2/2/2018 CHM210: Testing for Cations & Anions Pre-lab Assignment Due at the star
ID: 579525 • Letter: 2
Question
2/2/2018 CHM210: Testing for Cations & Anions Pre-lab Assignment Due at the start of the lab 3 points Name 1. What ions are predictable charge ions? Name two cations and two anions that the charge is known and WHY the charge is known. Sodium thiocyanate has the formula NaSCN. Using your knowledge of the charge for the Na cation, what is the formula and charge of the thiocyanate ion? 2. 3. What ions are considered ALWAYS soluble? What does this mean? 4. Use the test results below to determine the ion(s) (cations& anions) present in a solution Test Results Ions Color of Solution colorless 2 Flame Test 3 Calcium Ion: Ca 4 Iron (III) Ion: Fe no solid formed and/or no color change 5 Chloride Ion: Cl a white solid formed orange no solid formed and/or no color change Sulfate Ion: SO no solid formed and/or no color change 7 Carbonate Ion: CO,2 bubbles were observed 5. If possible, write the chemical formulas of the ionic compounds present in the solution? 1/8Explanation / Answer
1. The ions get their charges depending on the electrons the metals have in their valence shell. For the cations, the +ve charge denotes that it has lost the electrons and -ve charge denotes that it has gained electrons. The element loses or gains electrons in order to get a configuration which makes it highly stable. For example, for sodium, it has 11 electrons. The ion of sodium is Na+. This means that it has lost one electron. Now it has 10 electrons, which is inert gas configuration and it makes it stable. Similarly, we can consider magnesium. It has 12 electrons, and by losing 2 electrons, it becomes Mg2+ and thus it is stable.
For -vely charged element. For example, fluorine has 9 electrons. If it gains 1 electron, it will have 10 electrons, which is again inert gas configuration. Thus the ion of fluorine is F-. Similarly, we can take example of oxygen. It has 8 electrons and by gaining 2 electrons, it becomes O2-, which is highly stable. So, we can easily predict the charge on the ions.
2. Sodium thiocyanate is NaSCN. Sodium has +1 charge, as it is Na+. So, the thiocyanate ion will have -1 charge, to make the whole compound neutral. Thiocyanate ion is SCN- and the charge is -1.
3. When a compound is dissolved in water, it dissociates into its ions, i.e. a cation and an anion. When the cation combines with anion of another solution, it should not form a solid compound. If it does, then it forms a precipitate and is considered insoluble. But if the compound remains in the form of ions, it will be considered as soluble. So, such ions are always soluble.
4. The solution for table is:
The table was completed by using the information given in the text.
Test Ions 1 Li+, Na+, K+, Ca2+, Sr3+, Ba2+, NH4+ 2 Na+, Ca2+ 3 NO3-, CO32-, PO43-, OH- 4 NO3-, CO32-, PO43-, OH- 5 Ag+, Ca2+, 6 Li+, Na+, K+, Ca2+, Sr3+, Ag+, Pb2+ 7 CO32-Related Questions
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