Stoichiometry topic

Question

1.How many moles of sodium are in a frozen pizza containing 4.20 g?

 

2.How many molecules of the fictional metal adamantium are in 853 moles (the approximate number of moles of metal found in Wolverine’s body if steel is used to approximate the conversion of his 105-pound {47.6373 kg} metallic skeleton to moles)?

 

 

 

3.Based on the following equation, how many moles of Z can be made from 0.825 moles of X?

 4 X -----> 3 Z

 

 

4.Based on the following (unbalanced) equation and a starting amount of 42.158 grams of solid calcium (Ca), determine the following:

Ca_(s) + H₂O_(l) → H_2(g) + Ca(OH)_2(aq)

  

 

The number of moles of H₂O that will react with the given mass of Ca. 

 

 

 

The number of molecules of H₂ that are produced by the given mass of Ca. (5 points)

 

 

 

The mass of Ca(OH)₂ produced by the given mass of Ca (this can also be called the “theoretical yield”).

 

 

 

Answer 1

Hello, Iris,

1. I only see 4.2 g of sodium, not sodium chloride. If you get a pizza with 23 grams of metallic sodium, send it back before it catches fire. If you decide to keep it, you may report to the fire insurance company that you had 0.18 moles of Na on the pizza. You can explain to them that since the molar mass of sodium is 23 g/mole, the 4.2 grams is 4.2 g/(32g/mole) or 0.18 moles of Na. (2 sig figs). Despite the seemingly small number, that is still 0.18moles * 6.02x10²³ atoms/mole or 1.1x10²³ atoms of sodium.

2. By definition, Avogadro's number of 6.02 x 10²³ is the number of anything found in 1 mole of anything. Although commonly used just in science, it can apply to Legos, paperclips, eggs, or anything else, just like a dozen. You can declare you just won one mole of dollars from the state lottery, if you'd like. That is $602,300,000,000,000,000,000,000,000. Good luck fitting that on your IRS return. In this case, it is 853 moles of that superstitious metal adamantium. So that means

853 moles x 6.02E23 = 5.14E26 atoms of that metal.

3.4 X -----> 3 Z means that you get 3 moles of Z for every 4 moles of X consumed. The ratio is (3 moles Z)/(4 moles X). If you start with 0.852 moles X you will get 3/4 of that for Z. ).852 * (3/4) = 0.619 moles Z.

4. Ca_(s) + H₂O_(l) → H_2(g) + Ca(OH)_2(aq) needs to be balanced, first. I get:

a. The 42.16 g of calcium is 1.052 moles of Ca (the mass is divided by Ca's molar mass of 40.08 g/mole). The equation says we need 2 moles of H2O for every mole of Ca, so moles H2O = 2.104 moles H2O.

b. The moles of hydrogen produced is the same as the moles of Ca consumed, or 1.052 moles. The number of H2 molecules is therefore 1.052 * (6.02E23) or 6.33E23 molecules of H2.

c. We get one mole of Ca(OH)2 for every mole of Ca reacted. We started with 1.052 moles of Ca, so we should get, theoretically, 1.052 moles of Ca(OH)2. [Note: not always the case when you have a sloppy lab partner, as I did one year. He scrapped everything off the lab counter after he spilled the sample, and reported, with pride, a 105% yield. Duh. He also set fire to one of my textbooks in another failed lab]. Assuming your experiment was done properly, you'd get all the 1.052 moles of Ca(OH)2 the equation predicts. To convert this into grams, calculate the molar mass of Ca(OH)2 and multiple by 1.052 moles. I got 74.08 g/mole for the molar mass of Ca(OH)2. Therefore; 1.052 moles x 74.08 g/mole = 77.92 grams ca(OH)2

I hope this helps explain everything,

Bob

Answer 2

1.How many moles of sodium are in a frozen pizza containing 4.20 g?

... What is the 4.20 g? 4.20 g of pizza or 4.20 g of sodium chloride? Or what?

 

2.How many molecules of the fictional metal adamantium are in 853 moles (the approximate number of moles of metal found in Wolverine’s body if steel is used to approximate the conversion of his 105-pound {47.6373 kg} metallic skeleton to moles)?

... 853 moles x 6.02x10²³ molecules/mole = 5.14x10²⁶ molecules

  

3.Based on the following equation, how many moles of Z can be made from 0.825 moles of X?

 4 X -----> 3 Z

... 0.825 moles X * 3 moles Z/4 moles X = 0.61875 moles = 0.619 moles of Z (3 sig.figs.)

 

4.Based on the following (unbalanced) equation and a starting amount of 42.158 grams of solid calcium (Ca), determine the following:

Ca_(s) + 2H₂O_(l) → H_2(g) + Ca(OH)_2(aq) ... BALANCED EQUATION

 moles of Ca = 42.185 g Ca x 1 mol Ca/40.078 g = 1.0526 moles Ca

The number of moles of H₂O that will react with the given mass of Ca. 

... 1.0526 mol Ca x 2 mol H2O/mol Ca = 2.1052 moles H2O  

 

The number of molecules of H₂ that are produced by the given mass of Ca. (5 points)

... 1.0526 mol Ca x 1 mol H2/mol Ca x 6.02x1023 molecules/mol = 6.3367x1023 molecules of H2

The mass of Ca(OH)₂ produced by the given mass of Ca (this can also be called the “theoretical yield”).

... 1.0526 mol Ca x 1 mol Ca(OH)2/mol Ca x 74.09 g/mol = 77.99 g Ca(OH)2