Chapter 6/7 Test Chemistry Flashcards
What is a chemical reaction and what occurs in one?
- One or more substances change into different substances, a process where substances interact to form new substances with new properties
- Familiar type of combustion
- Reactant particles collide where their ions or atoms rearrange and form products
What is energy in chemical reactions?
→ Chemical reactions can either absorb or release energy
→ All chemical reactions involve energy. However, not all chemical reactions release energy, as rusting and burning do. In some chemical reactions, energy is absorbed rather than released.
Where is energy written when it is released and absorbed?
→ If more energy is released than is absorbed, then the word energy is written on the right side of the equation with the products
→ If energy is absorbed then it is written with the reactants
What occurs during the release of energy?
→ Besides rusting and burning, examples of exothermic(release energy) reactions include chlorine combining with sodium to form table salt(a great amount of light and heat is released). The decomposition of organic matter also releases energy because of exergonic reactions. In a chemical process similar to combustion, called cellular respiration, the sugar glucose is “burned” to provide cells with energy.
→ Reactants→Products+Energy
What occurs during the absorption of energy?
→ A chemical reaction that absorbs energy is called an endergonic reaction. This type of reaction can also be represented by a general chemical equation: Reactants+Energy→Products
→ Many other chemical processes involve endergonic reactions. For example, most cooking and baking involve the use of energy to produce chemical reactions. You can’t bake a cake or cook an egg without adding heat energy. Arguably, the most important endergonic reactions occur during photosynthesis. When plants produce sugar by photosynthesis, they take in light energy to power the necessary endergonic reactions. The sugar they produce provides plants and virtually all other living things with glucose for cellular respiration.
What is a word equation?
the names of the chemicals are written out in full, chemists use these equations to describe the chemical reactions by using the full name of the reactants and products
What is a chemical equation?
formulas of reactants and products
What is a reactant?
substances used up during reaction, they are present at the start of the reaction
What is a product?
substances produced during reaction
What are the state symbols?
a symbol indicating the physical state of the chemical at room temperature
→ (s) solid
→ (l) liquid
→ (g) gaseous
→ (aq) dissolved in water
What does the law of conservation of mass state?
- the total mass of the reactants equals the total mass of the products, mass is conserved
→ The atoms in reactant molecules are rearranged to form products, therefore, all the atoms that existed in the reactants are still present in the products of the reaction
→ Atoms CANNOT be created or destroyed which explains this law
What is a skeleton equation?
an equation in which reactant and products are not balanced
Ex. hydrogen chloride → hydrogen monochloride
H2 + Cl2 → HCL
Why does H2 + Cl2 → HCL not correct?
This does not accurately describe the reaction between hydrogen and chlorine:
→ 2 atoms of H react with 2 atoms of Cl, however the product only contains 1 atom of H and 1 of Cl
→ 1 atom of H and 1 of Cl are unaccounted for
What is a balanced equation?
A balanced equation in chemistry shows the same number of atoms for each element on both sides, making sure nothing is lost or gained
Ex. H2 + Cl2 → 2HCl
What do the coefficients do in a balanced equation?
give the ratio of reactants and products in a reaction, equations can only be balanced by using coefficient, the coefficient applies to all the atoms in the molecule
What do the subscripts in an equation describe?
give the ratio of elements in a chemical formula, they cannot change
When 7.8 g of reactant A and 7.8 g of reactant B are added to a container and stirred, a paste is formed, and a gas is produced. If the mass of the paste was 8.1 g, what was the mass of the gas?
Reaction A + reactant B → paste + gas
7.8 g + 7.8 g → 8.1 g + x
15.6 g = 8.1 g + x
7.5 g = x
What is synthesis?
Synthesis: Combine atoms and/or compounds into larger compounds.
TWO OR MORE REACTANTS AND ONLY ONE PRODUCT
X + Y → XY
2H2 (g) + 02(g) → 2H2O(l)
What is this type of chemical reaction 2H2 (g) + 02(g) → 2H2O(l)?
Synthesis
What is decomposition?
Decomposition: Opposite of synthesis, compounds break down into elements or smaller compounds.
XY → X + Y
2NI3(g) → N2(g) + 3I2(g)
What type of chemical reaction is this 2NI3(g) → N2(g) + 3I2(g)?
Decomposition
What is single displacement?
Single displacement: one element displaces or replaces another in a compound
ELEMENT + COMPOUND → NEW ELEMENT + NEW COMPOUND
(A metal (cation) can displace another metal (cation) or hydrogen)
X + YZ → Y + XZ
Mg(s) + ZnCl2(aq) → Zn(s) + MgCl2(aq)
What type of chemical reaction is this Mg(s) + ZnCl2(aq) → Zn(s) + MgCl2(aq)?
single displacement
What is double displacement?
Double displacement: elements (or polyatomic ions) in different compounds displace each other by changing places
TWO COMPOUNDS TO REACT TO PRODUCE TWO NEW COMPOUNDS
WX + YZ → WZ + YX
AgNO3(aq) + KI(aq) → AgI(aq) + KNO3(aq)
What type of chemical reaction is this AgNO3(aq) + KI(aq) → AgI(aq) + KNO3(aq)?
Double displacement
What is combustion?
- the rapid reaction of a substance with oxygen to produce compounds called oxides. Energy is also produced
- MOST IMPORTANT TYPE IS THE COMBUSTION OF HYDROCARBONS (coal, oil, natural gas)
What is complete combustion?
Complete combustion: occurs when there is sufficient oxygen, always produce carbon dioxide, water and energy
Hydrocarbon + oxygen gas → water + carbon dioxide + energy
C3H8(g) + 5O2(g) → 3CO2(g) + 2H2O(g) + energy
What type of chemical reaction is this C3H8(g) + 5O2(g) → 3CO2(g) + 2H2O(g) + energy?
Complete combustion
What is incomplete combustion?
Incomplete combustion: when there is insufficient oxygen, may produce carbon monoxide, carbon dioxide, soot (solid carbon), water and energy
→ Gets 2 more products than complete combustion
→ Proves to never barbecue inside
Hydrocarbon + oxygen gas → water + carbon dioxide + carbon monoxide + carbon + energy
C4H10(g) + 5O2(g) → 2CO2(g) + 5H2O(g) + CO(g) + C(g) + energy
What type of chemical reaction is this C4H10(g) + 5O2(g) → 2CO2(g) + 5H2O(g) + CO(g) + C(g) + energy?
incomplete combustion
What is the difference between acids and bases?
Difference between bases and acids: acids have hydrogen and bases have hydroxide
Explain conductivity between acids and bases
Acids → Many acids are good conductors of electricity when dissolved in water
Ex. HCl(aq) → H+(aq) + Cl-(aq)
Bases → Many bases are good conductors of electricity when dissolved in water
Ex. NaOH(aq) → Na+(aq) + OH-(aq)
Explain reaction with metals between acids and bases.
Acids → Acids react with metals to produce HYDROGEN GAS
Ex. 2HCl(aq) + Zn(s) → H2(g) + ZnCl2(aq)
Bases → No reaction
Why do acids react with metals and bases can’t?
Acids:
Metals that are high up in the reactivity series, such as potassium, sodium, and calcium, react vigorously with acids. They can displace hydrogen from the acid, resulting in the formation of a salt and hydrogen gas
Bases:
Metals have 2,3 electrons in their valence shell. They readily donate electrons to the combining atom. A base is an electron pair donor. Both the metal and the base tend to give up electrons, and no preferred direction for the electrons to go, no reaction occurs.
Explain reaction with carbonates between acids and bases:
Acids → acids react with carbonates to produce CO2 gas
Bases → No reaction
Why does acids react with carbonates but bases don’t?
Acids:
Acids react with carbonates because acids produce hydrogen ions
Bases:
Bases don’t react with metal carbonates because metal carbonates have basic nature, so there is no reaction occurred when they are reacted with bases.
Why are acids conductive in water?
→ All acids release at least one HYDROGEN ion (H+) when they dissolve in water
Ex. hydrofluoric acid, HF(aq) forms one H ion and one F ion
HF(aq) → H+(aq) + F-(aq)
Acids conduct electricity in water because they dissociate into ions (positively charged hydrogen ions and negatively charged ions), which are mobile and can carry an electric current.
What explains the acidic properties of acids?
→ Hydrogen ions give acids their acidic and general properties
→ All acids have the state of aq because acidic properties are only shown when the acid is dissolved in water
Acids are typically studied and characterized in their aqueous solutions because this is where their acidic properties, such as the ability to donate protons (H+), become apparent.
What are binary acids?
Binary Acids: composed of hydrogen + non-metal (always starts with hydrogen)
Written as: Start with hydro, name of non-metal (first 3 letters), then -ic acid ending
Ex.
Hydrofluoric acid → HF(aq)
HCl(aq) → hydrochloric acid
What are oxyacids?
Oxyacids: composed of hydrogen + polyatomic ion (always starts with hydrogen)
Ex.
Nitric acid → HNO3(aq)
H2CO3(aq) → carbonic acid
**Sulfuric acid → H2SO4(aq)
** Phosphoric acid → H3PO(aq)
What are the chemical formulas of bases?
→ Many bases are ionic compounds containing hydroxide (OH) and carbonate (CO3) ions
Ex.
NaOH → sodium hydroxide
Mg(OH)2 → magnesium hydroxide
NaHCO3 → sodium hydrogen carbonate
What are acid-base indicators?
→ A substance that changes colour depending on the acidity or basicity of the solution is known as an acid-base indicator
What is pH?
a measure of how acidic or basic a solution is
What is the pH scale?
a numerical scale ranging from 0 to 14 that is used to compare the acidity of solutions
What are the pH values and type of solution?
Less than 7 → acidic
7 → neutral
More than 7 → Basic
What do acids form in water?
→ Acids form hydrogen ions (H+) in solution (H2O), thus the more hydrogen ions, the stronger the acidic properties.
What determines the pH in acids?
→ The concentration of the hydrogen ions determines the pH
→ Highly acidic solutions have a low pH
What is concentration?
the quantity of a substance dissolved in a volume of solution
What do solutions with a pH greater than 7 have?
→ Solutions with a pH greater than 7 have more hydroxide ions than hydrogen ions
What do bases form in water?
→ Bases form hydroxide ions (OH-) in solution, thus the more hydroxide ions in solution, the stronger the basic properties
→ Highly basic solutions have a high pH
Why is pH 7 neutral?
→ Solutions with a pH of 7 are neutral because their hydrogen and hydroxide concentrations are equal and balance each other out
Why does pH of soil vary?
→ pH of soil can vary, depending on the type of rock in the area, the kinds of plants growing and the materials that have been added intentionally or not
Explain soil acidity for plants.
→ Different plants grow best in different conditions of soil acidity
→ Legumes: grow best in soil that is slightly basic (pH 7-10)
→ Corn: mildly acidic soil (pH 5 to 6)
→ Potatoes: acidic soil (below pH 5)
How can pH in soil be altered or raised?
→ pH of soil can be altered to improve growing conditions (Ex. adding compost (decaying organic matter) or aluminum sulfate makes the soil more acidic)
→ Soil pH can be raised by mixing in calcium oxide (lime)
→ Calcium oxide neutralizes any acid in the soil so increases the pH
Why is soil contaminated?
→ Many sites now no longer has clean soil as it is contaminated with toxic chemicals
→ These contaminants are metals like cadmium which come from batteries buried in the ground and come from industrial processes
How do you treat soil that is contaiminated?
→ One way of treating soil involves a technology called acid leaching (the process of removing heavy metals from contaminated soils by adding an acid solution to the soil and catching the solutions that drains through)
→ Here, soil is removed, acidified to dissolve its metal and washed. The clean soil goes back to its original site
→ But, this process is very expensive and disruptive to ecosystems
What is another way to treat contaminated soil?
→ Another way is that certain plants are natural sponges for metal toxins
→ As plants grow, they absorb metals from the soil and later they are harvested and burned
→ The metals are then recycled from the ashes
→ The process of using plants to remove toxins from an area is called phytoremediation
What is pH of shampoo and skincare? Why?
→ Shampoo and skincare were designed to have a pH close to neutral
–> Shampoos with a pH close to 7 are less likely to disrupt the hair’s natural pH balance, potentially leading to less frizz, dryness, and damage.
–>A pH of 7 is also considered safe for sensitive skin and eyes, which is important for products like baby shampoos.
What do cleaning products have? Why?
→ Many cleaning products have high concentration of hydroxide ions, very corrosive but effective yet damaging to skin and eyes
→ For warning, products with very high or very low pH are labelled with Hazardous Household products symbols
–> Cleaning products often contain high concentrations of hydroxide ions (OH-) because they are alkaline (basic) and effective at breaking down and removing acidic soils like grease, oil, and some proteins, which are common household stains.
What should the pH in the pool be?
→ Keeping a close watch to pH of swimming pools is important
→ pH of the pool water should be maintained within narrow range of 7.2 to 7.8
Explain dangers is pH rises or falls in pools.
→ If pH falls too much below 7, pool water irritates the eyes
→ If pH increases above 8, the pool water becomes cloudy and irritating to the eyes and chlorine compounds used to disinfect the pool begin to lose its effectiveness
What is added to pools if pH is too high or low?
→ That is why pH test kit is used
→ Hydrochloric acid (muriatic acid) is added to pool water to reduce the pH if it is too high
→ Products containing sodium carbonate can be added to raise the pH when it is too low
What is a neutralization reaction?
Neutralization reaction: a chemical reaction in which an acid and a base react to form an ionic compound (a salt) and water. The resulting pH is closer to 7
What produces when acid and base reatc?
→ When an acid (H+) reacts with a base (OH-), the hydrogen ions and hydroxide ions react to produce water, a neutral substance with a pH of 7:
GENERAL EQUATION: Acid + base → water + ionic compound (salt)
Ex. Hydrochloric acid + sodium hydroxide → water + sodium chloride
HCl + NaOH → H2O + NaCl
What are all acid-base neutralizations?
**All acid-base neutralizations are double displacement reactions
Write formula for
Stomach contains hydrochloric acid (pH 1.5). If this acid irritates the lining of the esophagus, you can take an antacid (milk of magnesia contains magnesium hydroxide) to neutralize the acid
Hydrochloric acid + magnesium hydroxide → water + magnesium chloride
2HCl + Mg(OH)2 → 2H2O + MgCl2
What are powered antacids and write formula?
→ Powered antacids usually contain sodium hydrogen carbonate (baking soda), NHNCO3(s), as the active ingredient
Hydrochloric acid + sodium hydrogen carbonate → carbon dioxide + water + sodium chloride
HCl + NaHCO3 → CO2 + H2O + NaCl
What are commonly used chemicals that are transported?
→ Sulfuric acid and sodium hydroxide are commonly used chemicals and are transported by truck, rail or ship
→ If an accident occurs, these chemical may cause an ecological disaster
What is the two-step neutralization used to clean the spill with sulfuric acid and sodium hydroxide
Calcium oxide + water → calcium hydroxide ← MAKE A BASE FIRST
CaO + H2O → Ca(OH)2
Synthesis reaction
Calcium hydroxide + sulfuric acid → water + calcium sulfate
Ca(OH)2 + H2SO4 → H2O + CaSO4
Double displacement reaction
How is pH related to acidity?
pH decreases as acidity increases
Why is calcium oxide a base?
When the metal oxides are reacting with the water, they form strong bases. The calcium oxides when reacting with the water form a strong base. Therefore, Calcium oxide is a base.
When a metal oxide dissolves in water, it doesn’t simply dissociate into ions like a typical salt. Instead, the oxide ions (O²⁻) react with water molecules (H₂O). This principle applies to most metal oxides that are soluble in water, making them basic or alkaline in nature.
What color does red litmus paper change with acids and bases? Why?
Acid: remains red
Red litmus paper stays red in acidic solutions because the litmus indicator, a natural dye, is already in its acidic form and doesn’t change color when exposed to acidic condition
Base: turns blue
Red litmus paper turns blue when exposed to a basic (alkaline) solution because the hydrogen ions from the acid in the red litmus paper react with the base, forming a conjugate base that has a blue color
What color does blue litmus paper change with acids and bases? Why?
Acid: turns red
The pigment in blue litmus reacts with H+ ions and changes chemically so the bonds are ‘tuned’ to reflect a longer wavelength of light to appear red to our eyes.
Base: remains blue
Blue litmus paper remains blue in the presence of bases because the litmus dye, a natural indicator, is already in its blue form when the paper is blue, and bases do not cause it to change to its red form
