CHEM 121 Lecture Notes - Lecture 12: Molar Mass, Relative Atomic Mass, Chemical Formula

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9 Feb 2018

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Matter: anything that has mass and occupies space. Property: characteristic that allow you to recognize a type of matter. Compounds: composed of 2 or more elements or 2 or more kinds of atoms. Law of constant composition: elemental composition of a compound is always the same. Intensive properties: independent of the amount of matter. Extensive properties: relate to amount. (mass, volume, energy ) Precision: how closely individual measurements agree with one another. Accuracy: how closely they agree with correct value. (how close to being correct?) Zeroes at the beginning are never significant. Zeroes at the end are only significant in decimals. When you multiply or divide you count the whole thing and use the least amount of sig figs. When you add or subtract you take in account the decimal point and use the least amount of sigfigs from the decimals. Law of conservation of mass: mass is the same after the process takes place.

Related Questions

1.Which of the following is a physical property?

A) ozone reacts with silver to give silver oxide

B) platinum metal does not react with hydrochloric acid

C) the density of lead

E) Sulfur burns in oxygen to form sulfur trioxide

2. Which of the following is a chemical property of gold?

A) is malleable

B) does not react with hydrochloric acid

C) is a good conductor of heat

D) is a good conductor of electricity

3) Which of the following is a physical change?

a) the freezing of water to form ice

B) the inability of gold react with water

C) the burning of paper

D) the sodium metal vigorously with water

E) the reaction of zinc with hydrochloric acid

4. Which one of the following would be classified as a heterogenous mixture?

A) copper nitrate solution

B) mix of table salt and black pepper

C) Salt water

D)brass

E) a sugar solution

5. Which of the following is a chemical change?

A) the boiling of water to form steam

B) crushing of lump of sulfur into yellow powder

C) the reaction of chlorine gas and sodium to form salt

E) hammering zinc into a thin film

6) An extensive property is

A) independent of the quantity of matter observed

B) difficult to measure

C) always strongly dependent on the external conditions

D) dependent on the quantity of matter observed

E) is a unique value regardless of the measurement conditions

7) Which of the following defines or expresses the concepts of accuracy?

A) average of the data

B) differences between the accepted answer and the average value of the data

C) deviation of the average

D) the closest value to the expected answer

E) reproducibility of a measurement

8) Hydrates are:

A) orgainc compounds that contain oxygen together with usual carbon and hydrogen

B) readily soluble in water and release energy

C) concentrated solutions of salts in water

D) moistyre sensitive hygroscopic inorganic salts

E) compounds in which each formula unit has one or more water molecules associated with it

9) Which of the following is the correct defintion of isomer?

A) Isomers are molecules with the same empirical formula but have different isotopes

B) Isomers are molecules that have the same molecular formula but contain different istotopes.

C) Isomers are molecules that have the same molecular formula but different arrangement of atoms in space

D) Isomers are molecules that have the same arrangements of atoms in space but different empirical and molecular formulas

E) Isomes are molecules that have the same empirical formula but different arrangements of atoms in space

10) Most water-soluble compounds of Group 1A or 2A elements are:

A) nonelectrolytes

B) weak electrolyes

C) weak acid

D) strong electrolytes

E) strong acids

11) to precipitate Cd2+(aq) from solution one could add:

A) KI(Aq)

B) NaCl(aq)

C) H2S(aq)

D)HNO3(aq)

E) HCl(aq)

12) Select a statement that best describe the oxidation process

A) in the oxidation process all elements experience an increase in oxidation state

B) in the oxidation process all elements change oxidation state

C) in the oxidation process some elements change their oxidation state

D) in the oxidation process some elements experience oxidation state increase

E) In the oxidation process only oxygen increases its oxidation state.

13. A disproportionation reaction is one in which:

A) the dame substance is oxidized and reduced

B) the equation is not balanced

C) both reactants are reduced

D) water must be added

C) more of one substance reacts than another

14) The energy of molecules of a gas:

A) is the same for all molecules at constant temperture

B) is dependent on concentration

C) increases with an increase in pressure

D) is distributed over a wide rande at constant temperature

E) increase with a decrease in temperture

15. The volume correction term in the van der Waals equation is present because:

A) molecules occupy volume

B) molecules attract each other

C) barometers are inaccurate

D) molecules repel each other

E) molecules are diatomic

Chromatography: Separating Mixtures

Introduction:

Magic marker inks are often mixtures of several compounds. Paper chromatography is a common method of separating various components of a mixture. After separation, you can observe the different colors that make up a particular color of magic marker ink.

You can also calculate a ratio Rf, which compares how far each compound traveled to how far each solvent (substance that dissolves another substance) traveled during the experiment.

Rf = Ds/Df

Ds = Distance traveled by the compound

Df = Distance traveled by the solvent

Materials:

coffee filter, tape, isopropyl alcohol (rubbing alcohol), water, 3 different color magic markers (not permanent); 3 identical tall, narrow drinking glasses; metric ruler, 3 pencils

Pre-lab Questions:

List one extensive and one intensive property of marker ink.

Intensive: Amount Doesn't Matter

Extensive: Amount Matters

An extensive property of marker ink would be volume or ink.

An intensive property of marker ink would be the color of ink.

Define mixture.

A combination of two or more substances that are not chemically combine with one another.

Is tap water a heterogeneous or homogenous mixture? Explain your answer.

Tap water is a homogeneous mixture. I think this because I can see that it has uniform. It doesnât contain any different molecules as well.

Is isopropyl alcohol (rubbing alcohol) a heterogeneous or homogenous mixture? Explain your answer.

I believe rubbing alcohol is a homogeneous mixture. I think this because I can physically see that it has uniform. It also stays in the same phase.

Procedure:

1. Cut 3 strips of coffee filter. Be sure that the strips are much narrower and slightly taller than the drinking glasses.

2. In the center the strips, about 3 cm from one end, place a dot of the marker to be tested. The dots should be about 0.2 cm in diameter and dark enough to be clearly visible.

3. Place about 2 cm of water in each glass.

4. Tape the unmarked end of each strip to the center of a pencil so that the strip hangs down when the pencil is held horizontally.

5. Carefully insert the strips into the glasses, dotted end down. The dot must be above the water, and the sides of the coffee filters cannot touch the sides of the glasses.

6. Let the setup stand for 20 minutes. Follow procedure 8 as your set up stands.

7. Record your observations after 20 minutes in the table below. Measure Df (in cm) for the solvent. Measure the Ds (in cm) for each color that you see on the coffee filter (there may not be three). Calculate the Rf for each color using the equation in the Introduction section.

8. Repeat steps 1â7, except place about 2 cm of isopropyl alcohol (rubbing alcohol) in each glass instead of water.

9. Clean up your work area.

Solvent: isopropyl alcohol (rubbing alcohol)

5. What evidence is there that marker ink is a mixture?

The marker ink is a mixture. The evidence is when the marker ink separated.

6. Each compound in the marker ink is represented by a color. Did one compound travel farther than the others? Explain why you think that this is the case.

Yes, I found out that the darker of the three colors traveled further.

7. Did the compounds travel farther in the water or the isopropyl alcohol (rubbing alcohol)? Explain why you think that this is the case.

The compounds traveled faster in the water than the rubbing alcohol. I think the reason why is because water is smaller on a molecular level versus rubbing alcohol. So it is easier for the dyes to separate.

8. How could you improve upon the accuracy of your Rf measurements?

I feel that accuracy could be improved if we changed the scale measurement to millimeters (mm) instead of cm (centimeters).

Water traveled faster than the rubbing alcohol. I personally think it has to do with something like the size of the molecule like the smaller the molecule the easier it is.

CHEM 121 Lecture Notes - Lecture 12: Molar Mass, Relative Atomic Mass, Chemical Formula

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