15.3 Laboratory work ?8.
Properties of group 2 elements and their compoundsMaterials: calcium carbonate (chalk or marble), test tubes, indicator, burner, Decomposition of carbonatesProcedure:Heat the calcium carbonate gently with a low non-luminous burner flame. Observe the change taking place in the tube.When the first gas collecting tube is full of gas, shift the lower end of the delivery tube to the other inverted test tube.When no more gas is evolved, stop heating. Do carbon dioxide test for the collected gas in the test tubes.Add a drop of water to calcium oxide and check with an indicator.
Conclusion and questions:Note your observations on the calcium oxide and surface of the test tube.Write the chemical reaction equation for the experimentCan all compounds be decomposed by heating as this experiment? Explain Flame testProcedure:Place a few salts of calcium, barium and strontium on watch glasses (or pieces of paper) and label them. Take concentrated hydrochloric acid in a 10 ml graduated cylinder.Adjust the burner flame for a non-luminous flame.
Clean the nichrome wire by dipping it into the hydrochloric acid solution and heat it to redness.Take a few crystals of calcium chloride salt on nichrome wire loop, and then hold the wire in a non-luminous burner flame.Observe the colour of the flame and note your observation.
Clean the nichrome wire loop as in the step-1 for each flame test.Repeat above steps for other metal salts and record the color of the flame on the table.Perform a flame test for an unknown sample given to you and try to determine the metal ion in it.Conclusion and questions:Complete the following tableMetallic ion Ca2+Sr2+Ba2+Flame colorExplain how the colors in the flame test are produced?Which of the elements produce the similar colour in the flame test? Why? Can the flame test be used to distinguish metals in a sample? ExplainReactions of sulfur with metalsProcedure:Examine the copper foil and sulfur, then note your observations.Heat the test tube to boil sulfur and form vapor of sulfur which does not condense immediately.Wait until the test tube is about half-filled with sulfur vapor.Hold the magnesium ribbon with tweezers and insert it into the test tube. Let the ribbon comes in contact with the sulfur vapor.
Allow the test tube to cool and observe the magnesium ribbon strip. Record your observations.Practice work ?4. Solving experimental problemsMaterials: 10 g fresh calcium turnings, 100 ml water, 1% phenolphthalein indicator, 26.5 g sodium carbonate, beaker 250 ml, distilled water 1L, filter paper, scale Procedure and calculationsStep 1Look up the molar mass and calculate the moles of calcium in each sample.
Show your calculations below:_____________ gram Ca. _____________ mol Ca.Mass of water __________________ g H2O.Mole number of water _________________ mol H2O.Write the reaction of calcium with water: _________________________________________How many gram of water reacts with calcium? ________________ g H2OMass of calcium hydroxide after reaction: ______________ g Ca(OH)2. Molarity of calcium hydroxide solution: _________M Ca(OH)2.Step 2Prepare 0.25M sodium carbonate solution.
Dissolve 26.5 g of sodium carbonate in the 1 L of water. Find mole number of sodium carbonate in the solution: _________ mol Na2CO3Pour sodium carbonate solution into the calcium hydroxide solution.
Write the reaction of calcium hydroxide with sodium carbonate solution: _____________________________________________________Find theoretical mass of calcium carbonate precipitate: ____________ g CaCO3.Filter the formed precipitate and weigh the mass of CaCO3. Actual mass of calcium carbonate precipitate: ________________ g CaCO3. Step 3Find percent yield of chemical reaction by formula ? = (actual mass) × 100% /(theoretical mass) ? = __________%.
Conclusion and questions:What happens when you added calcium metal to water in the beaker? What gas is produced by the reaction of Group 2 metals with water?What color results when phenolphthalein indicator is added to the solution in which calcium is reacting?What is the compound that forms in the beaker after Step 2?