Now weigh out the mass of beans that you think would contain 100 beans. NO COUNTING!!! Set this sample aside.

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1 Exercise: Passels & Moles All mater is made up of atoms. In a chemical reaction, atoms are never created or destroyed. They are just rearranged so that they appear in different combinations. Atoms, of course, are extremely small, and billions of atoms are involved in a typical reaction. Determining the number of such small particles is very difficult, so chemists have devised ways of keeping track of them. INVESTIGATION Weight 20 dried beans. Calculate the mass of 1 bean. Mass of 20 beans g Mass of 1 bean g Calculate the mass of 100 beans Mass of 100 beans g Now weigh out the mass of beans that you think would contain 100 beans. NO COUNTING!!! Set this sample aside. Now weigh 20 rice grains. Calculate the mass of 1 rice grain Mass of 20 rice grains g Mass of 1 rice grain g Calculate the mass of 100 rice grains Mass of 100 rice grains g Now weigh out the mass of rice grains that you think would contain 100 rice grains. Again, NO COUNTINGı!!! Count your two samples and see how close your samples were to 100 units. Record your results and those of three other teams.

2 Dried Beans Your Count Group 1 Group 2 Group 3 Rice Grains Your Count Group 1 Group 2 Group 3 Imagine that you were asked to obtain 1000 beans or 1000 rice grains. Counting these samples would be tedious. Obviously, weighing out the appropriate amount would be much faster. Write out clear directions for counting 1000 beans and 1000 rice grains by weighing appropriate amounts. Exercise: Passels & Moles Calculate the mass of 2000 dried beans. Show set up. Calculate the mass of 15,000 rice grains. Show set up.

3 Passels? When the number of particles gets large, it becomes increasingly awkward to talk about them. Consider the following recipe for beans and rice. Mix 15,000 grains of rice with 2,000 dried beans. It would be much easier if we would define a large set of rice grains or beans. (One convenient set is a dozen or 12 units. We need a much larger set however.) We could define a new set called a passel. A passel will be defined as 1000 individual things or particles. A passel of beans would be 1000 beans. Four passels of students would be 4000 students. 500 paper clips could be expressed as 0.5 passels of paper clips. Now reconsider the recipe for Beans and Rice. It could also be expressed this way: Mix 15 passels of rice with 2 passels of beans. We could also associate a mass with these two quantities. Look back at your data for this investigation. One passel of beans has a mass of g One passel of rice grains has a mass of g The recipe would require g of rice and g of beans. It is more convenient to measure out passels by weighing them. So, although we defined a passel as a number of things, a passel also represents a specific mass of each substance used. Do the following calculation: 1. If we mix 5.00 passels of rice with 4.00 passels of beans, how many total particles are present in the mixture? What is the total mass of the mixture? Show the set up. 2. How many passels of rice are there in 500.0g of rice? Show set up.

4 MOLE? Atoms are much smaller than rice grains or beans. Chemists have created a much larger counting unit for atoms. Instead of 1 passel, which equals 10 3 particles, chemists use 1 mole, which equals approximately 6 x particles. To see why this particular number was selected, look at the following table. Element Average Mass of 1 atom Mass of 6 x atoms Hydrogen (H) 1 amu 1 g Carbon (C) 12 amu 12 g Sodium (Na) 23 amu 23 g Gold (Au) 197 amu 197 g It takes 6 x atoms of any element to have a mass in grams equivalent to the relative atomic mass of a single atom of that element. (a gram is 6 x times larger than an atomic mass unit. This has been determined experimentally.) We can say, therefore, that a mole of hydrogen atoms has a mass of 1 g and a mole of gold atoms has a mass of 197g. To determine the mass of one mole of any element, look up its atomic mass and change the unit to grams Try it. 1 mole Cu= g 1 mole O= g 1 mole U= g MOLES OF MOLECULES When dealing with compounds, its molar mass of molecular mass in the sum of the molar masses of its component elements. For example, each H 2 O molecule has 2 hydrogen atoms and 1 oxygen atom. One mole of H 2 O molecules contains 2 moles of hydrogen atoms (2 x 1g) plus 1 mole of oxygen atoms (1 x 16g), so the molar mass of H 2 O is H: 2x 1g= 2 g O: 1x 16g= 16g 18g = molar mass

5 Another example: find the molar mass of CaCO 3 Ca: 1 x 40g= 40g C: 1x 12g= 12g O: 3x 16g= 48g 100g = molar mass Determine the molar mass of the following substances. Show set up. 1. Ammonia NH 3 5. Aluminum Oxide Al 2 O 3 2. Nitrogen N 2 6. Tetrasulful Decoxide, P 4 O Sucrose C 12 H 22 O Potassium Permanganate, KMnO 4 4. Copper(II) Nitrate Cu(NO 3 ) 3 8. Iron (III) Chromate, Fe 2 (CrO 4 ) 3