Research Question: What are some of the properties of ionic compounds?
Background:
Ionic compounds are formed from a crystal lattice, a cation ionically bonded with anion in an alternating three-dimensional pattern, whose bond strength determines the compound’s properties. Ionic crystals have high melting and boiling points. They conduct electricity when dissolved in water or melted. They are insoluble in organic solvents (like alcohol, ether, acetone, etc.). All of these properties are caused by the amount of lattice energy (the energy required to separate 1 mol of ions in an ionic compound) required to divide them. The higher the lattice energy, the harder the compound as the bond is stronger, the smaller the compounds, the higher the charge, and higher the melting and boiling points. This experiment is to figure out the physical and chemical properties of ionic compounds by testing the lattice energy through a series of observations. Salt (NaCl) and sugar will be tested throughout, both will be compared and contrasted with each other.
Objectives:
- Observe the crystal shape of NaCl (Salt)
- Compare and contrast ionic compounds with nonionic compounds
- Explain the differences in the conductivity of ionic compounds in different forms
Materials:
- Salt
- Sugar
- Hammer
- Hand lens
- Stereoscope or Microscope
- Crucible
- Bunsen burner
- Ring stand and clamp
- Wire gauze
- Conductivity indicator
- 100 mL beaker
- Clay triangle
- Distilled water (H2O)
Safety Precautions:
- Always wear safety goggles and lab coats
- Hot objects will not appear to be hot. Be careful
- Do not touch nor taste any chemicals used or formed in the laboratory
Procedure:
Part A: Crystal Lattice Structure:
- Salt was poured (NaCl) in a bowl, with the hand lens, stereoscope or microscope each member observe its particles, later recorded their observations
- A hammer was used to tap on the granules till they broke lightly. Vice verse noted the observation through a hand lens, stereoscope or microscope.
Part B: Melting Point:
- Set up the apparatus as shown in Figure A
- NaCl was sprinkled(pea-sized) in the crucible and heated under low flame for two minutes. And then members recorded the melting point and observed before melting.
- If salt melts within two minutes, melting point is low
- If salt does not melt within two minutes, the melting point is high.
- After the crucible had cooled, the same steps were applied to sugar (It was noted: As many compounds in living organisms, sugar is nonionic)
CAUTION: Do not touch the crucible until cooled, estimated ten minutes.
Part C: Conductivity:
Solid:
- Member sprinkled three peas sized piles of salt on paper tissue
- Another placed contact wires of a conductivity indicator in the pile. And the other recorded observations
Solution:
- 50 mL of distilled water was poured into a clean 100mL beaker
- After cleaning the contact wires of the conductivity indicators, they were placed in distilled water. Then recorded the conductivity number
- Salt dissolved in the distilled water. Clean contacts wires were then placed in the saline. Then recorded the conductivity number
- Repeat previous steps for sugar
- Some nonionic compounds do dissolve in water, however many do not.
Data and Observations
Part A: Crystal Lattice
| Observations on NaCl particles | Observations on NaCl particles after hammering |
| Cubic crystals Translucent Odourless | Cubic crystals Translucent Odourless Fine |
Part B: Melting Point:
| Observations on NaCl’s melting point (high or low) | Observations on sugar’s melting point (high or low) |
| High melting point during the heating: Popping Salty odour | High melting point during the heating: Popping Salty odour |
Part C: Conductivity:
| Test Substance | Conductivity Indicator (Record light as off, dull, bright, or blinking) | Conductor Rating |
| Solid NaCl | 1 | None |
| Distilled Water | 944 | Poor |
| NaCl dissolved in distilled water | 140 | Good |
| Sugar dissolved in distilled water | 409 | Poor |
Questions on Data and Observation:
- From the results of Part A, and using words like soft, ductile, malleable, brittle, hard pliable, how would you describe sodium chloride?
Salt is a hard, brittle, translucent crystalline solid ionic compound.
- Sodium chloride and lithium chloride are typical ionic compounds, while sugar represents a typical nonionic compound. In general, how do these two types of compounds compare in their melting points?
Ionic compounds’ melting points are generally higher than nonionic compounds, because of the large amounts of lattice energy required to break ionic bonds.
- In Part C, why was it important to use distilled water instead of tap water for the conductivity measure?
The aqueous solution’s conductivity is proportional to the concentration of ions in the solution. When comparing the conductivity of tap water to that of distilled water, one could see it has a higher conductivity as it contains ions.
Discussion
- Recognizing Cause and Effect: In a crystal lattice structure, the electrons are held tightly by the ions, which are rigidly held in place by electrostatic attraction. Discuss how this characteristic explains why ionic compounds generally (a) have high melting points and (b) do not conduct electricity in the solid-state. When ionic substances are dissolved in water, they dissociate into ions. Solid solids do not carry electricity, whereas ionic compound solutions and molten ionic compounds do.
- Comparing and Contrasting: Nonionic compounds do not exist in crystal lattice structures but rather as individual particles, which are affected by other particles. In other words, nonionic compounds experience forces between particles. Based on what you learned in Part B about the melting points of ionic versus nonionic compounds, how do you think the attractive energy between particles compares with the energy of the crystal lattice? Ionic compounds, like salt or lithium chloride, ionic bonds are formed from strong electrostatic interactions between ions, which result in higher melting points and electrical conductivity compared to covalent compounds. Covalent compounds, like sugar, have covalent bonds where electrons are shared between atoms.
- Thinking Critically: Explain how ionic compounds, which do not conduct electricity in the solid form, can conduct electricity when they are in the molten state or dissolved in water. Ionic compounds when molten or in an aqueous solution, can conduct electricity as their electrons are mobile. However ionic solids can not conduct electricity as their electrons are immobile
- Drawing a Conclusion: All ionic compounds exist in only one state at room temperature. From what you learned in this investigation, what is that state and why do you think they do not exist in the other states at room temperature? Ionic compounds are at room temperature solid due to their high melting points. Previously mentioned, their high melting points are caused by the amount of lattice energy needed to separate.
- Error Analysis: What could be done to improve the precision and accuracy of your investigation? To verify the accurate and precise results, an increase in sample size would have been easier and an exact conductivity device.
Bibliography:
- Ionic and Covalent Bonds. 13 Sept. 2020, https://chem.libretexts.org/@go/page/839. Accessed 3 Mar. 2022.
- CK-12 Foundation. “8.2 Ionic Bonds and Ionic Compounds.” CK-12 Foundation, CK-12 Foundation, 29 June 2013, www.ck12.org/book/CK-12-Chemistry-Basic/section/8.2/. Accessed 3 Mar. 2022.
