Chemistry Test Units 3 and 4 Finals

A tray of ice cubes (-20 ̊C) is placed on the kitchen table where it melts and warms to + 20 ̊C. (A) Use an energy bar chart to represent the ways that energy is stored in the system and flows into or out of the system. (B) Then, draw particle diagrams for the initial and final states of water.

-According to the previous problem, when a solid melts, the environment around the solid should get: Colder -

What evidence do we have that the "compound" of hydrogen and oxygen is not just a mixture of hydrogen and oxygen?

-Hydrogen is a flammable gas. Oxygen causes a glowing stick to burst into flame. Water does not burn and will put out a flame.

CFU 13

1.) Attractions are weakening particles are separating enough to move freely 2.)not moving faster 3.)The particles are going from liquid to liquid. They are getting faster. 4.) Separating or breaking apart 5.)Takes more energy to totally separate the particles to make them a gas than to separate them a little to make them a liquid 6.)It takes energy to melt a solid and vaporize a liquid

Salt can separated from sand by...

1.) dissolving the salt in water and then 2.)filtering sand and catching the salt water after it passes through the filter paper or decanting the salt water, leaving behind sand

CFU 9

1.) substance like 2.)change, energy 3.)moving particles 4.)arrangement, attract 5.)attractions 6.)low, high

Pure water can be obtained from salt water water by the process called......which involves ( 2 steps)

1.)Boiling the water(which has a lower boiling point than salt) which turns the water to a gas, leaving behind the salt, and then 2.)Condensing the water vapor back to liquid form

Take a look at this graph for the heating of water. a. What does this graph tell us about particles that we did not know about particles when we were studying gases prior to Unit 3?What is the evidence for what you said?

1.)The particles are sticky. There are attractive forces between particles that hold them together. 2.)It takes energy to separate the particles (melt the solid, boil or evaporate the liquid).

The gaseous elements hydrogen and nitrogen are examples of .....that consist of .....

1.)molecules 2.)2 atoms

The graph at right represents the temperature vs. time behavior of what was initially a sample of water at 100 ̊C, as it is cooled over time.

1.During region B the thermal energy is decreasing . 2. During region C the thermal energy is not changing . 3. During region A the phase energy is decreasing . 4. Tell the specific phase or phases present in -region A: gas + liquid -region B liquid -region C liquid + solid -During region C of the graph above the energy being given away is decreasing the distance between the water particles and reducing their phase energy. -During region B of the graph above the energy being given away is decreasing the speed of the water particles.

Molecules

A single particle composed of 2 or more atoms, which may be different elements of the same element.

Explain why the technique at left would not be effective in separating a mixture of salt and sugar.

Both sugar and salt are soluble in water. Both would be in the solution that passes through the filter paper.

A tray of water (20 ̊C) is placed in the freezer and turns into ice cubes (-8 ̊C) Where does the energy that leaves the system go? How does this energy transfer affect the room temperature in the kitchen? Do you have any experience that supports your answer?

Energy leaves the system and goes to the surroundings. If you stand next to a refrigerator while it is on you can feel heat leaving it from the back .

What is evidence?

Evidence is something you observe or measure that supports an argument.

Definition of element

Fundamental substance that cannot be broken down to a simpler substance by chemical means

What are the common diatomic elements?

Hydrogen (H2), nitrogen (N2), oxygen (O2), Chlorine (Cl2).

-One of the ice cubes described in #3 is placed in a glass of room temperature (25 ̊C) soft drink. Do separate bar charts for the ice cube and the soft drink. -Describe how the arrangement and the motion of the particles in each system change from the initial to the final state.

Ice - particle attraction decreases; particles change from fixed in place to moving randomly as it melts; and then the particles speed up a little. Soft Drink - the particles slow down as it gets colder.

Why is the high temperature plateau so much longer than the low temperature plateau?

It takes relatively little energy just to overcome the attractions of the solid and separate particles a little bit. It takes a lot more energy to separate the particles completely to make the liquid into a gas.

A cup of hot coffee cools as it sits on the table.

Particle arrangement does not change as it is always a liquid.Particle speed decreases as the temperature drops

What is inside the bubble? Why do you think so?

Particles of water, widely separated, make up the bubbles in boiling water.

Compounds

Substances formed by the chemical combination of 2 or more atoms of different elements

Elements

Substances that are composed of one type of particle.Simplest form of matter and cannot be broken down into simpler substances by physical or chemical methods

Suppose the burner under the pan of boiling water is turned to a higher setting. How will this affect the temperature of the water in the pan? Explain.

The water continues to boil at 100°C. It will vaporize more rapidly if more heat is supplied to it.

What characteristics of salt, oil and water allowed you to separate them from each other during distillation?

They all have very different boiling points (temperature at which they boil or vaporize). Water needs to be heated only to 100°C, while the temperature needs to be much higher (300°C) to boil (vaporize) oil, and the temperature needs to be extremely high (1400°C) to boil (vaporize) salt.

What characteristics of salt, silicon dioxide and salicylic acid allowed you to separate them from each other?

They have different solubilities in water and alcohol. Salicylic acid will dissolve in alcohol (but not water). Salt will dissolve in water but not alcohol. Silicon dioxide does not dissolve in either water or alcohol.

Some of the water you spilled on your shirt evaporates.

Water particles gain enough energy to break apart completely from each other.

A pan of water (25 ̊C) is heated to boiling and some of the water is boiled away. Do separate energy bar charts for each stage of the process.

Water particles speed up to boiling temperature, then break apart from each other.

Water vapor in the room condenses on a cold surface

Water vapor loses enough energy to form attractions and become liquid

What Dalton say about how elements combine to form compounds?

When elements react to form compounds, they react in defined, whole-number ratios

Why water is H2O and not HO2. Explain.

When you perform electrolysis on water, it splits into 2 gases, which are identified as hydrogen and oxygen. The length (volume) of the hydrogen gas in its tube is about 2.2 times the length (volume) of the oxygen gas in its tube. Avogadro's Hypothesis says that equal volumes of different gases (at the same temperature and pressure) have the same number of particles. Therefore, for every 1 oxygen particle in its tube there are 2.2 hydrogen particles in its tube. This suggests that water must be H2.2O. However, Dalton told us that elements combine in simple, whole number ratios. This means that water is H2O.

What is the evidence for Why water is composed of hydrogen and oxygen?

When you perform electrolysis on water, it splits into 2 gases. One of the gases makes a pop when lit, which is evidence for it being hydrogen. The other gas causes a glowing ember to burst into flame, which is evidence for it being oxygen.

definition of atom

a single individual u it of particles in an element.

What are the four of Daltons Atomic Theory?

a.)All matter is composed of tiny undividable particles called atoms b.)All atoms of a given element are identical, but atoms of different elements have different properties c.)chemical reactions involve the combinations of atoms. d.)when elements react to form compounds, they react in defined whole numbered ratios

The graph below left represents the heating curve for water heated from below its freezing/melting temperature to a temperature above its boiling point. a.) Why is the high temperature plateau so much longer than the low temperature plateau? b. What does the last upward slant on the right represent? Explain at particle level.

a.)It takes a lot more energy to totally separate the particles (convert a liquid to a gas) than to separate the particles a little (convert a solid to a liquid). b.)Gas particles moving faster as the temperature increases.

Pure Substances and Mixtures, Key Features

appearance: color, shiny/dull,texture density: g/ml Melting Point: The temperature of melting or freezing Boiling point: Temperature at which a gas condenses to a liquid, or a liquid boils Solubility: How much something dissolved in a particular solven (water, alcohol) Conductivity: How well an electric current moves Magnetism:it is a property of certain substances which pull closer or repel other objects.

Avogadro's hypothesis

at the same temperature and pressure, equal volumes of different gases contain the same number of particles

law of definite proportions

compounds always react in specific proportions, when elements react or combine.

What is the difference between a molecule and a compound? Give an example.

• Compounds are composed of the atoms of 2 or more different elements that are chemically bonded together. • A molecule is a single particle composed of 2 or more atoms, which may be of different elements or of the same element. Examples: H2O N2 NH3 NO2 H2 • Some molecules are compounds: H2O NH3 NO2 • Some molecules are elements: H2 N2 O2 Cl2

Describe two different ways to isolate elements from compounds.

• Electrolysis uses electricity, to separate compounds into its component elements, for example, water into hydrogen and oxygen. • Heating can drive off oxygen from metals leaving a pure metal. For example, heating malachite removes carbonate and oxygen from copper, leaving just copper.

What is the difference between an atom and an element?

• Elements are fundamental substances that cannot be broken down to a simpler substance by chemical or physical means. • An atom is a single, indivisible particle of an element.

What happens to water as it boils? List 3 different things. Here are 4 things:

• Phase changes from liquid to gas • Phase energy increases • Particle-particle attractions are completely broken; particles are separated a lot! • Thermal energy is constant; particle speed is constant.

What is different about the bubbles formed during electrolysis and the bubbles formed during the boiling of water?

• The bubbles formed during electrolysis consist of hydrogen gas and oxygen gas. • The bubbles formed during boiling consist of water vapor. How do you know? When water boils, it vaporizes, becomes a gas. That is what is in the bubbles.