CK-12 Chemistry Concepts - Intermediate Answer Key Chapter ...

1 CK-12 Chemistry Concepts - Intermediate Answer Key Chapter 10: The Mole Avogadro s Number Review Questions is the SI unit for amount of a substance? is the representative particle for an element? formula unit is the representative particle for what? Answers mole. most elements, it would be the atom. For diatomic elements, it would be the molecule. compounds. Conversions Between moles and Atoms Review Questions conversion factor would we need to convert moles of helium to atoms of helium? want to convert atoms to moles . My friend tells me to multiply the number of atoms by 10 23 atoms/mole. Is my friend correct? do you need to know the formula for a molecule in order to calculate the number of moles of one of the atoms?

2 Many atoms of fluorine are in 10 22 molecules of MgF 2 ? Answers mole = 10 23 atoms , your friend is wrong. The units you will end up with are (atoms) 2 /mole, which is not what you want. you know the number of molecules and want to find how many atoms of an element are present. You need to multiply the number molecules by the number of the element s in the molecule. To determine the number of an element s atoms CK-12 Chemistry Answer Keys - updated July 20191 in the molecule you need the molecular formula. Refer to question 4 for an example. 4.( 10 22 molecules MgF 2 ) (2 atoms F / 1 molecules MgF 2 ) = 10 23 atoms F Molar Mass Review Questions is the molar mass of Pb? do you find the molar mass of an element?

3 Many moles of Cl are in one mole of the CaCl 2 ? many moles of H are in one mole of the compound (NH 4 ) 3 PO 4 ? the molar mass of CaCl 2 . Answers g/mol. periodic table lists the molar mass for each element. moles Cl moles H mol Ca ( g Ca/1 mol Ca) + 2 mol Cl ( g Cl/1 mol Cl) = g/mol CaCl 2 Conversions between moles and Mass Review Questions have grams of a material and wonder how many moles were formed. Your friend tells you to multiply the mass by grams/mole. Is your friend correct? many grams of MgO are in moles ? many moles of H 2 O are in grams of pure ice? Answers To find the moles formed, you need to multiply grams by mole/grams. mol MgO ( g MgO/1 mol MgO) = g MgO g H 2 O (1 mole H 2 O g H 2 O) = g H 2 O CK-12 Chemistry Answer Keys - updated July 20192 Conversions between Mass and Number of Particles Review Questions can t we convert directly from number of particles to grams?

4 Many atoms of chlorine are present in 10 23 molecules Cl 2 ? many molecules of BH 3 are in grams BH 3 ? Answers don t know how much a single particle weighs. 10 23 atoms. g BH 3 (1 mole BH 3 g BH 3 ) ( 10 23 molecules BH 3 /1 mole BH 3 ) = 10 23 molecules of BH 3 Avogadro s Hypothesis and Molar Volume Review Questions container is filled with gas, what do we know about the space actually taken up by a gas? do we need to do all our comparisons at the same temperature and pressure? standard temperature and pressure, 1 mole of gas is always equal to how many liters? Answers space actually taken up by the gas particles is very small compared to the actual space in the container. comparison of gas volumes must be done at one standard temperature and pressure because of the volume of gas will change if the pressure or temperature of the gas changes.

5 Standard temperature and pressure, 1 mol gas = L gas Conversions between moles and Gas Volume Review Questions CK-12 Chemistry Answer Keys - updated July 20193 the problems above, why was the gas always at standard temperature and pressure? container contains L of N 2 gas at STP. How many moles of N 2 gas are in the container? the gas in the previous problem was CH 4 gas at STP instead of N 2 gas, how many moles of CH 4 gas would there be? Answers gases were given at STP because at STP L of any gas equals 1 mole of that gas. L N 2 (1 mole N 2 / L N 2 ) = L N 2 would be L of gas because regardless of the type of gas L of gas will always contain L of gas. Gas Density Review Questions is density calculated?

6 Is molar mass calculated? would be the volume of moles of a gas? Answers mass/molar volume. x molar volume. L. Mole Road Map Review Questions the problem above, what is the formula weight of neon? value is at the center of all the calculations? we had grams of Xe, would we expect a volume that is greater than or less than that obtained with neon? Answers g/mol. CK-12 Chemistry Answer Keys - updated July 20194 mole. than, we would have 1 mol/165 g so that factor would be smaller than the one with neon. Percent Composition Review Questions is the formula for calculating percent composition? information do you need to calculate percent composition by mass? do subscripts in a chemical formula tell you?

7 Answers composition = (mass of element)/mass of compound) x 100%. mass of the compound and the masses of each of the elements in the compound. many of a specific atom are in the compound. Percent of Water in a Hydrate Review Questions is a hydrate? can you convert a hydrate to an anhydrous compound? does hexahydrate mean? Answers compound that has one or more water molecules bound to each formula unit. heating it to convert the associated water to a gas. water molecules are attached to the compound. Determining Empirical Formulas Review Questions CK-12 Chemistry Answer Keys - updated July 20195 is an empirical formula? does an empirical formula tell you? does it not tell you? Answers the lowest whole-number ratio of elements in a compound.

8 Gives you the ratio of elements. does not tell you the composition of the molecule. Determining Molecular Formulas Review Questions is the difference between an empirical formula and a molecular formula? addition to the elemental analysis, what do you need to know to calculate the molecular formula? does the empirical formula mass tell you? Answers empirical formula just gives the ratios of atoms while a molecular formula gives the exact numbers. molar mass. gives you the formula mass of the basic molecular unit. CK-12 Chemistry Answer Keys - updated July 20196