TITLE: CONDUCTIVITY & CHEMICAL BONDING
Objectives:
· Test a number of different substances and solutions for their ability to conduct an electric current
· Predict the bonding nature (ionic or covalent) of each substance
· Explain the differences in conductivity
· Utilize the CRC to look up values of melting point and solubility for a variety of solids
Hypothesis:
Data:
Beaker / Conductivity (NDC, Poor, Good) / Observations (solubility, etc.) / MP (°C) / Solubility(g/100 mL H2O)
Distilled Water / X
Tap Water / X / X
Ethanol, C2H5OH / X
NaCl (s)
NaCl (concentrated, aq) / X / X
NaCl (dilute, aq) / X / X
NaCl (alcohol) / X / X
Sucrose, C12H22O11(s)
Sucrose (aq) / X / X
Sucrose (alcohol) / X / X
Potassium chlorate, KClO3(s)
KClO3 (aq) / X / X
Silver chloride, AgCl(s) / X / X
Precaution: DO NOT TASTE! To detect an odor of a substance/solution, waft. DO NOT submerge the conductivity device. Only the tips of the two electrodes should be touching the substance/solution.
Procedure:
1. Read the labels carefully. Test the conductivity of the substance/solution in the beaker by dipping the tips of the copper electrodes into the substance/solution (do not submerge). Record results: No light = NDC (no detectable conductivity); Red = Poor; Red and Green (Good).
2. Record your observations on smell, texture, color, solubility, bubbling, etc.
3. In between beakers, RINSE the electrodes WELL with distilled water, and dry thoroughly with paper towel before testing another substance/solution.
4. Repeat for all 12 beakers.
5. Use the CRC to determine the MP (°C) and solubility( g per 100 mL of H2O; cold) of the indicated substances on your data table.
Conclusions
1. Three solids (sodium chloride, sucrose and potassium chlorate) were tested in this lab activity. Each of these three solids was dissolved in distilled water or alcohol. On the basis of their conductivity results, which of these solids is/are ionic and which is/are covalent? Explain your answer.
2. What would be the purpose of using two different solvents (alcohol and distilled water) in this lab?
3. What effect might concentration have on conductivity? Interpret the results for the NaCl (aq) and the NaCl dilute to answer this question.
4. What effect might solubility have on conductivity?
5. One of the beakers contained distilled water and another contained tap water. What were the probable differences? Explain why those differences exist.
6. The formulas for sucrose and ethyl alcohol are C12H22O11 and C2H5OH. Compare these formulas to those for sodium chloride (NaCl), potassium chlorate (KClO3), and silver chloride (AgCl).
7. Use the CRC to look up the melting points of sodium chloride, sucrose, potassium chlorate and silver chloride). Compare the melting point of the four solids. What does melting point help us predict about the bonding characteristics in these four solids?
8. Use the CRC to look up the solubility values for KClO3 and AgCl. Predict the conductivity results for AgCl in water. What if it were molten/melted? Explain your prediction.
9. Given the formulas for the two compounds CaBr2 (calcium bromide), and nitrogen trichloride (NCl3), predict the conductivity of each compound and explain your prediction.