Unit 6 - Chemical changes, acids and bases and solutions
What are 3 uses of acids?
- Acids are responsible for natural and artificial flavoring in foods, such as fruits. - Lactic acid is found in milk. - Acid in your stomach breaks down food. - Blueberries, strawberries, and many vegetable crops grow better in acidic soil - Acids are used to make products such as fertilizers, detergents, and plastics
List three properties of acids.
- Acids provide the sour taste in food (never taste acids in the laboratory) -Most can damage skin and eyes. -Acids react with some metals to produce hydrogen gas. -H₃O⁺ ions can conduct electricity in water -Acids react with bases to form neutral solutions.
List 3 properties of bases
-Bases provide the bitter taste in food (never taste bases in the laboratory) - Most can damage skin and eyes - Bases are slippery when mixed with water - Bases react with acids to form neutral solutions
What is a chemical change?
A change in matter that produces one or more new substances that have different chemical and physical properties.
What is the difference in composition between a solution and a compound?
A solution is made up of substances (elements and compounds) evenly mixed together; the composition can vary in a given mixture. A compound is made up of atoms bonded together; the combination of atoms is always the same in a given compound.
Which can you change the composition of ... a solution or a compound.
A solution.
What is a suspension?
A suspension is a heterogeneous mixture in which solute-like particles settle out of a solvent-like phase some time after their introduction. Ex: Dust in the air or Muddy water or salad dressing
The following are all examples of what? Hydrochloric acid, HCl Acetic acid, CH₃COOH Citric acid, H₃C₆H₅O₇ Lactic acid, C₃H₆O₃
Acids
The atoms that make up a given compound are bonded together, which means the composition of a given compound is always: A. Different B. The same
B. the same
The following are all examples of what? Sodium Hydroxide, NaOH Ammonia, NH₃ Sodium carbonate, NaCO₃ Calcium hydroxide, Ca(OH)₂
Bases
Adding 200g of water to a beaker Then adding 50g of salt to the water Then adding 75g of sugar to the water The solution is stirred until the salt and sugar dissolve. The mixture in the beaker weights 325g. What do these steps show: a. Addition of thermal energy b. Change in state of matter c. Conservation of mass d. Creation of a compound
C. Conservation of mass Because mass is neither created nor destroyed during physical and chemical changes) 200g + 50g+ 75g = 325g
Which of these common substances is a homogeneous mixture? A. Pure water B. Table salt C. Whole milk D. Maple syrup
D. maple syrup is a homogeneous mixture. It looks the same throughout. Remember milk is a heterogenous mixture called a colloid because the particles are really small and not fully mixed.
True or false: On a pH scale acids have a pH below 8?
False: Acids have a pH below 7. Bases have a pH above 7
Nearly all acid molecules contain one or more _____________ atoms.
Hydrogen
If you dissolve sugar in water is it a chemical or physical change?
IT is a physical change because the individual sugar and water molecules remain unchanged even after all sugar crystals have dissolved.
Are the substances that make up a mixture chemically combined?
No, they are not chemically combined.
Can you change the composition of a compound?
No. Changing the composition of a compound would change it into a new compound with new properties.
What are the three types of solutions?
Solid, Liquid, Gas
Can physical changes be reversed?
Some physical changes can be easily reversed, such as water melting and freezing. Some physical changes cannot be easily reversed, such as slicing bread.
A solution with a lower pH is more acidic or more basic?
The lower the pH the more acidic the solution is.
What is a sign of a chemical change?
The only sure sign of a chemical change is the formation of a new substance.
How is pH measured?
The pH of a solution can be measured by dipping a pH testing strip into the solution. A more accurate way to measure pH is to use a pH meter. A basic solution (pH 14) - would be dark purple A basic solution (pH 10) - would be blue A neutral solution (pH 7) - would show as green. An acidic solution (pH 3) - would be yellow An acidic solution (pH 0) - would be red
What are the properties of a compound?
The properties of the compound are different from the properties of the atoms that make it up.
Milk has a pH of 6.4. Soda has a pH of 2.5 to 3.5. Which mixture is more acidic?
The soda because it's pH is lower.
Which never changes during a physical change? a. state of matter b. temperature c. total mass d. volume
c. total mass
Is a match burning a chemical or physical change?
chemical change
Is a nail rusting a chemical or physical change
chemical change
What is a neutralization reaction?
is when an acid and a base react to form water and a salt and involves the combination of H+ ions and OH- ions to generate water. acid + base -> salt + water
What is the law of conservation of mass?
mass is neither created nor destroyed in ordinary chemical and physical changes. You must start and end with the same amount of mass. Ex: Log at 30kg plus Fire at 1 kg = Ashes at 28kg plus smoke at 3 kg
Name four examples of physical changes.
melting boiling changing shape mixing dissolving increasing or decreasing in temperature
Is a pH 7 acidic or basic?
neutral - they are not acidic or basic.
Is boiling water a physical or chemical change?
physical change
Is chocolate melting a chemical or physical change?
physical change
Is dissolving a physical or chemical change?
physical change
Is melting ice a physical or chemical change?
physical change
Compounds and solutions are alike in that they both look like ________ _________________.
pure substances.
What is filtration?
the process of separating solid particles from a liquid
What is a molecule?
two or more atoms held together by chemical bonds and act as a unit Ex: O₂ which is molecular oxygen made up of two oxygen atoms
What are 3 uses of bases?
- Bases are found in natural and artificial flavorings in food, such as cocoa beans. - Bases are in antacids, which neutralize stomach acid, alleviating heartburn - Bases are found in cleaners such as shampoo, dish detergent and window cleaner - Many flowers grow better in basic soil. - Bases are used to make products such as rayon and paper.
What is a colloid?
A heterogeneous mixture containing small, undissolved particles that do not settle out because they are too small. Ex: Foams, milk, fog, smoke, detergents, blood, paints, cosmetics, aerogel
What is a solution?
A homogeneous mixture that is made up of two parts - a solvent and one or more solutes.
What is the definition of a heterogeneous mixture and give an example.
A mixture having a non-uniform composition. The composition varies from one region to another, with clearly identifiable properties. Ex: trail mix
What is a homogeneous mixture?
A mixture in which 2 or more substances ARE EVENLY mixed, but NOT chemically bonded
What is a hetereogenous mixture?
A mixture in which the substances ARE NOT evenly mixed and ARE NOT chemically bonded. (uneven)
What is the difference between a molecule and a compound?
A molecule is two or more atoms of the same element are held together by a chemical bond. A compound is two or more atoms from DIFFERENT elements that are chemically joined in a specific combination.
What is a chemical symbol?
A one or two letter representation of an element. Many chemical symbols are the first letter of the element's name, such as H for hydrogen. Some chemical symbols represent Latin Names. For example, Au is from aurum, the Latin word for gold.
If you cut a log of wood, is it a chemical or physical change?
A physical change since the wood still has the same chemical properties
What is a pure substance?
A sample of matter, either a single element or a single compound, that has definite chemical and physical properties.
What is a solute?
A solute is the substance(s) that are present in the smallest amounts in the solution. The solute dissolves and mixes evenly into the solvent.
Which of the following mixtures is a suspension? A. Salad dressing B. Gelatin C. Whipped cream D. Apple juice
A. Salad dressing because it is a heterogeneous mixture in which the solute-like particles settle out of the solvent.
Solutions can exist in what states of matter?
All three - solid, liquid or gas
Seawater has a pH of 8.3. Ammonia has a pH of 11.9. Which is more basic?
Ammonia because it has the higher pH.
How is matter classified?
As a substance or a mixture according to the types of atoms and the arrangement of atoms in matter.
Which of these substance is a compound? A. Chlorine B. Ammonia C. Uranium D. Nitrogen
B. Ammonia It is a compound made up of the elements nitrogen and hydrogen.
A material being examined is the same throughout. The material contains carbon and oxygen, chemically combined. What type of material is it? A. Element B. Compound C. Homogeneous mixture D. Heterogeneous mixture
B. Compound Because it contains two elements chemically combined.
Some compounds are classified as acids or bases. The pH scale shows how acidic or how basic these compounds are. Sodium hydroxide, a compound commonly found in drain cleaners, has a pH of 13. Which of these phrases best describes sodium hydroxide? A. Highly basic B. Highly acidic C. Slightly basic D. Slightly acidic
B. Highly basic Because the pH is 13. The pH scale shows the most basic at 14.
A magnet was placed near a pile that contained both iron and sulfur. The magnet was moved gradually closer to the pile. As it neared the pile, the magnet started attracting small pieces of iron from the pile. Which of these statements best describes the contents of the pile? A. It is a homogeneous mixture of iron and sulfur B. It is a heterogeneous mixture of iron and sulfur C. It is a compound that contains both iron and sulfur D. It is a compound that can be separated by magnetism
B. It is a heterogeneous mixture of iron and sulfur.
When a hydroxide compound mixes with water, hydroxide ions separate from the base and form hydroxide ions in water. What happens if the base is not a hydroxide compound?
Bases that do not contain hydroxide ions produce hydroxide ions by taking the hydrogen atoms away from water (H₂O), leaving hydroxide ions (OH⁻)
What are two ways you could separate SOME homogeneous mixtures?
By boiling or evaporation.
Robert is hiking through the forest and writing down his observations. He steps on a branch and it breaks into several pieces. Which of the following best describes the resulting properties of the branch? A. The density of the branch decreased, since it now takes up less space B. The molecular arrangement of the branch changed as the broken pieces changed its state of matter C. The total mass of the branch pieces is the same, and only a physical change has occurred D. The chemical composition of the branch changed as the broken pieces reacted with the environment
C. The total mass of the branch pieces is the same, and only a physical change has occurred
Name four examples of chemical changes.
Changing color Burning Rusting Formation of gas Formation of a precipitate Spoiling (rotting) food Tranishing silver Digesting food
A water molecule is a ______________ bond.
Covalent
Suppose a candle is burned in a closed system where matter cannot enter or leave. Given this situation, what is equal to the mass of the original candle? A. The mass of the burned candle B. The mass of all the gases in the closed system C. The mass of the gases released while the candle is burned D. The mass of the burned candle plus the mass of the gases released while the candle is burned.
D. Since the law of conservation of mass says you cannot create or destroy mass in a chemical or physical change. This burning of the candle is a chemical change that created gases. These gases could not escape so the mass of the gases plus the burned candle mass equals the mass of the original candle.
Sucrose is another name for table sugar. Sucrose is a compound made from the elements carbon, hydrogen, and oxygen. Which statement best describes the properties of sucrose? A. They are similar to properties of carbon B. They are similar to properties of oxygen C. They are similar to the properties of hydrogen D. They are different from the properties of all the elements sucrose contains.
D. They are different from the properties of all the elements sucrose contains.
Which is true when a piece of paper is crumbled? A. Volume and mass increase B. Volume and mass decrease C. Volume and mass do not change D. Volume might decrease or increase, but mass does not change
D. Volume might decrease or increase, but mass does not change (Remember law of conservation of mass)
Bases produce what in water?
Hydroxide ions (OH-)
How does water change from one state of matter to another?
Ice (solid) melts to water (liquid) which evaporates into steam (gas). Steam (gas) goes through condensation to become water (liquid) and then freezes to become ice (solid).
If a solution is a gas, what state of matter is the solvent and solute?
If the solution is a gas, the solvent is a gas. The solute can be a gas only. Ex: A lighted sign contains a gaseous mixture of gaseous argon and gaseous mercury.
If a solution is a liquid, what state of matter is the solvent and solute?
If the solution is a liquid, the solvent is a liquid. The solute can be a solid, liquid, and/or gas. Ex: Soda is a liquid solution of liquid water, gaseous carbon dioxide, and solid sugar and other flavorings.
If a solution is a solid, what state of matter is the solvent and solute?
If the solution is a solid, the solvent is a solid. The solute can be a gas or a solid (called alloys). Ex: A saxophone is a solid solution of solid copper and solid zinc.
What is a hydronium ion H₃O⁺?
Is a positively charged ion formed when an acid dissolves in water. When an acid mixes with water, the hydrogen atom separates from the acid and quickly combines with water, resulting in a hydronium ion. Ex: Hydrochloric acid (HCl) + Water (H₂O) mixes and the Hydrogen (H) from the HCl combines with the H₂O to form .... Hydronium ion (H₃O⁺) + Chloride ion (Cl⁻)
What is an acid?
Is a substance that produces a hydronium ion (H₃O⁺) when dissolved in water.
If you burn wood is it a chemical or physical change?
It is a chemical change since the wood turns into a new substance, ASH, which has different chemical and physical properties.
Is an apple turning brown a physical or chemical reaction?
It is a chemical reaction called oxidation.
What does a chemical formula show?
It shows the symbol of each element in the compound and small numbers, called subscripts, that show the ratio of the elements in the compound.
Give an example of a Homogeneous mixture.
Kool-Aid Sweet Tea Jell-O
What is a mixture?
Matter that can vary in composition. A mixture is made of 2 or more substances that are blended but ARE NOT chemically bonded.
What is a substance?
Matter with a composition (make up) that is always the same. A certain substance always contains the same kinds of atoms in the same combination.
Can chemical changes be reversed?
Most chemical changes cannot be reversed. ex, if you burn wood you can't turn the ash back into wood
Give an example of a heterogeneous mixture.
Pizza Salad Chex Mix
What type of chemical symbol does a recently discovered element have?
Recently discovered elements have a temporary three-letter symbol until they get official names.
A change in one pH unit represents what?
Represents a tenfold change in the acidity or basicity of a solution.
What is a salt?
Salt is a mineral consisting primarily of sodium chloride, a chemical compound
Name the characteristics of a chemical change.
Substance is different after the change. Both physical and chemical properties change.
Name the characteristics of a physical change.
Substance is the same before and after the change. Chemical properties do not change Only the physical properties change.
Matter can be classified as either a ______________ or a _________________.
Substance or a mixture
What is the Tyndall effect?
The scattering of light by particles in a colloid or suspension. Ex: Solution: Water = light beam not visible Colloid: Milk = light beam visible Suspension: Flour and water = light beam visible
What are the parts of a solution?
The solute (substance dissolving) The solvent (liquid the solute dissolves in) Solution (when the solute if fully dissolve in the solvent)
What determines the state of a solution?
The solvent determines the state of the solution because it is in the greatest quantity. So, if the solvent is a gas, then the solution will be a gas, etc.
What is a solvent?
The solvent is the substance that is present in the LARGEST amount in the solution. The solutes dissolve, or break apart, and mixes evenly in the solvent.
What are the properties of the parts of a solution?
The substances keep their own properties when they are mixed.
What does neutral mean?
To have an equal number of positive and negative charges. The solution has a neutral pH of 7. It is not acidic or basic (alkaline)
When you toast a slice of bread is it a chemical or physical reaction?
Toasting bread is a chemical reaction.
True or False: Adding more of one substance to a mixture does not change the identity of the mixture.
True
True or False: The elements that make up a compound can be separated only by chemical processes.
True
True or False: All acids and base solutions contain both hydronium H₃O⁺ and hydroxide OH- ions.
True. Acids have a greater concentration of hydronium ions than hydroxide ions. Bases have a greater concentration of hydroxide ions than hydronium ions.
_____________ is one of the few substances on Earth that exists naturally in all three states - solid, liquid, and gas.
Water In nature, water almost always exists as a solution; it contains dissolved solutes.
Can you separate a mixture?
Yes, because they are not combined chemically. You can easily separate the substances by physical processes.
Can you change the composition of a solution?
Yes, the solution is still the same with similar properties. However, the relative amounts of the substance might be different.
Can the two different elements combine to form different compounds?
Yes, two different elements can form different compounds depending on the ratio of the elements. Ex. the elements nitrogen (N) and oxygen (O) can form to make ... Nitrous oxide (N₂O) which is a colorless gas used as an anesthetic - made up of two Nitrogen atoms and one Oxygen atom Nitrogen dioxide (NO₂) which is a brown gas, toxic, air pollutant - made up of one Nitrogen atom and two Oxygen atoms Dinitrogen trioxide (N₂O₃) which is a blue liquid - made up of two Nitrogen atoms and three Oxygen atoms
How do you separate a heterogeneous mixture?
You use the differences in the physical properties of the parts of the heterogeneous mixture to separate the parts.
What are physical changes?
a change in the size, shape, form or state of matter that DOES NOT change the matter's identity. The chemical properties of the matter stay the SAME when a physical change occurs.
What is a chemical reaction?
a process that changes, or transforms, one set of chemicals into another
What is an atom?
a small particle that is the building block of matter
What is an element?
a substance that contains only ONE kind of atom. EX, gold (AU) is only made of gold atoms and all gold atoms are alike. Ex: oxygen (O)
What is an ion?
an atom or molecule with a net electric charge due to the loss or gain of one or more electrons.
What is matter?
anything that takes up space and has mass
What is most matter made up of?
atoms
What is the pH scale used for?
describe whether a solution is acidic or basic
What are the three types of substances?
elements, compounds, mixtures
All chemical reactions involve ______________ ________________.
energy changes. Thermal or light energy is often needed for a chemical reaction to take place.
In a neutral solution, such as water, the concentrations of hydronium and hydroxide ions are ________________.
equal
What is the definition of alkaline?
having the properties of an alkali, or containing alkali; having a pH greater than 7
What are two types of mixtures?
heterogeneous mixtures and homogeneous mixtures
Acids produce what in water?
hydronium ion (H₃O⁺)
As the concentration of hydronium ions H₃O⁺ decrease, the pH _________________.
increases
What is a indicator?
is a compound that changes color at different pH values when it reacts with acidic or basic solutions. There are many different indicators - each indicator changes color over a specific range of pH values.
What is the definition of a homogeneous mixture and give an example.
is a solid, liquid, or gaseous mixture that has the same proportions of its components throughout any given sample Ex: orange juice
What is a compound?
is a substance made of 2 or more elements that are CHEMICALLY joined in a specific combination Ex. CO₂ which is carbon dioxide formed from one carbon atom and two oxygen atoms Ex: H₂O which is water formed from two Hydrogen atoms and one Oxygen atom
What is a base?
is a substance that produces hydroxide ions (OH⁻) when dissolved in water.
What is pH?
is an inverse measure of the concentration of hydronium ions H₃O⁺ in a solution.
What is a litmus test?
is to test whether a solution is acidic or basic. Blue litmus paper turns red under acidic conditions and red litmus paper turns blue under basic or alkaline conditions, with the color change occurring over the pH range 4.5-8.3 at 25 °C (77 °F). Neutral litmus paper is purple
The substances that make up a mixture are ____________ bonded together.
not
What is the range of the pH scale?
ranges from 0-14
What is solubility?
the ability of a substance to dissolve
What is distillation?
the action of purifying a liquid by a process of heating and cooling. It separates liquids with different boiling points
