mixtures and how chemicals react


mixtures

How do you separate fresh water from sea water?
Can a fish drown in water?
Where do sugar crystals go when you dissolve them in water?

The answers all have to do with mixtures.

mixtures

A mixture is a combination of two or more substances in which each substance retains its own chemical properties.

Examples:

Stainless steel: iron, chromium, nickel, carbon.

Seltzer water: water and carbon dioxide.

Our atmosphere: nitrogen, oxygen, argon, plus CO2 and H20


mixtures

Mixtures can be separated by physical means.
A solid and liquid mixture?  Use a filter.
Different boiling points? Heat the mixture and distill.

mixtures

Pure: single element (e.g., Au) or compound (NaCl)
Impure: two or more compounds

mixtures

"Pure" is relative -- 99.9% pure has more impurities than 99.999% pure.

Heterogeneous mixture: different compounds can be seen as individual components (pulp in orange juice, for example)

Homogeneous mixture: same composition throughout
  • can be in solution or suspension
  • in a solution, all matter is in the same phase (e.g., salt water is liquid)
  • in a suspension different components are in different phases: milk, blood, clouds

solutions

Mix sugar into water, what happens?
(video on solutions...)

The sucrose loses its crystalline form, but its bonds are unchanged.

solutions

The sugar solution is homogeneous - i.e., the sweetness of the first sip is the same as the sweetness of the last sip (assuming it is properly stirred!)

Solutions do not have to be liquid: Rubies are solutions of red chromium in transparent aluminum oxide.  Alloys are mixtures: brass is a mixture of copper and zinc.  Bronze is copper and tin.

Gaseous mixtures: air - x% oxygen, y% nitrogen, z% CO2, w% argon, etc.

solutions

Solvent: component present in the largest amount (does the dissolving)
Solutes: the matter that gets dissolved
Saturated solution: no more solute can be dissolved
Unsaturated: has not yet reached the limit of solute that can be dissolved
Concentration: amount of solute / amount of solution
(usually measured in Moles / L).   "Amount" normally means the number of molecules, not the mass.
Mole: 6.02 x 1023 of anything.

check question


How many moles of sucrose are there in 0.5L of 2M solution?
How many molecules is this?


Does 1L of a 1M solution of sucrose in water contain 1L of water, less than 1L of water, or more than 1L of water?

check question


How many moles of sucrose are there in 0.5L of 2M solution?
(2M/L) * 0.5L = 1Mole

How many molecules is this?
1 Mole = 6.02 x 1023 molecules


Does 1L of a 1M solution of sucrose in water contain 1L of water, less than 1L of water, or more than 1L of water?

Less -- the total solution adds to 1L, including the sucrose

solubility

Solubility: the ability for a solute to dissolve in a solvent.
Depends on submicroscopic attractions of solvent particles and solute particles.

solubility

Some solutions will not saturate (e.g., water and ethanol)
Such solutions are called infinitely soluble.

Gasses are generally infinitely soluble.

Some solutes have very little solubility, such as oxygen in water.  Oxygen only dissolves 0.004g in 1L of water.

A material that does not dissolve in a solvent is said to be insoluble in that solvent.  Examples: sand and glass do not dissolve in water.

solubility and temperature

Solubility generally increases with increasing temperature.
Why?  Ex.: hot water molecules have greater kinetic energy and can therefore collide with the solid solute more vigorously.  This can disrupt electrical particle-to-particle attractions in the solid.


solubility

Gasses in liquids generally decrease in solubility as the temperature increases.  Example: sodas go flat faster as temperature increases.

Higher pressure generally means greater solubility.  Soda bottles are kept under pressure so more carbon dioxide will remain in solution.


soaps and detergents

Dirt and grease make grime, which does not easily come off with water.  We use a non-polar solvent, such as turpentine, which dissolves the grime by dipole attractions.

For clothes, we use soap, which has polar and non-polar properties.
 

soaps


purifying water

What do the "NO POTABLE ICE" signs on the ice boxes around camp mean?

purifying water

Step 1 to purify water:
1. Remove dirt and pathogens (e.g., bacteria).
- mix with slaked lime or aluminum sulfate

2. Aerate the water to add air and remove unpleasant volatile compounds such as sulfur.
3. Disinfect with ozone or chlorine.

purifying water

Or...the Life Straw

"LifeStraw contains PuroTech Disinfecting Resin (PDR) - a patented, extraordinarily effective material that kills bacteria on contact. Textile pre-filters are used in the LifeStraw to remove particles up to 15 microns. Active carbon withholds particles such as parasites."

desalination

Two primary methods: distillation and reverse osmosis.



osmosis


More salt water, not less...

reverse osmosis


More fresh water!
(but, you have to pressurize the salt water side to more than 24.8 atmospheres.


how chemicals react

chemical equations

How can 50g of wood burn to produce more than 50g of products?

chemical reactions

During a chemical reaction, one or more new compounds are formed as a result of the rearrangement of atoms.


chemical equations

Law of Mass Conservation: No atoms are gained or lost during any reaction.
The number of times atoms appear before the arrow must be equal to the number of times they appear after the arrow.

check question

Is the following chemical equation balanced?


  1. No, because the molecules have changed.
  2. Yes, because the coefficients on each side add up to the same number. 
  3. No, because there are more oxygen atoms in the products.
  4. Yes, because the same atoms appear before and after.

chemical equations

Is the following chemical equation balanced?


  1. No, because the molecules have changed.
  2. Yes, because the coefficients on each side add up to the same number. 
  3. No, because there are more oxygen atoms in the products.
  4. Yes, because the same atoms appear before and after.

counting atoms and molecules by mass


counting atoms and molecules by mass


counting atoms and molecules by mass


check question

How many moles are in 45.5 grams of chlorine gas?

  1. 0.55 moles
  2. 0.64 moles
  3. 1.28 moles
  4. 1.34 moles

Hint: chlorine is diatomic.

check question

How many moles are in 45.5 grams of chlorine gas?

  1. 0.55 moles
  2. 0.64 moles
  3. 1.28 moles
  4. 1.34 moles


check question

How many grams of water are produced from 1.25 moles of methane?


  1. 11.25 grams
  2. 22.5 grams
  3. 45 grams
  4. 90 grams

check question

How many grams of water are produced from 1.25 moles of methane?


  1. 11.25 grams
  2. 22.5 grams
  3. 45 grams
  4. 90 grams
Explanation: 
1 mole of methane will produce 2 moles of water, so 1.25 moles of methane will produce 2.5 moles of water.
1 mole of water is 18g, so 2.5 moles of water is 45g.

check question

How many moles of carbon dioxide are produced from 50 grams of methane?


  1. 0.78 moles
  2. 1.57 moles
  3. 3.13 moles
  4. 6.26 moles

check question

How many moles of carbon dioxide are produced from 50 grams of methane?


  1. 0.78 moles
  2. 1.57 moles
  3. 3.13 moles
  4. 6.26 moles
Explanation:  First convert the 50 grams of methane to moles of methane. Because there is a 1:1 ratio of methane to carbon dioxide, this is the same number of moles of carbon dioxide that will be formed. Convert this number of moles to grams knowing that 1 mole of carbon dioxide is 44 grams.

reaction rates

Reaction rate: The speed with which products form from the reactants.


reaction rates

Concentration:

The more concentrated a sample of nitrogen and oxygen, the greater the likelihood that N2 and O2 molecules will collide and form nitrogen monoxide.

reaction rates

Temperature:

Slow-moving molecules may collide without enough force to break the bonds. In this case, they cannot react to form product molecules.

reaction rates

Catalysts:

Reactant molecules must gain a minimum amount of energy, called the activation energy, Eact, in order to transform into product molecules.

catalysts


A catalyst has the effect of lowering the activation energy, which allows for the reaction to proceed at a quicker rate.
(why is the reaction shown up above bad news?)

check question


  1. Nitrogen dioxide, NO2
  2. Nitrogen monoxide, NO
  3. Atomic oxygen, O
  4. Oxygen, O2

check question

Nitrogen monoxide, NO
Explanation: The NO reacts with O2 to form O, which reacts with O2 to form O3. In other words, the NO gets this reaction going. As another clue, note how NO is regenerated after the second reaction.

energy and chemical reactions


check question

Use the bond energies below to determine whether the following reaction is exothermic or endothermic:

  1. Exothermic, with more than 50 kJ of energy released.
  2. Endothermic, with more than 50 kJ of energy absorbed.
  3. Endothermic, with less than 50 kJ of energy absorbed.
  4. Exothermic, with less than 50 kJ of energy released.

check question

Use the bond energies below to determine whether the following reaction is exothermic or endothermic:

  1. Exothermic, with more than 50 kJ of energy released.
  2. Endothermic, with more than 50 kJ of energy absorbed.
  3. Endothermic, with less than 50 kJ of energy absorbed.
  4. Exothermic, with less than 50 kJ of energy released.

chemical reactions and entropy

It is the natural tendency of energy to disperse from where it is concentrated to where it is dilute. 

Examples:
  • A hot pan radiates heat
  • Gasoline combusts into smaller molecules
  • Marbles bouncing on the floor come to a stop

Entropy:  The term used to describe the degree to which energy has become dispersed.
Reactions that result in an increase in entropy (energy dispersal) tend to occur on their own. 


chemical reactions and entropy


mixtures and how chemicals react

By Chris Gregg

mixtures and how chemicals react

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