Prepare for your exams
Get points
Guidelines and tips

Sell on Docsity

Prepare for your exams

Study with the several resources on Docsity

Earn points to download

Earn points by helping other students or get them with a premium plan

Guidelines and tips

Sell on Docsity

Prepare for your exams

Study with the several resources on Docsity

Find documents

Prepare for your exams with the study notes shared by other students like you on Docsity

Search Store documents

The best documents sold by students who completed their studies

Search through all study resources

Docsity AINEW

Summarize your documents, ask them questions, convert them into quizzes and concept maps

Explore questions

Clear up your doubts by reading the answers to questions asked by your fellow students

Earn points to download

Earn points by helping other students or get them with a premium plan

Share documents

20 Points

For each uploaded document

Answer questions

5 Points

For each given answer (max 1 per day)

All the ways to get free points

Get points immediately

Choose a premium plan with all the points you need

Study Opportunities

Choose your next study program

Get in touch with the best universities in the world. Search through thousands of universities and official partners

Community

Ask the community

Ask the community for help and clear up your study doubts

University Rankings

Discover the best universities in your country according to Docsity users

Free resources

Our save-the-student-ebooks!

Download our free guides on studying techniques, anxiety management strategies, and thesis advice from Docsity tutors

From our blog

Exams and Study

Go to the blog

Mole-Mass Relationships in Chemical Reactions, Study notes of Stoichiometry

Western International University (WIU)Stoichiometry

One mole of NaCl contains 6.022 x 1023 NaCl formula units. ... Molar mass of NaCl = atomic mass of Na (22.99 amu) + the atomic mass of Cl (35.45 amu) 22.99 ...

Typology: Study notes

2021/2022

Uploaded on 09/12/2022

alannis 🇺🇸

4.7

(13)

263 documents

1 / 62

This page cannot be seen from the preview

Don't miss anything!

Chapter 3. Stoichiometry: Mole-Mass Relationships in

Chemical Reactions

• The mole (or mol) represents a certain number of objects.

• SI def.: the amount of a substance that contains the same

number of entities as there are atoms in 12 g of carbon-12.

• Exactly 12 g of carbon-12 contains 6.022 x 10 23 atoms.

• One mole of H 2O molecules

contains 6.022 x 10 23 molecules.

• 1 mole contains 6.022 x 10 23 entities (Avogadro’s number)

Concept 1. The meaning and usefulness of the mole

Partial preview of the text

Download Mole-Mass Relationships in Chemical Reactions and more Study notes Stoichiometry in PDF only on Docsity!

Chapter 3. Stoichiometry: Mole-Mass Relationships in Chemical Reactions

The mole (or mol) represents a certain number of objects.
SI def.: the amount of a substance that contains the same number of entities as there are atoms in 12 g of carbon-12.
Exactly 12 g of carbon-12 contains 6.022 x 10 23 atoms.
One mole of H 2 O molecules contains 6.022 x 10 23 molecules.
1 mole contains 6.022 x 10 23 entities (Avogadro’s number)

Concept 1. The meaning and usefulness of the mole

One mole of NaCl contains 6.022 x 10 23 NaCl formula units.
Use the mole quantity to count formulas by weighing them.
Mass of a mole of particles = mass of 1 particle x 6.022 x 10^23
The mass of an atom in amu is numerically the same as the mass of one mole of atoms of the element in grams.
One atom of sulfur has a mass of 32.07 amu; one mole of S atoms has a mass of 32.07 g.

Mass of 1 H atom: 1.008 amu x 1.661 x10-24^ g/amu = 1.674 x10-24^ g

Mass of 1 mole of H atoms: 1.674 x10-24g/H atom x 6.022 x10^23 H atoms = 1.008 g

To obtain one mole of copper atoms (6.02 x 10 23 atoms), weigh out 63.55 g copper.

•The molar mass ( M ) of a substance is the mass of one mole of entities (atoms, molecules, or formula units) of the substance.

Molar mass has units of grams per mole (g/mol).

Concept 3. The relations among amount of substance (in moles), mass (in grams), and number of chemical entities

Problem : (a) How many grams of silver, Ag, are in 0. mol Ag? (b) How many atoms of Ag are in 0.0342 mol Ag?

Plan : (a) To convert moles Ag to grams Ag, use the molar mass of Ag from the periodic table. (b) To convert moles to number of atoms, use Avogadro’s number.

Solution : (a) Converting from moles of Ag to mass:

(b) Converting from moles of Ag to number of atoms:

= 2.06 x 10^22 atoms Ag

Problem : Iron is a most important metal in our society. How many iron atoms are present in a piece of iron weighing 95.8 g?

Plan :

Solution : Converting from mass of Fe to moles:

Converting from moles of Fe to number of atoms:

Problem : How many moles and formulas are in 41.6 g ammonium carbonate?

Solution : Calculating molar mass:

Dividing by the mass of one mole of glucose gives the element’s mass fraction; multiplying this fraction by 100% gives the mass percent.

(b) Determining the mass of carbon.

Plan : To find the mass of C in the glucose sample, multiply the mass of the sample by the mass fraction of C from part (a)

Solution :

•A preliminary formula based on the data is Zn (^) 0.21P (^) 0.14O (^) 0..

•Convert the fractional subscripts to whole numbers. :

Divide each subscript by the smallest subscript:
If any subscripts are still not integers, multiply through by the smallest integer that will turn all the subscripts into integers.

The conventional way to write this formula is Zn 3 (PO 4 ) 2 ; the compound is zinc phosphate, a dental cement.

Skill 3-4 : Analysis of a sample of ionic compound gave: 2.82 g Na, 4.35 g Cl, and 7.83 g O. What is the empirical formula and name of the compound? Plan :

Solution : Find moles of elements:

From the moles of each element, construct a preliminary formula and convert to integer subscripts. (^) PT

Molecular Formulas

The actual number of moles of each element in the smallest unit of the compound. •In water (H 2 O), ammonia (NH 3 ), methane (CH 4 ), and ionic compounds, the empirical and molecular formulas are identical. •In some cases the molecular formula is a whole-number multiple of the empirical formula.
Using the empirical formula to obtain the molecular formula.

Hydrogen peroxide has the empirical formula HO (17.01g/mol) Dividing its molar mass (34.02 g/mol) by the empirical formula mass gives the whole-number multiple:

The molecular formula is H 2 O 2.

Skill 3-5 : Lactic acid ( M = 90.08 g/mol) contains 40.0 mass % C, 6.71 mass % H, and 53.3 mass % O. (a) Determine the empirical formula of lactic acid. (b) Determine the molecular formula.

Plan : Assume 100 g lactic acid to express each mass % as grams. Convert grams to moles and find the empirical formula.

Solution : Express mass % as grams; assume 100 g lactic acid:

Similarly, there are 6.71 g H and 53.3 g O. Converting from grams of elements to moles:

Mole-Mass Relationships in Chemical Reactions, Study notes of Stoichiometry

Related documents

Partial preview of the text

Download Mole-Mass Relationships in Chemical Reactions and more Study notes Stoichiometry in PDF only on Docsity!

= 2.06 x 10^22 atoms Ag