnesium chloride and hydrogen:

Magnesium chloride is the primary salt found in the Dead Sea. With a salinity of over 30 percent, it is one of the world's saltiest bodies of water.

Nitric acid

Nitric acid makes things a little more complicated. Group 2 metals can also reduce the nitrogen atoms found within nitric acid, forming all manner of nitrous oxides. However, the main reaction produces a metal nitrate and hydrogen gas.

Sulphuric acid

Group 2 elements react with sulphuric acid to produce metal sulphates and hydrogen gas. However, in reality, strontium and barium don't tend to react much. This is because the sulphate forms an insoluble layer on the surface of the metal, preventing any further reaction. Likewise, calcium sulphate is only sparingly soluble, so calcium doesn't react much with sulphuric acid either. Nevertheless, here's the general reaction between a group 2 metal and sulphuric acid:

We look at the solubility of metal sulphates in more detail in Group 2 Compounds.

One further reaction involving group 2 metals uses magnesium to extract titanium. Discovered in Cornwall in 1791 by William Gregor, titanium is an extremely useful transition metal. It has a low density but high strength, and is resistant to both seawater and chlorine. You'll find it in the aerospace industry as well as in mobile phones and orthopaedic implants.

Titanium is found deep within the Earth's crust as titanium oxide. This is first reacted with chlorine to produce titanium tetrachloride, . Magnesium is then added. This reduces the titanium within titanium tetrachloride, forming magnesium chloride and titanium metal:

Group 2 summary

Here's a handy table that summarises the reactions of group 2 for you.

ElementReactantProductEquation
All group 2 elementsCold waterMetal hydroxide and hydrogen
MagnesiumSteamMagnesium oxide and hydrogen
All group 2 elementsOxygenMetal oxide
Strontium and bariumOxygenMetal peroxide
All group 2 elementsChlorineMetal chloride
All group 2 elementsHydrochloric acidMetal chloride and hydrogen
All group 2 elementsNitric acidMetal nitrate and hydrogen
All group 2 elementsSulphuric acidMetal sulphate and hydrogen

Testing for group 2

Right at the start of the article, we mentioned how all group 2 elements are pretty similar in appearance. They are all silvery metals. This can make them quite tricky to tell apart. However, one way of distinguishing group 2 metals is by putting them in a flame. The different metals burn to produce different-coloured flames in a spectacular show.

Get a clean metal loop and dip it in acid. Hold it in a Bunsen burner flame until there is no colour change. This cleans the loop. Next, dip the loop in a solid sample of your metal and hold it back in the Bunsen burner once again. Observe the colour of flame produced. With any luck, you'll get the following results.

MetalColour
CalciumOrange-red
StrontiumRed
BariumGreen

Note that beryllium and magnesium don't produce a coloured flame. You'll have to rely on other chemical tests to tell them apart.

Uses of group 2 elements

Lastly, let's focus on some of the uses of group 2.

  • Calcium is the fifth-most abundant element in the human body and plays a role in bone health, muscle contraction, and neurotransmission.
  • Calcium compounds are used in agriculture to raise the pH of soil. They can also be used to remove sulphur from flue gas.
  • Barium compounds are used in x-rays, and beryllium alloys are used in mechanical parts.
  • Magnesium is the third-most commonly used structural metal, mostly used in lightweight alloys.

Check out Group 2 Compounds for more uses of group 2.

Group 2 - Key takeaways

  • Group 2, also known as the alkaline earth metals, is a group of metals in the periodic table.
  • Group 2 contains the elements beryllium, magnesium, calcium, strontium, barium, and radium.
  • Group 2 elements each have two electrons in their outer shell.
  • Atomic radius and reactivity increase as you move down the group.
  • Melting point, first ionisation energy, and electronegativity decrease as you move down the group.
  • Group 2 elements (with the exception of beryllium), react with water, oxygen, chlorine, and acids in redox reactions. When they react, they lose their two outer shell electrons to form cations with a charge of 2+.
  • Magnesium is used to extract titanium from titanium oxide.
  • You can distinguish between some of the group 2 elements using flame tests.

Group 2

Group 2 on the periodic table refers to the alkaline earth metals.

Group 2 elements are fairly reactive metals with relatively low densities and melting and boiling points. Their reactivity and atomic radius increase as you move down the group, whilst their melting point, electronegativity, and first ionisation energy decrease as you move down the group.

Group 2 elements are called alkaline earth metals because they form alkaline metal oxides and hydroxides. These metal oxides are found in the Earth.

The solubility of group 2 hydroxides increases as you move down the group, whereas the solubility of group 2 sulphates decreases as you move down the group.

Final Group 2 Quiz

Question

Name the six members of group 2.

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Answer

  • Beryllium
  • Magnesium
  • Calcium
  • Strontium
  • Barium
  • Radium

Show question

Question

What is another name for group 2?

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Answer

The alkaline earth metals.

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Question

Why is group 2 also known as the alkaline earth metals?

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Answer

They react with water to form alkaline metal hydroxides.

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Question

How many electrons do group 2 elements have in their outer shell?

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Answer

2

Show question

Question

True or false: Group 2 elements always react to form ions with a charge of 2+.

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Answer

False

Show question

Question

Atomic radius ____ as you move down group 2.

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Answer

Increases

Show question

Question

Predict which element has a larger atomic radius.

Show answer

Answer

Calcium

Show question

Question

Melting point _____ as you move down group 2.

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Answer

Decreases

Show question

Question

Predict which element has a higher melting point.

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Answer

Beryllium

Show question

Question

First ionisation energy _____ as you move down group 2.

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Answer

Decreases

Show question

Question

Predict which element has a higher first ionisation energy.

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Answer

Calcium

Show question

Question

Electronegativity _____ as you move down group 2.

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Answer

Decreases

Show question

Question

Predict which element has a higher electronegativity.

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Answer

Beryllium

Show question

Question

Reactivity _____ as you move down group 2.

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Answer

Increases

Show question

Question

Predict which element is more reactive.

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Answer

Strontium

Show question

Question

When taking part in redox reactions, group 2 metals are _____.

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Answer

Oxidised

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Question

Some group 2 elements can react with oxygen to form a metal peroxide. Which elements are they?

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Answer

Strontium

Show question

Question

True or false? Reacting a group 2 metal with nitric acid produce a metal nitrate only.

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Answer

False

Show question

Question

Which group 2 element is used to extract titanium?

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Answer

Magnesium

Show question

Question

How do you carry out flame tests?

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Answer

  • Dip a metal loop in acid and hold it in a Bunsen flame until there is no colour change. This cleans the loop.
  • Dip the loop in a solid sample of your metal and hold it in the Bunsen burner flame once again. Observe the colour change.

Show question

Question

Which of the following statements are true about group 2 flame tests?

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Answer

Calcium produces an orange-red flame.

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Question

What are group 2 elements?

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Answer

Group 2 elements also known as the 'alkaline earth metals' are a part of the s-block on the periodic table, having two electrons in the outermost shell. 


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Question

What are the properties of group 2 elements?

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Answer

-  The melting points of group 2 elements generally decrease as you go down the group.

- The reactivity of group 2 elements increases as you go down the group.

-  When these group 2 elements react, they lose their outer electrons and gain a charge of 2+.

Show question

Question

What are some common group 2 compounds?

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Answer

- Calcium hydroxide, Ca(OH)2

- Magnesium carbonate, MgCO3

- Strontium oxide, SrO

Show question

Question

Which group 2 element does not react with water?


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Answer

Beryllium 

Show question

Question

What does magnesium produce upon reaction with steam?

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Answer

Magnesium reacts with steam to produce magnesium oxide. 

Mg(s) + H2O(g) —› MgO(s) + H2(g)

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Question

What does magesium produce upon reaction with cold water?

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Answer

Magnesium reacts extremely slowly with cold water producing magnesium hydroxide. 

Mg(s) + 2H2O(l) —› Mg(OH)2(aq) + H2(g)

 

Show question

Question

What are the observations when group 2 elements react with cold water?


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Answer

- The metal dissolves. It dissolves faster going down the group.

- Fizzing 

- The solution heats up.

- With calcium, the solution becomes more saturated, and a white precipitate forms.

 

Show question

Question

What do the oxides of group 2 metals produce when reacted with acid?

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Answer

- Salts

For example, 

CaO(s) + 2HNO3(aq) —› Ca(NO3)2(aq) + H2O(l)

 This equation shows calcium oxide reacting with dilute nitric acid, producing calcium nitrate and water. 

Show question

Question

What is the solubility of group 2 hydroxides?

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Answer

The group 2 hydroxides become more soluble as you go down the group.

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Question

What is the solubility of group 2 sulfates?

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Answer

As you go down group 2, the solubility of the sulfates decreases.

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Question

What do group 2 carbonates produce when reacted with dilute acid?

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Answer

The group 2 carbonates react with dilute acid to produce a salt, water and carbon dioxide. 

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Question

What do group 2 hydroxides produce when reacted with dilute acids?

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Answer

When group 2 hydroxides react with dilute acids, the product is a colourless solution of metal salts. 

 An example of this is:

 Ca(OH)2(aq) + 2HCl(aq) —› CaCl2(aq) + 2H2O(l)

Show question

Question

Which group 2 oxide is not a basic oxide?

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Answer

Beryllium oxide

Show question

Question

Are hydroxides of group 2 elements soluble ?


Show answer

Answer

The hydroxides of group 2 elements from magnesium to barium are soluble in water and form alkaline solutions.

Show question

Question

 What is the use of barium sulfate (BaSO4)?

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Answer

It is insoluble and is used in medicine. It absorbs X-rays strongly and is used to diagnose disorders of the intestines and stomach. Due to its insolubility, it is not absorbed into the bloodstream from the gut.

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