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### Chapter 10

Chemical Quantities

Before We Begin…

- I can write numbers in scientific notation.
- I can write numbers in standard notation.
- I can multiply numbers written in scientific notation.
- I can divide numbers written in scientific notation.

Before We Begin…

- We need to review some scientific notation.
- Scientific notation is a way of writing very large and very small numbers.

How to Write Numbers in Scientific Notation

- Always written as a coefficient multiplied by 10 raised to a power.

3.5 x 1034

coefficient

power

Examples:

- Write the following in scientific notation:
- 234560000
- 0.00056974
- 8524000000
- 0.000000044258

How to Multiply in Scientific Notation

- To multiply numbers written in scientific notation you multiply the coefficients and add the powers.

(2.35x1014) x (3.25x10-23)

Multiply

Add

(2.35x3.25) x 1014+-23

How to Multiply in Scientific Notation

- To multiply numbers written in scientific notation you multiply the coefficients and add the powers.

(2.35x1014) x (3.25x10-23)

Multiply

Add

Answer = 7.64x10-9

Examples:

- Multiply the following numbers:
- (1.23x104) x (4.56x107)
- (7.89x10-1) x (1.23x1010)
- (4.56x107) x (7.89x10-10)
- (1.23x10-11) x (4.56x10-23)

How to Divide in Scientific Notation

- To divide numbers written in scientific notation you divide the coefficients and subtract the powers.

(2.35x1014) ÷ (3.25x10-23)

Divide

Subtract

How to Divide in Scientific Notation

- To divide numbers written in scientific notation you divide the coefficients and subtract the powers.

(2.35x1014) ÷ (3.25x10-23)

Divide

Subtract

Answer =0.72x1037

Examples:

- Divide the following numbers:
- (1.23x104) ÷ (4.56x107)
- (7.89x10-1) ÷ (1.23x1010)
- (4.56x107) ÷ (7.89x10-10)
- (1.23x10-11) ÷ (4.56x10-23)

Section 1

The Mole: A Measurement of Matter

Section 1 Learning Targets

10.1.1 – I can describe methods of measuring the amount of something.

10.1.2 – I can define Avogadro’s number as it relates to a mole of a substance.

10.1.3 – I can distinguish between the atomic mass of an element and its molar mass.

10.1.4 – I can describe how the mass of a mole of a compound is calculated.

Measuring Matter

- You often measure the amount of something by one of three different methods – by count, by mass, and by volume.

Example:

- If 0.20 bushel is 1 dozen apples and a dozen apples has a mass of 2.0kg, what is the mass of 0.50 bushel of apples?

What Is a Mole?

- Mole (mol) – 6.02x1023 representative particles of that substance (SI unit for measuring the amount of something).
- Avogadro’s number - 6.02x1023 named after Amadeo Avogadro diQuarenga (1776-1856)

A mole of any substance contains Avogadro’s number of representative particles, or 6.02x1023 representative particles.

Converting Number of Particles to Moles

- You can use Avogadro’s number as a conversion factor.

Example:

- How many moles is 2.80x1024 atoms of silicon?

Converting Moles to Number of Particles

- The reverse also works.

Example:

- How many molecules are in 5.6 moles of NO2?

The Mass of a Mole of an Element

- The atomic mass of an element expressed in grams is the mass of a mole of the element.
- Molar mass – the mass of a mole of an element.
- Find the element on the periodic table and the mass that’s listed is the mass of one mole.

The Mass of a Mole of a Compound

- To calculate the molar mass of a compound, find the number of grams of each element in one mole of the compound.
- Then add the masses of the elements in the compound.

Example:

- What is the mass of 1.00 mol of sodium hydrogen carbonate?

Section 2

Mole-Mass and Mole-Volume Relationships

Section 2 – Learning Targets

10.2.1 – I can describe how to convert the mass of a substance to the number of moles of a substance, and moles to mass.

10.2.2 – I can identify the volume of a quantity of gas at STP.

The Mole-Mass Relationship

- Use the molar mass of an element or compound to convert between the mass of a substance and the moles of a substance.

Example:

- Find the mass, in grams, of 4.52x10-3mol of C20H42.

Example:

- Calculate the number of moles in 75.0g of dinitrogen trioxide.

The Mole-Volume Relationship

- Avogadro’s hypothesis – states that equal volumes of gases at the same temperature and pressure contain equal numbers of particles.

Standard temperature and pressure (STP) – means a temperature of 0°C and a pressure of 101.3kPa or 1 atmosphere (atm).

At STP, 1 mole or 6.02x1023 representative particles, of any gas occupies a volume of 22.4L

- Molar volume – the 22.4L of a gas.

Calculating Volume at STP

- 22.4L = 1 mol at STP provides a nice conversion factor.

Example:

- What is the volume of 3.70 mole N2 at STP?

Example

- How many moles are in 102 L of carbon dioxide, CO2?

Calculating Molar Mass from Density

- Different gases have different densities and is usually measured in g/L so we can calculate different things using density as a conversion factor.

Example:

- A gaseous compound composed of sulfur and oxygen, which is linked to the formation of acid rain, has a density of 3.58 g/L at STP. What is the molar mass of this gas?

The Mole Road Map

- A helpful tool to figure out easily which conversion factor to use.

This can also be found on page 303 in your Chemistry book

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