Question

Question 1 .Solve all the problems

a)How many moles of nitrogen, N, are in 90.0 g of nitrous oxide, N2O?

Express your answer with the appropriate units.

b)

The fuel used in many disposable lighters is liquid butane, C4H10. Butane has a molecular weight of 58.1 grams in one mole. How many carbon atoms are in 1.00 g of butane?

Express the number of atoms to three significant figures.

c)

Calculate the number of moles of aluminum, sulfur, and oxygen atoms in 7.00 moles of aluminum sulfate, Al2(SO4)3.

Calculate the number of moles of magnesium, chlorine, and oxygen atoms in 8.70 moles of magnesium perchlorate, Mg(ClO4)2.

A sample of propane, C3H8, contains 12.9 moles of carbon atoms. How many total moles of atoms does the sample contain?

Express the number of moles of Al, S, and O atoms numerically, separated by commas.

d)

Caffeine is a bitter stimulant drug and is found in varying quantities in seeds, leaves, and so on. Its formula is C8H10N4O2. Match the number of moles of each element found in the specified number of moles of caffeine.

Match the numbers in the left column to the appropriate blanks in the sentences on the right. Make certain each sentence is complete before submitting your answer.

1.6 2.0 4.0 7.0 8.0 10 16 27 1. There are _ mol of carbon in 2.0 mol of caffeine. 2. There are _ mol of hydrogen in 2.7 mol of caffeine. 3. There are _ mol of oxygen in 3.5 mol of caffeine. 4. There are _ mol of nitrogen in 0.40 mol of caffeine e) In the gaseous state, chlorine exists as a diatomic molecule Cl2 (Molar mass = 70.9 g/mol). Calculate the number of moles of chlorine present in 150  g of chlorine gas. Express the quantity in moles to three significant figures. f) Sodium hydroxide, NaOH, is a strong base that is used in industrial synthesis and processes such as making paper. What is the mass of 2.60 ×1022 molecules of NaOH (Molar mass = 40.0 g/mol)? Express the mass in grams to three significant figures. g) Ascorbic acid, or vitamin C (C6H8O6, molar mass = 176 g/mol), is a naturally occurring organic compound with antioxidant properties. A healthy adult’s daily requirement of vitamin C is 70-90 mg. A sweet lime contains 2.86×10−4 mol of ascorbic acid. To determine whether the ascorbic acid in a sweet lime meets the daily requirement, calculate the mass of ascorbic acid in 2.86×10−4 mol of ascorbic acid. Express the mass in grams to three significant figures. .

Answer 1

1)  Molar mass N2O = 44.0129 g/mol
65.0g = 65.0/44.0129 = 1.477mol N2O

You ask for mol N which I take to mean moles of nitrogen atoms:
1mol N2O contains 2 atoms N
1.477mol N2O will contain 1.477*2 = 2.954 mol N atoms

2) In this problem, you first have to convert to moles. Then you can use Avogadro's number.

First, convert 3.00g of butane into moles of butane by using the molar mass, which is 58.144 g/mol:

grams * (1 / molar mass) = number of moles

3.00 g * (1 / 58.144 g/mol butane) = .0516 mol butane

Multiply the number of moles by Avogadro's number. This will let you obtain the number of butane molecules:

.0516 mol butane * 6.023 * 10^23 molecules of butane / mol butane = 3.1076 * 10^22 molecules of butane

Now multiply this number by four (due to four carbon atoms per butane molecule) to obtain the answer:

3.1076 * 10^22 molecules of butane * 4 atoms of carbon / 1 molecule of butane = 1.24305 * 10^23 atoms of carbon

Your question provides three significant figures. Thus, you have to round this number:

1.24 * 10^23 atoms of carbon

I hope this helps!

3)

  I advise my students who are new to chemistry to make things easy for themselves, and to use some of the mathematics they have learnt. Take a piece of scrap paper and expand the formula just as you would do in maths:

Al2(SO4)3 = Al2S3O12
1mol contains 2mol Al, 3mol S and 12 mol O atoms
5 mol will contain: 10mol Al 15mol S and 60mol O atoms.

Now you do the same for Mg(ClO4)2

3) If C3H8 contains 11.9 mol C atoms - it must contain 8/3*11.9 = 31.7 moles H atoms
Total moles of atoms = 11.9+31.7 = 43.6 moles of atoms.

4)   The easiest way to do this problem is to calculate the mass of each element that is present in one mole of caffeine and divide by the molar mass of caffeine. So if you calculate the molar mass, you'll get 194.195 g.

Because of the subscripts, one mole of caffeine has 8 moles of carbon atoms, 10 moles of hydrogen atoms, 4 moles of nitrogen atoms, and 2 moles of oxygen atoms.

Let's tackle the carbon first. Since there are 8 moles present, take 8 and multiply by carbon's atomic weight:

8 mol C * 12.011 g/mol = 96.088 g

Now take this and divide by the molar mass of caffeine, since that's the total mass of one mole of caffeine, and multiply by 100 to convert to percent:

96.088 g / 194.195 g * 100 = 49.5 % carbon

Now just repeat these for the other elements:

( 10 mol H * 1.0079 g/mol ) / 194.195 g = 0.0519 = 5.19% hydrogen

( 4 mol N * 14.007 g/mol ) / 194.195 g = 0.289 = 28.9% nitrogen

( 2 mol O * 16.00 g/mol ) / 194.195 g = 0.165 = 16.5% oxygen

5)  Divide 150 g by the molar mass of Cl2.

6) (2.80 ×10^22 molecules NaOH) / (6.022 ×10^23 molecules/mol) x (40.0 g NaOH/mol) = 1.86 g NaOH

7) 2.88 x 10^-4 mol x 176 g/mol = 0.05072256 g = 0.0507 g

50.7 mg does not meet the daily requirement.