Question

procedure, observation and result of this lab

PHYSİCALAND CHEMICAL CHANGES FURPOSE: To determine whether changes in matter are physical changes or chemical changes. Sodium Chloride (NaCI) Magnesium Ribbon MATERIALS: Iodine Crystal Sucrose Sulfuric Acid PROCEDURE: 1. Salt. Dissolve a little table salt NaCI) in a test tube which is one fourth full of water. Dip a stirring rod into the solution and hold it over the Bunsen flame. What is the white substance? Has there been a physical or chemical change? 2. Examine a crystal of iodine. Put it in a dry t.t. and warm gently till it vaporizes. Describe the vapor. Let the tube cool and look for a deposit on its side. Has it the same general appearance as the original iodine? Warm it gently. Does it act like the original iodine? Has there been a physical or chemical change. Examine a piece of magnesium ribbon. Record its color and flexibility Hold it by one and with the forceps and light it in the Bunsen flame. Describe the flame. Compare the resulting ash with the original magnesium. Was the change physical or chemical? 3. Heated -> 2Mgo 2 Mg+02 Physical and Chemical Change 4. Demonstration will be done by instructor. To a concentrated solution of cane sugar concentrated sulfuric a be added. The beaker will be heated. Notice the result. Listen carefully to the explanation. cid will C12H22011 Hso 12 C+ 11 H20 + heat Dehydrating Agent Define the term sublimation. Give an example from this experiment. 5.

Answer 1

1. The white substance is salt (pure NaCl) after evaporation of water. It is a technique to purify a salt sample. It is a chemical change because the chemical composition of water and NaCl is not altered. There is only a phase change of water from liquid to gaseous form and and NaCl to solid from solution.

2. The vapour is gaseous iodine. Yes the deposited solid will also have the same appearance as original iodine. It will also act as original iodine. It was a physical change from solid state to gaseous state and vice-versa. It is also called sublimation.

3. The flame is white in colour. The resulting ash is white amorphous solid salt. It is a chemical change because magnesium changes to Magnesium oxide and thus there is a clear chemical composition change.

4. This is also a chemical change because sugar will decompose to carbon black and water which is clearly a change in chemical composition of sugar.

5. Sublimation is conversion of a solid state matter to gaseous state without going to its liquid state when heated. The conversion of solid iodine to its vapour is an example of sublimation.