Moles Avogadro' s Number

Transcription

1 CHEM 0 (BEAMER) Solutions Set PW46B Last Name Do Date First Name Section M T W R PW46B: Mole Calculations Solutions Set Mass Mole Particles General Information Do Date: M (4/25) Relevant Notes: Notes-52, Notes-53; Relevant Reading: Chapters Mass molar mass Moles Avogadro' s Number Particles Note: For the first three questions, I will break the question into individual pieces for you. On tests, the questions will be written like Questions 4 6, and you will be expected to see the pieces yourselves. ) A sample of carbon dioxide contains molecules of carbon dioxide. Calculate the mass (in grams) of carbon dioxide. A) First, calculate the molar mass of carbon dioxide (you do not have to show your work): 44.0 g/mol CO2 B) Next, write your answer to Question A in conversion factor form: 44.0 g CO2 = mol CO2 C) Next, write the conversion factor between moles of carbon dioxide and molecules of carbon dioxide: mol CO2 = CO2 molec D) Use the conversion factors that you have written above to solve the problem particles particles to moles moles to mass initial value Avogadro s Number molar mass final answer, sigdigs, units ( CO 2 molec mol CO CO 2 molec 44.0 g CO 2 ) = x4. g CO 2 x mol CO 2 Page of 5

2 CHEM 0 (BEAMER) Solutions Set PW46B 2) A sample of lye contains grams of sodium hydroxide. Calculate the number of particles of sodium hydroxide in the sample. 2A) First, calculate the molar mass of sodium hydroxide (you do not have to show your work): g/mol NaOH 2B) Next, write your answer to Question 2A in conversion factor form: g NaOH = mol NaOH 2C) Next, write the conversion factor between moles of carbon dioxide and molecules of carbon dioxide: mol NaOH = NaOH form 2D) Last, use the conversion factors that you have written above to solve the problem mass mass to moles moles to particles initial value molar mass Avogadro s Number final answer, sigdigs, units g NaOH mol NaOH ( g NaOH NaOH form ) mol NaOH = x NaOH formx Note: I have broken Problems 3 through 6 into parts just like I showed for Questions and 2. Unless I state otherwise, you do not have to write out the individual conversion factors. For those of you who are more methodical, you might need to write them down in order to get to the correct answer. Don t skip steps if you are getting the wrong answers. Page 2 of 5

3 CHEM 0 (BEAMER) Solutions Set PW46B 3) Calculate the number of particles of CCl4 in 400. ml CCl4. The density of CCl4 is.59 g/ml. 3A) First, calculate the molar mass of CCl4 (you do not have to show your work): g/mol CCl4 3B) Next, write your answer to Question 3A in conversion factor form: g CCl4 = mol CCl4 3C) Second, write the conversion factor between moles of CCl4 and molecules of CCl4: mol CCl4 = CCl4 molec 3D) Third, write the conversion factor for the density of CCl4:.59 g CCl4 = ml CCl4 3E) Last, use the conversion factors that you have written above to solve the problem: volume volume to mass mass to moles moles to particles initial value density molar mass Avogadro s Number final answer, sigdigs, units ( 400. ml CCl 4.59 g CCl 4 mol CCl CCl 4 molec ) = x CCl ml CCl g CCl 4 mol CCl 4 molecx 4 Page 3 of 5

4 CHEM 0 (BEAMER) Solutions Set PW46B 4) A sample of hydrogen gas contains molecules of hydrogen. Calculate the mass of hydrogen in kilograms. (You must show the conversion of grams to kilograms in your dimensional analysis work.) 4A) First, calculate the molar mass of hydrogen gas (you do not have to show your work): 2.02 g/mol H2 4B) Next, write your answer to Question 4A in conversion factor form: 2.02 g H2 = mol H2 4C) Next, write the conversion factor between moles of hydrogen gas and molecules of hydrogen gas: mol H2 = H2 molec 4D) Last, use the conversion factors that you have written above to solve the problem particles particles to moles moles to mass g to kg initial value Avogadro s Number molar mass g to kg final answer, sigdigs, units ( H 2 molec mol H H 2 molec 2.02 g H 2 kg H 2 ) = x40.39 kg H mol H g H 2 x 2 5) The price of gold, as of April 6, 2006, is $50.80 per gram (treat this as a conversion factor). Determine the number of atoms of gold present in a sample of gold that costs $285,000 dollars. (Assume three sigdigs). 5A) First, find the molar mass of gold (you do not have to show your work): 97.0 g/mol Au 5B) Next, write your answer to Question 5A in conversion factor form: 97.0 g Au = mol Au 5C) Second, write the conversion factor between moles of Au and atoms of Au: mol Au = Au atoms 5D) Third, write the conversion factor for the price of Au: $285,000 = g Au 5E) Last, use the conversion factors that you have written above to solve the problem: cost cost to weight mass to moles moles to particles initial value price molar mass Avogadro s Number final answer, sigdigs, units ( $285,000 g Au mol Au $ g Au Au atoms ) = mol Au x Au atomsx Page 4 of 5

5 CHEM 0 (BEAMER) Solutions Set PW46B 6) This is an example of an extra credit question: A chemical pipeline is leaking ammonia gas at a rate of molecules per minute (assume this is a measured value). Convert the rate of leakage from molecules per minute to metric tons (t) per day. Note: 000 kg = metric ton (t) 6A) First, find the molar mass of ammonia (you do not have to show your work): 7.03 g/mol NH3 6B) Next, write your answer to Question 6A in conversion factor form: 97.0 g NH3 = mol NH3 6C) Second, write the conversion factor between moles of NH3 and molecules of NH3: mol NH3 = NH3 atoms 6D) In the margins somewhere, you should write out the time conversion factors: 60 min = hr 24 hr = day 6E) Last, use the conversion factors that you have written and the given conversion factors to solve the problem: initial rate particles to moles moles to mass g to kg kg to t min to hr hr to day initial value Avogadro s Number molar mass g to kg kg to t time conversions final answer, sigdigs, units ( NH 3 molec min mol NH NH 3 molec 7.03 g NH 3 kg NH 3 t NH 3 60 min mol NH g NH kg NH 3 hr 24 hr day ) = x7.4 t NH 3/dayx (4 pts4 pts4 pts4 pts4 pts4 pts4 pts3 pts) ( H 2 /min ) If you set up the initial value like this, you will receive zero credit for this type of problem. It s the wrong way to set up this problem, and it s important that you learn this. This is one of the few instances that I do not give partial credit. This will be on the test in the normal section as well as in the extra credit section. Page 5 of 5