Detailed explanations are given for the carbonates because the diagrams are easier to draw, and their equations are also easier. CAMEO Chemicals Mixtures of metal/nonmetal nitrates with alkyl esters may explode, owing to the formation of alkyl nitrates; mixtures of a nitrate with phosphorus , tin (II) chloride, or other reducing agents may react explosively [Bretherick 1979 p. 108-109]. Exceptions include BaSO 4, PbSO 4, and SrSO 4. 3.19 Recall the general rules which describe the solubility of common types of substances in water: all common sodium, potassium and ammonium salts are soluble; all nitrates are soluble; common chlorides are soluble except those of silver and lead… A/AS level. Group 2 nitrates decompose on heating to produce group 2 oxides, oxygen and nitrogen dioxide gas. They are : 1.Heat of Hydration (Hydration Energy) and 2. For more information contact us at info@libretexts.org or check out our status page at https://status.libretexts.org. :D The inter-ionic distances are increasing and so the attractions become weaker. 10 Points to Best Answer for all chemicals listed. In other words, it has a high charge density and has a marked distorting effect on any negative ions which happen to be near it. On that basis, the oxide lattice enthalpies are bound to fall faster than those of the carbonates. The size of the nitrate ions are larger than the size of the metal cations, and the difference in size between the cations and anions are large but decreasing when going down the group as the size of the cations increases. The chlorides, bromides, and iodides of all metals except lead, silver, and mercury(I) are soluble … I can't find a value for the radius of a carbonate ion, and so can't use real figures. The Thermal Stability of the Nitrates and Carbonates, [ "article:topic", "enthalpy", "lattice enthalpy", "authorname:clarkj", "carbonate ion", "showtoc:no", "Nitrates", "Thermal Stability", "Polarizing", "Carbonates", "Group 2", "enthalpy cycle" ], https://chem.libretexts.org/@app/auth/2/login?returnto=https%3A%2F%2Fchem.libretexts.org%2FBookshelves%2FInorganic_Chemistry%2FModules_and_Websites_(Inorganic_Chemistry)%2FDescriptive_Chemistry%2FElements_Organized_by_Block%2F1_s-Block_Elements%2FGroup__2_Elements%253A_The_Alkaline_Earth_Metals%2F1Group_2%253A_Chemical_Reactions_of_Alkali_Earth_Metals%2FThe_Thermal_Stability_of_the_Nitrates_and_Carbonates, Former Head of Chemistry and Head of Science, The Solubility of the Hydroxides, Sulfates and Carbonates, Group 2: Physical Properties of Alkali Earth Metals, The effect of heat on the Group 2 carbonates, The effect of heat on the Group 2 Nitrates, Explaining the relative falls in lattice enthalpy, information contact us at info@libretexts.org, status page at https://status.libretexts.org. A saturated solution has a concentration of about 1.3 g per 100 g of water at 20°C. The shading is intended to show that there is a greater chance of finding them around the oxygen atoms than near the carbon. BaSO4 is the least soluble. All the nitrates in this Group undergo thermal decomposition to give the metal oxide, nitrogen dioxide and oxygen. Its charge density will be lower, and it will cause less distortion to nearby negative ions. For the sake of argument, suppose that the carbonate ion radius was 0.3 nm. There is little data for beryllium carbonate, but … It describes and explains how the thermal stability of the compounds changes as you go down the Group. All the Group 2 carbonates are very sparingly soluble. Today we're covering: Properties of Group 2 compounds Reactions Oxides with water Carbonates with acid Thermal decomposition Carbonates Nitrates Solubility Hydroxides Sulfates Let's go! Silver acetate is sparingly soluble. SO 4 2: Most sulfates are soluble. By contrast, the least soluble Group 1 carbonate is lithium carbonate. If "X" represents any one of the elements, the following describes this decomposition: Down the group, the carbonates require more heating to decompose. The effect of heat on the Group 2 carbonates. Reactivity increases down the group. The argument is exactly the same here. Exactly the same arguments apply to the nitrates. This page offers two different explanations for these properties: polarizability and energetics. If the attractions are large, then a lot of energy will have to be used to separate the ions - the lattice enthalpy will be large. Lattice Energy. For example, a typical Group 2 nitrate like magnesium nitrate decomposes like this: In Group 1, lithium nitrate behaves in the same way - producing lithium oxide, nitrogen dioxide and oxygen. Missed the LibreFest? The positive ion attracts the delocalised electrons in the carbonate ion towards itself. Gallium nitrate localizes preferentially to areas of bone resorption and remodeling and inhibits osteoclast-mediated resorption by enhancing hydroxyapatite crystallization and reduction of bone mineral solubility. We also acknowledge previous National Science Foundation support under grant numbers 1246120, 1525057, and 1413739. I had explained all of the trends except one, group 2 nitrates. To compensate for that, you have to heat the compound more in order to persuade the carbon dioxide to break free and leave the metal oxide. Here we will be talking about: Oxides Hydroxides Carbonates Nitrates Sulfates Group 2 Oxides Characteristics: White ionic solids All are basic oxides EXCEPT BeO BeO: amphoteric The small Be2+ … Group 2 carbonates are virtually insoluble in water. Brown nitrogen dioxide gas is given off together with oxygen. The lattice enthalpies fall at different rates because of the different sizes of the two negative ions - oxide and carbonate. For reasons we will look at shortly, the lattice enthalpies of both the oxides and carbonates fall as you go down the Group. Here's where things start to get difficult! Covers the elements beryllium (Be), magnesium (Mg), calcium (Ca), strontium (Sr) and barium (Ba). Lattice enthalpy is the heat needed to split one mole of crystal in its standard state into its separate gaseous ions. If you calculate the enthalpy changes for the decomposition of the various carbonates, you find that all the changes are quite strongly endothermic. The nitrates, chlorates, and acetates of all metals are soluble in water. We say that the charges are delocalised. For nitrates we notice the same trend. Remember that the reaction we are talking about is: You can see that the reactions become more endothermic as you go down the Group. Detailed explanations are given for the carbonates because the diagrams are easier to draw, and their equations are also easier. The Group 2 nitrates undergo thermal decomposition to the metal oxide, nitrogen dioxide and oxygen gas. 3. The rates at which the two lattice energies fall as you go down the Group depends on the percentage change as you go from one compound to the next. But they don't fall at the same rate. 2. The substances are listed in alphabetical order. NO 3: All nitrates are soluble. The LibreTexts libraries are Powered by MindTouch® and are supported by the Department of Education Open Textbook Pilot Project, the UC Davis Office of the Provost, the UC Davis Library, the California State University Affordable Learning Solutions Program, and Merlot. Remember that the reaction in question is the following: \[XCO_{3(s)} \rightarrow XO_{(s)} + CO_{2(g)}\]. The nitrates are white solids, and the oxides produced are also white solids. This is a rather more complicated version of the bonding you might have come across in benzene or in ions like ethanoate. Mg(OH) 2 → MgO + H 2 O. Carbonates These are prepared by precipitation reactions with the solubility decreasing down the group. The term we are using here should more accurately be called the "lattice dissociation enthalpy". The general fall is because hydration enthalpies are falling faster than lattice enthalpies. As the positive ions get larger down the group, they affect on the carbonate ions near them less. The smaller the positive ion is, the higher the charge density, and the greater effect it will have on the carbonate ion. You will need to use the BACK BUTTON on your browser to come back here afterwards. I can't find a value for the radius of a carbonate ion, and so can't use real figures. Figures to calculate the beryllium carbonate value weren't available. You wouldn't be expected to attempt to draw this in an exam. For the purposes of this topic, you don't need to understand how this bonding has come about. The size of the lattice enthalpy is governed by several factors, one of which is the distance between the centres of the positive and negative ions in the lattice. CaCO 3 → CaO + CO 2. Includes trends in atomic and physical properties, trends in reactivity, the solubility patterns in the hydroxides and sulfates, trends in the thermal decomposition of the nitrates and carbonates, and some of the atypical properties of beryllium. The ones lower down have to be heated more strongly than those at the top before they will decompose. If you worked out the structure of a carbonate ion using "dots-and-crosses" or some similar method, you would probably come up with: This shows two single carbon-oxygen bonds and one double one, with two of the oxygens each carrying a negative charge. (e.g., AgCl, Hg 2 Cl 2, and PbCl 2). The enthalpy changes for the decomposition of the various carbonates indicate that the reactions are strongly endothermic, implying that the reactions likely require constant heating to proceed. You would observe brown gas evolving (NO2) and the White nitrate solid is seen to melt to a colourless solution and then resolidify 2Mg(NO3)2→ 2MgO + 4NO2+ O2 In other words, as you go down the Group, the carbonates become more thermally stable. Legal. The increasing thermal stability of Group 2 metal salts is consistently seen. This process is much more difficult to visualize due to interactions involving multiple nitrate ions. Nitrates All nitrates break down to produce the oxide, nitrogen dioxide and oxygen. You have to supply increasing amounts of heat energy to make them decompose. Although the inter-ionic distance will increase by the same amount as you go from magnesium carbonate to calcium carbonate, as a percentage of the total distance the increase will be much less. The lattice enthalpy of the oxide will again fall faster than the nitrate. All sodium, potassium, and ammonium salts are soluble in water. Explaining the trend in terms of the polarizing ability of the positive ion. CO 3 2: All carbonates are insoluble except NH 4 + and those of the Group 1 elements. But they don't fall at the same rate. All group 2 nitrates and chlorides are soluble, but the solubility of the group 2 sulphates decreases down the group-Magnesium sulphate is classed as soluble-Calcium sulphate is classed as slightly soluble -Strontium and barium sulphate are insoluble solubility : Nitrates of group -1 and group-2 metals are all soluble in water. The smaller the positive ion is, the higher the charge density, and the greater effect it will have on the carbonate ion. THERMAL STABILITY OF THE GROUP 2 CARBONATES AND NITRATES. In the oxides, when you go from magnesium oxide to calcium oxide, for example, the inter-ionic distance increases from 0.205 nm (0.140 + 0.065) to 0.239 nm (0.140 + 0.099) - an increase of about 17%. That's entirely what you would expect as the carbonates become more thermally stable. A bigger 2+ ion has the same charge spread over a larger volume of space. N Goalby chemrevise.org 5 Solubility of Sulfates Group II sulphates become less soluble down the group. Gallium Nitrate is a hydrated nitrate salt of the group IIIa element gallium with potential use in the treatment of malignancy-associated hypercalcemia. Even for hydroxides we have the same observations. You can dig around to find the underlying causes of the increasingly endothermic changes as you go down the Group by drawing an enthalpy cycle involving the lattice enthalpies of the metal carbonates and the metal oxides. Most nitrates tend to decompose on heating to give the metal oxide, brown fumes of nitrogen dioxide, and oxygen. In real carbonate ions all the bonds are identical, and the charges are distributed over the whole ion, with greater density concentrated on the oxygen atoms.In other words, the charges are delocalized. No headers. It explains how the thermal stability of the compounds changes down the group. A bigger 2+ ion has the same charge spread over a larger volume of space, so its charge density is lower; it causes less distortion to nearby negative ions. The carbonate ion becomes polarized. For example, for magnesium oxide, it is the heat needed to carry out 1 mole of this change: The cycle we are interested in looks like this: You can apply Hess's Law to this, and find two routes which will have an equal enthalpy change because they start and end in the same places. It reacts with cold water to produce an alkaline solution of calcium hydroxide and hydrogen gas is released. Here's where things start to get difficult! Magnesium carbonate (the most soluble one I have data for) is soluble to the extent of about 0.02 g … If you think carefully about what happens to the value of the overall enthalpy change of the decomposition reaction, you will see that it gradually becomes more positive as you go down the Group. If the attractions are large, then a lot of energy will have to be used to separate the ions - the lattice enthalpy will be large. Solubility of the carbonates. It has a high charge density and will have a marked distorting effect on any negative ions which happen to be near it. The calculated enthalpy changes (in kJ mol-1) are given in the table below (there is no available data for beryllium carbonate). Covers the elements beryllium (Be), magnesium (Mg), calcium (Ca), strontium (Sr) and barium (Ba). Trends in solubility of group 2 nitrates. The oxide lattice enthalpy falls faster than the carbonate one. The oxide ion is relatively small for a negative ion (0.140 nm), whereas the carbonate ion is large (no figure available). The larger compounds further down require more heat than the lighter compounds in order to decompose. More heat must be supplied for the carbon dioxide to leave the metal oxide. SOLUBILITY RULES. The lattice enthalpies of both carbonates and oxides fall as you go down the Group because the positive ions are getting bigger. For example, for magnesium oxide, it is the heat needed to carry out 1 mole of this change: \[ MgO_{(s)} \rightarrow Mg^{2+}_{(g)} + O^{2-}_{(g)}\]. A small 2+ ion has a lot of charge packed into a small volume of space. If this is heated, the carbon dioxide breaks free to leave the metal oxide. The size of the lattice enthalpy is governed by several factors, one of which is the distance between the centres of the positive and negative ions in the lattice. Watch the recordings here on Youtube! a) Virtually no reaction occurs between magnesium and cold water. Down the group, the nitrates must also be heated more strongly before they will decompose. The small positive ions at the top of the Group polarise the nitrate ions more than the larger positive ions at the bottom. This is clearly seen if we observe the reactions of magnesium and calcium in water. The lattice enthalpy of the oxide will again fall faster than the nitrate. The shading is intended to show that there is a greater electron density around the oxygen atoms than near the carbon. You should look at your syllabus, and past exam papers - together with their mark schemes. The nitrate ion is bigger than an oxide ion, and so its radius tends to dominate the inter-ionic distance. The cycle we are interested in looks like this: You can apply Hess's Law to this, and find two routes which will have an equal enthalpy change because they start and end in the same places. The amount of heating required depends on the degree to which the ion is polarized. Magnesium and calcium nitrates normally have water of crystallisation, and the solid may dissolve in its own water of crystallisation to make a colourless solution before it starts to decompose. For reasons we will look at shortly, the lattice enthalpies of both the oxides and carbonates fall as you go down the Group. The lattice enthalpies of both carbonates and oxides fall as you go down the Group because the positive ions are getting bigger. They are in Group 2 (Acids, Inorganic Oxidizing). The carbonates become more thermally stable down the group. THERMAL STABILITY OF THE GROUP 2 CARBONATES AND NITRATES This page looks at the effect of heat on the carbonates and nitrates of the Group 2 elements - beryllium, magnesium, calcium, strontium and barium. If you aren't familiar with Hess's Law cycles (or with Born-Haber cycles) and with lattice enthalpies (lattice energies), you aren't going to understand the next bit. The term "thermal decomposition" describes splitting up a compound by heating it. group ii) Reaction with water: ... Their solubility increases down the group since their lattice energy decreases more rapidly than their ... Alkali metal nitrates (MNO 3) decompose on strong heating to corresponding nitrite and O 2 except LiNO 3 which decomposes to its oxides 2NaNO 3 2NaNO 2 + O 2 But 4LiNO 3 2Li 2 O + 4NO 2 + O 2 In order to make the argument mathematically simpler, during the rest of this page I am going to use the less common version (as far as UK A level syllabuses are concerned): Lattice enthalpy is the heat needed to split one mole of crystal in its standard state into its separate gaseous ions. if you constructed a cycle like that further up the page, the same arguments would apply. The majority of compounds formed by group II elements are ionic. ... As you descend group II hydroxide solubility increases. The inter-ionic distances in the two cases we are talking about would increase from 0.365 nm to 0.399 nm - an increase of only about 9%. The nitrates are white solids, and the oxides produced are also white solids. Don't waste your time looking at it. I was just wondering the solubilites of nitrates, chlorides, hydroxides, sulphates and carbonates. A shorthand structure for the carbonate ion is given below: This structure two single carbon-oxygen bonds and one double bond, with two of the oxygen atoms each carrying a negative charge. The balance between the attraction of oppositely charged ions to one another and the attraction of separate ions to water dictates the solubility of ionic compounds. It describes and explains how the thermal stability of the compounds changes as you go down the Group. As the positive ions get bigger as you go down the Group, they have less effect on the carbonate ions near them. The solubility of the Group 2 nitrates increases from magnesium nitrate to calcium nitrate but decreases later down the group. These compounds are white solids and brown nitrogen dioxide and oxygen gases are also given off when heated. If you think carefully about what happens to the value of the overall enthalpy change of the decomposition reaction, you will see that it gradually becomes more positive as you go down the Group. Brown nitrogen dioxide gas is given off together with oxygen. Just a brief summary or generalisation. Unfortunately, in real carbonate ions all the bonds are identical, and the charges are spread out over the whole ion - although concentrated on the oxygen atoms. Forces of attraction are greatest if the distances between the ions are small. Ca(s) + H2O(l) → Ca(OH)2(aq) + H2(g) The enthalpy changes (in kJ mol-1) which I calculated from enthalpy changes of formation are given in the table. Don't waste your time looking at it. Explaining the trend in terms of the polarising ability of the positive ion. Contents The small cations at the top of the group polarize the nitrate ions more than the larger cations at the bottom do. If "X" represents any one of the elements: As you go down the Group, the carbonates have to be heated more strongly before they will decompose. Inorganic chemistry. The rates at which the two lattice energies fall as you go down the Group depends on the percentage change as you go from one compound to the next. All the carbonates in this group undergo thermal decomposition to the metal oxide and carbon dioxide gas. The oxide lattice enthalpy falls faster than the carbonate one. Forces of attraction are greatest if the distances between the ions are small. Brown nitrogen dioxide gas is given off together with oxygen. All of these carbonates are white solids, and the oxides that are produced are also white solids. The following is the data provided. Nitrate is a polyatomic ion with the chemical formula NO − 3. The inter-ionic distances in the two cases we are talking about would increase from 0.365 nm to 0.399 nm - an increase of only about 9%. In my lab report, we are required to explain the trends in solubility of group 2 salts, going down the group. Lattice enthalpy is more usually defined as the heat evolved when 1 mole of crystal is formed from its gaseous ions. Magnesium and calcium nitrates normally crystallize with water, and the solid may dissolve in its own water of crystallization to make a colorless solution before it starts to decompose. None of the carbonates is anything more than very sparingly soluble. A higher temperature is required to decompose Ba(NO 3) 2 as compared to Mg(NO 3) 2. Thermal decomposition is the term given to splitting up a compound by heating it. Solubility Rules . Again, if "X" represents any one of the elements: As you go down the Group, the nitrates also have to be heated more strongly before they will decompose. The nitrate ion is bigger than an oxide ion, and so its radius tends to dominate the inter-ionic distance. 2Mg(NO 3) 2 → 2MgO + 4NO 2 + O 2 You can dig around to find the underlying causes of the increasingly endothermic changes as you go down the Group by drawing an enthalpy cycle involving the lattice enthalpies of the metal carbonates and the metal oxides. The carbonates tend to become less soluble as you go down the Group. Most nitrates tend to decompose on heating to give the metal oxide, brown fumes of nitrogen dioxide, and oxygen. If you aren't familiar with Hess's Law cycles (or with Born-Haber cycles) and with lattice enthalpies (lattice energies), you aren't going to understand the next bit. The inter-ionic distances are increasing and so the attractions become weaker. The lattice enthalpies fall at different rates because of the different sizes of the two negative ions - oxide and carbonate. This page examines at the effect of heat on the carbonates and nitrates of the Group 2 elements (beryllium, magnesium, calcium, strontium and barium). Impermanence causing depression and anxiety Relation between factors and their sum Is there a theoretical possibility of having a full computer on a silicon wafer instead of a motherboard? Explaining the trend in terms of the energetics of the process. Although the inter-ionic distance will increase by the same amount as you go from magnesium carbonate to calcium carbonate, as a percentage of the total distance the increase will be much less. If the carbonate is heated the carbon dioxide breaks free, leaving the metal oxide. Group 2 nitrates also become more thermally stable down the group. The carbonates become more stable to heat as you go down the Group. The effect of heat on the Group 2 nitrates. Unless otherwise noted, LibreTexts content is licensed by CC BY-NC-SA 3.0. On that basis, the oxide lattice enthalpies are bound to fall faster than those of the carbonates. Hot Network Questions Should the helicopter be washed after any sea mission? Most of the precipitation reactions that we will deal with involve aqueous salt solutions. The effect of heat on the Group 2 nitrates All the nitrates in this Group undergo thermal decomposition to give the metal oxide, nitrogen dioxide and oxygen. Both carbonates and nitrates become more thermally stable as you go down the Group. Now imagine what happens when this ion is placed next to a positive ion. ( alkali metals = Na, Li, K, Cs, Rb ) are soluble in.. And energetics when 1 mole of crystal in its standard state into its separate gaseous ions and. 4, PbSO 4, PbSO 4, PbSO 4, and 1413739 lithium carbonate of formation given. 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