Download presentation
Presentation is loading. Please wait.
1
Group Reading Assignment pg 170-71
Grade 10 Chemistry Unit Group Reading Assignment pg Try This Activity Pg 171
2
LAB SAFETY View Safety Video at:
Count the number of safety violations in the video Lab Equipment Checklist (CA 2) Set up Lab Tables – Use the equipment listed in the Activities
3
LAB SAFETY Safety Quiz on the next slide
WHMIS and Safety Worksheet (CA3 , 4) Use the internet and your textbook pg Q 1,2 pg 179 Safety Quiz on the next slide Number a blank piece of notepaper 1-15 Label each activity Place an *next to the safety violations in your list
4
12 13 11 10 14 9 8 4 7 6 5 2 3 1 15
5
Chemistry in a Bag Lab (CA 5,6)
Introductory Lab Chemistry in a Bag Lab (CA 5,6)
6
Chapter 5 Chemicals in Action
What is chemistry? Chemistry is the study of matter, its properties and its changes or transformations. Matter is anything that takes up space and has mass. All types of matter have physical and chemical properties.
7
Physical properties include: state at room temperature (solid, liquid or gas), temperature, colour, odour, lustre, solubility and melting and boiling points.
8
Chemical properties include how matter reacts with: air (oxygen),acids, bases, and water
9
5.1 Chemicals and chemical Change
There are many different types of matter that make up our world: Pure substance – all the particles that make up this matter are the same, as a result this matter has constant properties e.g. pure water is a clear colourless substance that freezes at 0 C and boils at 100 C.
10
a) Pure substances can be classified as:
Elements – cannot be broken down into a simpler substance because they are made of only 1 kind of atom e.g. gold, oxygen, and mercury. These elements can be identified by a chemical symbol found on the periodic table (Au, O, Hg). Some elements consist of molecules, which are formed when 2 or more atoms join together; for example oxygen (O) occurs in nature as pairs of oxygen atoms or molecules of oxygen (O2)
11
Compounds – contain 2 or more different elements in a fixed proportion
Compounds – contain 2 or more different elements in a fixed proportion. Compounds can be identified with chemical formulas e.g. carbon dioxide (formula CO2) is a compound. Each molecule of carbon dioxide is made of 1 atom of carbon and 2 atoms of oxygen. Other examples of compounds are water (H2O), sodium chloride (NaCl or salt), and ammonia (NH3).
12
Mixtures can be classified as:
2) Another type of matter is a mixture. Mixtures are made of 2 or more pure substances and can be separated by some physical method e.g. filtering, evaporation, and magnet. E.g. salt water with sand in it. The sand can be filtered with filter paper and the salt can be separated from the water by evaporating the water. Mixtures can be classified as:
13
Solutions – a mixture where one pure substance is dissolved in another pure substance e.g. salt in water, oxygen in air, copper in a brass loonies.
14
Homogeneous mixtures – a mixture that has 2 pure substances but appears to be only 1 pure substance e.g. Kool-Aid is a mixture of flavour crystals, sugar and water
15
Heterogeneous mixture – a mixture that has 2 or more pure substances that can be seen as separate parts or layers e.g. pizza is made of cheeses tomato sauce and pepperoni
16
Matter Pure Substance Mixture Element Compound Solution Heterogeneous Homogeneous
17
Properties of Matter A physical change is a change in the size or form of a substance, which does not change the chemical properties of the substance e.g. boiling water, or dissolving sugar in water.
18
A chemical change occurs when a substance changes into a new substance with different chemical properties e.g. iron rusting or burning charcoal.
19
The starting materials in a chemical change are called reactants and the new materials made are called products. Iron oxygen makes rust or iron (III) oxide Fe O makes Fe2O3 Reactants Products
20
Chemical Tests How are chemical changes useful? Chemical changes can be used to make a new substance or identify an unknown substance. There are 4 chemical tests that can be used to identify an unknown colourless gas: 1) Oxygen Gas – a glowing splint bursts into flames Oxygen Test
21
2) Hydrogen Gas – a lit splint will cause a small explosion or pop sound
Hydrogen Test POP!!
22
3) Carbon dioxide Gas – a chemical called limewater will turn from colourless to white if exposed to carbon dioxide
23
4) Water Vapour (Gas) – cobalt chloride paper will change from blue to pink
24
Assignment Lab : Properties Testing Properties of Substances (CA 7,8)
Homework : Questions 1-10 pg 175 Assignment Answer Key
25
5.5 Elements and the Periodic Table
In Lab E1 you discovered that some substances are electrolytes and some are non electrolytes or conductors or non conductors of electricity when they are dissolved in water. What makes electrolytes different from nonelectrolytes? We can use the periodic table of Elements to help answer that question.
26
Periodic Table – an organized arrangement of elements that help us to explain and predict physical and chemical properties. The periodic table is generally arranges with metals toward the left side and the nonmetals towards the right side. One exception is hydrogen (H). Although it is located on the top left hand side of the periodic table it behaves mostly as a non-metal.
28
Chemical Families – elements have been grouped in columns or families
Chemical Families – elements have been grouped in columns or families. Chemical families are groups of elements in the same vertical column that have similar physical and chemical properties. 1) Alkali metals (group 1) – include lithium (li) , sodium (Na), and potassium (K) and all are shiny, silvery metals. They form compounds that are white solids and very soluble in water
29
2) Alkaline Earth Metals (group 2) – include magnesium (Mg), calcium (Ca), and barium (Ba) and all are shiny , silvery metals, but they form compounds that are not soluble in water
30
3) Halogens (group 17) – include fluorine (F), chlorine (Cl), and bromine (Br) and are all poisonous elements that react easily with sodium and all other alkali metals.
31
4) Noble Gases (group 18) – include helium (He), and neon (Ne) and do not form compounds. The other term for the noble gases is inert gases. Inert means does not react.
33
Elements and Atomic Structure
What are atoms made of? The Bohr-Rutherford model of the atom suggests that atoms are made of 3 types of subatomic particles 1) protons – heavy positively charged particles that are found in a dense positive core of the atom called the nucleus. The number of protons equals the atomic # of the element on the periodic table
34
2) Neutrons – neutral particles that have the same mass as a proton and are also found in the nucleus. The number of neutrons in an atom can vary. (atomic mass – atomic # on the periodic table)
35
3) Electrons – negatively charged particles with almost no mass that circle the nucleus at different energy levels, also called orbits or shells. Since atoms are electrically neutral that number of electrons equals the number of protons
37
The key to understanding the formation of compounds is to understand the arrangements of electrons around the nucleus. The farther away an electron is from the nucleus the more likely it is to be involved in a chemical change.
38
The electrons in the outer orbit (valence electrons) are involved in bonding atoms together to form compounds.
39
Bohr diagrams are used to represent the arrangement of electrons in various orbits of an atom
35 17 Or Cl
40
nucleus 1st nrg level 2nd nrg level 3rd nrg level
41
Atomic Symbols A full atomic symbol includes the symbol of the element with the atomic number at the bottom left corner and the mass number at the top left corner. Copy Atomic Symbol Here 84 Kr 36
42
Consider what might happen to the charge of a neutral atom if the outer orbit of electrons are decreased or increased in number.
43
When this occurs the atom becomes a charged particle called an ion.
Ion’s can be positively charged (caused by a loss of electrons from the outer orbit) or negatively charged (caused by a gain of electrons in the outer orbit).
44
The symbol of the atom changes to indicate the change in ionic charge Li becomes Li +1 when a lithium atom loses 1 electron or N becomes N –3 when a nitrogen atom gains 3 electrons. Positive ions have the same name as their original atom, but negative ions are renamed by changing the ending of atom (ine) to (ide) e.g. fluorine (F) becomes fluoride (F-1).
45
magnesium lost 2 electrons
Mg Symbol of a Magnesium Atom Metal Atoms to Ions Mg 2+ Symbol of a Magnesium Ion Notice 2+ means magnesium lost 2 electrons Mg Atom 12p+ 2e- 8e- Mg Ion 12p+ 2e- 8e- Ne 2e- 8e- Magnesium atom Magnesium Ion by losing 2 electrons becomes To be like Its nearest Noble Gas
46
sulphur gained 2 electrons
Symbol of a Sulpur Atom Nonmetal Atoms to Ions S 2- Symbol of a Sulphide Ion Notice 2- means sulphur gained 2 electrons And the name changed S Atom 16p+ 6e- 2e- 8e- Ar Atom 18p+ 8e- 2e- S Ion 16p+ 8e- 2e- Its nearest Noble Gas Sulphur atom To be like becomes Sulphide ion
47
Worksheet – Model of an atom (CA 11)
Homework : Worksheet – Model of an atom (CA 11) Worksheet – Model of an Ion (CA 12) Activity 5.7 :Ionic Charges and Chemical Families (Use BLM 5.7a-c) (CA 9,10) Worksheet – Table of Ions (CA 13) Lab Testing for Ions (CA14-15) BLM 5.1b (CA 16) BLM 5.5b (CA 16) Answer Key
48
5.6 How Elements Form Compounds
There are 2 types compounds : 1) ionic compounds – formed when a metal loses 1 or more valence electrons to a non-metal, forming a positive (cation) and a negative ion (anion)which then are attracted to each other and are held together by an attraction called an ionic bond.
49
Ionic compounds dissolve in water and separate into positive ion and negative ions. These charged particles carry electric current through the water (electrolyte) Video
50
2) Molecular compounds are formed when 2 or more nonmetals combine together. When dissolved in water the molecules do not separate into charged particles and do not carry an electrical charge (non electrolyte) Video
51
Assignment Homework : Questions 1-8pg 187 Questions 1-4 pg 189
Ionic Compound Formation Example Homework : Questions 1-8pg 187 Questions 1-4 pg 189
52
5.8 Ionic Compounds Elements in the same chemical families form ions with similar ionic charges. Such ionic charges may also be called a valence charges or carrying capacity. Na 1+ or S 2- Metals and non metals combine to form ionic compounds by transferring electrons from the metal to the non metal. The metal atom loses electrons and becomes positively charged and the non metal gains the electrons and becomes negatively charged.
53
The result is a compound that is neutrally charged or the sum of the charges on the positively charged ions equals the sum of the charges on the negatively charged ions Na 1+ S2- becomes Na2S
54
e.g. aluminum chloride Al loses 3 electrons = Al +3 Chorine gains 1 electron = Cl –1 To make the compound electrically neutral we would need 1 aluminum and 3 chloride ions 1 aluminum(+3) + 3 chlorines(-1) = 0
55
Writing Formulas for Ionic Compounds
Follow these steps: e.g. What is the formula for aluminum chloride 1) write the symbols, with the metal first Al Cl
56
2) write the ionic charge above each symbol to indicate the stable ion that each element forms
Al Cl
57
3) criss cross the charge numbers and use them as subscripts after each element. This balances the charges and makes the compound electrically neutral Al1Cl3 1 Al (+3) and 3 Cl (-1) = 0 1(+3) (-1) = 0
58
Naming Ionic Compounds
Just as in the chemical formula the name of the metal is first followed by the name of the non-metal. However the ending of the non-metal changes to “ide” A compound made of aluminum and chlorine AlCl3 is called aluminum chloride Some metals can have 2 or more carrying capacities. These compounds are named the same way as other ionic compounds except a roman numeral is used after the metal to identify which ionic charge is used the metal in the formula
59
e.g.Copper has 2 carrying capacities
Cu +1 and Cu +2 When copper combines with oxygen we must identify which positive ion is being used. Copper (I) Oxide - Cu2O Copper (II) Oxide – CuO * notice that we have reduced from Cu2O2 to CuO because this is still electrically neutral
60
Activity : ION Dominoes (CA17)
Make a table to record your score Cation/Anion/Formula/Name You must play an oppositely charged ion to any domino played Record the Cation and Anion in your table Play continues until one player is out of dominoes Remaining players add up superscripts(Ca2+, N3- = -1) Play the basic game first Play the advanced game for marks
61
Assignment Homework : Q 1-10 pg 195 Worksheet A1 (CA18)
Answer Key..\..\School\20S Notes ppt\Chemistry Unit\2008\Chemistry Activities 2009 Answer Keys.doc Assignment Homework : Q 1-10 pg 195 Worksheet A1 (CA18) BLM 5.8, A3, A4 (CA19, 20)
62
5.9 Polyatomic Compounds Some compounds like calcium carbonate and copper (II) sulphate do not end in “ide” like other ionic compounds. Why? Such compounds are pure substances that involve a metal ion and a polyatomic or complex ion. Polyatomic ions are groups of atoms that tend to stay together and carry an overall charge. E.g. sulphate ion is SO4 -2
64
Writing Formulas for Polyatomic Compounds
We use the same steps that we learned in section 5.8 What is the formula for copper (II) sulphate 1) write the symbols for the metal and the polyatomic group Cu SO4
65
2) write the ionic charges
Cu SO4
66
3) Criss Cross and reduce the subscripts to their simplest terms if possible. (Brackets) may be needed if there is 2 or more polyatomic ions. Never change the subscript of the polyatomic group. Cu2 SO42 = Cu2 (SO4)2 = Cu SO4
67
Naming Polyatomic Compounds
The name of the above compound is Copper (II) Sulphate The name is simply the name of the metal (use a roman numeral if the metal has more than 1 positive charge) and the name of the polyatomic ion . Both can be found on the periodic table by looking them up.
69
Homework BLM 5.9, A5, A6 (CA21,22)
70
Molecular Compounds (COVALENT)
Most of the compounds you encounter each day do not contain ions. Most everyday compounds are molecular or made of only nonmetals. E.g. sugar, plastic and water
71
Molecular compounds are formed when 2 non-metal atoms share their outer electrons to fill each others outer orbits. This sharing of electrons results in a covalent bond that holds the atoms together as a molecule. Atoms become more stable when their outer orbit is full Some elements exist as molecules rather than atoms for this reason (Diatomic Elements) I2 , Br2 , Cl2 , F2 , O2 , N2 , H2
73
Writing Formulas for Molecular Compounds
The method is similar to writing ionic formulas. The number of electrons an atom wants to share to become stable is a clue to the number of covalent bonds that atom will form. The combining capacity of a non-metal is a measure of the number of covalent bonds. These combining capacities are listed below :
74
4 3 2 1 H C N O F Si P S Cl As Se Br I C O = C2O4 = CO2
H C N O F Si P S Cl As Se Br I What is the formula for the compound made of carbon and oxygen? 4 2 C O = C2O4 = CO2 simplify
75
Naming Molecular Compounds
Some molecular compounds have common names like : H2O = water NH3 = ammonia CH4 = methane H2O2 = Hydrogen Peroxide O3 = Ozone
76
H2O = diHydrogen monOxide NH3 = Nitrogen triHydride
Or they can be named using prefixes which represent the number of each atom in the compound H2O = diHydrogen monOxide NH3 = Nitrogen triHydride CH4 = Carbon tetraHydride
77
Tri =3 Hept(a) = 7 Tetr(a) = 4 Oct(a) = 8 Pent(a) = 5 Non(a) = 9
Notice the second part of the name still ends in “ide” like many of the ionic compounds. You must know the following prefixes: Mon(o) = 1 (optional on first name not the second) Di =2 Hex(a) = 6 Tri =3 Hept(a) = 7 Tetr(a) = 4 Oct(a) = 8 Pent(a) = 5 Non(a) = 9 Dec(a) = 10
78
P2 H4 is Diphosphorous Tetrahydride CO is carbon monoxide
e.g. CO2 is carbon dioxide P2 H4 is Diphosphorous Tetrahydride CO is carbon monoxide SiO2 is silicon dioxide P3Br8 = = Tetrasulfur nonoxide N2O2 = = HeptaSelenium DecaIodie
79
BLM 5.11(CA 23) A7 (CA 23)
80
Oxyacids Oxyacids are compounds formed when hydrogen (H +1) combines with polyatomic groups that contain oxygen E.g. HNO3 is nitric acid H +1 NO3 –1 = HNO3
81
Use the acid naming table on the back of your periodic table to name and write the formulas of all ionic compounds that begin with hydrogen Hydrogen _______ide becomes hydro_________ic acid Hydrogen _______ate becomes _____________ic acid Hydrogen _______ite becomes ____________ous acid chlor chlor chlor chlor chlor chlor
82
Assignment Acid Naming Worksheet (CA24) Review Sheet A8 (CA25)
83
5.12Hydrocarbons : A Special Group of Molecules
Organic compounds are molecular substances that contain carbon atoms as basic building blocks. Carbon will bond covalently with oxygen,nitrogen and hydrogen to form very stable molecules. This is due to the combining capacity of carbon (4).
84
Carbon is found in many forms - plants (sugar) made from
photosynthesis - animals (proteins) - fossil fuels (oil) - liquid natural gas (LNG) All are classified as hydrocarbons (made of hydrogen and carbon)
85
-Crude oil (the source of hydrocarbons) comes from the decay of plants or the animals which fed on them. These plants and animals then died and over a period of millions of years heat and pressure turned them into crude oil
86
-When a hydrocarbon burns it must have Oxygen
-When a hydrocarbon burns it must have Oxygen. This is known as combustion or respiration. The main products of combustion are carbon dioxide and water vapor. - Fossil fuels are a non-renewable energy source. Once used, they are gone.
87
methane + oxygen carbon dioxide + water
methane + oxygen carbon dioxide + water. CH4(g) + 2O2(g) CO2(g) + 2H2O(g) ethane + oxygen carbon dioxide + water. 2C2H6(g) + 7O2(g) 4CO2(g) + 6H2O(g) CO H2O + C CO CO2 + H2O Incomplete Combustion Complete Combustion
88
Assignment Homework : Questions 1-5 pg 207
Activity : BLM 5.12 Hydrocarbons Word Search (CA 25) Homework : Chapter 5 BLM Review (CA26)
89
Chapter 6 – Understanding Chemical reactions
How do chemical reactions happen? How do chemists categorize the thousand’s of different chemical reactions? In chapter 5 you saw patterns in how chemical compounds can be categorized as ionic or molecular. In this chapter you will learn to recognize patterns that will help you understand and predict different types of chemical reactions.
90
6.1 Word Equations Chemical reactions involve many chemicals, as in explosions of dynamite, bathroom cleaners working on a stain or as in the growth of your body. Chemists use a word equation to represent these types of reactions : it tells us what reacts and what is produced.
91
Word equation format: Reactants and products can be separated by a (+) sign e.g. The pop test for hydrogen gas All the reactants All the products Reactant Reactant Product 1 + Product 2 hydrogen + oxygen water
92
Assignment Try This Activity Pg 219 Understanding Concepts1-5 pg 219
Lab 6.2 Measuring masses in Chemical Changes (CA27) UC Questions 1-4 pg 221
93
6.3 Conserving Mass In Investigation 6.2 you saw that when two solutions react to form a solid precipitate, the mass stays the same. In all chemical reactions mass is conserved. This is because during the chemical reaction the individual atoms that make up the reactants are simply rearranged into new patterns or products, no matter is lost or added during the process. This is a scientific law that sums up the conclusions of many experiments called the Law of Conservation of Mass The Law of Conservation of Mass states that in a chemical reaction, the total mass of the reactants is always equal to the total mass of the products 25 g g ?g hydrogen + oxygen water
94
Assignment Understanding Concepts 1-7 pg 223
Lab 6.4 Finding the Missing Mass (CA28) UC questions 1-4 BLM 6.5b (CA29)
95
6.5 Balancing Chemical Equations
Because mass is always conserved in a chemical reaction we will have the same number of atoms of each element on both the reactant and product sides of a chemical equation. The equation must be balanced to make this happen. A skeleton equation is representation of a chemical reaction in which the formulas of the reactants are connected to the formulas of the products by an arrow. e.g. methane + oxygen carbon dioxide + water (word equation) CH O CO H20 (skeleton equation)
96
CH4 + O2 CO2 + H20 (skeleton equation)
The problem with a skeleton equation is that it does not follow the Law of Conservation of Mass. By looking at the # of atoms on each side of the above equation we can see that they are not the same on both sides of the equation. 1 C O 1 C + 2 H 4 H 2O 1 O 16g 32g 44g 18g 48g g (mass is not the same)
97
To make the above equation follow the Law of Conservation of Mass we must rewrite it as a balanced equation. To do this we will use multipliers at the front of each chemical formula . These multipliers are called coefficients. By using the coefficients we have been able to show that there are the same number of atoms of the same element on each side of the equation. This would mean that the mass on each side of the equation is the same allowing us to support the Law of Conservation of Mass. CH O CO H20 1 C O 1 C H 4 H 2O 2 O 16g 64g 44g 36g 80g = 80g (mass is now the same)
98
How to balance an Equation
1) write the word equation for the reaction 2) Write the skeleton equation by replacing each name with the correct formula Lead (II) Nitrate + Potassium Iodide Lead(II) Iodide Potassium Nitrate Pb(NO3) KI PbI KNO3
99
3) Count the # of atoms of each type in the reactants and products Pb(NO3) KI PbI KNO3 Type of atom reactants products Pb N K I O *** Use the ECHO rule : Count and balance the atoms in this order Element (all) then Carbon Hydrogen and finally Oxygen
100
4) multiply each of the formulas by the appropriate coefficients to balance the number of atoms Type of atom reactants products Pb N K I O Pb(NO3) KI PbI KNO3
101
Polyatomic short cut : if you can see a polyatomic ion group that is unchanged in the reaction you could balance it as a group rather than as individual atoms Pb(NO3) KI PbI K(NO3) Type of atom reactants products Pb K I NO
102
Pb(NO3) KI PbI K(NO3) Type of atom reactants products Pb K I NO
103
Assignment Homework – Understanding Concepts 1-3 pg 229
A10,A11, Balancing Equations Worksheet (CA30,31) BLM 6.5c (CA31)
104
6.6 Combustion There are different types of chemical reactions. One of the most common and useful chemical reactions is combustion (burning of a fossil fuel). Fuel + oxygen oxides energy For a fuel to burn we need oxygen and since the Earth’s atmosphere is 21% oxygen, combustion can occur very easily. It is combustion that gives us heat energy for our homes, electricity, and allows is to run our cars. The most important fuels that we burn are hydrocarbons or fuels made of hydrogen and carbon like gasoline (C8H18), natural gas (CH4), and even candles (C25H52).
105
The word equation for the combustion of a hydrocarbon is :
Hydrocarbon Oxygen Carbon dioxide water energy Complete Combustion Incomplete Combustion
106
The only variable or change in the above equation is the type of hydrocarbon burned
In each case we need oxygen and produce carbon dioxide and water vapour as well as energy, which we use to run our car, keep us warm or give us light. Gasoline Oxygen Carbon dioxide Water energy C8H O CO H2O energy Methane Oxygen Carbon dioxide Water energy CH O CO H2O energy Candle Wax Oxygen Carbon dioxide Water energy C25H O2 CO H2O energy
107
The above combustions are called complete combustions because the fuel is completely burned up. You can tell if the combustion is complete if the flame you see is a bright blue color. Sometimes the fossil fuel or hydrocarbon does not burn completely and this is called incomplete combustion. You know it is incomplete combustion if the flame color is bright yellow-orange. Candles will often burn incompletely producing other products other than carbon dioxide and water Candle Wax Oxygen Carbon dioxide Water energy + carbon + carbon monoxide C25H O CO H2O energy + C CO poisonous
108
Assignment Lab Demo – Who has the Hot Hand
Understanding Concepts 1,3,4,5,6 pg 232
109
HCl + NH3 NH4Cl 6.7 Types of Chemical Reactions :
Synthesis or Combination Reaction (putting things together) Involves the combination of smaller atoms or molecules becoming larger molecules A B AB Element Element Compound 2H O2 2H2O Compound Compound Compound HCl NH NH4Cl
110
AB A + B 6.7 Decomposition Reaction (taking things apart)
Involves the breaking apart of a larger molecule into smaller molecules AB A B Compound Element Element 2H2O H2 O2 Compound Compound + Compound NH4Cl NH HCl
111
Assignment 1) Lab Heating Bluestone (CA32)
112
element + compound element + compound
6.10 Single Displacement Reaction Involves the displacement of one element in a compound by another similar element, metals will replace metals and nonmetals will replace nonmetals element + compound element compound A + BC B + AC metal + compound metal compound Fe AlCl Al FeCl3 D + BC C + BD nonMetal + compound nonmetal compound F AlCl3 Cl2 + 2FeF3
113
Assignment 1) Lab – Single Displacement Reactions (CA33)
114
AY + BZ BY + AZ Compound + Compound Compound + Compound
6.10 Double Displacement Involves the displacement of an element in one compound for a similar element in another compound Compound + Compound Compound + Compound AY BZ BY AZ Lead(II) Chloride + Potassium Iodide Potassium Chloride + Lead(II) Iodide PbCl KI KCl PbI2 In the above example the metals switched places
115
Lab – Double Displacement Reaction (CA34,35)
116
Review Assignment BLM 6.13 (CA36) BLM Chp 6 Review (CA 36)
Similar presentations
© 2025 SlidePlayer.com Inc.
All rights reserved.